B e t t e r F a... B e t t e r A i... A scientifi c analysis of farming practice

B e t t e r   F a... B e t t e r   A i... A scientifi c analysis of farming practice
Better Farming
Better Air
A scientific analysis of farming practice
and greenhouse gases in Canada
Better Farming
Better Air
A scientific analysis of farming practice
and greenhouse gases in Canada
March 2008
Scientific Editors:
H.H. Janzen, R.L. Desjardins, P. Rochette, M. Boehm and D. Worth
For additional copies of this publication or to request an alternate format, please contact:
Publications Section
Agriculture and Agri-Food Canada
Sir John Carling Building
930 Carling Avenue
Ottawa, Ontario K1A 0C5
Telephone: (613) 759-6610
Fax: (613) 759-6783
E-mail: [email protected]
Electronic version available at http://www.agr.gc.ca/nlwis-snite/
This publication may be reproduced without permission provided the source is fully acknowledged.
© Her Majesty the Queen in Right of Canada, 2008
Library and Archives Canada Cataloguing in Publication
Janzen, H. Henry, 1956Better Farming, Better Air: A scientific analysis of farming practice and greenhouse gases in Canada /
H. Henry Janzen.
Issued also in French under title: Une agriculture efficace pour un air plus sain: une analyse scientifique des liens entre les pratiques agricoles et les gaz à effet de serre au Canada.
ISBN 978-0-662-47494-4
Cat. no.: A52-83/2008E
AAFC No. 10530E
1. Greenhouse gas mitigation--Canada. 2. Carbon dioxide mitigation--Canada. 3. Sustainable
agriculture--Canada. 4. Agriculture--Environmental aspects--Canada. 5. Agricultural industries--Environmental aspects--Canada. 6. Agriculture and state--Environmental aspects--Canada. I. Canada.
Agriculture and Agri-Food Canada II. Title. III. Title: Scientific analysis of farming practice and greenhouse gases in Canada.
HC120.E5J36 2008
363.738’7460971
100% post-consumer content
C2008-980015-X
FOREWORD
As Assistant Deputy Minister, Agriculture and AgriFood Canada (AAFC) Research Branch I am proud to
present you with this book: Better Farming Better Air.
It is the result of a collective work initiated in response
to a commitment by AAFC to Treasury Board in 2001
under the Results-Based Management and Accountability Framework (RMAF) as part of the Model Farm
program. Better Farming Better Air summarizes our
understanding of Greenhouse Gas (GHG) fluxes on
Canadian farms. It describes the contribution of agriculture to Canadian GHG emissions and agriculture‘s
role in mitigating GHG emissions.
The composition of air is a complex phenomenon
which can be influenced by human activities. As a
provider of food and as a driver of our economy,
agriculture is one of the human activities on which we
can act in order to ensure better-quality air, thereby
contributing to the well-being of future generations of
Canadians. By studying the complex processes by
which agriculture impacts on our air, AAFC scientists
contribute to improving our understanding of the system. They use this understanding in the development
of improved agricultural practices. Better Farming Better Air presents world-class research which describes
the state of our knowledge in relation to agricultural
practices; provides examples of how agriculture can
contribute to improving air quality; and outlines our
substantial achievements reached in recent years.
This book is a valuable addition to the collection of
information on the environment that we are proud to
make available to the agriculture sector, policy makers
and Canadians in general.
Marc Fortin
Assistant Deputy Minister
Research Branch
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
iii
Preface
A phrase taken from the concluding paragraph of
this outstanding book sums up perfectly the spirit of
the publication: we must restore the vision of “seeing
our farmlands not as resources to be spent, but as
a home in which we live, whether we reside there or
not.” This statement is precisely in accord with what
eminent American ecologist, forester and environmentalist Aldo Leopold wrote. He said, “We abuse
land because we regard it as a commodity belonging
to us. When we see land as a community to which we
belong, we may begin to use it with love and respect.”
Indeed, the adoption of agriculture-management
practices based on ecological principles must be an
integral component of any solution to the environmental problems of the modern era. This is important
not only to meet the food demands of the world’s 6.5
billion inhabitants (expected to grow to nine billion
by 2050), but also to offset emissions from fossil-fuel
combustion. Agriculture, managed ecologically, can
sequester carbon in soils and trees, denature contaminants through phyto-remediation and microbial
processes, filter pollutants from natural waters through
the soil as a biomembrane and produce biomass
needed for modern biofuels (ethanol, biodiesel).
The intent of the Model Farm Program, the origin of
this book, was to improve the accuracy of estimates
of greenhouse gas (GHG) emissions from Canadian
farms and agriculture, and to identify ways to reduce
emissions from farms. The theme is in accord with
the Kyoto protocol, ratified by Canada in 2002, for
the emission period 2008–2012 and beyond. Three
specific objectives of the Model Farm Program were:
to improve scientific understanding of emissions from
Canadian farms, to verify the inventory of Canadian emissions for international commitments and to
devise a method for holistic analysis of GHG emissions from entire farming systems. Reliable data are
essential to the sustainable management of agricul-
iv
tural soils. Only through long-term planning, based
on solid data, can agriculture hope to meet society’s
numerous and emerging demands.
Assessing emissions in terms of CO2 (carbon dioxide) equivalent involves obtaining credible estimates
of all GHGs: CO2, CH4 (methane) and N2O (nitrous
oxide) from diverse soils and management scenarios (e.g., tillage and other farm operations, livestock,
nitrogenous fertilizers). Scientific models, specifically
developed to predict emissions from Canadian farms,
need to be validated against direct measurements
under diverse land uses and management practices.
The Model Farm Program project team, comprising
world-class professionals, has meticulously developed
a methodology and model that can be used in other
countries. The model’s merits are numerous:
•
•
•
•
•
•
Based on an ecosystem approach and a holistic view
Identifies win-win solutions
Considers the role of biofuels
Involves diverse farming systems
Addresses all GHGs and not just CO2
Based on a positive approach of using agriculture
as a solution to the issue of global warming
Better Farming, Better Air is an outstanding reference for diverse stakeholders, including agricultural
researchers, policy makers, environmentalists, and
the general public. It is prepared in a simple and
reader-friendly format. It delivers a strong message
about how farm management affects our air and
how the adoption of prudent land-use and management practices can alleviate global environmental
stresses of the 21st century.
Rattan Lal
Professor of Soil Science
The Ohio State University
Columbus, OH 43210 USA
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Acknowledgements
Authors
The findings presented were funded, in part, by the
Model Farm Program of Agriculture and Agri-Food
Canada (AAFC). We thank those who established
this program and the many administrators and collaborators who supported and guided these efforts.
In particular, we acknowledge our indebtedness
to innumerable collaborators—researchers from
outside AAFC, producers, industry specialists, and
concerned members of the general public—who
encouraged and helped steer the research. Earlier
versions of this book were reviewed by Richard
Asselin, Con Campbell, Henry Hengeveld, Barry
Grace, Chang Liang, Alex Milton, Claudel Lemieux,
Leslie Cramer and Sheila Torgunrud, who graciously
provided many perceptive and corrective comments. Rattan Lal kindly agreed to draft the preface
of this book, for which we owe him gratitude. Most
of all, we thank the technicians, clerical staff, layout
artists, plot personnel, livestock herders, local managers and many others who worked diligently and
quietly behind the scenes. They performed much of
the work described in this document and we do not
always thank them enough.
Agriculture and Agri-Food Canada recognizes the
significant contributions made by the following
authors of this book (lead authors of one or more
sections are identified by an asterisk): D. Angers *,
K.A. Beauchemin, C. Benchaar, S. Bittman, M.A.
Bolinder, M. Boehm*, S. Claveau, R.L. Desjardins*,
C.F. Drury, J.A. Dyer, S. Gameda, B. Grant, E. Gregorich*, L.J. Gregorich, H.H. Janzen*, R.L. Lemke*,
D.I. Massé*, L. Masse, T.A. McAllister, B. McConkey,
S.M. McGinn*, N.K. Newlands*, E. Pattey*, R.L.
Raddatz, P. Rochette*, E.G. Smith*, W. Smith, F.
Tremblay, A.J. VandenBygaart, D. Worth, X. Vergé
and B. Zebarth.
To make this publication readable for a wide audience, many of the references originally cited by
authors have been removed and replaced with a
sampling of general sources at the end of each
section. This does not minimize our indebtedness
to many unmentioned scientists whose insights and
findings reside in these pages.
The text and layout of this document reflects the
craft and creativity of the following:
The editors
Technical editor:
Tina Reilly
Stiff Sentences Inc.
Ottawa, Canada
Design:
Mark Taylor
Friction Design Group
Ottawa, Canada
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
v
Contents
Summary
Introduction
2
14
The Gases
Carbon Dioxide
20
Nitrous oxide
34
Methane
50
The Amounts
Measuring Ebbs and Flows
70
The Emissions we Produce
78
Reckoning the Total Budget
90
The Bigger Picture
A Holistic View
Finding Win-Win Solutions
98
108
The Future
The Promise of Biofuels
114
Rejuvenating the Air
124
What Could Happen
134
A Vision Restored
142
mma
OUR CHANGING AIR
W E B A R E LY N O T I C E T H E A I R A B O U T U S — invisible and silent, it seeps
among and through all living things, enshrouding the earth in its fluid continuity. Yet unseen to us in air’s apparent placidness are torrents of activity: gaseous
molecules of all kinds flitting about, reacting, recombining, breathed in and out by
plants and animals, chased endlessly about by the warmth of the sun.
Through these ceaseless flows, the air keeps us all alive. It gives us food; for
the carbon that fuels us comes from air, invested with energy from the sun. It
provides the oxygen we inhale to burn the food we eat. It yields the proteins we
need, for the nitrogen therein comes ultimately from air. We and all life on Earth
are sustained by the gases that circulate among us in what we call air.
There is yet another reason we depend on air: it keeps us warm. Some of the
gases in our atmosphere—carbon dioxide, methane, and nitrous oxide, among
them—prevent the Earth’s heat from escaping quickly back into space. Without
these greenhouse gases, or GHGs, our planet would not be the oasis it has been
for aeons now in the cold expanse of space.
But the air today is not as once it was. Humans occupy this planet in increasing
numbers—our population has doubled in just 40 years—and we have devised
more powerful means to rearrange our world, changing our air. Foremost is
an increasing concentration of carbon dioxide: 280 parts per million (ppm) just
centuries ago, but now surging past 380 ppm, mostly from burning fossil fuels
and clearing tropical forests. Concentrations of other GHGs—nitrous oxide and
methane—have increased too. So scientists increasingly worry: if these trends
continue, will we bring about climate change, unpleasant and irreversible?
The role of farms
Farms—their fields and pastures, soils and animals—are tied closely to the changing
air. They are important sources of GHGs: CH4 (methane) from the breath and excreta
of livestock; N2O (nitrous oxide) from nitrogen in soils and manure; and CO2 (carbon dioxide) from fuel burned in tractors and barns. Beyond that, farms also store
carbon, mostly in their soils. When managed poorly, this carbon can be lost to air
as CO2, as it has been in the past. But if managed better, some carbon lost can be
regained, actually removing CO2 from the air. Because farms are so connected to the
air, what farmers do—how they manage their land and livestock—affects profoundly
the air that surrounds us all. Although few of us see much of what happens on farms,
farmers’ choices influence us all, often to our benefit.
2
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Our intention is to show, briefly, how farmers’ actions affect our air and how their
future choices can help relieve some of the environmental stresses building globally.
The Gases
To see how better farming can lead to better air, we need to review the processes
whereby GHGs—CO2, N2O, and CH4—are exchanged with the air. Though these
processes are often interwoven, we first consider each gas separately for clarity.
Carbon dioxide
Nature uses carbon to store energy. In the air, carbon exists mostly as CO2;
through photosynthesis, green plants invest the sun’s energy in this CO2, building from it first sugars and then other energy-rich forms. Plant materials are then
eaten by other organisms—microbes, cows, and humans, among others—who,
in effect, burn the material back to CO2, using the solar energy it contains to live
and grow. Some of the energy-rich carbon materials can be stored for thousands
or millions of years before being converted back to CO2. For example, soils
contain vast amounts of carbon held in organic matter (humus), and the carbon
in fossil fuels such as coal, oil and natural gas is solar energy trapped by plants
aeons ago. Farms and other ecosystems can be likened to batteries; building
carbon stocks is like charging the battery and losing carbon like discharging it.
On Canadian farms, carbon is stored mostly in the organic matter of soils.
Changes in amounts stored depend on the rate of carbon coming in as plant
litter, compared to the rate of carbon lost through decay. If rate of carbon input
exceeds rate of loss, carbon accumulates; if rate of carbon added is less than
rate of loss, carbon is depleted.
Historically, when lands were first cropped, large amounts of carbon were lost
because cultivation accelerated decay and removal of harvests meant less carbon was returned to soil. But today, farmers can rebuild some of the lost carbon
through improved practices: using no-till methods, planting more perennial hay
or pasture crops, avoiding summer fallow (lands left unplanted), adding nutrients
and manures to increase yields, restoring grasslands and using better grazing
techniques. By increasing the amount of carbon stored in soils, these practices
not only remove CO2 from the air, but also make soils more productive and resilient for use by future generations. Some practices, such as no-till farming, also
decrease CO2 emissions by reducing the use of fossil fuel.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
3
Methane
Sometimes, when carbon-containing materials decay without sufficient oxygen,
microbes produce CH4 instead of CO2. On Canadian farms, this occurs mainly
in two places. First, CH4 is produced inside the rumen (fore-stomach) of ruminant animals such as cattle and sheep through a bacterial process called enteric
fermentation. This process, the biggest source of CH4 from Canadian farms, is
important because it enables livestock to convert otherwise indigestible materials
such as grass and hay into usable energy. Second, CH4 is released from manure
storage sites, especially when manure is stored wet or as a slurry, because water
prevents entry of oxygen during decay.
Scientists have long studied CH4 emissions from ruminants because such emissions mean the animal has not efficiently utilized the energy content of the feed
to produce meat or milk. Through research, scientists have found effective ways
of reducing these emissions. One way is to alter the diets of livestock: using highgrain rations, adding fats or oils to rations, and using anti-microbial agents called
ionophores, which reduce emissions at least for a time. Feeding cattle higherquality forage—replacing grass hay with alfalfa, for example—can also reduce
emissions of CH4 per unit of animal product. Scientists are also experimenting
with compounds such as tannins, naturally present in some forages, as a way of
suppressing CH4. Various other agents, including yeasts, organic acids, halogenated compounds such as chloroform, and possible vaccines are also being
investigated, although in some cases their effectiveness in reducing emissions
has not been widely confirmed.
Beyond these direct methods, CH4 emissions can be reduced indirectly by
choosing practices that enhance productivity: extending lactation periods of
dairy cows, using more efficient breeds, improving reproductive performance and
increasing rates of gain in beef animals so they reach the market sooner. These
practices, while they may not reduce emissions per animal per day, can lower the
amount of CH4 emitted per kilogram of milk or meat produced.
Research has shown also that CH4 from manures can be reduced. Practices
sometimes effective include: aerating manure, storing manure at low temperatures (below ground, for example), removing manure from storage more frequently, using bedding material to improve aeration and composting manure
(although the overall effectiveness of this practice may vary, in part because of
possible emissions of N2O). Another way to reduce emissions from manures is to
remove CH4 using biological filters or, even better, to trap the CH4 and burn it as
fuel, thereby offsetting fossil fuel otherwise needed.
Nitrous oxide
Nitrous oxide is an important GHG emitted from Canadian farms, accounting for
about half the warming effect of agricultural emissions. This gas, familiar to us as
laughing gas, is produced in nature by microbes as they process nitrogen in soils.
4
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
All soils emit some N2O, but farm soils often produce more than others because of the nitrogen added to soil in fertilizer, manures and other amendments.
Without these additions to replace the nitrogen removed from farms in harvested
grain, milk, meat, and other products, crop yields would soon decline. But as the
amount of added nitrogen increases, so do potential losses into the environment,
including losses of nitrogen to the air as N2O. Typically, scientists assume that
about 1% of the nitrogen added to farm fields is emitted as N2O, though this can
vary widely with soil water content (hence oxygen availability), hilliness of the land
and soil clay content.
Aside from the N2O released directly from soils, farms can also give rise to indirect emissions—N2O produced elsewhere from nitrogen leached from fields or
emitted into the air as ammonia gas. This nitrogen, once lost from the farm, can
find its way into adjacent environments where it can be converted and emitted
as N2O. Although not produced on farms, this N2O is from nitrogen used on the
farm; hence, it must be counted as farm-derived N2O.
Since N2O is produced mostly from excess available nitrogen in soils, one way
to suppress emissions of this gas is to apply fertilizer judiciously: adding just
enough, at the right place and time, to meet crop demands, but avoiding excess
amounts left over. This aim, long a goal of scientists, becomes ever more important in light of the high cost of fertilizers and environmental damage caused by
nitrogen leaking from farms. Fertilizer can be used more efficiently by: adjusting fertilizer rates to coincide with plant needs; placing fertilizer near plant roots
(but not too deep in the soil); applying fertilizer several times each year, rather
than only once; and using slow-release forms. Similarly, using manure efficiently
can also help limit N2O emissions—not only because less is released from the
manure, but also because less fertilizer now needs to be used. Perhaps the most
fundamental way of reducing N2O from manures is to alter feeding rations so that
less nitrogen is excreted in urine and feces in the first place.
Other practices that can sometimes reduce N2O emissions from farms include:
greater use of legumes as a nitrogen source; use of cover crops (sown between successive crops) to remove excess available nitrogen; avoiding use of
summer fallow (leaving the land unplanted, with no crop nitrogen uptake, for a
season); and adjusting tillage intensity (sometimes, but not always, no-till practices can reduce emissions).
Most methods of reducing N2O emissions depend on improving the efficiency
of nitrogen use on farms. Progress toward this aim has many other benefits: it
makes farms more profitable because fertilizer is expensive; it saves on fossil fuel
use (and hence CO2 emissions) because producing nitrogen fertilizer is energyintensive; and it lessens the amounts of nitrates, ammonia and other nitrogen
pollutants entering the environment. Despite much progress, the nitrogen cycle
on farms is still quite leaky; stemming these leaks remains a research priority,
both to reduce N2O emissions and for many other urgent reasons.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
5
The Amounts
How and why scientists measure emissions
We measure GHG emissions from farms in part to honor international commitments; for example, Canada needs to provide reliable annual estimates of
emissions from all important sources, including farms. But emissions are also
measured for scientific reasons: if you cannot measure emissions precisely, how
can you know which of various practices best reduces emissions? And without
good estimates of emissions, how can you understand the underlying principles
of GHG formation and release?
But measuring emissions of GHGs from farms is not easy; emissions come from
many places on the farm: soils, animals of all kinds and machinery. Sometimes the
gases seep slowly into the air; other times they spew in sporadic gusts. To capture
these emissions, scientists have had to devise a host of methods: small chambers
placed on soils or large chambers housing cows; instrumented towers downwind
of fields or instrumented aircraft flying over farming regions; methods that require
patient analysis of carbon change in soils over tens of years, or measurements of
CO2 in air, several times a second; analysis of air in tubes buried in the soil, or from
tubes hung high in the air on balloons. No method is perfect, but each has its role.
By pooling results from all methods, scientists obtain reasonably good estimates
of emissions and the factors that control them. This understanding is then usually
captured in models—sets of mathematical equations that can predict GHG emissions for any set of conditions. Such models are already widely used, but research
continues to make them even more robust and reliable.
The emissions we produce
Agriculture emits (and sometimes removes) all three GHGs: CO2, CH4, and
N2O (see Figure 1). These gases differ, though, in their ability to trap heat;
tonne for tonne, CH4 is more than 20 times as effective at trapping heat as
CO2, and N2O is about 300 times as effective as CO2. To compare the emissions of these gases on equal terms, therefore, we usually speak of CO2
equivalents (for example, N2O has 298 CO2 equivalents).
6
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 1
Sources of GHG Emissions from Canadian Agriculture in 2005, Excluding CO2
Emissions Associated with Energy Use. Mt CO2e
T
O
T
A
L
24.5
CH4
ENTERIC
FERMENTATION
E
M
13.0
N2O + CH4
MANURE
MANAGEMENT
I
S
S
I
O
N
S
=
5
7
12.7
0.5
6.3
N2O
CO2
N2O
N 2O
FROM SOILS
CO2
FROM SOILS
INDIRECT
EMISSIONS
In 2005, Canada produced 747 million tonnes of CO2 equivalents (Mt CO2e) from
all sources, mostly as CO2 from energy use. Agriculture accounted for about 8%
of these emissions, largely as CH4 and N2O in roughly equal proportion. (This
value does not include emissions from energy use; if these are counted, then
agriculture accounts for roughly 10% of Canada’s emissions). As mentioned, farm
soils remove substantial CO2 from the air when soils gain carbon under improved
practices (about 10 Mt CO2e were removed in 2005), but because these removals
are almost exactly balanced by carbon losses from recently cultivated forestlands,
the net exchange of CO2 between agricultural land and air is small.
The annual total GHG emissions from farms in Canada have stayed reasonably
constant from 1990 to 2005, falling by 6% (see Figure 2). But this stability hides
trends in the individual gases. Methane emissions, for example, have increased
by 24% because of larger animal herds (the beef cattle population increased by
30%). Nitrous oxide emissions have risen by 14%, mostly from higher fertilizer
use and more manure produced. Emissions of CO2 from cultivated croplands
have fallen, however, so that total annual emissions have declined slightly.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
7
FIGURE 2
Carbon Dioxide, Methane and Nitrous Oxide Emissions From
Canadian Agriculture, 1990 to 2005
70
CO2
CH4
N 2O
GHG EMISSIONS MT CO2e
60
50
40
30
20
10
0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
These estimates may not be perfectly accurate; all carry some uncertainty,
in particular those for N2O. But they provide a reliable view of general trends
and their uncertainty may slowly shrink with further research and gradually
improving methods.
What will happen to GHG emissions in coming years? With growing demand for
food and other products, livestock numbers and nitrogen additions may rise further, perhaps increasing CH4 and N2O emissions, unless new ways can be found
to suppress them. Soil carbon gains (CO2 removals from the air), which have
offset past increases in CH4 and N2O emissions, may continue for some years,
but not indefinitely; eventually, soil carbon approaches a maximum, typically a
few decades after introducing new practices. Even with good practices, therefore, it is hard to foresee farm GHG emissions falling appreciably over time. More
important than reducing total emissions, however, may be finding ways to reduce
emissions per unit of product. In the last 15 years, for example, dairy farmers
have reduced CH4 emissions per kilogram of milk by about 13%, and similar
trends are occurring with beef and pork.
Reckoning the total budget
Farming practices affect the climate not only through emitted GHGs, but also by
the way they affect the colour of the land. In general, the whiter the landscape,
the more of the sun’s radiation is reflected back into space. A snow-covered
field, for example, will reflect more radiation (and absorb less heat) than a dark
forest with snow beneath the canopy. Cropping practices can also affect the timing of thunderstorms and severe weather by affecting water vapour release from
8
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
plant pores (transpiration). And air temperature and precipitation can be influenced by practices such as summer fallow and irrigation. These examples show
that the effects of farming practices on climate cannot be judged solely by the
amounts of GHG emitted; other factors need also to be considered.
The Bigger Picture
A holistic view
An ecosystem, short for ecological system, is a community of organisms within
its environment and all the interactions among them. The ecosystem, then, is
more than the sum of its parts; it encompasses the fluid coherency of the whole
system. This means that studying ecosystems is not an easy task, for many
different disciplines are needed and they need to be applied over long spans of
time, since ecosystems often change only gradually. But the approach allows us
to see living systems as a whole; it lets us see the forest and the trees.
At first the ecosystem concept was applied mostly to landscapes untouched
by humans. But farms also can be viewed as ecosystems; they are complex
assemblages of organisms, interacting with each other and their environment.
Seeing farms this way has several benefits: it forces us to take a holistic view;
and it allows us better to study farms alongside natural systems, such as forests,
wetlands and lakes.
The ecosystem approach may be especially useful in studying GHG emissions.
We might even argue that this is the only way to study them, for GHG fluxes
emanate from myriad processes, all interwoven and entangled. The emissions
of one gas depend on emissions of another. For example, some practices may
increase soil carbon, thereby withdrawing CO2 from the air. But if those practices require more fertilizer, then will N2O emissions be affected, and what will be
the net effect? A new feeding practice may effectively suppress CH4 emissions
from cows; but how does that feed now influence the emission of GHGs from
manure produced, and what are the GHG emissions on fields where the feed is
grown? Even more complicated are the spillover effects of any new practice. For
example, if land once cropped is planted to grass, will the crop displaced merely
be grown elsewhere? And what will be the emissions there? These few examples
illustrate that GHG emissions can be properly understood only from a broad ecosystem perspective and the effectiveness of proposed practices can be gauged
only by looking at all the gases across space and across time.
Given this complexity, how can we study all the intertwined processes that emit
GHGs from farms? The only practical way is to build mathematical models, equations that describe in mathematical language what we know about the system.
Building such models, whether they be simple or highly sophisticated, forces us
to include and connect all the many processes involved. Further, models offer a
way of storing and updating what we know. As new findings emerge, they can
be reflected in refined models. What’s more, building models helps us recognize
our ignorance, pointing scientists to those areas most in need of further study.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
9
Scientists in Agriculture and Agri-Food Canada are now building such models
for simulating GHG emissions from whole farms. One such model, a simple
GHG calculator that predicts emissions for a single year, is now available for
use by scientists, producers, policy makers and other users. Work is also
underway to build more sophisticated dynamic models, which will simulate
changes in emissions over time.
Greenhouse gas emissions are just the first focal point of such ecosystem models; they are merely a convenient, topical starting point. With time, other environmental issues may also be considered: biodiversity, water quality, food quality,
alternative energy sources, ammonia emissions and other queries still beyond
our view. Once the underlying processes of carbon, nutrient and energy flows are
inscribed in an ecosystem model, it can be retuned and redirected to illuminate
these and other pressing societal questions.
Ecosystem Services
Like all ecosystems, farms provide many benefits, many ecosystem services.
Some of these services are obvious: farms give us food, fibre and now even fuel.
But some, equally important, are more subtle: farms act as environmental filters,
cleaning air and water, removing wastes; they offer habitat to us and other creatures; they provide livelihood for rural families; they give us all places to play; and
they uplift our spirits with aesthetic appeal.
When enumerating the ecosystem services of farms, those who study climate
change often think first of reducing GHG emissions. This indeed is an important function, especially since farms can remove CO2 from air. But it is only one
service among many and may not even rank as the highest priority. Few GHGmitigating practices will be adopted if they do not also serve some other function, such as reduced cost, enhanced conservation or expanded biodiversity.
Scientists therefore look especially for those practices that can reduce GHGs and
enhance other ecosystem services. One such win-win opportunity is no-till farming. In some cases, it not only reduces GHG emissions, but it can also cut costs,
conserve soils by preventing erosion, offer nesting habitats through improved
ground cover and improve air quality by avoiding dust storms. Indeed, the widespread adoption of no-till farming likely stems more from these benefits than from
its effectiveness in reducing GHGs.
No-till is a rare case, however. Often, a gain in one service demands a sacrifice in
another. Indeed, even no-till farming may exact a cost somewhere along the way.
Choosing practices therefore often involves trade-offs, looking for big-win/small
loss opportunities. For example, are we willing to incur small yield losses (small
loss) to achieve substantial GHG mitigation (big win)? Or small increases in CH4
emission to achieve large increases in milk yield? Or a slight increase in ammonia
emission to drastically reduce N2O emission? Add to this mix all the other ecosystem services and the decisions grow even more dizzying.
10
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Clearly, choosing best practices depends on a holistic approach, examining all
ecosystem services, deciding how to value them and opting for the best of any
number of trade-offs. Such an approach requires the counsel of more than scientists. The decisions belong to society as a whole and need to be instructed by all
who live and depend on these farmlands.
Studying GHGs may help us reduce emissions, but that may not be its biggest
reward. Critically, GHGs tell us also how well an ecosystem is performing. Eruptions of N2O, for example, signal that the nitrogen cycle may be uncoupled; high
CH4 emissions may show that feeds are not efficiently used; excess CO2 emissions may point to depleting carbon stores or unwise use of energy. Our farms
and our planet may be on the threshold of tumultuous changes: changes in
climate, water availability, energy use and global food demands, to name a few.
In light of these coming changes, we need ways to see how our ecosystems are
holding up, ways of taking their pulse. Measuring the GHGs is one method for
doing that; they can direct us to better farming and better air.
The Future
The promise of biofuels
Farms, and what society expects from them, are in a constant state of change.
One recent impetus has been a surging interest in growing biofuels. Humans
have long used biomass for energy, burning wood or crop residues as fuel, for
example. Today, new technologies and the escalating cost of fossil fuels have
spawned interest in a range of other fuels produced from farm crops. Most advanced is the production of ethanol from corn or wheat. In Canada, once processing plants under construction are completed, grain ethanol will provide about
2% of motor gasoline consumption. Less advanced, but perhaps with more
long-term potential, is the making of ethanol from cellulosic biomass—switchgrass, woody biomass, or crop residues. Other possible biofuels include biodiesel, made from soybean or canola oils; biogas (CH4) from digested manures or
other organic materials, or biocombustibles—biomass from trees, grasses or
crop residues burned to generate heat, steam or electricity.
These biofuel crops may help reduce GHG emissions. Burning biofuel still releases CO2, but it is from carbon recently absorbed from the air by the growing
crop, so the CO2 is recycled, rather than added to the air as it is when fossil fuels
are burned. But some GHGs may be emitted when biofuels are produced (N2O,
for example, may be emitted when corn is grown). These emissions need to be
subtracted when estimating the net benefit of burning biofuel.
Other factors come into play when analyzing the overall benefits of biofuel. For
example, will the increased removal of harvested carbon affect soil quality, which
depends on plant litter to replenish organic matter? Will land used for biofuel
displace crops that will then be grown elsewhere, perhaps with higher environmental impacts? These and other questions emphasize the need for a holistic
perspective in evaluating the system-wide effects of proposed practices.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
11
Rejuvenating the air
There is emerging consensus among scientists that impending climate change
is a serious challenge meriting a concerted global response. But crafting policies
to meet this challenge is not easy, in part because we do not know exactly the
magnitude of changes coming and how fast they will appear. Global efforts to
combat climate change began in 1979, with the First World Climate Conference
in Geneva. These were bolstered in 1988 with the establishment of the Intergovernmental Panel on Climate Change (IPCC), which delivered its first assessment
report in 1990. (Its fourth report appeared in 2007).
The first IPCC report led to an international climate change agreement, the United
Nations Convention on Climate Change, adopted by 192 countries. The agreement aims to stabilize GHG concentrations at levels below those that would cause
dangerous climate change. Underlying this goal is the precautionary principle, the
idea that we cannot afford to wait for complete certainty before acting to prevent irreversible damage that may await us in the future. Continued international negotiations culminated in the Kyoto Protocol, which aims to reduce annual GHG emissions between 2008 and 2012 to 5% below those in 1990. Countries could meet
their individual commitments in two ways: by reducing emissions or by generating
biological carbon sinks (increasing stores of carbon in trees or soils).
Canada ratified the Kyoto Protocol in 2002, with far-reaching effects on farms.
An important effect has been increased interest in storing soil carbon, seen as an
important element of Canada’s commitment to reduce overall emissions.
What could happen
The world of our grandchildren, living 50 years from now, will likely look different
than it does today. One important change coming may be in climate. Climate
models project gradual warming in coming decades, and temperature increases
in Canada, because of its high latitude, may be more pronounced than the global
average. Precipitation may also be affected, though estimates are more uncertain than those for temperature. Because agriculture is so sensitive to climate,
these changes may alter how we farm our lands and how the land behaves; they
may influence the crops we grow, the way we house our livestock, the resilience of our soils, the pests we need to control. Any coming changes may affect
the amounts of GHG emitted, requiring new ways to mitigate them. Thus, we
must not only avoid emissions where we can, but also be prepared to adapt to
changes that may happen.
12
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Change, however, will not be limited to climate; indeed other stresses may
be even more transformative. With the global population growing, reaching perhaps 9 billion by 2050, there will come greater demands for food from
limited land, growing thirst for water from dwindling reserves, increased need
for energy from depleting stocks and higher demand for space among competing interests. These impending pressures require sober, long-term vision to
find ways of reducing GHG emissions and still meet the many other ecosystem
services we expect from farms.
A vision restored—dreams of future solutions
As we have seen, scientists have made important advances recently in understanding GHG emissions from farms and in finding ways to reduce them. But
the solutions are not yet all in place, especially in light of impending stresses.
So scientists will continue to look for answers to these questions and to new
questions still unseen. They might seek alternative energy sources and find ways
to use energy more efficiently on farms: using biological nitrogen fixation more effectively, for example, or recycling nutrients from farms more efficiently, including
the nutrients from the food we eat.
Whatever our responses, an underlying approach may be to reconnect consumers to the land. This would remind us that what happens on farmlands profoundly
affects all, and, in turn, that how we consumers behave profoundly affects the
land. Such an emerging way of thinking, enlightened by the ecosystem approach, would prompt scientists to seek solutions not only in their laboratories
and field experiments, but also in the lessons of history, in the perceptiveness of
art, and in the wisdom of those who farm the lands.
The best answers may emerge from a vision restored; from seeing our farmlands
not as resources to be spent, but as a home in which we all live, whether we
reside there or not.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
13
Introduction
O U R C H A N G I N G C L I M AT E
The air about us is changing. Its concentration of CO2 (carbon dioxide), once 280
parts per million (ppm), is now pushing past 380 ppm and is rising quickly (Figure
3). These changes, we know now with certainty, are mostly the result of human
activities; they bear our fingerprint.
Each year, we emit into the air about 9 billion tonnes of carbon, primarily from
burning oil, gas and coal (Figure 4), but also from the burning of forests, mostly in
the tropics. So every year the concentration of CO2 is about 2 ppm higher than
it was the year before. And there is no sign that these increases will slow; for the
next few decades, at least, we will depend on the burning of fossil fuels to power
our societies.
The changes to our air are not directly noticeable to us. Carbon dioxide is colourless, odourless, and not at all toxic at present levels—indeed, growing plants
depend on this gas. Still, the rapidly rising concentrations are worrisome, because
CO2 is a greenhouse gas (GHG): its presence in the atmosphere helps slow the
escape of heat back into space. In many ways, this is a good thing; without the
greenhouse effect, our planet would be a cold and lifeless place (Figure 5). But if
the concentration of CO2 continues to increase—perhaps doubling by the end of
the century—the world may warm appreciably. Already, there are signs that global
temperatures have increased and models predict more warming in the future.
Why does this matter? If the climate warms, the sea will rise, because warmer
water expands and because land ice will melt, increasing the amount of water in
the oceans. Many people live on the ocean’s edge, so even small rises—much
less than one metre—would inundate vast areas now populated. A warming
climate may change rainfall patterns and severe weather events may become
more common. As Figure 6 explains, climate change may affect a host of basic
human needs: food production, human health, biodiversity and access to water
for starters. Not all of these effects would be unpleasant, but many could be.
Much uncertainty still remains, but that uncertainty is itself a worry, since it makes
preparing for the future more difficult.
14
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Carbon dioxide is not the only greenhouse gas; methane (CH4) and nitrous oxide
(N2O), among other gases, also trap heat. And their concentrations too have
risen, adding to the effect of increasing CO2.
How agriculture is involved
Agriculture is closely tied to GHGs, three in particular: CO2, N2O, and CH4. Historically, large amounts of CO2 were released when forests were burned and
grasslands ploughed to clear lands for farming. Even today, farming is a significant
source of GHGs, accounting for about 10 to 12% of global emissions. (This does
not include emissions from land-use change, which releases additional amounts.)
FIGURE 3
FIGURE 4
Increases in Atmospheric CO2 Concentrations Annual Emissions of CO2 from Fossil(Concentrations of atmospheric CO2
fuel Burning, Cement Manufacture, and
measured at Mauna Loa, Hawaii.)
Gas Flaring (1 Pg = 1000 Mt).
10
380
CO2 EMISSIONS (Pg C y-1)
ATMOSPHERIC CO2 (ppm)
400
360
340
320
8
6
4
2
300
1950
1960
1970
1980
1990
2000
2010
Source: C. D. Keeling, S. C. Piper, R. B. Bacastow, M. Wahlen, T. P. Whorf, M. Heimann, and H.
A. Meijer, Exchanges of atmospheric CO2 and 13CO2 with the terrestrial biosphere and oceans
from 1978 to 2000. I. Global aspects, SIO Reference Series, No. 01-06, Scripps Institution of
Oceanography, San Diego, 88 pages, 2001. Data available online at: http://scrippsco2.ucsd.
edu/data/data.html, accessed November 14, 2007.
0
1750
1800
1850
1900
1950
2000
Source: Marland, G., T.A. Boden, and R. J. Andres. 2007. Global, Regional, and National CO 2
Emissions. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis
Center, Oak Ridge National Laboratory, U.S. Department of Energy: Oak Ridge, Tenn., U.S.A.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
15
FIGURE 5
The Greenhouse Effect
REFLECTED
H2O
SHORT-WAVE
RADIATION
CH4
N2O
CO2
H2O
N2O
LONG-WAVE
RADIATION
CH4
WARM LAYER NEAR
EARTH’S SURFACE
CO2
The earth continually receives radiation from the sun, part of which (about 30%), is
directly reflected back into space by clouds, other material in the atmosphere and the
Earth’s surface, especially where it is covered by snow or other light-colored material. The
rest, about the energy equivalent of several light bulbs per square metre, is absorbed by the
Earth. The Earth, having been warmed, emits radiation back into space, but this
radiation does not pass easily through the atmosphere. Some of the gases in air—termed
greenhouse gases (GHGs)—absorb and re-emit the Earth’s radiation, creating a layer of
warmth next to the Earth’s surface. The greenhouse effect, therefore, arises because of the
difference between the sun’s radiation, called short-wave radiation, which passes through
the GHGs, and the Earth’s radiation, called long-wave radiation, which does not. The
two forms of radiation differ because of the temperature of their sources—the sun is much
hotter, so its radiation has a shorter wavelength visible to our eyes; the Earth’s radiation is
more like the warmth we feel emanating from a hot-water radiator.
The greenhouse effect is essential to life on earth; without its warming effect, the Earth
would be cold and inhospitable. Increasing concentrations of the GHGs, however, could
lead to an enhanced greenhouse effect, causing some unpleasant changes to our climate.
In agriculture, unlike other sectors, most GHG emissions occur as CH4 and N2O,
two very potent GHGs. As Table 1 shows, agriculture is the main anthropogenic,
or human-derived, source of these GHGs. Methane is emitted mostly from ruminant livestock, such as cattle and sheep, and N2O comes mostly from the action
of soil microbes as they process nitrogen, especially in soils with high amounts of
added nitrogen from fertilizer or manure.
16
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 6
Possible Global Impacts
These are examples of what could happen as a result of varying levels of surface temperature increase in the 21st century.
Source: IPCC, Working Group II. 2007. Summary for Policymakers. Available online at: http://www.ipcc.ch/SPM13apr07.pdf, accessed November 14, 2007.
0
1
2
3
4
5˚C
INCREASED WATER AVAILABILITY IN MOIST TROPICS AND HIGH LATITUDES
DECREASING WATER AVAILABILITY AND INCREASING DROUGHT IN MID-LATITUDES AND SEMI-ARID LOW LATITUDES
WATER
HUNDREDS OF MILLIONS OF PEOPLE EXPOSED TO INCREASED WATER STRESS
UP TO 30% OF SPECIES AT
INCREASING RISK OF EXTINCTION
INCREASED
CORAL BLEACHING
ECOSYSTEMS
MOST
CORAL BLEACHED
SIGNIFICANT† EXTINCTIONS
AROUND THE GLOBE
WIDESPREAD
CORAL MORTALITY
TERRESTRIAL BIOSPHERE TENDS TOWARD A NET CARBON SOURCE AS:
~15%
~40% OF ECOSYSTEMS AFFECTED
INCREASING SPECIES RANGE SHIFTS AND WILDFIRE RISK
ECOSYSTEM CHANGES DUE TO WEAKENING OF
THE MERIDIONAL OVERTURNING CIRCULATION
COMPLEX, LOCALISED NEGATIVE IMPACTS ON SMALL HOLDERS, SUBSISTENCE FARMERS AND FISHERS
TENDENCIES FOR CEREAL PRODUCTIVITY
TO DECREASE IN LOW LATITUDES
FOOD
PRODUCTIVITY OF ALL CEREALS
DECREASES IN LOW LATITUDES
TENDENCIES FOR SOME CEREAL PRODUCTIVITY
TO INCREASE AT MID-TO HIGH LATITUDES
CEREAL PRODUCTIVITY TO
DECREASE IN SOME REGIONS
INCREASED DAMAGE FROM FLOODS AND STORMS
ABOUT 30% OF GLOBAL
COASTAL WETLANDS LOST‡
COASTS
MILLIONS MORE PEOPLE COULD EXPERIENCE
COASTAL FLOODING EACH YEAR
INCREASING BURDEN FROM MALNUTRITION, DIARRHOEAL, CARDIO-RESPIRATORY AND INFECTIOUS DISEASES
INCREASED MORBIDITY AND MORTALITY FROM HEAT WAVES, FLOODS AND DROUGHTS
HEALTH
CHANGED DISTRIBUTION OF SOME DISEASE VECTORS
SUBSTANTIAL BURDEN ON HEALTH SERVICES
0
1
2
3
4
5˚C
Global mean annual temperature change relative to 1980-1999 (˚C)
†Significant is defined here as more than 40%
‡Based on average rate of sea level rise of 4.2mm/year from 2000 to 2080.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
17
TABLE 1
The Main GHGs Emitted or Absorbed by Farms
A gas’s global warming potential indicates how effectively the gas warms the atmosphere. For example, a kilogram of CH4 is 25
times more powerful than a kilogram of CO2 in warming the air. The estimates for global warming potentials keep evolving as
scientists learn more. The estimates shown here were reported by the Intergovernmental Panel on Climate Change in 2007.
CHEMICAL SYMBOL
PRE-INDUSTRIAL
CONCENTRATION
CONCENTRATION
IN 2005
GLOBAL WARMING IMPORTANT HUMANPOTENTIAL
DERIVED SOURCES
Carbon dioxide
CO2
280 ppm
379 ppm
1
Fossil fuel burning;
deforestation
Methane
CH4
715 ppb
1774 ppb
25
Agriculture;
fossil fuel use
Nitrous oxide
N2O
270 ppb
319 ppb
298
Agriculture
Agriculture, however, also has an important role in decreasing the concentration
of GHGs in the atmosphere. When farmlands were first settled, they lost a great
deal of the carbon stored in their soils; the Canadian Prairies, for example, lost to
the air as much as 30% or more of the carbon stored in their organic matter (humus) within decades of initial ploughing. As our chapter on carbon explains, we
now know that with improved agricultural practices, we can rebuild the carbon
stored, thereby extracting CO2 from the air. Every tonne of new carbon stored in
soil is a tonne less carbon in the air. This process, called carbon sequestration,
is seen by many countries—including Canada—as one way to reduce net overall
emissions of GHGs.
Given the prominence of agriculture as both a source and potential sink—or
absorber—of GHGs, much research has been undertaken recently to understand
both processes. The immediate aim of these activities is to help meet Canadian
targets for reduced emissions of GHGs. At present, improvements in farming
practices alone can play only a small part in the overall challenge. But they serve
as an example of one response that, when joined by small responses from other
sectors of society, can add up to robust reductions.
18
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
GHGs are our bellwethers
There is another benefit to all this research—one often overlooked. GHGs emitted
in excess tell us something about how efficiently an ecological system—for our
purposes, a farm—is performing. If the land is emitting large amounts of N2O we
may conclude that nitrogen, an expensive commodity and potential pollutant, is not
being used wisely. If livestock are releasing excess amounts of CH4, we know that
feed energy is not being used optimally. If soils are losing carbon, we know that
solar energy stored as soil organic matter is not being prudently invested.
Put simply, GHGs are signals that indicate how well our ecosystems perform and
that point us toward more efficient methods for farming land and livestock. This
benefit, not always seen, already merits devoted study of GHGs, even apart from
goals of meeting reduction targets.
Our aim for this publication is to review recent findings about GHG emissions
from farms in Canada. Much of what we present is from research carried out
over the past five years under the Model Farm Program of Agriculture and AgriFood Canada. We have bolstered this information freely with results from other
Canadian and international scientists. We seek not only to show how better farming practices can reduce GHG emissions, but also how the emerging science of
GHG reduction can help steer us toward better farming practices.
The science stories we tell here are of interest to those in farming communities and
to all citizens. As the freely circulating GHGs demonstrate, we are all connected; the
gases do not honor the boundaries between farms and forests, between farmland
and city centres, or between those living today and generations unborn.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
19
Carbon Dioxide
M A N A G I N G C A R B O N I N A G R I C U LT U R A L S Y S T E M S
As Charles Darwin concluded his seminal work, The Origin of Species, he
reflected on the intricacies of life on Earth and the variety of forms that have
arisen through natural selection. “There is grandeur in such a view of life,” he
said. Had Darwin been a biochemist, he would undoubtedly have marveled at
the simplicity and beauty of the chemical thread that connects all living things
and ties them firmly to their surroundings—a thread spun from carbon atoms.
Carbon is a chemical element found in all living organisms. Bonded to itself, it
forms chains and rings that create the backbone of biochemically important
compounds, from sugars to the hereditary molecule DNA. This chapter describes
the flow of carbon through agricultural systems and pays particular attention to
its presence in soils. To begin this discussion, it is helpful to place agriculture in
the context of the global carbon cycle and to understand the role of carbon in
climate change and energy transfer.
The carbon cycle on a global scale
All of the carbon present in the global carbon cycle today was present at the formation of our solar system. The fourth-most abundant element on Earth, carbon
moves through a major biogeochemical cycle, through living organisms on its
way to or from the air, through the Earth’s interior and surface lands and through
the oceans and other waters. Carbon atoms reside in certain chemical forms for
thousands of years and in others for mere hours.
In the nonliving environment, carbon exists in a number of forms:
• CO2 in the atmosphere and water
• Carbonates, such as calcium carbonate, found in limestone and coral
• Fossil fuel deposits, such as coal, petroleum and natural gas, formed
from the tissues of organisms that lived in the distant past
• Organic matter in soils
Carbon enters the living organisms through photosynthesis. Plants, known as
primary producers, absorb CO2 into their leaves from the atmosphere and use
energy from the sun to fix the carbon into sugars. These sugars provide energy
for the plant and become basic building blocks of plant tissue. Carbon moves
through the food chain when herbivores eat the plants and other creatures eat
the herbivores. In this way, carbon comes to be found in all living tissues.
20
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 7
The Global Carbon Cycle
A
T
M
O
S
P
H
E
R
I
C
C
O
2
FOSSIL FUEL
FIRE
VEGETATION
SOIL
SPEED OF EXCHANGE PROCESSES:
SURFACE WATER
VERY FAST (LESS THAN 1 YEAR)
FAST (1 TO 10 YEARS)
SLOW (10 TO 100 YEARS)
DEEP WATER
VERY SLOW ( MORE THAN 100 YEARS)
SEDIMENT
Source: The Third Assessment of the Intergovernmental Panel on Climate Change, 2001
FIGURE 8
Photosynthesis and Respiration
PHOTOSYNTHESIS:
CO2 + LIGHT+ H2O
RESPIRATION:
CH2O + O2
Photosynthesis transforms solar energy into chemical energy.
Carbon dioxide from the atmosphere is combined with light
from the sun and water taken up by plant roots. This reaction forms in plant compounds such as carbohydrates while
releasing oxygen to the atmosphere.
CH2O + O2
CO2 + H2O + ENERGY
Respiration allows organisms to use the energy
manufactured during photosynthesis. The carbon in
plant compounds is combined with oxygen. This reaction
releases carbon as CO2 and releases water and some
energy as heat.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
21
Carbon returns to the atmosphere or water through the cellular respiration of living
organisms. During this process, sugar is burned in the presence of oxygen. This
generates CO2, which is released by the organism as a waste gas into the surrounding air. An important example of such respiration is decomposition or decay,
whereby the tissues of once-living organisms are consumed by microbes, releasing
the carbon they once held. Similar combustion chemistry takes place during forest
fires or when humans burn fossil fuels to supply their energy needs. All of these actions release CO2 into the atmosphere. Some carbon is also released as CH4 when
decay happens in the absence of enough oxygen to produce CO2.
M E T H A N E O X I D AT I O N I N
A G R I C U LT U R A L S O I L S
Agricultural soils emit large amounts of N2O and can
be either a source or a sink for atmospheric CO2.
They can also produce or consume CH4, but in
much smaller quantities.
Methane is the main constituent of natural gas and
its oxidation releases considerable amounts of
energy. Some soil bacteria called methanotrophs
can metabolize CH4 as a source of energy and
carbon when conditions are well aerated. In soils
on farms being drained to eliminate excess water,
this reaction occurs in most of the agricultural land
during the growing season, but at very low rates.
Indeed, approximately 100 hectares of land are
required to oxidize the quantity of CH4 produced
by one lactating dairy cow.
Other soil bacteria, or methanogens, produce CH4
during anaerobic decomposition of organic substrates.
Their activity in water-logged portions of the farm such
as ditches or near leaky manure storage structures
can result in small net CH4 emissions.
22
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
The carbon cycle on the farm
As in natural ecosystems, plants in agroecosystems absorb, or fix, carbon
through photosynthesis. Some of this carbon is returned to the atmosphere in
the form of CO2 through cellular respiration. Some is removed from the system
through harvesting. The remainder remains in the soil in the roots of plants or is
incorporated into the soil in the form of aboveground crop residues.
As microbes decompose these residues, part of the carbon is returned to
the atmosphere as CO2, some is incorporated into the microbes and the rest
becomes soil organic matter. In farming systems that include animals, carbon
may be removed from the system in the form of animal forage and feed and
subsequently in animal products such as meat—and then returned to the soil in
manure. Animals also respire, emitting CO2 directly into the atmosphere.
FIGURE 9
The Carbon Cycle in an Agricultural Ecosystem
CO2
1.
HARVEST
ECOSYSTEM
BOUNDARY
3.
2.
ORGANIC
MATTER
Soil carbon is dynamic. Changes in the amount of carbon stored in soil organic matter
depend on the relative rates of carbon input from plant litter and carbon emitted as CO2 via
decomposition. If carbon inputs are greater than carbon loss, then the amount stored increases; if carbon input is less then carbon loss, the amount of carbon stored decreases. To increase
stored carbon, practices must either: 1) increase plant yield (photosynthesis); 2) increase the
proportion of fixed carbon added to soil; or 3) slow the rate of organic matter decomposition.
Carbon’s importance to climate change
Since the beginning of industrialization—about 150 years ago—the amount of
carbon in the atmosphere has risen by more than 30%, from 280 to 380 ppm.
Between 1970 and 2004, global CO2 emissions increased by 70%, making it
the most important anthropogenic—man made—of the greenhouse gases. This
increase has resulted mostly from the growing use of fossil fuels for energy and,
to a lesser extent, from changes in land use, such as deforestation to make room
for agriculture and settlements.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
23
Rising atmospheric levels of CO2 have raised fears of disruptive changes in climate, prompting scientists and policy makers to look for ways to slow down the
rate of increase. This concern begs a more comprehensive understanding of how
carbon cycles through the Earth’s ecosystems, including agroecosystems and
how this flow is tied to energy.
Carbon as energy currency
Virtually all of the energy used by living systems can be traced back to the sun.
Photosynthesis ultimately traps light energy from the sun in the bonds that hold
sugar molecules together. Thus, the energy in all organic compounds resides in
their constituent chemical bonds and flows through ecosystems in the form of
these bonds. During fuel combustion this energy is released as heat, which humans use to heat their buildings, power the pistons in their car engines and drive
turbines to generate electricity. As cells respire, the combustion of sugars inside
cells releases energy. That energy is either captured in the molecule adenosine
triphosphate (ATP) or lost as heat. It is ATP that drives most of the energy-requiring reactions at the cellular level, moving the body’s muscles and synthesizing
complex chemical compounds.
FIGURE 10
Energy
Carbon and Energy Flows Through
an Ecosystem
CO2
SUN
HEAT
CO2
PLANTS
CONSUMERS
(ANIMALS, HUMANS)
In photosynthesis, plants transform radiant energy from the
sun into chemical energy, which is stored in the plant. This
energy is passed from organism to organism through the food
chain. Plants are consumed by animals and humans, who
either use the energy—to move, eat and think—or lose the
energy as heat. Decomposers, such as earthworms, bacteria
and fungi, eat dead organic matter from plants and waste
from consumers and use the energy or lose it as heat. All the
energy in ecosystems comes from the sun and is eventually
lost as heat. Energy is not recycled through the ecosystem.
Carbon
CO2
DECOMPOSERS
(EARTHWORMS,
BACTERIA, FUNGI)
HEAT
24
In photosynthesis, plants take up carbon in the form of CO2
from the atmosphere. Plants use this carbon to make sugars
and starches that then become the plants’ leaves and fruits.
As plants are consumed by other organisms, carbon is passed
on. Each time carbon is passed to another organism some
of it is lost to the atmosphere as CO2, where it can be used
again by growing plants. All the carbon in the ecosystem
comes from the atmosphere and will ultimately be returned to
the atmosphere. Carbon is recycled through the ecosystem.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
U N D E R S TA N D I N G E N E R G Y U N I T S
The amount of energy held in the food we eat is often
referred to as calories. A calorie is simply a unit for
measuring energy. Technically speaking, it is the amount
of heat needed to raise the temperature of one millilitre
of water by one degree Celsius. The calorie as a unit of
energy has been replaced by the “joule” in the scientific
community. One calorie is equivalent to about four
joules, and the kilojoule (kJ) is 1000 joules.
Some of the energy held in organic compounds remains stored in ecosystems
for years, even millennia. It can be stored either in plant materials, such as
wood, or in soil organic matter—called humus—which is derived from the
decaying tissues of dead organisms. The more carbon stored in an ecosystem,
the more energy it holds. A very small proportion of organic matter becomes
trapped over long periods of time in deposits of fossil carbon, such as coal, oil
and natural gas. Humans harvest these deposits, called fossil fuels, and burn
them to meet energy needs—in effect releasing solar energy that has been
trapped underground for millions of years.
Globally, plants remove about 120 billion tonnes of carbon from the atmosphere
each year. Averaged over the Earth’s total land area, this translates to about eight
tonnes of carbon per hectare (roughly the size of a football field). About half of
this carbon is used by the plants themselves for their own energy requirements,
leaving about 60 billion tonnes (four tonnes per hectare) to be stored in plant tissue. This storage value is termed net primary production (NPP). The amount of
carbon stored at any given site is influenced by many factors, including climate
and plant type. For example, the NPP in a tropical rainforest is much higher
than that in a desert. All this carbon is either eaten by animals, burned by fire, or
returned as plant litter to soil where it eventually decays.
The energy content of plant material ranges from 15 to 20 kilojoules per gram.
Plants with higher carbon content contain more energy. Important plant compounds with a very high carbon content, and thus a high energy content, are
lipids, lignin and proteins.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
25
TABLE 2
The Energy Content of Some Substances
MATERIAL
ENERGY CONTENT
(KJ-1 g-1)
Cellulose
18
Starch
17
Lipid
39
Terrestrial plants (whole)
19
Terrestrial plants (seeds)
22
Insects
24
Wood (oak)
21
Peat
20
Forest humus
21
Soil organic matter
20
Charcoal
34
Coal
29-34
Crude oil
42
Diesel
48
Natural gas
38-50
Biodiesel
38
Methane
55
Ethane
52
Uranium-235
77,000,000
Nuclear fusion (2He-3He)
300,000,000
Sources: Energy Content of Biofuel. Available online at: http://en.wikipedia.org/wiki/Energy_content_of_biofuel. Accessed Nov. 12, 2007.
Discharging soil battery
Soils can hold a lot of carbon. For example, in a field of corn, the amount of carbon present in the top 60 centimetres of soil may be 10 times the amount held in
the above-ground vegetation. Soil carbon represents a high reserve of energy in
the soil. In effect, soil is much like a battery that can be depleted of its energy in
some ways and recharged in others.
In an untouched native ecosystem, the soil has been charged up over the millennia, allowing soil carbon levels to reach maximum capacity, or equilibrium level.
Any disturbance of this equilibrium results in a loss of carbon and thus a loss of
energy. Cultivation and erosion are what most deplete soil carbon and discharge
energy from the soil battery.
26
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 11
The Effects of Cultivation on Soil Carbon
120
NATIVE
SOIL ORGANIC CARBON (t ha-1)
REVERT TO NATIVE
100
CONVERSION TO AGRICULTURE
ENHANCED PRODUCTION POTENTIAL
80
REALISTIC PRODUCTION POTENTIAL
60
STEADY STATE
40
SOIL DEGRADATION AND EROSION
20
0
0
10
20
30
40
50
60
70
80
90
100
YEAR
Changes in soil carbon content occur whenever there is change in land-use or management
practice. When virgin native land in Canada was first broken and cultivated, about one
third of the carbon content was lost within 20 to 30 years. There is potential in Canadian
agricultural systems to gain back some of the carbon lost by using improved practices such
as no-till and by planting crops, such as legumes, that build soil organic matter levels.
Even more carbon gain can be realized through alternative farming practices such as
incorporating perennials into cropping systems.
Farmers ploughed the Canadian Prairies for the first time about 100 years ago.
Within a few decades, these rich grassland soils had lost 30 percent or more of the
total carbon they had stored. This loss of carbon happened in a number of ways:
• Crop plants often contributed less carbon below ground than the native
plants they replaced.
• As crops were harvested, carbon was removed from the system. This meant
less plant carbon was returned to the soil every year.
• Tillage disrupted stable, protected organic matter in the soil and, along with
short-term cropping, often created temperature and moisture conditions in
the soil that hastened the decay of carbon-laden organic matter.
• Cultivated soils are more prone to the loss of carbon-rich topsoil via wind, water
and tillage erosion.
Cultivation makes soils more susceptible to erosion—the physical movement of
soil particles by wind or water. Erosion redistributes soil, removing it from some
areas and depositing it in others. Some fields lose 75% of soil organic matter
once they have been cultivated.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
27
Severe erosion can strip away surface soil, causing subsequent tillage to mix the
now thinner surface soil with subsoil, which is lower in organic matter. This mixing
has the effect of diluting the organic matter in the surface soil. Meanwhile, the
organic matter eroded from one area is transported to another area, creating a
thicker, organic-matter-rich deposit there. Thus, erosion changes both the lateral
and vertical distribution of organic matter—and thus of carbon and energy—in
the landscape. Reduced levels of organic matter constrain plant growth, and
therefore net primary production, which further reduces the amount of dead plant
tissue returned to the soil. Soils with less soil organic matter are more susceptible
to erosion. The downward spiral continues and the soil is further degraded.
Recharging the soil battery
Soil organic matter levels rise when the input of carbon into the soil (recharging
the battery) exceeds the output (discharging the battery). The balance can be
swung in this direction by:
• adding more carbon to the soil through increased crop production or by
returning to the soil more of plant residue remaining after harvest, or
• decreasing the rate of decomposition of plant residues and organic matter
in the soil.
The amount of soil carbon that potentially can be stored—and the rate at which it can
be added to the soil—depend on many local factors, including climate, topography, soil
properties such as clay content, and cropping history. For example, soils with a history
of excessive loss of carbon may have more potential for future gains.
The various agricultural practices that contribute to higher levels of soil carbon
can be grouped into the following strategies:
•
•
•
•
•
•
Reduced tillage
Intensified cropping systems
Improved crop nutrition
Organic amendments of soil
Greater use of perennial crops
Improved grassland management
Reduced Tillage
Since farming began, tillage has been used to kill weeds, prepare soils for planting and bury crop residues. In recent decades, the development of new herbicides and advances in the design of seeding implements have made it possible
to greatly reduce tillage in many farming systems. No-till, or zero tillage, the most
extreme reduced-tillage system, involves complete elimination of tillage apart
from the seeding operation.
28
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Tillage is a critical factor in the overall condition of soils. It alters the soil’s water
storage properties, which affects crop production and the rate at which organic
matter decomposes; it ruptures soil aggregates, which exposes new organic
matter to decomposition; it mixes plant residues into the soil, which alters the soil
profile and it enhances contact between soil and plant residues.
Clearly, to eliminate tillage is to alter the distribution of carbon in the soil profile. In
no-till systems, carbon tends to accumulate near the soil surface and is moved
only gradually into deeper layers by natural processes such as earthworm activity. No-till systems also affect the amount of carbon stored because organic matter often decomposes more slowly in no-till soils; contact between soil and plant
residues is reduced, isolating plant litter near the surface and leaving aggregates
that protect organic matter undisturbed.
Since soil disturbance tends to stimulate soil carbon losses through enhanced
decomposition and erosion, the elimination of tillage often results in soil carbon
gain, but not always. The amount and rate at which soil-carbon content increases
when tillage is eliminated varies with climatic conditions, soil type and the soil’s initial carbon content. Elimination of tillage usually has a greater impact on soils with
depleted reserves of soil carbon. Soil carbon tends to accumulate most rapidly in
less-humid conditions. This is because, in drier areas, no-till has greater potential
to conserve moisture and enhance crop yields. Higher crop yields leave more plant
litter near the soil surface, which slows decomposition and increases soil carbon
in the surface soil layer. Evidence shows that eliminating tillage may increase soil
carbon reserves, but may not guarantee higher soil carbon reserves; the amount of
carbon that accumulates depends on location and other management factors.
Intensive cropping
Summer fallow, the practice of leaving the soil unplanted for a growing season,
was once widely used in western Canada to replenish soil moisture, control weeds
and increase nutrients in the soil. However, summer fallow results in losses of soil
carbon; because no crop residue is produced in the fallow year, carbon inputs decline. Summer fallow also creates conditions such as higher moisture content and
temperature that favor faster decomposition of organic matter already in the soil.
Thus, eliminating summer fallow can significantly increase carbon reserves in soil.
Improved farming practices, notably the development of reduced-tillage systems,
have allowed farmers in many parts of western Canada to eliminate summer fallow.
This change, along with the reduction in tillage, has been largely responsible for the
net storage of carbon in the western provinces since 1990.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
29
Improved crop nutrition
Any practice that increases crop yields adds carbon to the soil, provided that the
increased residues produced are returned to the land. Thus, applying fertilizers to
nutrient-deficient soils to increase yields often increases soil carbon. This effect is
not always measurable since carbon increases can be small relative to the carbon already present. Furthermore, many agricultural soils in Canada are already
fertilized at or near optimal levels, so additional carbon gains from adding more
fertilizer may be insignificant.
Organic amendments
Farmers have known for millennia that spreading animal manure on a field can
improve soil fertility. Manure is rich in organic matter and nutrients and applying
it to land usually results in a build up of organic carbon and energy in soil. Applying manure to soil can also indirectly build soil carbon content by increasing
crop yields, thereby providing more carbon input to the soil, or by improving soil
structure and further protecting soil organic carbon from decomposition. These
effects can be considered as true gains in soil carbon, as they either increase net
primary productivity or decrease carbon decomposition.
On a global scale, however, recycling of plant carbon through animal manure
may not truly increase soil carbon storage. There are really only two ways of storing more carbon: increasing inputs of photosynthesized carbon or slowing decomposition (or a combination of the two). Adding manure accomplishes neither,
except to the extent that it increases yield by providing nutrients or improving
soil structure. The carbon applied in manure is merely recycled plant carbon and
does not represent additional carbon extracted from the atmosphere.
Greater use of perennial crops
As with manure application, the beneficial effects of perennial forage crops on
soil quality and fertility have been known for a long time. Today, extensive use of
perennial crops is recognized as one of the most effective ways to increase soil
carbon. Perennial forages, such as alfalfa, clover, timothy grass and bluegrass,
promote the accumulation of soil carbon, because they:
• grow over a longer season than most annual crops, and thus fix more
atmospheric carbon;
• transfer a large proportion of their fixed carbon to the roots—up to three times
their above-ground production—which may be more important for soil carbon
formation; and
• maintain and increase soil structural stability through their extensive roots
and because of the absence of tillage during their growth, thereby reducing
carbon decomposition.
30
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Improved grassland management
Most of Canada’s farmland was once under grass, but conversion of grassland
to cropland resulted in large losses of soil carbon. Re-establishing grasses on
these lands could replenish soil carbon, perhaps eventually restoring carbon
reserves to pre-cultivation levels. When this practice is used on what are often
referred to as set-aside lands, there may be large gains of soil carbon. However,
because this method involves taking land out of crop production, it is probably
suited only to marginal lands.
Canada currently has about 28 million hectares of grazing land. Management of
these lands—altering the amount and type of vegetation, the amount of residues
returned, and the redistribution of soil carbon via livestock activity and erosion—
can affect soil carbon reserves. Potential rates of soil carbon gains from improved
grazing practices are probably highest on lands that have been degraded. However, rates of accrual have not been extensively documented.
Measuring carbon
It is difficult to estimate the effectiveness of soil recharging practices because changes tend to occur in tiny increments—typically by a fraction of a tonne of carbon
per hectare per year. Meanwhile, carbon already present in the soil can amount to
100 tonnes per hectare or more; against such a background it can take years to
make definitive measurements. Many of the proposed soil charging practices have
not been studied for long enough in sufficient locales to establish with certainty
how effective they are. However, some initial estimates are available from measurements in long-term experiments and from running simulation models.
Removing carbon from the atmosphere and locking it up in soils—officially known
as carbon sequestration—is promoted as a strategy to mitigate climate change.
The essence of this strategy is that soil is transformed from being a source that
emits carbon into a reservoir that removes CO2 from the air, often referred to as
a carbon sink. Although using soil as a carbon sink has potential for reducing
atmospheric CO2 and curbing climate change, the strategy cannot be used
indefinitely. Over several decades in a field where agricultural practices have been
improved, the rate of carbon gain will gradually diminish, eventually approaching zero. As organic matter accumulates, its decomposition also increases, until
eventually carbon losses equal carbon inputs. This is when a field’s soil reaches a
new equilibrium. Therefore, sequestration of carbon in soil is a temporary measure
for extracting carbon from the atmosphere. Furthermore, the carbon stored as soil
organic matter may be vulnerable to losses if the climate warms or if carbon-saving
management practices are interrupted. For example, carbon gains in soil following
elimination of tillage can be rapidly lost when the soil is once again ploughed.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
31
TABLE 3
Some Agricultural Practices to Store Carbon in Soil, the Total Area of Land
Affected and the Potential Rates of Carbon Gain over 20 Years
AREA
(106 ha)
RATES
(t C ha-1 y-1)
CONFIDENCE
HIGH,
MEDIUM,
LOW
4-6
0.0 to 0.4
M
2. Eliminate summer fallow
3
0.0 to 0.5
H
3. Include more forages in rotations
4
0.0 to 0.5
M
4. Increase residue return by increasing yields (e.g., nutrient amendment,
irrigation, better varieties) or avoiding removal or burning
5
0.0 to 0.3
M
5. Restore permanent grass or woodland
1
0.2 to 1.0
H
6. Use organic residues (e.g., manures, biosolids, crop residues) more efficiently,
especially to restore depleted soil
1
0.1-0.5
H
1. Improved grazing practices
(e.g., changes in grazing intensity or frequency)
10
0.0 to 0.1
L
2. Increase productivity
(e.g., nutrients amendment, irrigation, new species)
1
0.0 to 0.3
M
PRACTICE
Cropland
1. Reduce tillage
Grazing land
The critical importance of soil organic matter
Soil fertility and plant nutrition
In addition to carbon and energy, soil organic matter also contains large quantities of the critical plant nutrients phosphorus, sulphur and nitrogen. Nitrogen is
the most important plant nutrient. In fact, a lack of it is the key limiting factor for
productivity in natural and agricultural ecosystems. Practices that promote the
accumulation of soil organic matter and soil carbon also increase the potential
supply of nitrogen as 99% of it is contained in organic matter.
Soil organic matter also contributes to fertility through its influence on the cation
exchange capacity (CEC) of soils—the soil’s ability to hold onto positive ions,
such as the nutrient potassium and some micronutrients. In fine-textured soils
the CEC is largely controlled by clay content, but in some sandy soils almost all
CEC can be attributed to soil organic matter.
32
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Physical condition of the soil
Soil organic matter affects the physical properties of soil, stabilizing its structure
and holding its particles together in small clumps called aggregates. In doing this,
organic matter helps prevent soil erosion by water, wind and tillage. By holding
soil particles together, soil organic matter also helps to create pore space in the
soil, permitting the circulation of air and water and encouraging the proliferation
of living organisms, including plants.
Continuous or repeated incorporation of fresh plant material into soil is a good
way to maintain its structural stability. Fresh plant material and other organic residues accelerate microbial growth in the soil, generating more compounds that
glue soil particles together. These binding agents include microbial gum, humic
substances, lipids and microbial structures such as filamentous fungal hyphae.
Improved aggregation protects the decomposing organic matter from further decomposition through a feedback mechanism. If organic matter is not replenished
regularly, or if soil is disturbed by heavy rainfall or intensive tillage, the aggregates
can be broken, exposing their interiors and accelerating the decomposition of
organic matter and binding agents. Without organic matter, sandy soils would
look like beach sand and many other soils would feel like concrete.
Soil organic matter also improves the water-holding capacity of soils. This feature
is particularly critical in sandy soil, which would otherwise be able to hold little
water for plant use.
Good soils contribute to great farming
In short, a soil that has more organic matter, and hence carbon, is usually a better soil, which means conserving or enhancing soil organic matter has benefits
far beyond concerns about climate change mitigation. Replenishing soil carbon
reserves—an issue that was the subject of intensive research for decades before
climate change issues came to prominence—is simply good agricultural practice.
FU RTHE R R E AD I NG
Janzen, H.H. 2005: Soil carbon: A measure of ecosystem response in a changing world? Canadian Journal of
Soil Science 85: 467–480.
Jenkinson, D.S. 1981. The fate of plant and animal residues in soil. Pp. 505–561. In: D.J. Greenland and
M.H.B. Hayes (ed.) The chemistry of soil processes. John Wiley & Sons Ltd.: New York.
Smith, P., D. et al. 2007. Agriculture. Pp. 497-540. In B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A.
Meyer (eds), Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press:
Cambridge, United Kingdom and New York.
Swift, M.J., O.W. Heal, and J.M. Anderson. 1979. Decomposition in terrestrial ecosystems. University of
California Press: Berkeley, CA.
Energy Content of Biofuel. Available online at: http://en.wikipedia.org/wiki/Energy_content_of_biofuel.
Accessed Nov. 12, 2007.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
33
Nitrous oxide
PLUGGING LEAKS TO THE ENVIRONMENT
P L A N T S A R E I M M E R S E D I N A S E A O F N I T R O G E N — 78% of the air is
nitrogen gas—yet this nutrient is the one most often lacking in plants and, therefore, limiting their growth. That is because nearly all the nitrogen in air is dinitrogen (N2), two nitrogen atoms bound together by a sturdy triple chemical bond.
Only when this bond is broken, can plants use the nitrogen.
In nature, the breaking apart of dinitrogen to create reactive nitrogen occurs mostly
by the activity of select bacteria through a process known as dinitrogen-fixation.
One such group of bacteria, known as Rhizobia, reside in nodules attached to the
roots of legumes such as alfalfa, beans and peas. Once fixed, the nitrogen reformulated by these bacteria can be used by plants. When the plants decay, they
release their nitrogen into the soil for use by other plants. Alternatively, the plants
may be consumed by animals, which return nitrogen to the soil when animals’
bodies decay or via animals’ wastes. Livestock, for example, obtain their nitrogen
from protein they consume in feeds and then excrete most of the nitrogen through
their urine and feces, returning it to the soil to be reused by plants.
The advent of synthetic fertilizers
About a century ago, humans learned how to fix nitrogen industrially, using intense
heat and pressure through a process known as the Haber-Bosch process. This
discovery revolutionized agriculture, making vast amounts of reactive nitrogen available and launching more intensive and productive farming methods. About 40% of
the nitrogen in protein now consumed by humans worldwide is fixed industrially.
Unfortunately, the reactive nitrogen so essential for crop production is unstable.
The nitrogen cycle is therefore leaky—nitrate and soluble organic nitrogen leach
out of the soil profile, and gases (dinitrogen, ammonia, N2O, nitric oxide and
others) seep into the air. Such losses are especially prevalent in agricultural
systems that use a great deal of nitrogen to maintain productivity and replace
nitrogen lost in harvested materials.
Leaks cause damage
Many of the nitrogen forms lost through these leaks can cause environmental
damage. Nitric oxide and N2O, for example, can accelerate the breakdown of the
ozone layer in the stratosphere, a process that lets in an increasing amount of
34
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
harmful ultraviolet radiation. Nitrate in excess concentrations can make water unsafe to drink, leading to methaemoglobemia or blue-baby syndrome in infants; nitrate can also lead to algal blooms in standing water. Ammonia, when deposited
back onto land or water as a gas or in rain can acidify soils, affect water quality,
cause forests to die back and change the plant population in natural ecosystems
by making them more vulnerable to invasive species.
In this chapter we focus specifically on N2O, because it is a greenhouse gas
(GHG), and a very potent one at that. It is about 300 times as powerful as
CO2. Nitrous oxide emissions can emanate directly from farm soils and stored
manure. These are often referred to as direct emissions. But nitrogen is also
lost from agricultural systems in other forms, via leaching or volatilization. This
nitrogen can be a source of N2O emissions produced at sites outside the
boundaries of the farm. These N2O emissions, often referred to as indirect or
off-site emissions, must also be included in the overall accounting of N2O emissions originating from agricultural sources.
Although emissions of N2O represent only a small proportion of nitrogen lost
from farms, they account for about 50% of the warming from gases emitted from
agriculture. Finding ways of suppressing N2O releases, therefore, is critical if we
are to reduce the effects of farming on global warming.
How N2O is formed
The nitrogen cycle
Nitrous oxide is released as a product or byproduct when microorganisms convert nitrogen from one form to another in the soil. To understand these emissions,
we must review the processes whereby nitrogen flows through the soil.
Nitrogen can enter the soil in both organic and inorganic forms. Organic forms
include plant litter, animal manures and other materials derived from plant or
animal products. When these organic materials enter the soil they are gradually
decomposed by soil fungi and bacteria, which release the nitrogen as ammonia,
which, when dissolved in the soil water, becomes ammonium. Ammonium can
be taken up by plants, but is usually converted quickly to nitrate by soil microbes
in aerated soils (soils high in oxygen).
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
35
FIGURE 12
Conceptual View of the Nitrogen Cycle on Canadian Farms.
EXPORT
ON-FARM
OFF-FARM
DINITROGEN
N 2O
AMMONIA
ORGANIC MATTER
AMMONIUM
NITRATE
AMMONIUM
NITRATE
NITRATE
Nitrous oxide can be produced at many points in the cycle.
Thus, nitrogen typically flows from organic nitrogen to ammonium to nitrate,
which accumulates in soil and is readily taken up by plants again. In some conditions, especially when soils are poorly aerated (low in oxygen), the nitrate can be
reduced to dinitrogen gas through a process called denitrification. This process
renders the nitrogen unavailable to plants.
In agricultural lands, soil nitrogen is often supplemented with industrially fixed
nitrogen, applied as fertilizer. Once in the soil, this nitrogen behaves no differently than nitrogen from organic sources. Though forms vary, most fertilizers
contain nitrogen as ammonia, ammonium, nitrate or urea. The first three enter
directly through the processes already described; urea, a nitrogen form similar
to that in urine, is quickly converted to ammonia in soil and then enters the
same cycles. One important difference from incorporating nitrogen in organic
form, however, is that applying fertilizer typically adds instantly a large pulse of
reactive nitrogen that is immediately available to plants and microorganisms.
Since plants cannot take up all of this nitrogen immediately, it remains in solute
or gaseous forms and often produces more N2O emissions.
In addition to fixation of N2 by bacteria, nitrogen is also added to soils from the
atmosphere, either as gas or particulates or in precipitation. Small amounts of this
nitrogen are fixed by lightning, but most comes from ammonia or other forms of
nitrogen released from such sources as feedlots. Thus, the rate at which nitrogen
is deposited on soils varies depending on the proximity of a given field to sources
of gaseous nitrogen. In Canada, deposition of atmospheric nitrogen is usually quite
small compared to amounts from other sources.
36
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Whatever the source of nitrogen, once it takes the form of ammonium or nitrate,
it is readily absorbed by plants. If the plant is a farm crop, much of that nitrogen
is exported in harvested product—grains, forage or animal products. This export
is by far the largest loss of nitrogen from a soil-plant system. It will be consumed
by humans or animals, excreted and mineralized back into an inorganic form.
Each time a molecule of nitrogen is converted to an inorganic form it is susceptible to loss in gaseous forms such as nitric oxide, N2O, ammonia and particularly
dinitrogen. Thus, perhaps after many transformations, nearly all of the nitrogen
that entered soils from the atmosphere will be returned to the atmosphere,
thereby closing the nitrogen cycle.
In summary, a soil nitrogen molecule has an eventful existence. Some nitrogen is
incorporated into soil organic matter that will have a very slow turnover (decades
to centuries), but most of it is continually being transferred or cycled between
organic and inorganic forms. This cycling of nitrogen between organic and
inorganic forms may occur many times before the nitrogen is lost from the farm
system through leaching, gaseous exchange or crop removal.
Processes of N2O formation
Nitrous oxide can be released from various phases of the nitrogen cycle through a
multitude of biological processes. Although many processes in soils can produce
N2O, most soil-emitted N2O is thought to derive from two processes—nitrification
and denitrification. Broadly stated, nitrifiers oxidize ammonium to nitrate. The amount
of N2O produced per unit of ammonium nitrified is usually small, but cumulative
losses can be important on an annual basis. Denitrifiers transform nitrate to N2O and/
or dinitrogen. The amount of N2O produced per unit of nitrate denitrified can be quite
large and denitrification is a major pathway for N2O emission from agricultural soils.
Delving Deeper
Nitrification is carried out by both autotrophs and heterotrophs, but the latter group is thought to be a minor contributor in
agricultural systems. Autotrophic nitrification occurs in two stages, each stage conducted by separate groups of bacteria. The
oxidation of NH4+ to nitrite (NO2-), typically represented as NH4+ → NH2OH → HNO → NO2-, is followed by the oxidation of
NO2- to NO3, which is completed in a single step.
Denitrification can be defined as the dissimilatory reduction of ionic nitrogen oxides to gaseous products by essentially
aerobic bacteria under conditions of oxygen deficiency. The reaction sequence is usually represented as: NO3- → NO2- →
NO → N2O → N2. Most denitrifying bacteria possess all the reductase enzyme complexes necessary to reduce NO3- to
dinitrogen, but some are not equipped with N2O reductase and N2O is the terminal product.
Even the broad categories of nitrifier and denitrifier are not clear cut as, for example, some nitrifiers can also denitrify
(nitrifier-denitrification). In some situations nitrifier-denitrification can be an important contributor to soil-emitted N2O. In
addition, N2O might also be generated by dissimilatory reduction of NO3- to NH4+ (DNRA) and other unidentified biochemical
pathways, but the contribution from these pathways is likely negligible in Canadian agricultural soils.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
37
Indirect N2O emissions
Nitrogen can be lost from farms in many of its forms. Predominantly, it is lost in
the forms of N2O and dinitrogen via denitrification, nitrate via leaching, and ammonia via volatilization. Dinitrogen usually represents the largest loss, but it is not
an environmental concern since nitrogen simply returns to the atmosphere as an
inert gas. Leached nitrate and volatilized ammonia, on the other hand, are significant sources of N2O via processes occurring off-site.
Nitrate leaching
Soils are negatively charged and therefore attract positively charged ions such
as ammonium, K+, and Ca++. Nitrate, conversely, is negatively charged and will
remain dissolved in soil water. If, under excess precipitation or irrigation, soil
water flows through the soil and into groundwater below, the nitrate is carried
with it; in other words, it is lost via leaching and ends up in groundwater or
streams. Most nitrate loss from tile drains occurs in the late fall and early spring
(between cropping seasons).
Though it is difficult to determine the exact amount, a fraction of the nitrate
leached from farm fields can be further converted downstream to N2O. This N2O
could be either from out-gassing when drainage water leaves agricultural fields or
from denitrification if conditions are favourable.
FIGURE 13
N2O Degassed from Drainage Water
0.45
0.4
0.35
Some of the N2O that is produced in agricultural soils
can dissolve in soil water
and escape the field through
drainage tiles. In this example, the amounts of N2O
degassed from the drainage
water can be as large as soilsurface N2O emissions.
N2O EMISSIONS (kg ha-1 y-1)
DRAINAGE
0.3
SOIL SURFACE
0.25
0.2
0.15
0.1
Source: Dave Burton, Nova Scotia Agricultural
College, Truro, NS
0.05
0
2002
38
2003
2004
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
How much nitrogen is lost by leaching from Canadian farmlands? Estimates of
average losses vary widely, with values as low as 2 kilograms of nitrogen per
hectare per year in arid Canadian Prairies and as high as 30 kilograms of nitrogen
per hectare per year in humid regions, the central provinces falling somewhere in
between. Indirect loss of N2O associated with nitrate leaching in Canada contributes approximately 9% of total N2O emissions from agricultural sources.
Ammonia volatilization
Ammonia is released from ammonium dissolved in water. Thus, small amounts
of ammonia can be generated wherever ammonium exists in solution: from soils,
growing plants, even the breath of animals. Not surprisingly, most of the ammonia released from farms comes from highly concentrated sources: the urine
of livestock, which contains high concentrations of urea, quickly hydrolyzed to
ammonium; animal manures, which contain urine, but also ammonium from decomposing feces and bedding materials; ammonium-based fertilizers; and crop
residues, which release ammonium when they decay.
The amount of ammonia released from farms may range from negligible traces to
concentrated plumes that can be detected by smell. The most prominent factors
affecting amounts emitted include: the concentration of ammonium in solution,
which influences the strength of the ammonia source; the pH of the solution,
which determines the relative abundance of ammonia and ammonium; and the
degree of contact of the solution with the atmosphere, which affects how easily
the ammonia will be emitted into the atmosphere.
Much of the ammonia transported in the atmosphere is eventually absorbed in a
gaseous state by the ground or dissolved in precipitation. This is pertinent to the
study of GHG emissions in that re-deposited ammonia is subject to nitrification
and denitrification, which can release N2O. We estimate that this indirect source
of N2O contributes approximately 9% of national agricultural sources of N2O.
Factors that control the formation of N2O
The amount of N2O emitted from soils is determined by the rate at which N2O is
produced and the proportion of the N2O produced that is actually released from
the soil surface. These two factors are controlled at the cellular level according to
the supply of raw materials and prevailing environmental conditions. Of course,
mineral nitrogen is a key factor controlling nitrification and denitrification by soil
microbes but denitrifiers also require a source of easily decomposable organic
matter. For this reason, high N2O emission rates may not be observed following
application of mineral nitrogen in soils with low organic matter contents.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
39
Water content
Because soil-water content strongly influences the amount of oxygen present, as
well as the availability of nutrients, microbial activity and even soil temperature, it
is considered the primary factor controlling N2O emissions in soils. As seasonal
precipitation levels vary considerably across the Canadian agricultural zone, so
too does the magnitude of soil-emitted N2O. For example, N2O emissions in the
semiarid to subhumid prairies tend to be much lower than emissions for the more
humid areas in eastern Canada. This is not surprising as soil aeration is a strong
regulator of N2O emissions and soil aeration is affected significantly by soil water.
Precipitation patterns can also affect seasonal N2O emission patterns. Deep
snow packs insulate the soil, keeping temperatures near the surface hovering
near or just below freezing. This allows low levels of microbial activity to continue
through the winter, causing substantial over-winter emissions of N2O in some
cases. By contrast, in the arid and relatively snow free Prairies, soil temperatures
near the surface can drop to -20 ºC, leading to negligible emissions. Also, less
snow in winter means soils dry more quickly in spring, which results in a relatively
small spring burst of N2O emissions.
Soil type, landscape and climate
In general, N2O emissions from agricultural soils in Canada can be characterized
by low but reasonably consistent emissions with interspersed episodes of much
higher emissions. In the drier regions of the country these emissions likely arise
largely from nitrification and their magnitude is related to total nitrogen turnover. In
more humid regions, emissions likely result from a combination of nitrification and
denitrification. Bursts of N2O emissions are generally triggered by high soil-water
contents after rainfall, irrigation or snow melt, largely from denitrification.
Soil water content—and hence N2O emissions—also varies according to such
factors as soil texture, drainage and slope position. In some instances, scientists
found that drainage and soil texture could explain up to 86% of annual differences in denitrification. As the amount of clay particles increases in soils, water
infiltration slows down and soil water content increases. Accordingly, some scientists have reported N2O emissions that were on average twice as high on clay
as on loamy and sandy soils.
Water is not distributed equally over the landscape as it drains from higher grounds
and collects in depression areas. Thus N2O emissions are higher from moist depressional areas than from the dry upslope areas.
40
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 14
FIGURE 15
Cumulative N2O Emissions from Sandy
and Clay Soils near Québec City
Cumulative N2O Emissions (March-October)
from Upper and Lower (depression)
Positions of a Slope near Mundare, Alberta
4
3.5
1
0.5
0
SAND
CLAY
Soils with more fine particles (clay) usually emit more N2O
than sandy soils. Clay materials slow down water infiltration and result in poorly aerated, wetter soils. These conditions favour denitrification and high N2O production rates.
Source: P. Rochette, AAFC, Québec City, QC
N2O EMISSIONS (kg ha-1 y-1)
N2O emissions (kg ha-1 y-1)
1.5
3
2.5
2
1.5
1
0.5
0
UPPER
LOWER
Both slope positions were seeded to spring wheat and were
fertilized with 60 kilograms of nitrogen. Wetter conditions
in the lower portions of the landscape resulted in poorly-aerated conditions and higher N2O emissions.
Source: R. Lemke, AAFC, Saskatoon, SK
Minimizing N2O emissions from agricultural soils
We saw in earlier sections of this chapter that N2O production in soils is a function of two principal factors: the quantity of soil mineral nitrogen available for the
reactions of nitrification and denitrification, and the level of soil aeration, which will
determine if denitrification, the most important source of N2O, is favoured.
The following sections outline a few ideas for managing agricultural soils to minimize N2O emissions.
Nitrogen Management
In natural environments, nitrogen is often the nutrient limiting plant growth. The
nitrogen available in the soil of these ecosystems comes mostly from the decomposition of soil organic matter and plant residues (fallen leaves, dead roots,
dead trees) and is quickly absorbed by plant roots when it becomes available.
The mineral nitrogen content of these soils is usually low. Consequently, the N2O
emissions are very small.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
41
In agricultural fields, the situation is different. All agricultural crops contain nitrogen. For example, there are approximately 10 kg of nitrogen in each tonne of
corn or wheat. When crops are harvested, large quantities of nitrogen leave the
field and must be replaced to maintain soil fertility. In other words, fertilization of
agricultural soils is an essential component of most cropping systems and fertilizer nitrogen is one of the largest causes of N2O emissions.
Why is this the case? Plant roots and denitrifying microorganisms consume
nitrogen in the same forms: ammonium and nitrate. Therefore, fertilizer cannot be
made available to the plant roots without also being available to N2O-producing
microorganisms. Completely eliminating the N2O emissions from agricultural soils
is thus not a realistic objective. Our goal is rather to reduce them by ensuring that
as much of the applied nitrogen as possible is absorbed by the crops and not
transformed by the microorganisms.
How can we achieve this? Managing the following farming inputs may help.
Mineral fertilizers
If we are to reduce N2O emissions by managing how fertilizers are applied, it
makes sense to keep a key strategy in mind: apply only the amount of fertilizer
that plants need—and apply it at the correct time so that plants can absorb it immediately rather than leave it to microorganisms.
Nitrogen for crops comes from two sources: fertilizers (mineral and organic) and
crop residues. Fertilizers should fill the difference between the plants’ nitrogen
requirements and the nitrogen released by the decomposition of crop residues.
For example, if legumes have been planted in the previous growing season, 25
to 100 kilograms of nitrogen per hectare will be released gradually by decomposition over the growing season. Such releases must be factored into the overall
nitrogen fertilizer requirements of any given crop.
During the first weeks after planting, young seedlings take up relatively little nitrogen. During the period of rapid growth they take up a great deal. Once mature,
they take up none at all. Therefore, rather than apply one season’s nitrogen
fertilizer at seeding time, the application could be split; a portion could be applied
at seeding time with the balance applied when the crop is growing rapidly. It is
impossible to synchronize fertilization and plant growth perfectly, but it is certainly
worth considering split applications to lower soil mineral nitrogen early in the season and N2O emissions. This practice is not effective for all regions in Canada.
For example, on the semiarid prairies, the potential reduction in N2O emissions
would likely not justify the energy used for this additional field operation.
42
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 16
Cumulative N2O Emissions from a Potato Field in
Frederiction, New Brunswick
N2O EMISSIONS (kg ha-1 y-1)
2.5
2
1.5
1
0.5
0
N0
N120+80
N200
Experimental plots receiving no nitrogen fertilizer (N0) were compared to plots receiving
200 kg of nitrogen per hectare at planting (N200) or 120 kg of nitrogen per hectare at
planting and 80 kg of nitrogen per hectare at final hilling (N120+80). Application of
nitrogen fertilizers increased emissions by increasing soil mineral nitrogen availability to
soil microbes. However, splitting total fertilizer requirements in two applications lowered
soil nitrogen levels and N2O emissions.
Source: D. Burton, Nova Scotia Agricultural College, Truro, NS
The form and the mode of fertilizer application can also influence the efficiency
with which crops use nitrogen and thus affect the amounts of N2O produced. It
is important to make fertilizers easily accessible to plant roots. Therefore, surface
application is not recommended as the most effective way to encourage plants
to use nitrogen. Placing the fertilizer in bands near the seed row usually improves
nitrogen uptake by the crop, but depth of application may be an important consideration. In a study on a clay loam soil in southwestern Ontario, banding nitrogen fertilizer at a depth of 2 cm decreased N2O emissions by 25% compared to
banding at a depth of 10 cm. One explanation for higher N2O emissions is that
soils more frequently become anaerobic at depth due to wetter soil conditions.
Therefore, denitrification was favored.
If fertilizer application occurs under conditions of imperfect aeration (very wet or
compacted soils), the ammonium form is preferable because in the short run it
reduces the risks of denitrification, the major source of N2O. Conversely, in wellaerated soil, the nitrate form will generate less N2O than the ammonium form.
As the name implies, slow-release fertilizers release nitrogen slowly over time—at
a rate that better matches crop uptake. This avoids large accumulations of mineral
nitrogen in the soil and minimizes the potential for N2O production. Other substances, when added to the soil, can inhibit nitrification, maintain the applied nitrogen in
the ammonium form longer and result in low N2O emissions.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
43
Manure Nitrogen
Farm animals’ feed is often rich in proteins. The ammonia released as they digest
these proteins is toxic to the animal and is quickly excreted in their urine as urea
or ureic acid. What happens to this nitrogen depends on the conditions found
in the various manure storage structures. Oxygen being required for nitrification,
most mineral nitrogen will remain as ammonium if stored in absence of oxygen.
Such conditions are found in liquid storage systems and no or very little N2O is
produced and emitted from liquid manure tanks and lagoons. The situation is
very different in more aerated environments such as in solid manure. In manure
piles, N2O is produced during nitrification of ammonium and even more is formed
when a fraction of the product of nitrification—nitrate—is later denitrified if conditions become anaerobic.
Manure treatment can also influence N2O emissions during manure storage. For
example, while static composting does not increase N2O emissions compared
to standard solid manure piles, composting with frequent turning of the compost
pile can increase emissions 10-fold. This dramatic effect on N2O emissions is the
result of bringing nitrates produced in aerated outer parts of the pile to locations
inside the pile where oxygen is limited and denitrification occurs.
Animal excretions contain large amounts of nitrogen that can be used to fertilize
crops. Manure nitrogen, when applied to soils, increases N2O emissions in a way
similar to mineral fertilizers. Therefore, precautions recommended for increasing
the uptake of synthetic nitrogen by crops also apply to manure nitrogen. Efficient
use of manure nitrogen not only allows for appreciable savings in mineral fertilizers for the farmer but also results in important reductions in N2O emissions as
less synthetic fertilizers needs to be applied.
Legume crops
Legume crops such as soybean and alfalfa can fix nitrogen present in the atmosphere with help from bacteria in their roots called Rhizobium. These microbes
can convert atmospheric dinitrogen into ammonium that plants can use. Until
recently, it was believed that this nitrogen fixing was accompanied by a significant
release of N2O but recent studies no longer support this.
Legume crop residues returned to the soil after harvest are relatively rich in nitrogen; their decomposition does stimulate more N2O production than the residues
of non-nitrogen fixing plants. However, the production of N2O associated with the
legume crops is usually small compared to emissions generated by crops requiring nitrogen fertilizers.
Cover crops
Nitrogen uptake by plants is an important sink for soil nitrogen. When crops
are absent, mineral nitrogen can accumulate and be lost to the environment in
several forms, including N2O. Perennial crops have a long growing season and
little soil nitrogen accumulates in these systems. In annual crops, however, little
44
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
nitrogen uptake occurs early in the season and after maturity or harvest. The
accumulation of mineral nitrogen released by the decomposition of soil organic
matter and crop residues during these periods can result in important N2O emissions. Cover crops planted after the harvest of annual crops take up free soil
nitrogen, avoiding its accumulation in the soil and thereby reducing N2O losses.
Cover crops may not be a good option for the drier regions of the country, where
soil-water conservation is of utmost importance.
However, crop management is important to the efficiency of this practice. The
nitrogen stored in the cover crop’s tissues must be released into the soil at a time
when crops will take it up. Therefore, it may make sense to delay ploughing the
cover crop into the soil until the following spring.
Soil aeration
As we have seen, N2O is produced in much greater quantity in soils that do not
contain much oxygen. These include soils that have a high water content and
soils that are compacted. Soils poor in organic matter also have properties that
tend to decrease aeration as they have fewer tunnels formed by roots, earthworms and insects. These soils also tend to be more susceptible to compaction.
Soil management practices can minimize the release of N2O by their impact on
soil water content, soil organic matter content and soil compaction. These general principles, as seen below, can guide us in choosing management practices
that ensure enough soil water for an optimal crop growth while maintaining an
adequate soil aeration that limits denitrification rates and N2O production.
Soil tillage
Traditionally, the preparation of the seedbed and the control of weeds in agricultural fields were carried out by vigorous soil tillage. In Eastern Canada,
mouldboard plough followed by harrow passes incorporates the residues of the
previous crop and loosens the surface soil layer in preparation for planting. In row
crops, weed control during the growing season is often accomplished by periodic passes of adapted harrows. Because of a drier environment on the Canadian
Prairies, preparation of the seedbed was traditionally carried out by successive
passes with a field cultivator and/or harrows.
Aggressive soil tillage requires time, energy and resources, contributes to the destruction of soil structure and leaves the soil surface more vulnerable to erosion.
Reduced or no tillage is an alternative approach that avoids these problems.
It consists of a limited use of soil tillage implements; the crops are often sown
through the crop residues left on the soil surface after the previous year’s harvest.
Compared to conventional tillage, no tillage results in several important differences, which can influence the production and the emission of N2O.
Under no tillage, the crop residues, fertilizers and the organic amendments are
left close to the surface rather than incorporated into the soil. Their decompos-
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
45
ition and the transformations of mineral nitrogen are thus done under different
temperature and moisture conditions. The absence of soil mixing also makes the
soil denser and the presence of plant residues on the surface reduces evaporation and increases soil water content. This reduces soil aeration, which often
increases denitrification rates and the potential for N2O production. However, this
influence of no tillage on denitrification and N2O production is mostly observed
under wetter climates and particularly in clay soils. In Canada, it seems that, generally, no tillage increases N2O emissions in the humid east whereas it reduces
them in the semiarid Prairies.
Irrigation and drainage
We have seen how important water content is for soil aeration; it is easy to
understand how drainage and irrigation influence aeration. Heavy irrigation obstructs soil aeration, whereas less abundant but more frequent irrigation avoids
excessive soil water content resulting in lower N2O emissions. Similarly, slow
drainage of excess water in agricultural soils results in poor aeration, which leads
to denitrification and N2O production. Good soil structure that allows water to
enter rapidly and artificial drainage that ensures adequate conditions for crop
growth also help to avoid large N2O emissions.
Summer fallow
Crop growth in the southern Canadian Prairies is limited by low rainfall. To mitigate this problem, summer fallowing has been practiced since the first settlers
broke the land some 100 years ago. This practice consists of leaving the soil
free of vegetation for one complete growing season. During the fallow years, the
absence of plants reduces evaporation and replenishes soil water reserves to ensure a satisfactory harvest during the following crop year. Under summer fallow,
the soil is thus wetter but it is also warmer because of its direct exposure to solar
radiation. These conditions favour the biological decomposition of soil organic
matter and the accumulation of mineralized nitrogen that, in the absence of crop
uptake, can stimulate microbial transformations into N2O.
Indeed, it was shown that N2O emissions from soils under summer fallow are of
similar magnitude to emissions from cropped soils receiving nitrogen fertilizers.
Recently, the adoption of reduced or no tillage made it possible to increase the
crop water-use efficiency and to reduce the need for summer fallow. The shift from
summer fallow systems to continuous cropping with no tillage has made it possible
to increase agricultural production without increasing overall N2O production.
Reducing indirect emissions
The preceding practices can help reduce direct emissions of N2O. Reducing indirect emissions—those emitted away from farmlands but from nitrogen originally
from farms—involves finding ways to reduce leaching and volatilization. Because
losses by these mechanisms have high economic and environmental costs,
many studies have been conducted to seek ways of reducing them.
46
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Minimizing fertilizer use
As Table 4 shows, a wide range of practices has been advocated, grouped
under two broad approaches. To reduce losses from agricultural fields, the most
basic approach involves applying just enough nitrogen to satisfy crop needs, but
no more. This aim is simple in principle, but challenging to implement because
of the biological complexity and variability of the nitrogen cycle on farms. For
example, the amounts of nitrogen available to crops depends not only on the
amounts applied, but also on the rate at which organic nitrogen already present
mineralizes—a process hard to predict. Further, the amounts of nitrogen needed
by plants and the timing of these requirements is unpredictable, depending on
weather and other factors that affect plant growth.
TABLE 4
Possible Approaches for Minimizing Agricultural Nitrogen Losses via Leaching and
Ammonia Volatilization
APPROACH
EXAMPLES OF SPECIFIC PRACTICES
Minimizing losses from soils
Improved recommendations based on soil analyses, or nitrogen budget calculations
Avoid applying excess nitrogen
Applying nitrogen at variable rates to reflect plant needs (precision farming)
Adopting more efficient methods of nitrogen delivery to plants (e.g., banding)
Improved timing of manure and fertilizer applications
Improved timing of residue incorporation
Synchronize nitrogen additions
with plant needs
Improved fertilizer forms (e.g., slow release forms)
Use of cover crops
Avoiding fallow
Minimizing losses from livestock
Physical covers for manure stores
Conserve manure nitrogen during
storage
Chemical amendments (e.g., acidifying agents)
Careful composting practices
Prevent post-application losses
Improved placement of manure nitrogen (e.g., banding)
Timely incorporation of manure
To minimize losses, the nitrogen needs to be made available not only in the right
amounts, but also at the right times. This can be achieved by applying nitrogen
just prior to plant uptake (e.g., avoiding fall fertilization of spring-seeded crops),
by using controlled-release fertilizers or by ploughing under nitrogen-rich residues
so that mineralization is synchronized with the plants’ nitrogen demands. Often,
nitrogen losses can be reduced by methods such as banding that place nitrogen
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
47
in close contact with soil and near roots. Losses between crops can be minimized to some extent by planting cover crops and avoiding the use of summer
fallow, a practice that favours accumulation of soil nitrate when no plants are
present to absorb it.
Managing livestock
Livestock systems also are an important source of nitrogen losses, notably as
ammonia from excreted urea compounds. Typically, about 50% of the feed nitrogen consumed by cattle, for example, is excreted in urine. The most fundamental
approach to suppress these losses is to minimize nitrogen excreted by adjusting
the amount and nature of protein in animal diets. In the rumen of cattle, protein is
normally broken down into ammonia, which is then used by rumen microbes to
synthesize microbial protein, the major source of protein for the ruminant animal.
If too much rumen-degradable protein is fed, or if a lack of energy (carbohydrates) limits bacterial growth, unused ammonia is absorbed from the rumen into
the blood and is excreted in urine.
Dietary protein can be reduced without constraining animal production by
improving the balance between rumen-degraded intake protein and rumen-fermentable organic matter. This maximizes the microbial protein supply. Another
way of reducing nitrogen excretion is to supply amino acids to the small intestine
by feeding undegradable intake protein (also referred to as by-pass or protected
protein). A diet where total crude protein is reduced and specific amino acids are
added to meet dietary requirements has proven effective in reducing total nitrogen excretion in poultry and swine.
However, in ruminant livestock (cattle), amino acids in feed must be protected from
degradation in the rumen. Some protein sources consist of a relatively high percentage of undegradable intake protein. Care is needed to ensure that the proportion of undegradable intake feed is not excessive since excess nitrogen is excreted
in the urine. Ideally, the diet should optimise rumen-degradable intake protein while
not over feeding undegradable protein—that is, not exceeding growth and maintenance requirements. Such practices, however, still require further research to
ensure that they do not jeopardize yields of meat and milk products.
Volatile ammonia losses of nitrogen from manure stores can be effectively
controlled by installing physical barriers, applying chemical amendments (e.g.,
acidifying agents, absorbents), and by adjusting conditions during either storage or composting. Post-application losses of nitrogen from manures can be
minimized using methods similar to those described for other nitrogen sources;
particularly important is the timely and effective soil incorporation of manures to
prevent ammonia volatilization.
48
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
The best approaches for reducing losses will vary among regions and even among
farms in the same region. Many studies have shown, however, that the recovery of
applied nitrogen in crops is sometimes not much more than 50%, suggesting there
is still considerable room to reduce both N application and indirect N2O emissions.
Other benefits and costs of reducing N2O emissions
Methods for reducing emissions of N2O may have numerous corollary benefits;
indeed, these methods are generally adopted not so much to suppress N2O
emissions, but to reduce nitrogen inputs and thereby reduce farming costs.
Other benefits include reducing nitrate leaching, improving air quality (e.g., by
reducing aerosols formed from ammonia), improving odour control and reducing
energy used to manufacture and apply nitrogen fertilizers. (This, of course, reduces emission of CO2.)
However, these practices have potential drawbacks. Some involve investments
in infrastructure or equipment; others, especially those aimed at reducing application rates, may carry the risk of lower crop yields. Many can conflict with
other environmental objectives. For example, effective incorporation of manures
may require intensive tillage that jeopardizes soil quality and is energy intensive;
and avoiding losses of ammonia from manures may simply defer nitrogen losses
or increase losses via other forms (e.g., N2O). Thus, prospective practices for
reducing indirect N2O emissions can be effectively evaluated only in light of other
agricultural and environmental goals.
Despite the widespread advantages of avoiding nitrogen losses—and despite
abundant research devoted to reducing losses—the nitrogen cycle on farms is
still leaky, and these leaks still lead to significant (though poorly quantified) N2O
emissions. Stemming these leaks remains a prominent research objective, both
to improve productivity and to avoid environmental damage. Given the complexity of the nitrogen cycle and the sporadic progress to date, future improvements
in efficiency are likely to be incremental—but worthy of the effort.
FU RTHE R R E AD I NG
Beauchamp, E. G. 1997. Nitrous oxide emission from agricultural soils. Canadian Journal of Soil Science
77[2]:113–123.
Erisman, J.W., A. Bleeker, J. Galloway, and M.S. Sutton. 2007. Reduced nitrogen in ecology and the
environment. Environmental Pollution 150:140-149.
Freney, J. R. 1997. Emission of nitrous oxide from soils used for agriculture. Nutrient Cycling in Agroecosystems
49[1/3]:1-6.
Mosier, A. R., et al. 1998. Assessing and mitigating N2O emissions from agricultural soils. Climatic Change
40[1]:7-38.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
49
Methane
METHANE FROM LIVESTOCK AND METHODS TO
REDUCE EMISSIONS
Methane is a colourless, odourless gas, familiar to us as the main constituent of
the natural gas we use to heat our homes. It is produced in nature wherever plant
material decays without enough oxygen to form CO2. On Canadian farms, these
conditions occur in two main places: in the fore-stomachs (rumens) of ruminant
animals (cattle and sheep), where feeds are digested in oxygen-free conditions
and in manure storage sites where high water content limits the entry of oxygen.
Worldwide, animal agriculture is the largest source of atmospheric CH4 produced through human activity; an estimated 1.3 billion cattle account for 21%
of total anthropogenic CH4 emissions. In Canada, CH4 from ruminant animals
is by far the largest source, producing about eight times the CH4 that emanates from manure. We will refer to CH4 produced in ruminants as enteric CH4.
The first portion of this chapter discusses enteric CH4, while the second portion
discusses CH4 from manure.
Methane from ruminant livestock
Cattle farming in Canada
Canada’s 16 million cattle represent roughly 1.4% of the global population of
cattle. Most of Canada’s cattle, especially beef cattle, reside in Alberta and
Saskatchewan, while most dairy cattle reside in Québec and Ontario. There are
many regional influences that account for the distribution of cattle and how they
are managed in Canada; many of these influences are related to resources and
to the history of the industry.
The vast grassland and parkland regions of western Canada are conducive for
grazing cattle for a large part of the year. An ample supply of barley grain in those
regions also enables farmers to manage their cattle on feedlots, a practice more
common in Alberta than in Saskatchewan or Manitoba.
Farming meat and milk
The beef production cycle in Canada has three components. In the cow-calf
component, calves born in late winter/early spring are kept on pasture throughout the summer and weaned in the late fall. During the backgrounding period,
steer calves (males) and non-replacement heifers (females that will not be kept
as cows) are moved from pasture to a feedlot and fed a high-forage diet for up to
100 days. Finally, during the finishing period, cattle are shifted, over two to four
weeks, to a high-grain diet. Cattle are offered a high-grain diet when they reach
a weight of roughly 380 kg. For the next 130 days they gain about 1.4 kg per
50
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
day and are then slaughtered. In some operations, the backgrounding period is
extended throughout the winter and the cattle are reintroduced to pasture in the
following spring. These stocker or yearling cattle typically undergo a short finishing period of less than 80 days and are marketed in late fall or early winter.
Typically, farmers allow dairy cows to lactate (produce milk), for about 305 days
and then cease milk production for approximately 60 days. Just less than half a
dairy herd consists of non-lactating stock; this includes dry cows and replacement heifers. (Young females begin lactating at about 24 to 28 months, once
they have given birth.)
When lactating, dairy cows require a high-energy diet that consists of 40–60%
forage, supplemented with grain, protein sources, minerals and vitamins. The feed
intake for dairy cattle is generally greater than for beef cattle, because dairy cattle require a great deal of energy to produce milk (typically averages 30 to 35 litres of milk
per day). Unlike many countries, Canada typically houses its dairy cows in open or
closed barns, which means the cows do not experience extensive grazing periods.
The confinement of dairy cows in barns, and beef cattle in feedlots, means that
their feed can be managed to a high degree and their diets adjusted to reduce
CH4 production. In grazing systems, fewer options exist for producers to adjust
their cattle’s diet composition. In those systems, producers’ main strategy is to
improve the quality and availability of forage through pasture management.
How cows produce enteric methane
Cattle, being ruminants, are able to digest forages, which consist mostly of cellulose and hemicellulose. Although they can thrive on forages alone, grains, which
contain starch, are also fed to cattle in some operations.
To convert carbohydrates into usable energy, bacteria in the rumen break down
plant compounds into volatile fatty acids (VFAs). VFAs are the major energy
source for cattle, the most abundant VFAs being acetate, propionate and
butyrate. Different types of animal feeds produce different proportions of VFAs.
For example, a diet that consists of 90% grain—as opposed to a forage diet
or lower-grain diet—produces an increase in the proportion of acetate and a
decrease in the proportion of propionate. This is important because VFAs have
a critical role to play in the generation of hydrogen in the rumen. Hydrogen is
important in the production of enteric CH4. The formation of acetate generates
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
51
twice the amount of hydrogen as does the formation of butyrate, whereas the
formation of propionate actually uses hydrogen. The accumulation of hydrogen in
the rumen has a negative impact on the function of bacteria, thereby interfering
with the digestion of carbohydrates. Consequently, it makes sense to ensure that
hydrogen does not accumulate in the rumen.
Meanwhile, a group of bacteria known as methanogens (CH4-producing bacteria) plays a role in converting hydrogen and CO2 found in the rumen into CH4
and water. Therefore, restricting the hydrogen available in the rumen for methanogenic bacteria will limit the formation of enteric CH4. One way to do this is to
shift the fermentation process to form propionate or butyrate rather than acetate.
This reduces the available hydrogen required for the formation of enteric CH4 by
methanogenic bacteria.
FIGURE 17
Production of CH4 in the Rumen
PLANT MATERIAL
CELLULOSE,
HEMICELLULOSE
1
DIGESTION
BACTERIA ACTION
GLUCOSE
2
+ OTHERS
BUTYRATE
ACETATE
3
+4
PROPIONATE
+2
-2
HYDROGEN
PRODUCTION OR
CONSUMPTION
HYDROGEN POOL
METHANOGENIC
BACTERIA ACTION
4
CARBON DIOXIDE
METHANE
Cattle are able to utilize forages, which are composed of cellulose and hemicellulose material, as an energy source for maintenance, growth and milk production. These materials
are digested to form glucose (1) and other simple sugars in the rumen (stomach), which
are then converted to various types of volatile fatty acids (2). Increasing the proportion of
propionate produced in the rumen (3) through dietary changes decreases the amount of
hydrogen available to methanogenic bacteria (4) for the formation of CH4. The production
of propionate is a strategy that decreases enteric CH4 emission.
52
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Most of the enteric CH4 produced by cattle originates in the rumen through the
process described above. However, fermentation can also occur in the intestine of
the animal. One of the published studies on ruminal versus intestinal production of
CH4 indicates that although 13% of CH4 is produced in the intestine, about 89% of
it is absorbed across the intestinal wall into the blood stream. Likewise, about 95%
of CH4 generated in the rumen is absorbed into the blood stream. Methane in the
blood is transferred to the lungs where the animal breathes it out. As a result, 99%
of CH4 emission is lost via the nostrils and mouth and only 1% of the total CH4
emission of the ruminant is lost through the rectum.
Reducing enteric methane emissions
There are two main approaches by which CH4 emissions from beef and dairy
cattle can be reduced. One method is to reduce CH4 per unit of feed energy
consumed by modifying the diets and using other management options. A second method is to reduce enteric CH4 through the use of more efficient animals;
this can reduce emissions per unit of meat or milk produced so that fewer animals are required to grow or produce the same amount of product.
Note however, that increased animal productivity in itself does not lead to a decrease in CH4 emissions unless total production is fixed. An example is a supply
management system that limits the total amount of product produced—similar
to the way milk production is managed within the Canadian dairy sector. Table 5
offers an overview of these practices and their expected CH4 reduction. The elements of Table 5 are explained in detail in the following paragraphs.
Method 1: reducing CH4 emissions through diet and other
management options
Higher-grain diets control CH4
Feeding high-grain diets to ruminants—in which more than 90% of the animal’s
dietary dry matter is composed of grain—lowers the proportion of feed energy
converted to CH4 in the cow’s rumen. However, feeding grain to cattle—grain
that could be otherwise fed directly to humans—does not exploit ruminants’
unique ability to convert cellulose feeds, unsuitable for human consumption, into
high-quality protein sources such as milk and meat.
Feeding a high-grain diet to ruminants causes a change in rumen fermentation—it
results in a decrease in the proportion of acetate produced and an increase in the
proportion of propionate produced. Formation of acetate in the rumen promotes
CH4 production, whereas propionate production is associated with a decline in
CH4. It is also possible that higher acidity of the rumen is an important factor in
lowering enteric CH4 production. Fermentation acids produced may lower the pH
in the rumen to a level that inhibits the growth of methanogenic bacteria.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
53
TABLE 5
Possible Mitigation Practices for Reducing CH4 Emissions
MITIGATION METHOD
REDUCTION IN CH4 (%)
COMMENT
Reducing CH4 emissions per unit of feed energy consumed through diet and other options
Higher grain diets
10-100
High certainty
Composition of grains
5-10
High certainty
Fats and oilseeds
5-25
High certainty
Ionophores
0-15
Level dependent, transient
Forage and pasture quality
5-25
Moderate certainty
Forage species
10-25
Moderate certainty
Condensed tannins
0-15
Depends on source and level
Propionate precursors
0-75
Dose dependent response
Yeast
0-5
Depends on strain
Methane vaccine
Unknown
Experimental
Breeding for reduced methane production
Unknown
Theoretical
Reducing CH4 emissions through more efficient animals, reducing emissions per unit of product
Animal breeding to increase efficiency
5-25
Experimental
Reformulating diets to improve rate of gain or
milk production
10
High certainty
Extended lactation of dairy cows to reduce
replacement animals
10
Experimental
10-20
High certainty
Unknown
Experimental
10-25
High certainty
Lifetime management of beef cattle
Better reproductive performance
Breeding for increased productivity
Source: S. McGinn, AAFC, Lethbridge, AB
However, while increased use of grains reduces CH4 emissions, grain production increases the production and transportation of chemical nitrogen fertilizer.
Increased use of chemical fertilizers results in increases of N2O (released from the
fertilizers themselves) and CO2, which is released by the fossil fuels used to produce and transport fertilizers. The question that remains is whether increased grain
feeding reduces or increases total GHG from the livestock industry. The answer
to this question is not yet available.
Composition of grains—not all grains are equal
As the graph below indicates, the extent to which high-grain diets lower CH4
emissions depends on the type of grain. Greater reductions are achieved with
corn than with barley. Methane emissions of feedlot cattle fed a backgrounding
54
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
diet of 70% forage dropped by 38% when a barley-based feedlot finishing diet
was fed—and by 64% when a corn-based finishing diet was fed. This difference
may be due to a partial shift in the site of digestion from the rumen to the intestines, as corn is typically less extensively digested in the rumen than is barley.
In addition, barley contains more cellulose and hemicellulose than corn. These
structural carbohydrates ferment at slower rates than starch and sugars, resulting in higher proportions of acetate and lower proportions of propionate.
FIGURE 18
Example of Dietary Impact on CH4 Emission
180
CORN
8
BARLEY
GROSS ENERGY (% LOSS AS CH4)
CH4 EMISSIONS (kg CH4 head-1 d-1)
160
140
120
100
80
60
40
20
a
0
CORN
7
BARLEY
6
5
4
3
2
1
b
0
HIGH FORAGE
HIGH GRAIN
HIGH FORAGE
HIGH GRAIN
The emissions are expressed as (a) grams of CH4 per head per day, and (b) percent of energy contained in the feed that is
lost as CH4. Using (b) to calculate the amount of CH4 lost from an animal is more accurate since it reflects knowledge of
the diet that controls CH4 losses.
Source: Beauchemin and McGinn (2005)
Fats and oilseeds
Feeding fats offers much potential for lowering CH4 emissions—and is a logical
mitigation strategy. Fats such as oils, oilseeds and animal fats are already used
in commercial ruminant feed production to increase the energy density of dry
matter and reduce the amount of fermentation required to obtain the same level
of energy from the feed. Supplementing the diet with fat reduces CH4 emissions
mainly by inhibiting the growth of rumen protozoa; many CH4-producing bacteria
are physically associated with protozoa so decreasing protozoal numbers decreases methanogens as well. Further, adding fats to a diet replaces some of the
carbohydrates, which would otherwise be digested in the rumen and contribute
to CH4 production. For lipids rich in unsaturated fatty acids (mainly plant-derived
fats), the transformation or biohydrogenation of fatty acids that occurs in the
rumen is a process that competes for hydrogen.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
55
As Table 6 shows, studies have examined the effect on CH4 emissions of supplementing forage-based diets with fat sources. All types of fat sources (supplying
between 3.3 and 5.3% of the animal’s energy intake) reduced CH4 emissions.
Sources of long-chain unsaturated fatty acids (sunflower oil and seeds, canola
oil) were most effective in reducing emissions, with 21-27% less methane per unit
of gross energy intake. Tallow, a source of saturated fat, was slightly less effective, at 17% reduction. (The effectiveness of long-chain fatty acids in suppressing
enteric CH4 is inversely proportional to degree of saturation of the fatty acids.
Medium-chain fatty acids are also effective at reducing CH4 emissions, but these
fat sources—such as coconut oil and genetically modified canola oil—are often
cost-prohibitive for livestock producers.)
TABLE 6
Impact of Adding Supplemental Fat Sources to High Forage
Diets (75% forage, DM basis) Fed to Growing Cattle
SOURCE
LEVEL OF ADDED
FAT
(% OF DM
INTAKE)
DM INTAKE
DIGESTIBILITY
OF DM
IN THE
DIGESTIVE
TRACT
CH4
(% OF GEI)
Percentage change from control diet without added fat
3.3
-1.4
0.7
-21.3a
5.3
-1.5
-6.1
-21.5a
Sunflower seeds
3.3
-10.5a
-6.6a
-26.7a
Canola oil
4.6
-9.9a
-14.7a
-20.6
Tallow
3.3
-4.1
-1.2
-17.1a
Sunflower oil
a = different from control (P < 0.15).
DM = dry matter; GEI = gross energy intake
Sources : Results of three studies conducted at the Lethbridge Research Centre by S. McGinn and K. Beauchemin.
Although adding fat to the diet reduces CH4, it can also reduce feed intake and
fibre digestibility. The net result can be a decrease in the total intake of digestible
energy despite an increase in the energy density of the diet. Such was the case
when sunflower seeds, canola or tallow were provided at high inclusion rates in
a study. Long-chain fatty acids inhibit the fibre-digesting bacteria in the rumen;
thus, some decrease in fibre digestion is inevitable. Use of supplementary fats
can increase the energy intake of cattle if the negative effects on fibre digestion
and intake are minimized by feeding a higher proportion of grain in the diet, or by
limiting the total fat content of the diet to 6–7% of the dietary dry matter.
Ionophores
Ionophores such as monensin are antimicrobials that are typically used in Canadian commercial beef and dairy cattle diets to modulate feed intake, control bloat
and improve feed efficiency. Monensin decreases the proportion of acetate and
56
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
increases the proportion of propionate in the rumen—an effect that decreases
CH4 output. Sometimes, monensin can also cause a decrease in rumen protozoa. This is important, as a direct relationship has been established between
rumen protozoa numbers and CH4 formation. Rumen protozoa are estimated
to provide a habitat for up to 20% of ruminal methanogens while methanogens
living on and within protozoa are thought to be responsible for an estimated 37%
of CH4 emissions from ruminants.
In studies with beef cattle fed a 75% forage diet, CH4 emissions decreased by
9% with the addition of monensin to the diet at 33 mg/kg for a period of 21 days.
This reduction in CH4 is within the range (slight to 25%) reported previously.
However, several studies have reported that the effects of monensin on CH4
emissions are short lived. For example, scientists have reported that the CH4
suppression effect of monensin was lost after four to six weeks of feeding. This,
combined with increased public pressure to reduce the use of antimicrobials in
animal agriculture, would suggest that monensin is not a long-term solution to
enteric CH4 abatement in Canada.
Forage and pasture quality
Improved forage quality typically results in greater CH4 output per day, especially
when cattle are provided with free-choice access to feed. High-quality forages
have a faster passage rate from the rumen, which leads to greater feed intake and
more fermentable substrate in the rumen. This results in greater daily enteric CH4
production. However, the amount of CH4 produced per unit of energy consumed
or per unit of product typically increases as the quality of forages decreases.
Forage species
Methane emission is lower from animals fed legume forages compared to those fed
grasses, but this relationship is also influenced by the maturity of the forage consumed. Scientists have estimated a 21% decrease in CH4 production per unit of
digestible energy when alfalfa hay replaces timothy hay. Legumes produce less CH4
because they possess a lower proportion of structural carbohydrates and therefore
the feed passes more quickly through the rumen. This leads to a higher proportion of
propionate in the rumen, which reduces enteric CH4.
Condensed tannins
Tannins are phenolic compounds found in some plants. Several laboratory studies have shown that the use of forages containing condensed tannins and tannin
extracts reduce CH4 emissions. These in vitro studies prompted scientists in
New Zealand to conduct a series of studies in which tannin-rich forages were fed
to sheep and dairy cows. When conventional forages, such as perennial ryegrass, were replaced with tannin-rich forages, CH4 emissions decreased. However, it is not clear whether the CH4 reduction was a direct effect of the tannins
or a result of improved forage quality. Forages that have high levels of condensed
tannins may suppress CH4 production through a reduction in fibre digestibility in
a manner similar to the addition of fats and oilseeds to the diet.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
57
The use of tannins has potential as a CH4 abatement strategy, but further research is needed to determine the optimum level and source of tannin to avoid
potentially negative effects on animal productivity. Studies in Europe and Australia
have shown that although feeding tannins to some ruminants (sheep and dairy
cattle) will depress CH4 production, this procedure may have a negative impact
on productivity, making this approach questionable at present.
Propionate precursors
Fumarate and malate are organic acids that act as hydrogen sinks in the rumen.
They have the potential to decrease CH4 emissions by increasing the formation of
propionate, if added to feed in sufficient proportion. An addition of up to 2% of the
diet as fumaric acid had no effects on CH4 emissions of cattle. In a recent study in
Ireland, 3% malate added to the diet of lactating cows resulted in a very small reduction in CH4 emissions. In the U.K., a much higher inclusion rate, in which fumaric acid
made up 10% of the diet of sheep, reduced CH4 emissions by 40–75%, the higher
amount when the fumaric acid was encapsulated with fat to slow its rate of availability in the rumen. Unfortunately, these organic acids are expensive, which means
feeding high levels to reduce CH4 is uneconomical and impractical at present.
Yeast
Yeast cultures of Saccharomyces cerevisiae are widely used in ruminant diets in
Canada to improve the rumen function of cattle. Products vary in the strain of S.
cerevisiae used and the number and viability of yeast cells present. Laboratory
studies suggest that some live yeast strains can stimulate the use of hydrogen by
acetate-forming strains of ruminal bacteria, thereby enhancing the formation of
acetate without forming CH4.
Some commercially available yeast products can cause a 3% decrease in the
amount of feed energy converted to CH4. With strain selection, it is possible that
yeast products could be developed based on their anti-methanogenic effects. However, at present, available strains of yeast likely have only minor, if any, effects on CH4.
Methane vaccine and antibody therapy
Australian scientists have looked at the possibility of developing a vaccine against
methanogens and protozoa in an effort to lower ruminal CH4 production. Canadian scientists have also generated IgY antibodies against methanogens and
examined their impact on CH4 production in vitro. In some instances this approach has reduced in vitro CH4 production, but the technology has yet to be
evaluated in animals. Both technologies remain strictly at the experimental level
and have yet to be demonstrated as a viable means of lowering CH4 production.
Breeding for reduced CH4 production
Methane production in humans is heritable, but so far there has been no attempt
to breed cattle for reduced CH4 production. Selecting animals for a single nonproduction related trait could lower the production efficiency of cattle and, for
that reason, is not likely to be undertaken.
58
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Method 2: reducing CH4 through more efficient animals,
reducing emissions per unit of product
Animal breeding to increase efficiency
Methane production is highly dependent on the quantity of feed consumed,
which means reducing the amount of feed required to produce one unit of meat
or milk is one way to reduce emissions. Scientists in Canada and Australia have
recently bred and selected beef cattle based on residual, or net, feed intake (RFI),
which is a measure of feed efficiency. Cattle with low RFI eat less than expected
for their weight and growth rate and are therefore more efficient than cattle with
high RFI. A recent Australian study reported that efficient cattle produced 6.7%
less CH4 per kilogram of gain than less efficient cattle. In Canada, a similar
breeding program showed that low RFI cattle consumed less feed per kilogram
of gain. This was associated with reduced daily CH4 emissions. When all cattle
were fed the same amount, the low RFI cattle produced 28% less CH4 than the
high RFI cattle, indicating that low RFI cattle may be more metabolically efficient.
Reformulating diets
Improved diets can enhance the way cattle utilize their feed and nutrients and, as
a result, reduce CH4 emissions. Improved diets can be achieved by better characterizing the nutrient profiles of feeds, improving models used to formulate rations and by gaining a better understanding of the nutrient requirements of cattle.
Extending lactation of dairy cows
Scientists in many parts of the world are examining the feasibility of calving dairy
cows every second year, rather than once yearly, and extending lactation across
two seasons. Total milk production by the herd is expected to remain the same
with extended lactations. This approach would have the benefits of reducing
the number of days the cow is not lactating over her lifetime and lowering the
production costs associated with mating, calving, animal health and cow replacement. Such practices would also improve animal well-being by reducing the
metabolic stress associated with calving. In a recent study in Victoria, Australia,
400-day lactations were found to reduce the total farm feed budget by 10%
compared to traditional 305-day lactations, because fewer heifers were maintained. (There was a reduced need for replacement of mature cows.)
Lifetime management of beef cattle
To increase the productivity of beef cattle is to enable them to reach an acceptable
slaughter weight at a younger age, which can have a major impact on lifetime CH4
emissions. Scientists have calculated that reducing the age of steers at slaughter
from 30 to 25 months resulted in a 16.5% reduction in lifetime CH4 emissions and a
12% reduction in emissions per kilogram of carcass. (Carcasses reduced from 400
to 380 kilograms). It is also possible to reduce CH4 emissions per unit of product by
increasing carcass weights at slaughter, which lowers the number of animals required
to produce the same amount of meat.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
59
Better reproductive performance
Better reproduction of cattle can reduce the total amount of CH4 per herd by
reducing the total number of replacement stock. Scientists have estimated that
improvements in fertility could reduce overall CH4 emissions by 10% and by as
much as 24% in regions where fertility was particularly low. In New Zealand, an
increase in the incidence of twinning in ewes has resulted in substantial reductions in CH4 emission; fewer ewes are producing the same lamb crop. This
approach is particularly attractive as it offers obvious economic incentives quite
apart from potential reductions in GHG emissions.
Breeding for increased animal productivity can reduce enteric CH4 because it
leads to less feed per animal per unit of product. However, increased productivity, especially in the dairy sector, is often accompanied by reduced cow fertility.
Reduced fertility will increase the overall CH4 emission on the farm due to the
increased numbers of replacement animals.
Agricultural management practice
The agricultural strategies that lower enteric CH4 emissions not only reduce GHGs
in the atmosphere, but also promise to significantly increase the efficiency with
which cattle convert plant material into milk and meat. A 20% reduction in enteric
CH4 in Canada would translate to a 9% decline in GHG emissions from agriculture
and a 0.7% decline in Canada’s total GHG emissions. Meanwhile, this 20% reduction would improve the competitiveness of Canada’s livestock sector by increasing
the weight gain of growing beef cattle by 75 grams per day and milk production in
dairy cattle by one litre per day—a boon to farmers.
Although research has shown that CH4 reductions are achievable by changing
the diet of cattle, there is a financial cost to implementing these strategies. Further research on finding cost-effective strategies is required. It is also important
that mitigation strategies be assessed from a life-cycle perspective because a
reduction in greenhouse emissions at one point may lead to increases in emissions at other points along the production continuum.
One thing is certain with respect to the benefits of reducing enteric CH4 emissions
from cattle: it increases the energy efficiency of meat and milk production. Many
of these dietary strategies are relatively easy to implement on farm. Some of these
also lower the cost of producing meat and milk. The introduction of carbon-offset
trading programs may encourage producers to adopt other mitigation strategies
that are not, at present, economically viable. Importantly, reducing CH4 emissions
makes cattle husbandry a more environmentally friendly industry.
60
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Methane from manures
Manure production in Canada
There are far more livestock in Canada than there are people. In 2007, Canadian
farms had about 16 million cattle, 15 million hogs, 130 million poultry and additional millions of other animals. These herds produce considerable excrement:
more than 200 million tonnes on an annual basis, with about 70% from beef cattle. As Figure 19 shows, most of this manure is applied to farmland as a fertilizer.
But before it is applied to crops it accumulates, lingering in barns, manure piles,
lagoons and tanks. While there, microbes decompose and digest it, decaying the
nutrient-rich substrate and releasing considerable amounts of GHGs.
FIGURE 19
Manure is an Essential Component of Modern Farming Systems
CROPS ARE EATEN
BY LIVESTOCK
CH4
MANURE IS EXCRETED BY
LIVESTOCK AND IS
TRANSPORTED TO STORAGE
N2O
CO2
FOLLOWING STORAGE, MANURE IS APPLIED TO
AGRICULTURAL LAND. THE NUTRIENTS CONTAINED IN
THE MANURE ARE USED BY THE GROWING CROPS.
CH4, N2O AND CO2
EMISSIONS OCCUR DURING
MANURE STORAGE
Nutrients absorbed by crops are fed to livestock, which then excrete a portion of these nutrients in manure. Although manure represents a disposal liability to the farmer, it also represents a resource, as it contains valuable nutrients which can
be applied to fields to grow the following year’s crop. The cycling of nutrients from crop to animal to manure to crop again
allows farmers to dispose of manure while providing nutrients to the soil.
Manure is stored according to animal type and intended use of the manure. With
grazing animals, urine and feces are deposited onto the pastures or paddocks,
where they remain. The trend with swine and larger dairy operations is to use very
small amounts of bedding and to add cleaning and milkhouse wastewaters to the
manure and store it as a liquid in tanks or lagoons. Most other livestock systems
refrain from adding water and store manure as a solid. This solid manure usually
contains appreciable amounts of bedding—straw, wood chips, or other organic materials added to keep animals warm and dry. Some farmers now compost manure
or add it to anaerobic digesters, which produce energy by burning the CH4 from
the manure. These methods are not new, but their prominence is growing, in part
because they can sometimes help reduce GHG emissions and also because they
can provide energy for use on the farm. These biotechnologies substantially reduce
manure pathogens and odours, thereby improving conditions for nearby residents.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
61
Manures produce the most CH4 when they are stored as slurry or in other mostly
liquid forms. When they are stored as solids, oxygen diffuses into the manure,
reducing the formation of CH4 as it is oxidized to CO2 and H2O. The amount of
CH4 produced depends not only on the way manure is handled and stored, but
also on the type of animal and diet composition.
How manure produces CH4
Methane emissions from manure are the end product of organic matter decomposition under anaerobic—or oxygen free—conditions. Methanogenic bacteria
consume organic matter for their growth and emit gases, including CH4. This
gas is therefore a by-product of bacterial activities. The transformation of organic
matter into CH4 is performed by a series of different types of bacteria, which
sequentially decompose organic matter to CH4 and CO2 as follows:
Manure components that are too large to pass through the bacterial cell membrane are reduced in size by the process of hydrolysis, which occurs outside of
the bacterial cell. The enzyme used to break down large manure components is
produced by the bacteria themselves. The resulting sugars, alcohols and acids
go through a series of reactions that produce several types of molecules, including other types of volatile fatty acids, hydrogen and simple organic components.
The final stage ends with the production of CH4 and CO2. The whole process
can be divided into six parallel or series reactions presented in Figure 20.
FIGURE 20
The Conversion of Organic Material in Manure to CH4 and CO2
MANURE
PROTEINS
CARBOHYDRATES
AMINO ACIDS SUGARS
FATS
FATTY ACIDS ALCOHOLS
INTERMEDIARY PRODUCTS
(PROPIONATE, BUTYRATE, ETC.)
HYDROGEN
ACETATE
SINGLE CARBON
COMPOUNDS
METHANE
CARBON DIOXIDE
62
Livestock manure contains organic compounds such as
proteins, carbohydrates and fats. These compounds are too
large to permeate a bacterial cell membrane. Extra-cellular
enzymes produced by fermentative bacteria break down these
molecules into small soluble compounds such as amino
acids, sugars and fatty acids that can diffuse across the cell
membrane of fermentative bacteria. The sugars and amino
acids are transformed into acetate, propionate, butyrate,
hydrogen and CO2 by the same fermentative bacteria.
Hydrogen-producing acetogenic bacteria oxidize propionate
and butyrate into acetic acid, hydrogen and CO2. Finally,
acetoclastic methanogens transform the acetic acid into
CH4 and CO2, and hydrogen utilizing methanogenic
bacteria reduce CO2 to CH4.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Manure naturally contains all of the bacteria required to produce CH4. However,
the rate of CH4 emission from manure depends on the density of active methanogens and their activity level. There are many factors that can influence the
density and activity of methanogenic bacteria, including the following:
• Absence of oxygen—CH4 is only produced under strict anaerobic conditions.
• Temperature—bacterial activity, and therefore the efficiency of CH4
production, reaches a maximum at approximately 60-65 ºC.
• Animal species
• The quality and quantity of feed given to the animal
• Age and gender of the animal
• Manure collection method
• Manure storage period
• Storage management practices such as manure removal frequency, amount
of residual manure left in the structure after removal and amount of foreign
material (straw or sawdust bedding) incorporated into the manure.
• Manure characteristics such as acidity (pH) and compounds such as ammonia and Volatile Fatty Acids (VFA), which inhibit the development of anaerobic
bacteria at high concentrations, decreasing CH4 emissions.
Because of the wide range of environmental conditions and management practices that affect CH4 emissions from manure management systems, it is difficult
to compare the rate of emissions among regions, manure management systems
and animal types. Long-term monitoring of CH4 emissions from manure storage
systems and laboratory-scale studies that adequately simulate farm conditions
are necessary to evaluate the impact of individual environmental factors and
manure management practices on CH4 emissions.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
63
MEASURING CH4 EMISSIONS FROM
MANURE—AN EXAMPLE FROM DAIRY
SYSTEMS IN EASTERN CANADA
To evaluate the influence of manure storage temperature,
manure storage duration, manure composition and management
practices on CH4 emissions from dairy cattle manure, scientists
carried out a study on two representative commercial dairy farms
in eastern Canada.
Most of the difference between the two farms (A and B) was in
their animal feeding practices. On Farm A, lactating cows were
fed a concentrated ration mainly composed of corn and alfalfa
silage, soy bean, crushed corn, barley and mineral supplements.
The dairy cows receiving this diet produced a great deal of milk—
approximately 10,300 kg per year. On Farm B, cows received a
diet rich in hay, composed of timothy, alfalfa, crushed corn and
commercial dietary supplements. Dairy cows on Farm B had
average milk production of 8,200 kg per year.
Because of Farm A’s feeding practices, the manure from Farm A
had a higher concentration of soluble organic compounds, which
can be readily degraded into CH4. Therefore, based on manure
composition, the potential to produce CH4 was greater in the
manure from Farm A.
Methanogenic activity increases with temperature. At Farms A and
B, manure temperature was measured over a one-year period
(average monthly temperature is presented in Figure 21). During
fall and winter, air temperature decreased to approximately -10 ºC.
However, bacterial activity in the manure created heat and kept its
surface temperature above 0 ºC. In summer, manure temperatures
rose rapidly at both farms and reached an average of 20°C. The
rapid increase was mainly due to the shallow depth of manure in
the storage facilities after manure removal in the spring. Because
of the high manure temperatures during the summer period, CH4
emission potential was at its highest.
64
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 21
Ambient and Manure Temperature at Farms A and B
30
TEMPERATURE (°C)
20
15
25
AMBIENT AIR
TEMPERATURE
20
MANURE TEMPERATURE
AT HALF-DEPTH
TEMPERATURE (°C)
25
30
MANURE SURFACE
TEMPERATURE
10
5
0
-5
15
MANURE SURFACE
TEMPERATURE
AMBIENT AIR
TEMPERATURE
MANURE TEMPERATURE
AT HALF-DEPTH
10
5
0
-5
A
-10
FALL
WINTER
-15
SPRING
B
-10
SUMMER
FALL
WINTER
SPRING
SUMMER
-15
During winter, the addition of fresh manure and bacterial activity generates heat and maintains the manure well above
ambient air temperature. In spring and summer, manure and ambient air temperature are approximately the same. These
elevated temperatures correspond with the potential for the highest CH4 emissions. Here, average monthly temperature at
the surface and half-depth of the manure tank on Farm A and Farm B are compared to ambient air temperature.
Source: D. Massé, AAFC, Lennoxville, QC
METHANE EMISSION FACTORS WITH RESPECT
T O S T O R A G E D U R AT I O N , M A N U R E T E M P E R AT U R E
AND STORAGE MANAGEMENT PRACTICES
Manure slurries collected on Farms A and B were stored in eight 220-litre
miniature storage structures. The containers were placed in two controlledenvironment chambers maintained at 10°C and 20°C, respectively, to simulate
average seasonal temperatures in commercial manure storage facilities. A tube
inserted into the headspace of each barrel was equipped with a gas sampling
port. Biogas production was measured daily over a 350-day period.
Figure 22 shows cumulative CH4 production over the 350-day storage period
for both farms at both storage temperatures. Total CH4 production depended
on storage duration, manure temperature and manure characteristics. At 10°C,
there was no apparent methanogenic activity in the manure from Farm A over the
whole study period. At 20°C, manure from Farm A started producing methane
after about 250 days. Because this delay in CH4 production is longer than the
storage period between field applications on commercial farms, CH4 emissions
from the manure stored on Farm A is expected to be relatively small.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
65
FIGURE 22
7
6
FARM A
5
FARM B
4
3
2
1
a) 20˚C
0
CH4 EMISSIONS (L CH4 kg manure-1)
CH4 EMISSIONS (L CH4 kg manure-1)
Cumulative CH4 Production According to Time, Temperature and Type of Manure
7
6
FARM A
5
FARM B
4
3
2
1
b) 10˚C
0
0
50
100
150
200
250
300
350
400
0
50
100
150
DAYS
200
250
300
350
DAYS
Source: D. Massé, AAFC, Lennoxville, QC
Manure from Farm B produced CH4 at both temperatures. Methanogenic
activity occurred immediately after storage at 20°C and remained high for 120
days. At 10°C, methanogenic activity also occurred immediately after storage,
but at a substantially lower rate than at 20°C. Manure from Farm B produced
more CH4 than Farm A at both temperatures. Possible explanations are:
A significant quantity of manure (more than 60-cm high) was left at the bottom
of the Farm B storage structure after manure was removed for application to
the land. Residual manure contained important populations of microorganisms
already adapted to the storage temperature and the physico-chemical
composition of the manure. These microorganisms readily produced CH4.
On Farm A, the 250-day delay in methanogenic activity at 20°C could be due
to either a low population of methanogens in the manure or the presence of
inhibitory substances such as cleaning and disinfecting agents.
Manure compounds that could inhibit methanogenic activity when present in
high levels, such as ammonia or VFAs, were higher in the manure from Farm A
than in manure from Farm B. Scientists also reported higher CH4 production in
diluted as opposed to more concentrated manure.
66
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
400
Reducing CH4 emissions from manure storage
Discouraging bacteria
Although it is difficult to completely eliminate CH4 emissions from manure,
many techniques can be applied on farms to reduce emissions. Since CH4
emissions from manure are produced by bacteria, the best way to mitigate
emissions is to diminish their activity. One method is to lower the temperature
of the manure. During winter, manure should be removed frequently from barn
buildings so that it will cool rapidly outside. During summer, the use of below
ground storage tanks would help to maintain lower manure temperatures and
result in lower CH4 emissions.
A second way to reduce methanogenic bacterial activity is to ensure that manure
does not remain long under anaerobic conditions. This can be accomplished
by reducing the amount of time manure is stored; manure should be applied to
the land as frequently as possible, for instance following each cut of hay. Once
manure is applied to fields—and sufficiently aerated—CH4 emissions cease.
A third option is to ensure that a minimal amount of manure remains in a storage tank once it is emptied. This practice can dramatically reduce the number of
bacteria well adapted to the specific tank environment—and thus cut down on
the CH4 produced when fresh manure is placed in the tank.
Composting manures
Composting solid manure can reduce CH4 emissions while simultaneously
reducing odour emissions. However, some composting technologies may
negatively affect air and water quality because they produce N2O and ammonia emissions and also leach nitrate. For environmental and economical
reasons, it is important that composting technology be carefully selected to
minimize these nitrogen losses.
Utilizing CH4
There is also the option of treating—or using—CH4 after it is produced. By covering a manure storage tank with a flexible membrane, the biogas is trapped and
prevented from entering the atmosphere (Figure 23). The trapped gas can then
be treated in several ways to reduce the concentration of CH4.
Biogas combustion
The simplest option is to burn, or flare, the biogas produced by the manure,
which converts the CH4 to CO2, a much less potent GHG. However, if the gas
is flared, the potential energy contained in the CH4 is lost to the atmosphere as
heat. Instead of burning the CH4 in an open flame, it can instead be burned in a
furnace to create heat (Figure 24) or used to power an electric generator. Both
the heat and the electrical energy can be used on-farm. This is a more complex
GHG mitigation method, but has the dual benefit of decreasing GHG emissions,
while reducing costs for the farmer because of a decreased need for fossil fuels.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
67
FIGURE 23
Covered Manure Storage Tank
Covering a manure storage tank with
a flexible membrane prevents the biogas
from entering the atmosphere and
allows the gas to be treated prior to
release. Here, a covered manure storage
facility in Eastern Canada is shown.
Photo credit: D. Massé, AAFC, Lennoxville, QC
FIGURE 24
Anaerobic Digestion of Manure
Manure is removed from the livestock buildings and is pumped directly into the bioreactor (1),
where the manure is digested anaerobically. Gas flow from the bioreactor is monitored in the
control room (2), which passes a regulated flow of biogas to the furnace or electrical generator
(3). If the furnace or electrical generator is not operational, a flare tower (4) burns the biogas.
Finally, the treated manure is stored in the long-term storage tank, shown in the foreground.
Photo credit: D. Massé, AAFC, Lennoxville, QC
68
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 25
Biofiltration of Biogas
Biofiltration of biogas emitted during the decomposition of
manure is one method of reducing CH4 emissions. Manure
gases are drawn into the biofilter where bacteria consume
CH4 as a fuel and emit CO2 and water as waste products.
This portable biofilter is shown installed at the exhaust of a
covered manure storage facility in Eastern Canada.
Photo credit: D. Massé, AAFC, Lennoxville, QC
Biofiltration
One further option to remove CH4 is biofiltration, a natural bacterial process
that converts CH4 to CO2 and H2O. Using this technique, biogas is passed
through a substance containing CH4 consuming bacteria (Figure 25). Instead
of producing CH4 as a waste product, these bacteria feed on CH4. Biofiltration
technology is used for controlling odours and has the potential to reduce CH4
emissions by up to 80%.
These are examples of mitigation practices that have the potential to reduce CH4
emissions from manure. In most cases, mitigation practices not only reduce CH4
emissions, but also have other benefits such as improved air quality through
reduced odour emissions and reduced fossil fuel consumption through the
creation of green energy.
FU RTHE R R E AD I NG
Beauchemin, K.A. and S.M. McGinn. 2005. Methane emissions from feedlot cattle fed barley or corn diets.
Journal of Animal Science 83:653–661.
Benchaar, C., C. Pomar, J. Chiquette. 2001. Evaluation of dietary strategies to reduce methane production
in ruminants: a modelling approach. Canadian Journal of Animal Science 81:563–574.
Kebreab, E.K. Clark, C. Wagner-Riddle, and J. France. 2006. Methane and nitrous oxide emissions from
animal agriculture: a review. Canadian Journal of Animal Science 86:135-158.
Massé, D.I., Croteau, F., Patni, N.K., Masse, L. 2003. Methane emissions from dairy cow and swine manure
slurries stored at 10°C and 15°C. Canadian Biosystems Engineering 45:6.1- 6.4
McAllister, T.A., E.K. Okine, G.W. Mathison, and K.-J. Cheng. 1996. Dietary, environmental and
microbiological aspects of methane production in ruminants. Canadian Journal of Animal Science 76:231–243.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
69
g
The Amounts
H OW A N D W H Y S C I E N T I S T S QUA N T I F Y G H G E XC H A N G E
Scientists need to measure GHG emissions on farms to identify and understand
their source, to quantify the amounts produced and to find better ways of reducing them. They also need to measure more than one gas at a time, because
management practices that reduce the emissions of one gas can sometimes
increase the emissions of another. For example, applying less nitrogen fertilizer reduces emissions of N2O but eventually affects crop yield and reduces the
quantity of carbon stored in the soil as organic matter.
But measuring GHG emissions is not easy; the amounts measured depend on
where the sensors are located and what the conditions are like there. Nitrous
oxide, for example, is released in sporadic puffs, scattered across fields. And
emissions vary throughout the year; while there may be next to none emitted for
weeks or months, suddenly large emissions may occur in a single day, spread
unevenly over the field. This is particularly the case during spring thaw in Eastern
Canada when up to 40% of the N2O emissions are estimated to occur. Meanwhile, net release of CO2 from soil organic matter happens more gradually—so
slowly that in many cases it can be measured only by comparing the change
in soil carbon over many years. Methane emissions are probably the easiest to
measure. However, CH4 emissions from manure storage vary with air temperature while emissions from cattle vary with the feeding schedule.
A perfect solution would be to measure GHG emissions from an entire farm,
field or region. Such a method would measure them year-round for many years
and would in no way disturb the crops or animals from which the emissions
originate. Unfortunately, no such methods exist, so scientists must make do
with an array of techniques, each useful but none without weaknesses. As
shown in Figure 26, by using several methods, scientists can measure GHG
emissions over a wide range of scales. They can then assemble the data they
need to develop and test models, which, in turn, can be used to obtain emission estimates for farms, fields and regions.
Whatever methods are used, the data collected apply only to the places and times
where the measurements are made. For example, CH4 is only ever measured from
a few barns and N2O and CO2 from a few fields. To calculate emissions at either a
provincial or national scale scientists use models—equations that describe in mathematical language what we know about how GHGs are produced.
70
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 26
The Principal Measurement Techniques
SPATIAL SCALE OF MEASUREMENT
TIME SCALE OF MEASUREMENT
1m
100m
1km
10km
1 hour
CHAMBER
AIRCRAFT
1 day
LASER
BALLOON
1 month
1 year
TOWER
A variety of measurement techniques are used to estimate GHG emissions from Canadian
agriculture. Each measurement technique is appropriate over a specific time and area, represented by the size of the photograph in this figure. By combining measurement techniques
that cover different time frames and areas, scientists can estimate GHG emissions from
areas smaller than one square metre to several square kilometres and from time frames of a
few minutes to several years.
Source and Photo Credits: R. Desjardins, E. Pattey, AAFC, Ottawa, ON and P.-L. Lizotte, McGill University, Montreal, PQ
Models, discussed in more detail below, estimate the amounts of GHGs produced
on a farm, in a region or across a country based on the area of land in question,
how many animals live there, how farmers are managing their lands and the particular soil and climatic conditions. Models used to estimate GHG emissions have
improved a great deal in recent years and they will continue to change as scientists
learn more about how GHGs are produced and how farm practices affect GHG
emissions. We may find, for example, that our estimate of GHGs from farms in
2005 is different in 2008 than it was in 2006 because we have used new research
findings to improve our models.
How GHG measurements are taken
Measuring GHG exchange at the soil surface
The simplest way to measure GHGs seeping from the soil is to place an enclosure (or chamber) on the soil, trapping the air beneath, and repeatedly measure
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
71
the GHG in the trapped air. For example, if the soil is releasing N2O, the concentration will gradually increase in the chamber; the more rapid the increase in N2O,
the more N2O is being produced. If the soil is absorbing CH4, a decrease in CH4
will be observed in the chamber over time.
This method, still the most widely used, has several advantages: it is relatively
inexpensive and it can be used for comparing multiple practices at the same time.
For example, it can be used to compare N2O from side-by-side research plots
ploughed in different ways or receiving different forms of fertilizer. However, the
chambers have shortcomings: they can be used only for short periods of time—an
hour at most; they measure the gas emissions only from the small area covered
by the chamber; they sometimes disturb the soil surface, affecting the measurements; and they cannot be used easily where fields are under water or snow. Small
networks, based on chamber measurements, have been established for GHG
measurements. These have provided valuable information for model development.
Measuring GHG exchange from agricultural fields
Another way to measure GHGs is to sample the air above a field using sensors
mounted on towers (see Figure 27). This approach is predicated on the fact that
if a source is emitting a gas, the concentration is greatest near the source. Air
moving upward from the soil will contain more GHGs, while air moving downward
from the atmosphere will have a lower concentration. By measuring about 20 times
per second the vertical wind speed and GHG concentrations at a point above an
agricultural field, scientists can calculate how much GHG is released or absorbed
by the field. GHG emissions can also be estimated by measuring the difference in
gas concentration between two different heights above a field. In both cases, the
higher the sensors are from the ground, the larger the area they detect.
This approach has important advantages over the chamber method: it estimates
overall emissions from a large area and it allows continuous measurement over long
periods, even through winter and early spring—critical periods for N2O emissions.
However, this approach is unreliable when the air is not moving, which frequently occurs at night. Many techniques have been developed to fill these gaps in the data.
Measuring CH4 and CO2 from cattle
Unlike soils, animals do not always cooperate placidly with those who try to
measure the gases they emit, so scientists have had to devise some inventive
methods. One way is to use barns as giant chambers. By mounting sensors in
vents, scientists can measure the CH4 entering and leaving a barn and make
accurate calculations without disturbing the animals. As Figure 28 shows, such
a system has been used with good results in a dairy barn at the Dairy and Swine
Research and Development Centre in Lennoxville, Québec. By altering what the
cows are fed or how they are handled on different measurement days, scientists
can learn how these practices affect CH4 emissions and, from these findings,
recommend ways of reducing emissions.
72
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 27
Tower-based Measurement
Tower-based GHG measurement techniques are becoming
more common. They provide continuous measurements at
the scale of a field. Here, N2O emissions are being measured
above a wheat crop. The tower on the left collects air samples at two separate heights. The air samples are sent to an
analyzer that measures the difference in the N2O concentration. On the right-hand tower, an anemometer measures
vertical and horizontal wind speeds. By combining the N2O
concentration measurements with the wind-speed measurements, N2O emissions can be calculated.
Photo Credit: E. Pattey, AAFC, Ottawa, ON
FIGURE 28
Measuring CH4 Emissions in Barns
From the outside, the dairy barn at the Dairy and Swine Research and Development
Centre in Lennoxville Québec, does not look unusual. However, inside is sophisticated
equipment to measure CH4 emissions from animals. By monitoring CH4 concentrations
and air flow at the fan inlet and outlet of the barn, the amount of CH4 produced by the
dairy cows can be accurately estimated.
Photo Credit: D. Massé, AAFC, Lennoxville, QC
It is possible to place one or two animals inside smaller chambers—instrumented
rooms—for more meticulous measurements of CH4 emissions. Scientists can
measure precisely and swiftly the impact of several different types of feed or
feed additives; but the animals need to be trained and handled carefully so that
anxiety does not bias the results.
Recently, even more advanced ways of measuring CH4 emissions have been
developed. Highly sensitive laser instruments sample the air downwind of CH4
sources and count the number of CH4 molecules crossing a cross-section of the
plume downwind of an animal herd, a barn or a manure storage tank (see Figure
29). Combining the CH4 concentration measurements with wind flow information,
CH4 emissions are estimated using a computer model. This determines the re-
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
73
lationship between CH4 emission and concentration anywhere in the plume. The
method is ideal in that it yields measurements without the animals even being
aware of the process. However, like most measurement techniques that rely on
the wind speed to transport the GHG, it is inaccurate under light wind conditions.
FIGURE 29
Measuring CH4 in Plumes of Air
CH4
CH4
WIND
CH4
CH4
CH4 IS EMITTED FROM
BARNS, AND DRIFTS
DOWNWIND
LASER
WIND
SENSOR
Methane emitted from animals in a barn is transported downwind in the air. By
measuring the CH4 concentration using lasers, as well as wind flow, scientists can
estimate CH4 emissions from the barn.
Measuring CO2 exchange
Carbon dioxide is the most abundant GHG worldwide, mostly because of its release
from burning fossil fuels such as gasoline, diesel and coal. In agriculture, large quantities of CO2 are fixed by photosynthesis to produce biomass. However, an almost
equal amount of CO2 is released to the atmosphere by plant and soil respiration. For
example, in one year, the corn on one hectare of land might fix by photosynthesis 30
tonnes of CO2, but roughly the same amount is released to the air by respiration (onor off-site) and the decay of plant residues and organic matter in soil.
Measuring the net exchange of CO2 in the soil reservoir—the difference between
the absorption and emission of CO2—is not easy and requires continuous, yearround measurements. Therefore, scientists usually use a simpler approach: first,
they measure the amount of carbon stored in the soil; some years later, they
return to the same spot to measure it again. If the amount has increased, the
field has absorbed more CO2 than it has released; if the amount has declined,
the field has released more than it absorbed.
74
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Such measurements sound simple, but they must be made carefully. Changes
in soil carbon happen gradually, changing at a rate of perhaps 0.2 tonnes per
hectare per year. Meanwhile, the amount of carbon in soil is high, sometimes as
high as 100 tonnes per hectare. Therefore, changes can be measured only after
many years, often decades. Experiments must be carefully designed to take into
account the variability in soil carbon in one location versus another.
For a long time, year-round continuous measurements of GHG exchange were
considered almost impossible to obtain. However, a global network of CO2 towers has been established at approximately 462 sites. The equivalent of about
2,750 years of data have already been collected. This excellent data set is now
being used to quantify the net carbon budget for most major ecosystems.
Night-time GHGs from whole farms
Helium-filled balloons have long been used to probe the atmosphere. Now scientists
are using them to measure GHG emissions on a regional scale. At night when the
lower atmosphere is stable, GHGs emitted from agricultural sources are contained
and cannot escape above the lower 50 to 100 metres of the atmosphere—the nocturnal boundary layer—essentially an enclosed chamber of air over a region. Several
times a night, meteorological and GHG measurements are made in this chamber
from a tethered blimp. This enables calculation of the GHG released from a whole
farm during the night.
Aircraft measurements of GHG emissions from whole regions
To obtain GHG emissions for a region, fast-response instruments are mounted
on aircraft. Flying at about 50 metres above agricultural land at 180 km/h, the
aircraft measures GHG emissions over entire regions by calculating the difference in the concentration of upward and downward moving air for the gas of
interest. Data collected by such aircraft, one of which is available in Canada, are
especially useful to test the accuracy of simulation models and GHG emissions
estimates, such as regional and national CH4 and N2O inventory estimates. Since
aircraft are expensive and can measure GHG emissions only over short periods,
they are often used in combination with towers, which measure GHGs around
the clock. In this way, the aircraft can expand the “view” of the tower from 1
square km to 100 square km.
Simulation models for estimating GHG emissions
Scientists will never be able to make sufficient measurements over a long enough
period of time to capture GHG emissions from all farms. Therefore, estimates
must rely on mathematical equations—or models—which are based on available
measurements. Models are an attempt to describe in mathematical language how
scientists understand the real world. Because our understanding is still incomplete,
any model is always an over-simplification of the real world. As Figure 30 shows, if
we are to make reasonable estimates with models, we need to use flux measurements to build models and continuously test the models against our observations.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
75
FIGURE 30
The Development of Models
MEASURE GHG
EMISSIONS
CREATE GHG
MODEL
APPLY GHG
MODEL
TEST GHG
MODEL
GHG model development occurs alongside experimental measurements. Initially, GHG
emission measurements give scientists the knowledge they need to create a GHG model.
When the model is tested under conditions somewhat different from those under which it
was originally designed, shortcomings are sometimes revealed. This process can inspire
new research questions. To address any shortcomings that appear, and to resolve research
questions, further model refinements and GHG emissions measurements are often required.
The models for emission estimates vary widely in complexity. Some approaches
use simple arithmetic. For example, the amount of N2O emitted from a field can
be estimated by assuming that a certain percentage of all nitrogen added to soil
as fertilizer, manure and crop residue is released as N2O. The Intergovernmental
Panel on Climate Change has recommended a value of 1.25%. However, this
percentage has been modified based on measurements made in Canada to account for such factors as soil moisture and topography. Thus, to estimate emissions in Canada, scientists sum up all nitrogen added to a field and multiply by
a series of emission factors representing several processes. Such approaches,
based on observations from many years, are called empirical models.
Models can be highly complex, residing in sophisticated computer code developed over many years of study. These process-based models try to describe
each of the processes that lead to GHG emissions and try to capture all factors
influencing those processes. Figure 31 shows results obtained with such a model
for Canadian conditions. While the adoption of no-tillage, the elimination of summer fallow and conversion of lands to permanent grasslands all reduced both
CO2 and N2O emissions, it is possible for a management practice that reduces
CO2 emissions to actually increase net GHG emissions due to increased N2O
emissions associated with that practice. Such is the case when a crop is fertilized
with nitrogen above the recommended levels. In this situation, depicted in Figure
31, carbon sequestration will increase, however the CO2 sequestered will be less
than the increase in N2O emissions caused by the increased fertilizer. Therefore,
the net GHG emissions will increase when a crop is over-fertilized, despite the
increased carbon sequestration.
Over the long term, most scientists aim to use process-based models. However,
in the short term, scientists are often forced to use simpler empirical models,
which require less data and understanding.
76
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 31
Results from Process-based Models
0.5
NET EXCHANGE OF GHGS
(t CO2e ha-1 y-1)
0.0
-0.5
-1.0
-1.5
N2O EXCHANGE
-2.0
CO2 EXCHANGE
NET GHG EXCHANGE
-2.5
-3.0
CONVERSION TO
NO-TILLAGE
MANAGEMENT
ELIMINATION OF
SUMMER FALLOW IN
CROP ROTATIONS
INCREASED
N-FERTILIZATION
(+50%)
DECREASED
N-FERTILIZATION
(-50%)
CONVERSION OF ANNUAL
CROPPING TO PERMANENT
GRASSLAND
When evaluating management practices for their effectiveness in reducing GHG emissions it is necessary to determine
more than just CO2 emissions. Two process-based models were used to investigate the impact that several changes in farm
management practices had on both N2O and CO2 emissions across Canada.
Source: B. Grant and W. Smith, AAFC, Ottawa, ON
Building better models remains an important aim of scientists in GHG research.
Such models can give us better estimates of the amounts of GHG produced,
and, more importantly, help us to project in advance, which practices might best
reduce emissions. There is a further benefit of building these models: they point
to our ignorance, showing where our understanding is weakest, and where we
most need further study to expand our knowledge.
FU RTHE R R E AD I NG
Baldocchi, D.D. 2003. Assessing the eddy covariance technique for evaluating carbon dioxide exchange
rates of ecosystems: Past, present and future. Global Change Biology 9:479–492.
Desjardins, R.L., MacPherson, J.I., Schuepp, P.H. 2000. Aircraft-based flux sampling strategies. Pp. 3573–
3588. In: R.A. Meyers (ed.) Encyclopedia of Analytical Chemistry. John Wiley & Sons Ltd.: Chichester.
McGinn, S.M. 2006. Measuring greenhouse gas emissions from point sources in agriculture. Canadian
Journal of Soil Science 86:355–371.
Pattey, E., et al. 2006. Towards standards for measuring greenhouse gas flux from agricultural fields using
instrumented towers. Canadian Journal of Soil Science 86: 373–400.
Rochette, P. and Hutchinson, G.L., 2005. Measurement of soil respiration in situ: Chamber techniques. Pp.
247–286 in M.K. Viney, (ed). Micrometeorology in agricultural systems. ASA, CSSA, SSSA, Madison, WI.
Agronomy Monograph 47: 584 pp.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
77
The Emissions we Produce
E S T I M AT E S O F G R E E N H O U S E G A S E M I S S I O N S F RO M
C A N A D I A N A G R I C U LT U R E
As earlier chapters have explained, agriculture is a significant source of three
GHGs: CO2, CH4 and N2O. Figure 32 shows that for each GHG there are multiple sources, both on farms and off farms. In responding to international agreements such as the Kyoto Protocol and the United Nations Framework Convention on Climate Change (UNFCCC), and to track progress in addressing climate
change, Canada elected to quantify and report annually its GHG emissions
from all sources in a transparent and verifiable manner. This technical chapter
presents GHG emission estimates from the Canadian agricultural sector for the
period from 1990 to 2005.
FIGURE 32
On- and Off-farm Sources of GHG Emissions
OFF-FARM
VOLATILIZATION AND
RE-DEPOSITION OF AMMONIA
AND NITROGEN OXIDES
N2O
ON-FARM
N2O
FERTILIZER, PESTICIDE,
MACHINERY AND BUILDING
MANUFACTURING
CO2
CH4
CO2
FOSSIL FUEL
COMBUSTION
CULTIVATION
OF HISTOSOLS
SYNTHETIC AND
MANURE N
APPLICATION
ELECTRICAL
ENERGY
PRODUCTION
FOSSIL FUEL
FOR HEATING
CROP RESIDUE
DECOMPOSITION
ENTERIC
FERMENTATION
MANURE
DEPOSITED
ON PASTURE
LEACHING
AND RUNOFF
FARM
BOUNDARY
78
MANURE
STORAGE
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Global warming potential
Greenhouse gases differ in their ability to trap heat in the atmosphere and
therefore are not equal in their contribution to global warming. Global warming
potential (GWP) allows us to assess how much a given mass of GHG is likely
to contribute to global warming. The latest values are given in the introductory
chapter. For reporting purposes, the GWP for N2O and CH4 are considered to be
310 and 21 times more powerful than CO2 by mass over a 100-year period. By
indexing each gas to CO2 using the GWP, national GHG emissions are reported
as million tonnes (Mt) of CO2 equivalents, or Mt CO2e. One Mt CO2e is roughly
equal to the CO2 emissions that 220,000 mid-size cars produce when traveling
over a distance of 20,000 km.
There are many on-farm and off-farm sources of GHG emissions. On-farm N2O emissions are enhanced when nitrogen
is added to the environment. This happens when synthetic
fertilizer and manure are applied to the land, when manure
is stored, when manure is excreted on pasture and when organic soils (histosols) are cultivated. Off-farm N2O emissions
occur when nitrogen is transported away from the farm before
being converted to N2O. This occurs in water by leaching
and runoff and through the air by volatilization. Methane
emission occurs on-farm when organic material is decomposed by methanogenic bacteria under oxygen-free conditions.
This occurs during the digestive process in ruminants and
during the storage of manure. Carbon dioxide emissions
occur on-farm when crop residues and other organic matter
decompose and when fossil fuels are burned to propel farm
machinery and to heat farm buildings. Off-farm CO2 emissions occur when fossil fuels are consumed to produce goods
that are needed on-farm: fertilizer, pesticides, machinery,
building construction material and electrical energy.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
79
Delving deeper
Calculation methodology
The methodology to calculate emissions from the Canadian agricultural sector varies by gas depending on our level of
knowledge of each. Soil CO2 emissions are calculated by incorporating the results from a process-based model to estimate
net CO2 exchange between the plant-soil and the atmosphere. However, because of a lack of adequate process-based models,
CH4 and N2O emissions are calculated using empirical models developed by the Intergovernmental Panel on Climate Change
and modified for Canadian conditions. These methods of calculation allow flexibility to incorporate Canadian conditions and
research results, while allowing comparison with GHG emission inventories from other nations.
Equation 1: CO2 emissions from the soil
Changes in either land use or land management can cause soil carbon content to remain constant or increase or
decrease. If there is no change in land use or land management, and climatic conditions are relatively similar from year to year,
soil carbon stocks will tend, over many years, to approach an equilibrium.
The basic equation used to estimate a change in soil carbon as the result of a land management change (LMC) is given as:
ΔC = F × A
where:
ΔC = Change in soil C stock, t C y-1
F = Average annual change in soil organic carbon (SOC) from the LMC, t C ha-1y-1.
A = Area of the LMC, ha
As Figure 33 shows, the activity data—A in equation 1—are spatially referenced with respect to the boundaries of
the National Ecological Framework, a hierarchical eco-stratification of all land in Canada. The eco-stratification provides a
systematic basis for scaling the information from the smallest area for which soil information is available on a national scale
to larger ecologically related areas (i.e., ecodistrict, ecoregion, ecozone). We estimated agricultural soil carbon change for Soil
Landscapes of Canada (SLC). In Canada, there are 3,264 SLC units in which agricultural activities take place. The main source
of national activity data is the Census of Agriculture, available from Statistics Canada for all farms every five years.
A large body of Canadian and international literature describes how management practices are known to influence soil carbon
in cultivated cropland. To include such practices in the GHG inventory, a good understanding of soil carbon change expected for the
LMC and the area of the LMC are required. The LMC selected were reduction in tillage intensity, reduction in summer fallow and
conversion from annual to perennial crops. They are the three main strategies used in Canada during 1990-2005.
To estimate the average annual change in soil carbon due to LMC (F), a plant-soil organic matter model, CENTURY, was
used to simulate carbon nutrient dynamics for Canadian croplands. This process model has been used widely to simulate SOC
and has been tested and validated for Canadian conditions. Carbon factors (F) derived from model simulations were estimated
as the difference in soil carbon stocks over time between two simulations: a base run representing general land management
conditions (excluding specific changes in practices) and a factor run in which everything was held constant relative to the base
except for the LMC of interest.
Carbon dioxide emissions from fossil fuel use
Many activities on farm and off farm, which rely on the use of fossil fuel, result in releases of CO2 along with trace
amounts of CH4 and N2O. A large percentage arises directly from farm field operations and indirectly from electricity
production, heating fuel and the manufacture of fertilizer, pesticide and machinery. These emissions are very important as
far as managing GHG emissions. However, for the UNFCCC and reporting purposes, they are attributed to the transportation
and manufacturing sectors and are not included in the agricultural GHG inventory.
80
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 33
The Hierarchical Eco-stratification of all Land in Canada
ECOZONE
1: 7,500,000
ECOREGION
ECODISTRICT
SOIL LANDSCAPES
OF CANADA
1: 1,000,000
Canada has been
subdivided into small
spatial areas—called Soil
Landscapes of Canada—
that have similar soil and
climatic conditions. By
grouping estimates made
at the small scale, scientists
can estimate emissions at
much larger scales, such as
provincial or national.
Equation 2: N2O emissions
Nitrous oxide emissions from soil and manure management systems for each nitrogen (N) source are calculated by
multiplying the amount of N additions from various sources (e.g., synthetic fertilizer N, crop residue N, manure N, etc.) by a
particular empirical emission factor for that source.
N2O Emissions = N × EF
where:
N2O emissions = Emissions from various N sources, kg N2O–N y-1
N = Amount of N by source, kg N
EF = Emission factor, kg N2O–N kg N-1 y-1 for a particular source.
In Canada, the soil N2O emission factors are primarily a function of soil moisture conditions. As Figure 34(a) shows, in
drier climates such as the Prairie provinces, the emission factors are much lower than for Eastern Canada, where the climate is
generally more humid. In British Columbia, the emission factors are moderate in the wet coastal areas and low in the dry interior
areas. The N2O emission factors are also dependent upon soil texture, tillage intensity, and landscape position, as well as soil
moisture added during spring thaw and crop irrigation. Factors were derived for each SLC based on the climatic conditions.
Nitrous oxide emissions occurring from manure are a function of the manure storage system. As compared to CH4
emissions, aerobic conditions tend to enhance N2O emissions. Therefore, as Figure 34(b) shows, when manure is deposited
onto pasture by grazing animals or stored as a solid, N2O emissions are greater than for liquid manure.
Equation 3: CH4 emissions
Methane emissions from enteric fermentation are calculated by multiplying animal population in each animal category
by an empirical emission factor for that particular category.
CH4 Emissions = n × EF
where:
CH4 emissions = Emissions from a particular livestock class, kg CH4 y-1,
n = Animal population for a particular livestock class,
EF = Emission factor, kg CH4 animal-1 y-1 for a particular livestock class.
As Figure 34(c) shows, the emission factors are very different for various animal categories. They also vary with the diet
and the activity level of the animal. More information is available in the chapter on methane emissions.
Emissions associated with manure management are estimated using a similar approach: animal population × emission
factor. As Figure 34(d) shows, the emission factor is the largest for dairy cows. This is a function of the manure storage system
employed (e.g., liquid storage creates greater emissions than solid storage), the amount of manure produced per animal and
the temperature of the stored manure. The chapter on methane emissions offers more details.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
81
FIGURE 34
0.025
a
0.020
0.015
0.010
0.005
N2O EMISSION FACTOR (kg N2O-N kg N-1 y-1)
N2O EMISSION FACTOR (kg N2O-N kg N-1 y-1)
GHG Emission Factors in Canada
0
PRAIRIE
PROVINCES
BC
COASTAL
b
0.020
0.015
0.010
0.005
0
EASTERN
CANADA
BC
INTERIOR
MANURE ON
PASTURE
SOLID
MANURE
STORAGE
OTHER
MANURE
STORAGE
LIQUID
MANURE
STORAGE
50
c
150
125
100
75
50
25
0
CH4 EMISSION FACTOR (kg CH4head-1 y-1)
175
CH4 EMISSION FACTOR (kg CH4head-1 y-1)
0.025
d
40
30
20
10
0
DAIRY COW
BEEF CATTLE
SWINE
POULTRY
DAIRY COW
BEEF CATTLE
SWINE
POULTRY
Moisture enhances N2O emissions from soils. As a result, N2O emissions are higher per unit of area in the moist soils of the
eastern provinces, and lower in the dry Prairie provinces. Emissions are variable in British Columbia, where moist soils occur
on the west coast, but dry conditions prevail in the interior of the province (Panel a). Nitrous oxide emissions from manure
are enhanced when manure decomposes under aerobic conditions. Therefore, emissions are greatest when manure is stored as
a solid, or deposited on pasture by grazing animals, and smallest when the manure is stored as a liquid (Panel b).
The rate of GHG emissions is highly variable between animal categories and regions across the country. For instance, a
dairy cow produces approximately 150 kg of CH4 from enteric fermentation per year, whereas a beef cow, which is nearly
as large as a dairy cow, produces only 70 kg per year (Panel c). Methane emissions from manure management vary
depending on the storage type used. Dairy-cow and swine productions tend to store manure as a liquid, which promotes
CH4 emissions, whereas beef-industry manure tends to be stored as a solid, which restricts CH4 emissions (Panel d).
Source: R. Desjardins and D. Worth, AAFC, Ottawa, ON
82
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
GHG emission estimates from Canadian agriculture,
1990 to 2005
The UNFCCC has stipulated that GHG emissions be calculated annually from
1990 onwards. With respect to the international agreements, most sectors are
largely concerned with how current emissions compare with emissions in 1990.
From 1990 to 2005, Canada’s GHG emissions for all sectors increased by 25%.
As Figure 35 shows, agriculture is responsible for approximately 8% of national
GHG emissions if emissions associated with fossil fuel are not counted and 10%
if they are included. Meanwhile, agriculture is increasing its emissions of N2O and
CH4 at roughly the same rate as all other sectors and these gases continue to be
the most significant GHGs in agriculture (Figure 36).
Carbon dioxide emissions and removals by soils are accounted for under the
UNFCCC category of Land Use, Land Use Change and Forestry. The categories
pertaining to agriculture include grasslands converted to croplands, croplands
remaining croplands, forests converted to croplands, and grasslands remaining
grasslands. As Figure 37 shows, since 1990, grasslands converted to croplands
has been a relatively minor and decreasing source of CO2, croplands remaining
croplands has been a relatively major and increasing sink of CO2, and forests
converted to croplands has been a relatively major but decreasing source of
CO2. Canada has chosen to define grasslands as rangeland—unimproved
pasture in regions where it would not revert to forest if unmanaged. Under this
definition, grassland remaining grassland was assumed to be neither source nor
sink of CO2. On a net basis, these categories have gone from being a source of
14 Mt CO2e in 1990 to being almost neutral in 2005.
FIGURE 35
All Sector and Agricultural GHG Emissions in Canada for 2005
WASTE
4%
INDUSTRIAL
PROCESSES
7%
AGRICULTURE
8%
57 Mt CO2e
N 2O
51%
29 Mt CO2e
ENERGY
81%
ALL SECTOR TOTAL:
747 Mt CO2e
CH4
49%
28 Mt CO2e
In 2005, Canada emitted 747 Mt CO2e. Energy production was responsible for 81% of these emissions. Agriculture was responsible for a smaller, but significant, portion
of national GHG emissions, approximately 8% or 57 Mt
CO2e. Emissions from Canadian agriculture are nearly
evenly split between N2O and CH4. Emissions associated
with fossil fuel use in agriculture accounted for an additional 2% of the national emissions, however these are
counted in the transportation and manufacturing sectors.
Source: R. Desjardins and D. Worth, AAFC, Ottawa, ON
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
83
FIGURE 36
Agricultural N2O and CH4 Emissions in Canada, 1990–2005
60
CH4
N 2O
GHG EMISSIONS (Mt CO2e)
50
40
30
20
10
0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Nitrous oxide emissions from Canadian agriculture increased by 4 Mt CO2e (or 14%)
between 1990 and 2005 while CH4 emissions increased by 7 Mt CO2e (or 24%).
Source: R. Desjardins and D. Worth, AAFC, Ottawa, ON
FIGURE 37
Carbon Dioxide Emissions from Agriculture Related to Land
Use, Land Use Change and Forestry
20
GHG EMISSIONS (Mt CO2)
15
10
5
0
-5
GRASSLANDS CONVERTED TO CROPLANDS
-10
CROPLANDS REMAINING CROPLANDS
FORESTS CONVERTED TO CROPLANDS
NET CO2 EMISSIONS
-15
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Net CO2 emissions from agriculture related to Land Use, Land Use Change and Forestry
decreased by almost 14 Mt CO2 between 1990 and 2005. This is due to an increase in
carbon sequestration in croplands and a decrease in CO2 emissions caused by forests
converted to croplands.
Source: B. McConkey, AAFC, Swift Current, SK
84
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 38
The Change in Soil Organic Carbon Content of Agricultural Soils in Canada
1990–2005, t ha-1
N
<-1.5
-1.5 to -0.5
NO CHANGE
0.5 to 1.5
1.5 to 2.5
0
500 1,000 2,000
3,000
km
4,000
Farmers have the ability to change the amount of organic
carbon in their soils by adopting beneficial management
practices such as reduced tillage, reduced summer fallow and
the conversion of annual to perennial crops. In Canada, widespread adoption of such practices has led to an increase in soil
organic carbon in croplands of the Prairie provinces. However,
in many areas of Eastern Canada, there has been a decrease in
soil organic carbon in croplands because of a shift from perennial to annual crops such as corn and soybean. This conversion emits more CO2 even if it is accompanied by the adoption
of beneficial management practices. In this map the change in
soil organic carbon between 1990 and 2005 in the first 30cm
in the soil is shown for all agricultural lands in Canada.
Source: B. McConkey, AAFC, Swift Current, SK
Figure 38 shows the net change in soil carbon stocks between 1990 and 2005
to a depth of 30 cm in Canadian agricultural lands for cropland remaining cropland. These show a substantial gain in soil carbon, particularly in the Prairie provinces, after the introduction of beneficial agricultural practices such as reduced
summer fallow, increased use of conservation tillage and perennial crops.
Why have GHG emissions changed?
As Figure 36 shows, agricultural GHG emissions in the form of CH4 and N2O have
increased by 19% since 1990. However, when CO2 emissions from agricultural land
use are included in the comparison, total net agricultural GHG emissions decreased
by 6%. This is because of a large decrease in net soil CO2 emissions driven by the
increased adoption of beneficial agricultural practices. Specifically, a decrease in the
occurrence of summer fallow in the Prairie provinces, an increase in conservation tillage—tillage that minimizes disruption of the soil—and an increase in perennial crops
in the Prairie provinces have increased soil carbon content.
Minimum tillage and no-tillage practices often provide both economic and environmental benefits. As a result, the area under these practices in Canada has expanded
from 30% of the cropland in 1990 to 70% of the cropland in 2005. An extensive
discussion of beneficial agricultural practices is included in the carbon chapter.
Although soil organic carbon has been increasing in agricultural soils of the Prairie provinces, it is important to note that changes in farming practices can also
increase the emission of soil carbon stocks as CO2. This has been happening
in Eastern Canada, especially Ontario and Quebec where the area of perennial
forages has been decreasing in favour of growing annual crops such as corn and
soybeans. In fact, some areas of Quebec and Ontario are as large a source of
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
85
CO2 as parts of the Prairie provinces are a sink. It is also important to note that
if the beneficial agricultural practices discussed above were stopped, carbon
would be reemitted into the atmosphere, possibly at a faster rate than the rate at
which it was sequestered. Changes in economics, government policies or the climate could bring about different agricultural practices and, therefore an increase
or decrease of soil organic carbon.
Much of the decreased CO2 emissions from soil has been offset by increases in
CH4 and N2O emissions. From 1990 to 2005, CH4 emissions from the Canadian
agricultural sector increased by 24% due to larger populations of most animals.
As Figure 39 shows, the Canadian beef cattle population, increased by 30%.
Most of this expansion occurred in the Prairie provinces. Similarly, the swine, and
poultry populations have increased by 31% and 23%, respectively. Only the dairy
cow population decreased, by 29%. The net effect in Canada is that total CH4
emissions have continued to increase.
Nitrous oxide emissions in Canada increased by 14% between 1990 and 2005,
primarily because of an increase in the use of synthetic nitrogen fertilizer and the
increase in animal population. National synthetic nitrogen fertilizer sales increased
from 1.20 Mt of nitrogen to 1.54 Mt of nitrogen from 1990 to 2005. The increase
in nitrogen fertilizer use has occurred exclusively in the Prairie provinces; in all other
provinces consumption decreased or maintained its level during this period. Meanwhile, larger animal populations have contributed to greater N2O emissions because of greater manure production. Finally, emissions from crop residue nitrogen
addition are directly related to crop production, which depends on weather conditions. For example, 2002—a year in which severe drought led to crop production
44% lower than in 2005—resulted in the lowest N2O emission estimates from crop
residue decomposition for the 1990 to 2005 period.
Uncertainty in GHG emission estimates
Farm management practices change quickly, climate varies year to year and
precise agricultural data are difficult to collect. This makes estimating agricultural
GHG emissions an uncertain practice. Experts have long believed that uncertainties in Canadian agricultural GHG emissions are largest for N2O, followed
by CH4, the least uncertainty being associated with CO2. However, analyses
suggest these initial rankings may not adequately consider the uncertainty in
agricultural activities. In particular, changes in soil carbon stocks appear more uncertain than CH4 emissions because the uncertainty in land management change
is greater than the uncertainty in the livestock population. Unfortunately, it is not
possible to provide quantitative error estimates at this time.
GHG emission trends
Statistics Canada reports that between 1991 and 2006 the number of farms in
Canada decreased from 280,043 to 229,373 and that the average farm size has
increased from 242 hectares to 295 hectares. This trend is likely to continue.
86
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 39
16
160
DAIRY COWS
BEEF CATTLE
14
12
140
SWINE
POULTRY
120
10
100
8
80
6
60
4
40
2
20
0
0
POPULATION (MILLION POULTRY BIRDS)
POPULATION (MILLION NON-POULTRY ANIMALS)
Domestic Farm Animal Population in Canada, 1990–2005
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
The population of farm animals in Canada is directly related to GHG emissions from Canadian agriculture. Canadian farm-animal populations increased substantially for most animal categories between 1990 and 2005. Beef cattle
and swine increased by 30% and 31%, respectively, while poultry increased by 23%. Only the dairy-cow population
decreased, by approximately 29%.
Source: R. Desjardins and D. Worth, AAFC, Ottawa, ON
During the same period, crop production intensified and the number of animals
destined for meat products also increased markedly. Consequently, between
1990 and 2005, N2O, CH4 and fossil fuel CO2 emissions from Canadian agriculture have increased by 14%, 24% and 10% respectively. Because of improved
management practices related to soil conservation, agricultural soils have gone
from being a 14 Mt CO2 source to being nearly neutral in that respect. It is likely
that Canadian agricultural soils will become a net carbon sink in the near future.
However, the sink is likely to be fairly small and the question of permanence must
always be considered.
GHG emissions are unavoidable
Greenhouse gas emissions must be viewed as a necessary cost of food production as their emission is the inevitable result of growing crops and raising livestock. As the human population increases, so will the demand for food. Consequently, GHG emissions of CH4 and N2O are very likely to continue to increase
as Canadian farms respond. Since GHG emissions constitute a loss of energy
from the system, there will continue to be a search for more efficient practices
that reduce these economic losses. Scientists have determined that increased
efficiency in crop and animal production will lead to a small reduction in GHG
emissions per unit of product—but that these reductions will have a relatively
minor impact on total GHG emissions.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
87
FIGURE 40A
Dairy-cow Populations and Milk Production in Canada
DAIRY COW POPULATION
MILK PRODUCTION
1,300
11,000
10,000
9,000
1,100
8,000
900
7,000
6,000
700
5,000
500
4,000
300
3,000
MILK PRODUCTION (kg head-1 y-1)
DAIRY COW POPULATION (X 1000)
1,500
2,000
100
1,000
0
0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Although Canada’s dairy-cow population decreased between 1990 and 2005, total milk production remained relatively
constant as dairy cows became more productive (Panel A). The increase in productivity resulted in greater enteric CH4
emissions per cow, however, when expressed per kg of milk produced, CH4 emissions from enteric fermentation and manure management decreased by 13% (Panel B).
Source: R. Desjardins and X. Vergé, AAFC, Ottawa, ON
FIGURE 40B
Methane Emission Factor for Dairy Cows (enteric and manure) and CH4 Emissions
per kg of Milk
190
CH4 EMISSION FACTOR
EMISSIONS INTENSITY
185
0.40
180
175
0.35
170
165
0.30
160
155
150
0.25
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Source: R. Desjardins and X. Vergé, AAFC, Ottawa, ON
88
0.45
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
CH4 EMISSIONS INTENSITY (kg CO2e kg milk-1)
CH4 EMISSION FACTOR (kg CH4
COW-1
y-1)
195
If we are to realize significant emission reductions,
society must pursue alternatives for the types
of food it consumes, the way in which it produces that food and the way in which it deals with
agricultural wastes. For example, a decreased
dependence on animal products for food would
reduce emissions from enteric fermentation and
manure management. Society must also pursue
alternatives to the way it uses energy. The adoption of biofuels from biodiesel or biomass, or the
large-scale adoption of biodigestion as a manure
management technique could potentially displace
a substantial amount of GHG emissions from fossil fuels. Conversely, a policy of increased corn
and oilseed production for bioenergy along with
reduced livestock production could promote the
breaking of hayland and pasture and even the
clearing of trees to increase land for production.
At least in the short term, those actions would
greatly increase GHG emissions from the decomposition of soil organic carbon.
Clearly, a holistic analysis across all agricultural
activities is needed to assess optimal policies for reducing GHG emissions in the short and long terms.
A CONCRETE
EXAMPLE
As shown in Figure 40, CH4
emissions per liter of milk
produced are decreasing.
Improved dairy cattle breeding
led to a 21% increase in milk
production per head between
1990 and 2005—and a
concurrent 29% decrease in
the dairy cattle population. As a
consequence of producing more
milk per cow, CH4 emissions
per cow increased during the
same period. However, the CH4
increases have been smaller
than the rate of increase in milk
production. Therefore, GHG
emissions in the form of CH4
have decreased by about 13%
per unit of milk produced.
FU RTHE R R E AD I NG
Desjardins, R.L., et al. 2005. Greenhouse Gases. Pp. 142– 148 in Lefebvre, A., W. Eilers, and B. Chunn
(eds.) Environmental Sustainability of Canadian Agriculture: Agri-Environmental Indicator Report Series, Report #2.
Agriculture and Agri-Food Canada: Ottawa. Available online at: http://www.agr.gc.ca/env/naharp-pnarsa/
index_e.php. Accessed October 23, 2007.
Environment Canada, 2007. National Inventory Report: 1990–2005, Greenhouse gas sources and sinks in Canada.
Environment Canada, Greenhouse gas division.
Intergovernmental Panel on Climate Change (IPCC). 2001. Climate Change 2001: The Scientific Basis:
Contribution of Working Group 1 to the Third Assessment Report of the Intergovernmental Panel on
Climate Change. Cambridge University Press: New York.
Statistics Canada. 2007. Total farm area, land tenure and land in crops, by province (1986–2006 Censuses of
Agriculture). Available online at: http://www40.statcan.ca/l01/cst01/agrc25a.htm. Accessed October 23, 2007.
Smith, W., R.L. Desjardins and B. Grant. 2001. Estimated changes in soil carbon associated with agricultural
practices in Canada. Canadian Journal of Soil Science. 81: 221–227.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
89
Reckoning
the Total Budget
The
Amounts
NON-GREENHOUSE GAS EFFECTS
O F A G R I C U LT U R E O N C L I M AT E
Agricultural production is highly dependent on weather and climate. Without
adequate rainfall and appropriate temperatures, crops fail and pastures become
barren. Interestingly, the opposite is also true: weather and climate are influenced
by agricultural practices. By managing croplands and pastures farmers influence a
series of physical, chemical and biological interactions between the Earth’s surface
and the atmosphere that can affect air temperature and precipitation in many ways.
One reasonably well-accepted effect of agriculture on air temperature is agriculture’s production of GHG emissions, which contributes to the anthropogenic
(human caused) greenhouse effect. As Figure 41 shows, this is known as a biogeochemical effect of agriculture on climate. However, it is less well known that
agriculture affects weather and climate by changing the Earth’s albedo, that is,
the fraction of solar radiation that strikes the Earth and is then reflected back into
space. Albedo has a biogeophysical effect on weather and climate and is a key
determinant of climate on the Earth.
FIGURE 41
Biogeophysical and Biogeochemical Impacts on Climate
CLIMATE
AIR TEMPERATURE,
CONVECTIVE RAIN
ALBEDO, LATENT
AND SENSIBLE
HEAT FLUXES
CO2, CH4, N2O
EMISSIONS
BIOGEOPHYSICAL
INFLUENCE
BIOGEOCHEMICAL
INFLUENCE
AGRICULTURAL PRACTICES
Agricultural practices have an impact on climate by influencing the energy exchange
between crops and the atmosphere—a biogeophysical impact on climate. Agricultural practices can also influence climate by modifying the rate at which soils and plants exchange
GHGs with the atmosphere—a biogeochemical impact on climate.
90
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
The importance of albedo
The albedo of a given surface, or land cover, affects the temperature of the surface
and of the overlying air. Different land covers have different albedos. Land covers
with a higher albedo—ice and snow—tend to have lower temperatures because
they reflect back into space a high percentage (35-90%) of incoming radiation.
Land covers with lower albedo—such as grasslands and forests—tend to have
higher air temperature because they reflect back into space a smaller percentage
(5-25%) of incoming radiation. Globally, the Earth’s average albedo is about 30%.
A thorough understanding of the albedos of various land covers is important to
our overall understanding of climate. For example, scientists previously assumed
that the albedo of the boreal forest in winter was high, because of the presence
of snow. In reality, satellite measurements have shown that snow cover only marginally increases the albedo of boreal forests because snow is “hidden” under the
canopy. This error had been causing weather forecast models to underestimate
daily winter temperatures over boreal regions by as much as 10ºC. The albedo of
grasslands is sharply increased by snow cover. Thus, the difference in net radiation between grasslands and coniferous forests is largest in winter.
This is important because, contrary to popular belief, reforesting high latitude
agricultural regions may actually contribute to global warming, rather than slow
its progress. The dark canopy of Canadian, Scandinavian and Siberian forests
absorb solar radiation that would otherwise be reflected back to space by snow
if these regions were agricultural land.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
91
Delving Deeper
The biogeochemical and biophysical effects of agriculture on climate are quantified in
terms of the resulting energy received at the surface of the earth, measured in watts per
square metre (Wm-2). Values greater than zero—termed positive radiative forcing—indicate
warming, while values less than zero—termed negative radiative forcing—indicate cooling.
By studying the relation between global temperature and natural changes in net
radiative forcing, it has been estimated that the long term mean temperature increases by
0.4 to 0.7 ºC for each increase of 1 Wm-2 of net radiative forcing. Figure 42 shows the global
average radiative forcing estimates and their uncertainty in 2005 for anthropogenic CO2,
CH4, N2O and other radiative forcing components associated with aerosols, land use, ozone
and variations in solar irradiance together with the range in estimates.
Variations in solar activity are considered natural forcing. Periods of high solar activity
have been shown to be about 0.2 ºC warmer globally than periods of low solar activity and
warming is amplified near the Earth’s poles.
The largest positive radiative forcing is associated with the increase of long- and
short-lived GHGs in the atmosphere, which add up to +3.0 Wm-2. The largest negative
forcing is associated with the direct and indirect effect of aerosols in the air, which add up
to -1.5 Wm-2. The sum of all positive and negative anthropogenic forcings results in a net
positive forcing of approximately +1.5 Wm-2. Most of these forcings act at a global scale,
except for surface albedo, which has more of a local effect. Natural forcings such as volcanic
aerosols are not considered in Figure 42 because of their episodic nature. They tend to
cause a temporary negative forcing.
Energy Budget and Air Temperature
Land use and land-cover changes affect climate through the surface energy budget.
As Figure 43 shows, net radiation at the Earth’s surface, Qn, is determined by incoming
short-wave solar radiation (S↓) minus reflected short-wave solar radiation (S↑), plus the
difference between long-wave radiation emitted downward by the atmosphere (L↓) and the
long-wave radiation emitted by the Earth (L↑):
Qn = (S↓ - S↑) + (L↓ - L↑)
Net radiation is partitioned into energy used to heat the air, or the sensible heat flux
(QH), energy used for evapotranspiration, or the latent heat flux(QL), as well as the heat
conducted in or out of the soil (QG):
Qn = QL + QH + QG
An increase in radiative forcing due to biogeochemical changes in the composition
of the atmosphere results, primarily, from an increase in counter-radiation from the
atmosphere, (L↓), hence, the greenhouse analogy. The primary impact is on overnight,
or minimum, temperatures when the short-wave radiation terms do not come into play in
the net radiation budget of the Earth’s surface. In contrast, biogeophysical effects such as
changes to surface albedo and changes to vegetation and soil moisture have their greatest
impact on the maximum daytime temperatures.
92
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 42
Radiative Forcing Components
RF VALUES (Wm-2)
SPATIAL SCALE
LOSU
1.66 [1.49 TO 1.83]
GLOBAL
HIGH
0.48 [0.43 TO 0.53]
HALOCARBONS 0.16 [0.14 TO 0.18]
0.34 [0.31 TO 0.37]
GLOBAL
HIGH
-0.05 [-0.15 TO 0.05]
0.35 [0.25 TO 0.65]
CONTINENTAL TO GLOBAL
MED
0.07 [0.02 TO 0.12]
GLOBAL
LOW
-0.2 [-0.4 TO 0.0]
0.1 [0.0 TO 0.2]
LOCAL TO CONTINENTAL
DIRECT EFFECT
-0.5 [-0.9 TO -0.1]
CONTINENTAL TO GLOBAL
CLOUD ALBEDO
EFFECT
-0.7 [-1.8 TO -0.3]
CONTINENTAL TO GLOBAL
LOW
LINEAR
CONTRAILS
0.01 [0.003 TO 0.03]
CONTINENTAL
LOW
SOLAR
IRRADIANCE
0.12 [0.06 TO 0.30]
GLOBAL
LOW
RF TERMS
CO2
N2O
LONG-LIVED
GREENHOUSE
GASES
CH4
STRATOSPHERIC
NATURAL
TROPOSPHERIC
STRATOSPHERIC
WATER VAPOUR
FROM CH 4
SURFACE
ALBEDO
TOTAL AEROSOL
ANTHROPOGENIC
OZONE
BLACK CARBON
ON SNOW
LAND USE
TOTAL NET
ANTHROPOGENIC
MED-LOW
MED-LOW
1.6 [0.6 TO 2.4]
-2
-1
0
1
2
-2
RADIATIVE FORCING (Wm )
There are many anthropogenic contributions to radiative forcing (RF). The most significant contributions include the emission of GHGs such as CO2, CH4, N2O and halocarbons (a solvent and refrigerant); changes in stratospheric and tropospheric
ozone; changes in albedo through land-use change and deposition of black carbon on snow and from changes in aerosol concentration in the atmosphere. GHG emissions represent the largest anthropogenic climate forcing. There are also natural radiative
forcings, including the slow change over time in the sun’s intensity. This natural forcing is much smaller than the sum of
anthropogenic forcings, which are estimated to be +1.6 Wm-2, with a range in estimates from +0.6 to +2.4 Wm-2. The emission
of agricultural GHGs, a biogeochemical effect, and the change in albedo due to land converted to agriculture are relevant to this
chapter. Also shown in this figure is the spatial scale of the forcing and the current level of scientific understanding (LOSU).
Source: IPCC AR4 WG1 Summary for Policy Makers. Available online at: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf, accessed January 25, 2008.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
93
FIGURE 43
Energy Exchange Between the Earth’s Surface and the Atmosphere
INCOMING SHORT-WAVE
RADIATION AT THE TOP OF THE
ATMOSPHERE 342 Wm-2
SPACE
77 Wm-2 REFLECTED
67 Wm-2 ABSORBED BY
CLOUDS AND ATMOSPHERE
ATMOSPHERE
SENSIBLE
HEAT FLUX
(QH) 24 Wm-2
LATENT
HEAT FLUX
(QL) 78 Wm-2
REFLECTED
SHORT-WAVE
RADIATION (S↑)
30 Wm-2
LAND
GROUND HEAT FLUX
(QG) 0 Wm-2 ON AN
ANNUAL BASIS
INCOMING
SHORT-WAVE
RADIATION (S↓)
198 Wm-2
168 Wm-2 ABSORBED
BY SURFACE
INCOMING
LONG-WAVE
RADIATION (L↓)
324 Wm-2
ABSORBED
BY SURFACE
OUTGOING
LONG-WAVE
RADIATION (L↑)
390 Wm-2
EMITTED BY
SURFACE
Water vapour and energy are constantly being exchanged between the Earth’s surface and the atmosphere. Radiant energy
from the sun is reflected or converted into sensible heat-energy to heat the air, latent heat energy to evaporate water, transferred into the soil as ground heat or re-emitted to the atmosphere as long-wave radiation.
Source: The magnitude of Earth’s annual and global mean energy budget is adapted from Kielhl and Trenberth. 1997. Bulletin of the American Meteorological Society.
Agriculture can affect air temperature
The biogeophysical impact of agriculture on air temperature is a significant local and
continental issue. Increasing human population and the need for food production to
keep pace has resulted in conversion of vast areas of natural land to cropland and
pasture. Over the last three centuries, cropland has increased more than five-fold
and the area under pasture has increased more than six-fold. In recent years, increases in cropland and pasture have occurred largely at the expense of forests. This
has altered the net global radiation budget of the Earth’s surface.
At present, it is estimated that the practice of converting forested land to agricultural land has increased surface albedo, which results in an overall cooling of our
climate by 0.1 ºC. Another estimate is that were all forests replaced by grasslands, global climate would cool by more than 2 ºC once the full impact of the
land-cover change had come into play.
94
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 44
Mean Monthly Difference in the Net Radiation Between
Coniferous Forest and Grasslands.
150
GRASSLANDS - CONIFEROUS
FOREST MEAN ANNUAL
DIFFERENCE IN NET
RADIATION = 14 Wm-2
CONIFEROUS FOREST
NET RADIATION (Wm-2)
GRASSLANDS
GRASSLANDSCONIFEROUS FOREST
100
50
0
-50
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEPT
OCT
NOV
DEC
Coniferous forests keep their needles year round and are very efficient at absorbing solar
radiation, even in the winter when agricultural grasslands will be buried with snow.
The mean annual difference in net radiation between coniferous forest and grasslands
is approximately 14 Wm-2. For comparison, the mean annual difference in net radiation
between a coniferous forest and a deciduous forest is approximately 10 Wm-2.
Source: R. Desjardins and D. Worth, AAFC, Ottawa, ON
Crops can influence the timing of thunderstorms and
severe weather
As a crop grows, it transpires, absorbing water from the soil and transferring it to
the atmosphere. The rate of transpiration varies as the crop grows; that is, the
proportion of sensible heat (energy used to heat the air) to the latent heat (energy
used for evapotranspiration) changes. Scientists have shown that for the same
amount of net radiation, the larger the evapotranspiration, the higher the potential
for thunderstorms. For the Canadian Prairies, scientists have demonstrated how
the widespread transformation of native mixed perennial grasses to annual field
crops may have modified the seasonal pattern of thunderstorm days. They found
that agriculture has decreased the potential for thunderstorms early and late in
the growing season, but has enhanced the potential around the mid-point of the
growing season when rapid leaf growth results in high transpiration.
Agriculture also affects the availability of water vapour, and thus the prevalence of
rain, over portions of the globe. For the Canadian Prairies, in areas with normal
summer rain, 20% of the moisture in the air originates from the crops. It follows
that agricultural crops are an important source of water vapour for growing-season rain and that they play a role in the persistence of wet and dry periods.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
95
Impact of GHG mitigation practices on air temperature
Changes in agricultural management practices can affect not only weather, but
they can also reduce the rate of increase of atmospheric CO2 by sequestering
carbon in agricultural soils. Globally, it is estimated that agricultural soils could be
a significant carbon sink over the next century.
This is possible because in the past, soil carbon stocks have been considerably depleted in Canada and around the world by various farming practices.
Scientists believe that by adopting agricultural practices favourable to increasing
the soil carbon stock, farmers in Canada could store in the soil every year the
equivalent of the CO2 emitted from 2.5 million mid-sized cars. With enhanced
measures Canadian agricultural soil sinks could be made even more effective.
See the earlier chapter on carbon for a full explanation of carbon sequestration in
soils and the agricultural practices that best promote sequestration.
The reduction of summer fallow area in the prairies in recent years has been
shown to promote carbon sequestration in agricultural soils. Therefore, we can
say that the biogeochemical effect of reducing summer fallow had a cooling
effect on air temperature. It is estimated that more intensive cropping between
1976 and 2000 in the Prairie provinces, where annual crops and forages have
replaced summer fallow, has been associated with a decrease in the regional
maximum air temperature of 1.7 ºC per decade and an increase in precipitation
of 10 mm per decade from June 15 to July 15.
This is most likely the case because sensible heat flux is greater over summer fallow than over cropped land, whereas latent heat flux is greater over cropped land
than summer fallow. The latter effect adds moisture to the atmosphere. Therefore,
conversion of land from summer fallow to crops tends to decrease air temperature
and increase the water content of the air, resulting in greater precipitation.
The biogeochemical and biogeophysical impacts of a GHG mitigation strategy on climate are not all complementary. As stated in the discussion of albedo, planting trees
on agricultural land in northern ecosystems—particularly coniferous trees— results
in an increased air temperature through lower albedo, thus negating the beneficial
climatic effect of the trees’ ability to absorb CO2 and store carbon. The point is, the
biogeophysical effect of changing one hectare of land from wheat to forest in Canada, would be more significant to climate change than the biogeochemical effect of
sequestering 60 tonnes of carbon on that hectare of land over the next 50 years.
96
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Clearly, agricultural practices can affect weather and global climate through
biogeochemical and biogeophysical forcing. For example, irrigation cools air
temperature by as much as 5 ºC locally and possibly 1 ºC on a regional scale by
enhancing cloud cover that reflects sunlight. A relatively recent trend toward less
frequent ploughing of fields (reduced tillage) increases albedo and has a cooling
effect comparable to the biogeochemical cooling from reported carbon sequestration. There are many other examples.
It is critical to consider the effects of a whole range of management practices
in regions where production systems are vulnerable to weather variation. It is
unlikely that non-GHG effects can completely counterbalance the increase in
GHGs due to agricultural practices, but it is clear that their impact on climate
must be taken into account.
FU RTHE R R E AD I NG
Betts, R.A. 2000. Offset of the potential carbon sink from boreal forestation by
decreases in surface albedo. Nature. 408:187–190.
Desjardins, R.L., M.V.K. Sivakumar, and C. de Kimpe (eds.). 2007. The
contribution of agriculture to the state of climate. Special issue of Agricultural
and Forest Meteorology. Elsevier: Oxford, U.K. pp. 88–324.
Intergovernmental Panel on Climate Change (IPCC). 2001. Climate Change
2001: The Scientific Basis: Contribution of Working Group 1 to the Third
Assessment Report of the Intergovernmental Panel on Climate Change.
Cambridge Univ. Press, New York. 881 pp.
Intergovernmental Panel on Climate Change (IPCC). 2007. Climate Change
2007. The physical science basis. Summary for policy makers. Available online
at: http://www.ipcc.ch/SPM2feb07.pdf. Accessed February 15, 2007.
Raddatz, R.L., 2005. Moisture recycling on the Canadian Prairies for summer drought
and pluvials from 1997–2003. Agricultural and Forest Meteorology 131:13–26.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
97
A Holistic View
EXPLORING THE ECOSYSTEM PERSPECTIVE
T H E ECO S YSTE M— the word itself a contraction of ‘ecological system’—is the
fundamental unit of ecological study. First used in print in 1935 (although coined
much earlier) the word stands for a community of organisms within a given environment and all of the interactions that occur between those organisms (see Figure 45).
FIGURE 45
Components of Ecosystems and Their Interactions
CLIMATE
HUMANS AS
MANIPULATORS
ANIMALS
PLANTS
SOIL
Source: Adapted from Van Dyne. 1969
An ecosystem, therefore, includes not only the grasses, trees and mosses on
the ground; not only the owls, ants and bison that feed upon them; but also the
soils that support them and the air that wafts about them. When we speak of an
ecosystem, we speak also about how each constituent affects the others—the
fluid coherency of the whole.
How big is an ecosystem? The scale may vary, from a beehive to the global biosphere, though an ecosystem’s size will most likely be measured in hectares or
square kilometres. Whatever the scale, an ecosystem occupies a specific place,
with a fixed address and defined boundaries. Ecosystems are always open systems; energy and matter are continually lost and continually replaced. As a result,
a given ecosystem by its very nature is interdependent with others.
To understand an ecosystem is alarmingly complex, demanding expertise and
knowledge from various fields—and a way of melding information so it can be
clearly understood, explained and used. Another complicating factor is time;
ecosystems cannot be studied without considering history. This is because living
systems change; their activities and conditions at any given moment depend
on what has happened in that place before. Despite this daunting complexity,
viewing all life as part of an ecosystem has one great merit: it allows us—indeed,
it forces us—to study life systems as a whole, sparing us from the distortion that
results when we focus on components in isolation.
98
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Picture
An expanded focus
Once, those who studied ecosystems looked for sites untouched by human
hands; today, we admit that few such places remain. Humans are now part of
most ecosystems, inextricably intertwined with other organisms and their interactions. In any case, if an ecosystem includes all organisms and their interactions, we are forced to admit that the definition must also include us. And in
few places on the landscape is our influence more pervasive than on farmlands.
Farms are ecosystems
Farms are often viewed primarily as economic entities; a farm generates a livelihood for a farmer. From a broader ecological perspective, farms can also be seen
as ecosystems, with numerous functions, only one of which is to generate income.
This perspective has several advantages. First, it enforces a holistic view. Thus,
cows cannot be divorced from crops, or land from barns, or air from fertilizers. Second, examining farms as ecosystems helps us take into account their interactions
with the larger environment. Farms as ecosystems become part of the biospheric
continuum, alongside forests and wetlands, grasslands and lakes, all studied using
similar methods, with an eye to the energy and matter passing between them.
As ecosystems, however, farms have some distinguishing features: they are
deliberately maintained at a young successional stage (as opposed to mature,
long-standing vegetation). They are more open than other ecosystems; because
of large removals of energy and matter in harvests, they depend on correspondingly large inputs to keep the system running.
Farms are remarkably diverse, reflecting the land and the people who live there.
Farms encompass everything from sheep herded on sparse deserts to dairy
cows grazed on lush pastures; from vast mechanized wheat lands to raspberries plucked from backyard bushes. Regardless of the farming activity, the same
ecological processes undergird them all.
Compared to other ecosystems, farms are extensively manipulated. Farmers exert
control over plants grown, nutrients applied, type and number of animals present,
insects allowed to persist, amount of watering and drainage, and the degree to
which the land is disturbed by tillage. Many of these decisions depend on shortterm economic and social factors, which means that practices and conditions
imposed on the farm ecosystem may change unpredictably and sporadically.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
99
To view farms as ecosystems presents some challenges: farms are complex,
highly dynamic and subject to the whims of human intervention. But to view
them in this manner offers clear advantages: in particular, it helps us integrate
all a farm’s processes, capturing their net effects within the ecosystem and
beyond, over the short and long term. Regarding an individual farm as an
ecosystem also meshes nicely with the definition of ecosystems as fundamental
ecological units. Farms, after all, are the basic unit over which the farmer exerts
control, choosing practices and management options.
GHGs are part of our farms’ ecosystems
Examining farms as ecosystems provides a unique vantage for studying GHG
emissions. Indeed, it may be that GHG emissions can only be studied meaningfully from the ecosystem perspective. As Figure 46 shows, GHG fluxes emanate from myriad processes connecting all phases of the farming system. Consequently, efforts to reduce emissions of one gas from one source may have
offsetting (or amplifying) effects elsewhere; the full effect can be judged only by
assessing effects on net emissions. That is, they can be meaningfully quantified
only by adopting an ecosystem approach.
FIGURE 46
The Interwoven Flows of Carbon, Nitrogen and Energy in Farm Ecosystems
EXPORT
CO2
ENERGY
CH4
N2O
IMPORT
ECOSYSTEM
BOUNDARY
100
NUTRIENTS
ORGANIC
MATTER
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Consider some examples of the interplay among various fluxes on a farm. Perhaps
the most prominent is the removal of atmospheric CO2 by building soil carbon—
called soil sequestration. Many studies throughout the world show that under
some conditions the carbon content of soil can be increased by such practices as
reduced tillage, which reduces soil disturbance, or by re-seeding lands to grass,
which returns more plant carbon to the soil. Almost invariably, however, such
practices alter other properties and processes. For example, reducing tillage may
sometimes increase soil moisture, reducing aeration, thereby favouring the release
of more N2O. Or, in drier lands, adopting no-till might reduce emissions of N2O.
Either way, the net effect of the practice must consider not only the C sequestered,
but any effects on emissions of N2O, a potent GHG. There are other possible effects on the system as a whole. Reducing tillage intensity might lead to reduced
fossil fuel use—and hence reduced CO2 emissions—or might require temporary
increases in the use of fertilizer, which increases emissions from associated energy
use. Further complicating the question is the influence of time; responses in soil
carbon and N2O emission, CH4 removal and energy CO2 emission may have
different temporal patterns. Some, such as carbon accumulation, are temporary; others, such as savings in energy-derived CO2 emissions, persist indefinitely.
Thus, a single practice has cascading influences on GHG emissions throughout
the system. Only an ecosystem approach can hope to capture the full effect.
Similar arguments can be made for other examples. Opting for a new feeding
practice may effectively reduce CH4. But to know its full effect, we need also to
ask: what emissions are associated with producing that new feed crop? How
does the new feed affect emissions from manure produced, now with altered
composition? How does the new feeding practice affect the number of livestock
fed and their accompanying emissions?
Consider another practice, now widely studied: producing biofuel from farm
crops. Ethanol or biodiesel extracted from farm crops effectively reduces fossil-derived CO2 emissions. Though burning these biofuels still generates CO2, it
is from recently recycled atmospheric carbon and introduces no new CO2 into
the carbon cycle. But what emissions are associated with growing the crop from
which the biofuel is made? And how much energy is required to transport, process and eventually deliver the feedstock and the final product?
Even more complicated are the possible spillover effects of these practices. For
example, cultivated lands, when revegetated with grasses or trees, capture carbon
in soil and remove CO2 from the air. Similarly, growing biofuel crops reduces CO2
emitted from burning of fossil fuels. But will the land removed from farming in one
place be replaced by new lands elsewhere? And what are the emissions there?
GHG emissions can be effectively quantified and reduced only by considering all
emissions from the farming system—in short, by viewing farms as ecosystems
and counting all the processes there.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
101
Models enforce an ecosystem view
Given the many agricultural processes that emit GHGs, the way they
interact and the diversity of farms themselves, how can we estimate net
emissions from these ecosystems? How can we capture all that we know
and weave it together without getting entangled in details or lost in abstractions? Probably the only practicable approach is to build mathematical
models. Such models might range from the crude to the complex—from
back-of-the-envelope calculations scribbled by hand to dense software
crafted by teams of scientists and programmers.
Models capture pertinent processes from entire ecosystems, meld them and estimate net fluxes of GHGs from the whole. It is not that models invariably get the
right answer; often, equations are generalizations based on crude assumptions
or even timid guesses. But models enforce an ecosystem view of emissions and,
as such, enforce discipline; they tear off the blinkers that reductionist scientists
are prone to wear.
Models offer other benefits as well. First, they provide a focal point and repository
to capture and express research findings. In the absence of a model, the findings in
an avalanche of papers on soil carbon sequestration and GHG fluxes in agricultural
systems, for example, may soon lie neglected on dusty library shelves. To have
enduring influence, findings must somehow connect to a growing understanding.
As the chapter on quantifying GHG exchange explains, models are a skeleton on
which to hang findings; they provide a framework for growing understanding. In
the case of GHG fluxes, as new data emerge, algorithms and assumptions can
be adjusted and improved, slowly fleshing out our skeletal understanding. This
benefit, of course, relies on discipline, the will to meticulously collect the accumulated findings in a database or other suitable form.
A further advantage of using models is that they point to areas of scientific ignorance, identifying those places where our understanding is dimmest and inquiry
most needed. Without such reminders of the shadow areas, scientific research
can sometimes focus too much on the areas we already know best.
102
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Static and dynamic models
As noted in an earlier chapter, increasing efforts have been devoted to build
models that predict GHG emissions from farms. Though few of these comprehensively consider all of the facets of a farming system, many have started at
least to examine systems, rather than single components or processes.
The various models and approaches for such holistic efforts can be divided into
two broad categories: static models and dynamic models. Static models predict
cumulative net emissions for a given interval of time, typically one year or farming
season. Dynamic models are more complex; they introduce time, looking into the
future and the past and predicting how net emissions will change in response to
a practice or external factor.
Consider the ecosystem response to adopting no-till practice. The static model,
based on simple equations or coefficients, would predict the annual net change
in soil carbon, along with an average annual emission of N2O. The dynamic
model would trace out the accumulation pattern of soil carbon over several
decades, showing how the rate of accumulation changes with time, eventually
approaching zero. A full-fledged dynamic model might also take into account
coming changes in climate or other external factors. At present, there are few
if any dynamic models capable of measuring net emissions of all GHGs from
whole-farm ecosystems—though it remains a prominent research goal.
The static model
The following is an example of a static model to predict GHG emissions from
farms. As of 2007, this model had been released by Agriculture and AgriFood Canada and a new version Holos was being developed.
GHGFarm
A simple model, GHGFarm, was developed to permit users to estimate net GHG
emissions from Canadian farms. The model relies on two types of inputs, as
shown in Figure 47:
• Management practices under the control of the farmer, including such
variables as crop selection, fertilizer rates, tillage techniques, feeding practices
and manure management systems
• Farm conditions, largely beyond management control, including such factors
as soil type, temperature and precipitation.
The model estimates the effects of these variables on all three GHGs—CO2, CH4
and N2O—using simple equations based on globally accepted algorithms, but
modified to reflect Canadian conditions and practices based on recent research.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
103
FIGURE 47
A Simple Model for Estimating Net Whole-farm Emissions
DESCRIPTORS
ALGORITHMS
INTEGRATOR
ENERGY USE
CONDITIONS:
· CLIMATE
· LANDSCAPE
· SOIL
· HISTORY
CHANGE IN SOIL C
SOIL N2O
OFFSITE N2O
PRACTICES:
· CROPPING
· LIVESTOCK
· MANURE
· LAND USE
CHANGE
MANURE N2O
NET GHG
EMISSION
(CO2e)
LIVESTOCK CH4
MANURE CH4
SOIL CH4
The user describes the farm by stating its conditions (those factors not controlled by the
farmer) and the farm’s practices (options controlled by the farmer). These inputs are
then fed into equations or algorithms that estimate emissions from the various farm
components. The outputs from these equations are integrated to yield a single estimate of
overall net farm emissions.
The model has two potential applications. The first is to allow producers, policy
makers, scientists and other users to estimate current net emissions from a given
farm ecosystem (typically one commercial farm, or perhaps a small group of
closely-linked farms). The second application—and a more useful one—is to allow users to explore possible opportunities for reducing emissions; it allows them
to ask the what if questions. Thus, the current emissions are calculated as a
baseline and various possible changes in practices are then compared alongside:
What if we use a different feed or manage the manure differently? What if we
reduce tillage intensity or take some land out of production? These options can
then be examined together, comparing whole-farm net emissions as a criterion
for choosing the optimal set.
The model does not operate without uncertainty; in many instances, the degree
of uncertainty exceeds the difference between management options, which is
obviously a barrier to choosing best options. However, the process of building
the model and of applying it on real farms has been enlightening in understanding farms as ecosystems and ensuring that all facets and sources are considered
in calculating net GHG emissions from farm ecosystems. Perhaps GHGFarm is
best viewed as a tool for communication and education rather than for delivering
defensible predictions.
The dynamic model
The following describes a proposed dynamic model to predict GHG emissions
from farms.
104
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
The Virtual Farm
To reliably estimate the emission of GHGs from farms, one must consider that
emissions of CO2, CH4 and N2O all vary over time and are affected by the actions of humans and by nature. To see how emissions vary over time we need
to understand how their constituents—namely carbon and nitrogen—are cycled
through farm ecosystems.
As of 2008, a simple time-dependent model of a farm ecosystem for estimating
net GHG emissions over time was in development at Agriculture and Agri-Food
Canada. The ecosystem model consists of six main components: vegetation,
shelterbelt, crop, soil, livestock and manure. The model assumes that emission
losses can be attributed to three main contributions:
• farm management or activities (perturbed conditions),
• carbon and nitrogen flow in the ecosystem (un-perturbed conditions), and
• the interaction of the first two whereby they mediate changes in stored
amounts of carbon and nitrogen within each ecosystem component.
Benefits beyond the farm
Developing ecosystem-based models for estimating net GHG emissions from
farms will enhance our ability to mitigate climate change. But there are other
benefits as well: estimating GHG emissions may provide a sensitive measure of
ecosystem health—a way of taking the pulse of farms and other ecosystems.
Almost invariably, high losses of carbon and nitrogen signal some ecological
inefficiency in use of energy, carbon or nitrogen. For example, if N2O spews too
fast, the nitrogen cycle is probably disconnected. If CO2 losses are too high,
then soil carbon may be waning or energy is being used superfluously. If CH4 is
excessive, perhaps cows are not being fed efficiently and photosynthetic energy
has not been fully exploited. Thus, GHGs are biomarkers—biosignals of ecosystem ill health—pointing to opportunities for better management to make them
more robust, more efficient and more permanent. Such biosignals may be most
useful in agricultural systems, which are so intensely manipulated and which are
under increasing stress in the face of growing population demands.
The methods developed to study GHG emissions from ecosystems can also be
applied to other environmental problems. Models that predict GHG emissions
are built, by necessity, on the flows of energy, carbon and nitrogen through ecosystems. To predict GHG emissions from an ecosystem, a model must simulate
the energy, carbon and nitrogen cycles in that ecosystem and connect them to the
broader cycles in adjacent environments. These broader cycles are at the heart of
other ecological concerns: water quality, food quality, alternative energy sources,
and emissions of air pollutants such as ammonia. They also have a bearing on
broader social issues, such as rural vitality, biodiversity and wildlife habitat.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
105
There are likely issues still beyond our purview—perhaps years or decades in
the future—that will depend on knowing better how energy, carbon and nutrients flow within and among ecosystems. Ecosystems are changing, perhaps at
rates faster than our ability to understand. The primary benefits of modeling GHG
emissions, therefore, may be not to reduce emissions of these gases per se, but
instead to equip us with a better understanding of our fragile ecosystems, and
from that solid footing in ecological processes engender far-sighted solutions to
the ecological distresses that await us.
Reducing emissions may not be the final aim of ecosystem GHG models; that is,
just a temporary, incremental goal. The GHGs are merely a sensitive and timely
test case for an ecosystem modeling approach. The bigger prize, the long-term
aim, will be to understand our ecosystems well enough, describe them succinctly
enough, to help us speak with wisdom, insight and foresight about any of the
environmental stresses still to come. And, given the pace and unpredictability of
global change, such stresses are sure to come.
106
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FU RTHE R R E AD I NG
Evans, F. C. 1956. Ecosystem as the basic unit in ecology. Science. 123:1127-1128.
Janzen, H.H., D.A. Angers, et al. 2006. A proposed approach to estimate and reduce net greenhouse gas
emissions from whole farms. Canadian Journal of Soil Science. 86:401–418.
O’Neill, R.V., and J.R. Kahn. 2000. Homo economus as a keystone species. Bioscience. 50:333–337.
Palmer, M.A., E.S. Bernhardt, et al. 2005. Ecological science and sustainability for the 21st century. Frontiers
in Ecology and Environment. 3:4–11.
Van Dyne, G.M. 1969. Implementing the Ecosystem Concept in Training in the Natural Resource Sciences.
Pp. 327–367, in G.M. Van Dyne (ed.) The Ecosystem concept in natural resource management. Academic Press, NY.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
107
d
The Bigge
L I N K S B E T W E E N G H G M I T I G AT I O N A N D OT H E R
ECOSY STEM SERVICES
Ecosystem services—an emerging concept
Until recently, when ecologists wanted to study ecosystems they sought lands
untouched by people and unspoiled by human presence. Humans were regarded by ecologists as an invasive species. To study how nature behaved, ecologists trekked to the quickly dwindling tracts of land deemed natural.
Today, ecologists increasingly accept that few unaffected terrestrial areas remain.
For better or worse, humans are part of most ecosystems; indeed, often we are
the keystone, or dominant species, controlling our environment and dictating
which other species survive in our presence.
That perspective has led to the emergence of a new concept: ecosystem services. As one researcher has said, ecosystem services are “the conditions and
processes through which natural ecosystems…sustain and fulfill human life.”1
Ecosystem services include a host of natural functions: filtering impurities from
water, removing excess CO2 from air, keeping alive the diversity of life forms,
for example. Although conceived originally to describe natural ecosystems, the
ecosystem services concept can be applied also to agricultural lands, which are
managed to maximize human benefit. Usually, these benefits are perceived to be
what farms can sell: food, fibre and biofuel. Like all ecosystems, however, farms
also provide important services that are not readily apparent. As Table 7 shows,
farms act as environmental filters, as cleansing repositories for unwanted wastes,
as habitat for wildlife and people, and as places of aesthetic respite. These more
subtle ecosystem services also merit out attention.
An important ecosystem service of farms—one already discussed—is to help
ameliorate GHG emissions. Though usually net sources of GHGs—notably of
CH4 and N2O—farms can also be net absorbers of GHGs by absorbing CO2
from the air and sequestering that carbon in soils and plants. With growing
fears of unpleasant climate change, reducing GHGs from farms has become
an increasingly urgent goal. But, when a farm’s potential ecosystem services
are tallied and prioritized, reducing GHGs may not be a farmer’s main concern.
Rarely will a GHG-reducing practice be adopted if it does not also favour other
services. Consequently, finding and advocating GHG mitigation practices is
merely a pleasant academic diversion if it ignores these other, often more urgent,
ecosystem services.
1
108
Daily, G.C. 1997. Nature’s Services—Societal Dependence on Natural Ecosystems. Island Press: Washington D.C.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Picture
TABLE 7
Partial List of Ecosystem Services Provided by Canadian
Farms
PHYSICAL BENEFITS
SOCIAL BENEFITS
ENVIRONMENTAL BENEFITS
• Food
• Livelihood
• Water filtering
• Fibre
• Living space
• Air scrubbing
• Fuel
• Recreation
• Waste repository
• Aesthetics
• Wildlife habitat
• Gene preservation
• GHG mitigation
Finding win-win solutions
How do we acknowledge and accommodate other ecosystem services when
choosing GHG-reducing options? The obvious solution is to seek win-win options—those practices that reduce GHG emissions and favor other services.
One such practice is no-till farming. Many studies have shown that reduced
tillage can increase soil carbon, at least for a time, thereby removing CO2 from
the air. Reduced tillage also reduces emissions from fossil fuel combustion.
Meanwhile, no-till farming may contribute other ecosystem services unrelated
to reducing GHGs: improved livelihood for farmers through reduced costs;
preserved soil quality by holding soils in place; improved nesting habitats for
migratory birds; and enhanced air quality by reducing dust from wind storms.
Indeed, the wide acceptance of reduced tillage worldwide is probably mainly
for these other benefits.
Such win-win opportunities are ideal GHG mitigation practices. In fact, they may
be the only ones widely accepted. But few practices are purely win-win; few
do not exact some sacrifice, some cost somewhere along the way. Even no-till
farming may not have purely beneficial effects on all ecosystem services. For
example, it might sometimes lead to higher leaching of pesticides, affecting water
quality. In some areas it might limit yields, affecting food production.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
109
Big win-small loss
As Figure 48 shows, the possible positive and negative effects imply the need for
trade-offs—of making choices that will improve one ecosystem service while sacrificing another. The solution becomes one of seeking big-win/small-loss options.
Are we willing to recommend a practice that effectively reduces GHG emissions
(big-win), but exacts a small cost of reduced food yield (small-loss)? Conversely,
would we advocate a practice that incurs slightly higher CH4 emissions (smallloss) but dramatically improves the yield of milk (big-win)? If we include more than
two ecosystem services the questions grow more complex. Suppose we include
in our analysis of trade-offs also water quality, aesthetics, and wildlife habitat;
how do we choose the best options now?
FIGURE 48
FOOD & OTHER ECOSYSTEM SERVICES
The Tradeoffs Between GHG Emissions and Ecosystem Services
Provided by Farms
WIN-WIN
WIN-LOSE
LOSE-WIN
NET GHG FLUX
A matrix showing the potential relationships between reducing GHGs and increasing
food production. Ideally, we would opt for ‘WIN-WIN’ options. But would we be also
willing to choose a lose-WIN option (small sacrifice in food production and large gain
in GHG mitigation), or a ‘WIN-lose’ option (small sacrifice in GHG mitigation for a
large gain in food production)? A new dimension is added with the addition of each
new ecosystem service and the decisions grow ever more complex.
Source: Figure adapted from Janzen. 2007. (The concept of ‘WIN-lose’ was proposed by DeFries et al. 2004.)
Adding to the complexity are spillovers from one ecosystem to the next. A significant benefit to a service in one ecosystem might jeopardize services in another,
perhaps far away. For example, seeding cultivated land to grass can drastically
reduce GHG emissions by sequestering carbon and by reducing emissions from
inputs. Where it is adopted, this practice is powerfully effective in reducing emissions, clearly advancing the service of buffering GHG emissions. But will the reduced output from that land be replaced by increased output elsewhere, perhaps
causing a patch of forest somewhere to be burned, which would incur losses of
ecosystem services there?
110
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Choosing best practices involves more than identifying the practices that reduce
emissions, or those that make immediate economic sense. We may need a more
holistic approach, finding ways to understand and quantify the diverse services
provided by farming ecosystems. And we may need to develop new ways to
quantify success in reducing emissions. We might, for example, develop a method to compare practices on the basis of emissions per unit of output, rather than
merely on the basis of emissions alone. Whatever our approach, we will need to
understand all the services arising from agricultural systems and how they are
interwoven via the myriad processes that comprise the ecosystem. Increasingly,
scientists will aim to see farms as ecosystems, and policy makers will aim to find
ways to value all the services they provide.
GHGs: bellwethers of ecosystem performance
Measuring and understanding GHG fluxes is important not only so we can find
ways to reduce them, but also for judging how well an ecosystem is performing. Because GHGs are embedded and interwoven in the flows of carbon,
nutrients and energy throughout ecosystems, GHGs may be a way of taking an
ecosystem’s pulse.
There seems little question that such bellwethers will be needed, for the biosphere is changing, perhaps at rates unprecedented. In coming decades, the
Earth’s temperature may be higher, precipitation less reliable and CO2 more
concentrated in the air. Other physical factors—aerosols in the atmosphere and
the changing reflective properties of the landscape—also contribute to change,
adding further to uncertainty.
Perhaps more potent than physical changes are changes that stem from social
factors. These changes are driven by the burgeoning world population and our
increasing capacity to reshape the land and sea and air around us. Although global
population could almost level off by mid-century, it may increase by nearly 50% before then. This may pose further stresses on farmland as demands for food grow.
Perhaps more disconcerting than the prospect of increased demand is our dwindling resource base. There are few new productive lands left to cultivate, meaning higher yields will be expected of lands already in use. And, irrigation water,
so important for past yield increases, may be diverted to other uses. Reserves
of cheap energy are being exhausted and there may be other limitations that we
cannot foresee. Increasing demands and dwindling resources lead, inevitably, to
what E.O. Wilson calls a bottleneck.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
111
Clearly, in the face of coming stresses, we will need markers to tell us how our
ecosystems are performing. Are they holding up or are they winding down?
Without reliable signals, how will we know? Addressing these questions may
be the highest reward of studying GHGs. For GHGs are sensitive to flows of
nutrients and energy in ecosystems. Excess releases of CO2 tell us that carbon
stocks in the soil may be depleting or that fossil energy is being wasted; high
CH4 emissions may indicate that solar energy stored in plant feeds is not being
used efficiently; eruptions of N2O may signal that nitrogen flows are uncoupled.
By studying these fluxes we learn not only what the emissions are and how
they contribute to climate change, but also something about how changes
are affecting other ecosystem services: soil quality, water quality, biodiversity,
aesthetics and others.
This perspective vaults us beyond mere inventories, mere counting of gigatonnes
of emissions. It tells us whether or not our ecosystems are, in the end, permanent
or sustainable. It helps us focus on the question, as phrased by Berrien Moore III in
2002: “And what now are the sky, land, and sea saying to us? And are we listening?”
112
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FU RTHE R R E AD I NG
Cohen, J.E. 2005. Human population grows up. Scientific American 293:48-54.
Daily, G.C.(ed.) 1997. Nature’s Services--Societal Dependence on Natural Ecosystems Island Press,
Washington D.C.
DeFries, R.S., J.A. Foley, and G.P. Asner. 2004. Land-use choices: balancing human needs and ecosystem
function. Frontiers in Ecology & Environment 2:249-257.
FAO. 2003. World Agriculture: towards 2015/2030. Earthscan Publications Ltd., London.
Green, R.E., S.J. Cornell, J.P.W. Scharlemann, and A. Balmford. 2005. Farming and the fate of wild nature.
Science 307:550-555.
Janzen, H.H. 2007. Greenhouse gases as clues to permanence of farmlands. Conservation Biology 21:668-674.
MEA. 2005. Ecosystems and human well-being: Synthesis. Island Press, Washington, D.C.
Smil, V. 2002. The earth’s biosphere: Evolution, dynamics, and change. MIT Press, Cambridge, Massachusetts.
von Kaufmann, R.R., and H. Fitzhugh. 2004. The importance of livestock for the world’s poor, pp. 137-159, In C.
G. Scanes and J. A. Miranowski, eds. Perspectives in world food and agriculture 2004. Iowa State Press, Ames, Iowa.
Wilson, E.O. 2002. The future of life. Vintage Books, Random House Inc., New York, NY.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
113
The Promise of Biofuels
AN OPPORTUNITY AND A CHALLENGE
Toward the end of the 20th century, the world began to be increasingly concerned about declining energy supplies and the build up of CO2 in our atmosphere. Energy demand was growing fast, which resulted in higher energy prices.
Meanwhile, ethanol (ethyl alcohol) and biodiesel offered an alternative liquid fuel
source, but at the time the cost of producing them exceeded the cost of comparable petroleum products.
More recently, the economics of producing bio-based fuels has improved. As Figure 49 shows, this is mostly due to higher petroleum prices and partly because the
production of biofuels has been encouraged through tax breaks and subsidies.
FIGURE 49
1000
1.00
CANOLA OIL ($/T)
SOYBEAN OIL ($/T)
DIESEL FUEL ($/L)
CRUDE OIL ($/L)
ETHANOL OIL ($/L)
800
0.80
600
0.60
400
0.40
200
0.20
0.00
0
1984
1987
1990
1993
1996
1999
2002
$/LITRE (ETHANOL AND PETROLEUM)
$/TONNE (CANOLA AND SOYBEAN OIL)
Prices for Canola and Soybean Oil, Ethanol and Petroleum
Products (1984–2005)
2005
Source: Smith et al.
Another reason biofuel systems have become more interesting to producers and
consumers is that, unlike fossil fuels such as petroleum and coal, biofuels are renewable. This means they can generate electrical, thermal or mechanical energy
that at least matches the energy used to grow the living organisms and create
the byproducts that make them up. Importantly, the plants used to produce liquid
biofuels also pull CO2 out of the air as they grow, which offsets a portion of the
CO2 produced when biofuels are burned for energy.
114
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Canada’s renewable energy record
Canada’s annual primary energy supply is nearly 11 exajoules (exa denotes
a factor of 1018) and 17% of this is from renewable sources. The largest
supply of renewable energy comes from water (hydroelectricity) at 11% and
wood biomass at 6%.
Renewable bioenergy supplied from agricultural and forest wastes (with contributions from industrial, municipal solid waste and sewage biogas), energy crops,
wind and solar sources are increasing in Canada. The pulp and paper and forest-product industries recycle half of their total energy use by converting biomass
into electricity, steam and heat, while fuel-wood and gas from landfills are used to
heat residential spaces. The use of biofuel in Canada’s transportation sector is of
special interest given that this sector contributes about 26% of the nation’s CO2
emissions in addition to reducing environmental air quality.
Agriculture plays a critical role
When we use biofuels in place of fossil fuels, we reduce net emissions of carbon
into the atmosphere. The agricultural sector has a direct role in this replacement,
as products grown on farms are the main ingredient of many bio-based energy
systems, including ethanol (grains and cellulosic biomass), biodiesel (oilseeds),
biogas (waste products), and heat energy and biogas (woody biomass).
TABLE 8
Biofuels and the Processes for Making and Utilizing Them
SOURCES
FEED SOURCE
PROCESS
PRODUCTS
Ethanol
Starch (grains, sugar)
Fermentation
Ethanol, Distillers Dry Grains
Biodiesel
Oils (animal and vegetable)
Trans-esterification
Biodiesel, Protein Meal,
Glycerine
Biogas
Organic Material
Anerobic Digestion
CH4, Heat
Cellulose
Wood, Straw
Hydrolysis and Fermentation
Ethanol
Woody Biomass
Wood
Combustion, Gasification
Electricity, Heat, Synthetic Gas
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
115
BIOMASS ENERGY
Biomass energy—plant material used for energy—has been used for
thousands of years to cook food and provide heat. It provided a significant
part of human energy needs prior to the industrial revolution. Since then,
most energy requirements in the developed world have been provided by the
combustion of readily available and inexpensive fossil fuels such as coal, oil and
natural gas—but not without cost to the environment.
Biomass is still a predominant form of energy in much of the developing world,
where it provides more than one third of primary energy consumption—although
fossil energy consumption is growing. The International Energy Agency forecasts
that by 2020, world demand for energy will have increased by 50% over 2006.
While direct combustion is the cheapest, simplest and most common
method of obtaining energy from biomass, pyrolysis is a thermochemical
process that converts biomass into bio-oil, charcoal or methanol by heating
to about 1023 ˚C in the absence of air. Pyrolysis produces energy fuels with
high fuel-to-feed ratios, making it an efficient process for converting biomass
to crude oil for use in engines and turbines.
Scientists have estimated that in 2007 global forest and agricultural residues
would make up about one thirteenth of the world’s energy demand. Estimates
for potential future contributions of biomass to global energy use range
widely—the most generous estimates being four times that of the most
modest. Estimates vary widely because two key variables—land availability
and crop yield—are uncertain and open to interpretation. A more recent study
has estimated the global potential of bioenergy production from agriculture
and forestry residues and wastes at 76 to 96 exajoules per year by 2050. The
key to achieving that level of bioenergy production is to optimize agricultural
production systems so that food demand can be satisfied by using 50 to 75% of
the cropland required in 1998 to achieve the same result, making the balance of
land available for the production of energy crops.
116
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Ethanol
Ethanol is the major source of bio-based energy. It is made by fermenting and
distilling simple sugars. Sugars can be obtained from: sugar beets and sugar
cane; converted starch from cereal grains; cellulose sources such as trees,
grasses and crop residues; potatoes; and animal waste.
In Canada, ethanol production is from grains; either wheat in the west, or
corn in the east. The process is as follows: the grain is milled to obtain the
starch—the energy component of the grain—fermentation is used to produce
the ethanol, and the product is distilled to remove water and impurities. The
solid by-products have a high protein content and can be used in livestock
feed. When Canadian processing plants currently under construction are
completed, ethanol production will be enough to provide about 2.1% of motor gasoline consumption.
In the U.S., most of the ethanol production is from corn. About 15% of corn
production is used for ethanol, but this biofuel represents only a small fraction
(2.4%) of gasoline consumption. Projected increases for ethanol production are
expected to supply about 5% of motor gasoline consumption.
In Brazil, ethanol production from sugar cane provides an astonishing 40%
of the country’s motor fuel. The production cost of ethanol from sugar cane
has been comparable to the production cost of ethanol from corn in the U.S.,
but the cost advantage or disadvantage has depended on the price of the
feedstock over time.
The efficiency of ethanol production depends on many factors: crop yield, energy
inputs from fuel, amount of fertilizer used, pesticides, the genetics of the crop, specific cultivation practices and the proportion of energy that goes into co-products
compared to what goes into the main biodiesel/ethanol products. For example, dry
milling of corn is preferred over wet milling because it is more efficient.
Ethanol can also be obtained from cellulosic biomass such as switchgrass, or
woody biomass such as fast-growing, short-rotation, hybrid poplar and willow
trees. This technology offers the potential for low-cost ethanol production, but is
currently at the pilot-plant stage. Many limitations must be overcome for it to be
commercially viable.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
117
CONVERTING CELLULOSE
INTO FUEL
Sugars used to produce ethanol can be derived from
sources other than corn or wheat grain. One promising
option is to obtain sugars from cellulose, an abundant
organic compound on Earth. Conversion of cellulose
into sugars typically has three steps. The first step is pretreatment to increase the accessibility of the material
to enzymes. The second step is enzymatic hydrolysis,
which uses cellulose enzymes to increase the rate of
biochemical reaction, and/or thermal hydrolysis, to
convert cellulose into glucose. The third step is ethanol
fermentation. The lignin in the plant fibre is used to
generate steam as a heat source for distillation.
Biodiesel
Biodiesel is produced from animal fat or vegetable oil, such as soybean oil and
recycled cooking oil, or animal waste fats extracted while food is being processed. The transformation to biodiesel, referred to as transesterification, mixes
the fat or oil with methanol and a catalyst to produce biodiesel (methyl ester)
plus glycerine. Impurities are then removed. Glycerine is a by-product with
many commercial applications, such as soap making. Biodiesel is an attractive fuel in that it is non-toxic, biodegradable and contains no sulphur or other
aromatics (air pollutants).
In 2007, biodiesel production in Canada was limited to a few processing plants
that used either animal fats or yellow grease (waste grease obtained from restaurants and other sources). These plants produced about 0.09 gigalitres per year
(a relatively small amount). Several new plants have been proposed, which will
lead to an expansion of the biodiesel industry; at present, biodiesel sales represent about 0.3% of total diesel fuel sales in Canada. The U.S. currently produces
roughly one third of the world’s biodiesel and is set to nearly triple its production
by 2008, using primarily soybean oil as the feedstock. The tripled production is
expected to represent about 4% of diesel consumption in the U.S. At present,
worldwide production of biodiesel takes place mostly in Europe.
Biogas
Biogas can be produced through the anaerobic digestion of manure and other
organic materials. This process uses bacteria to convert complex organics into
simpler ones. The process releases CH4, CO2 and trace amounts of other gases.
Once biogas has been produced, unwanted gases can be removed, leaving
118
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
useful CH4, which has the potential to replace non-renewable energy sources
such as natural gas and propane for residential cooking and heating. Methane
can also be used in internal combustion engines to generate electricity and heat,
although the efficiency of the system is low if only used to generate electricity.
Anaerobic digester systems range from covered manure storage structures to
heated and regulated enclosed digesters. Large-scale, advanced anaerobic
digestion systems are currently in use, mostly in Europe. Canada has a few working digesters, most of which use biogas to generate electricity and heat. These
systems are continually improved through new technologies, more efficient anaerobic bacteria and better slurry composition, making them increasingly profitable
to install. The effluent from the system is high in fibre and has a higher nitrogen
concentration than untreated manure, which makes it an effective soil amendment
or mulch for farm fields.
Wood-combustion energy
Combustion of wood has been used for centuries as an energy source. The
production of fast growing woody biomass provides the potential to use it by
itself or with coal in the production of electricity. (Excess straw from crop production could be used in a similar way.) The forestry industry in Canada utilizes
waste wood products to generate steam, electricity and heat. Woody biomass
can be gasified to produce a synthetic gas, which can be used in place of propane or natural gas.
A convincing energy balance sheet?
For biofuel to be considered a viable alternative to fossil fuel, it must provide
a net energy gain, show environmental benefits, be economically competitive
and be producible in large quantities without reducing food supplies. To assess if a biofuel provides real benefits when displacing fossil fuels, detailed life
cycle analysis is required.
We can assess whether biofuels provide a net energy gain by viewing a farm as
an island economy, whereby one determines the total energy required to grow
and convert crops to biofuels. In growing crops as biofuel feedstock, one must
account for energy use in: seeds and seed treatment; all field operations including land preparation, seeding and harvest; heating and maintaining buildings;
producing and applying fertilizer and pesticide; and manufacturing machinery and
equipment. In converting crops to biofuels, one must consider transport from
farm-gate to a biofuel facility or processing plant, and all energy sources required
within the facility, including its construction.
From the 1970s until recently, the energy required to produce corn and convert
it to ethanol was greater than the energy in the ethanol produced. Today, with
higher corn yields, reduced energy inputs into corn production and increased
efficiencies in the industrial production of ethanol, corn ethanol can now provide
about 25% more energy than the energy required for its production. However, a
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
119
positive energy balance has not been found in all studies. The positive balance
is based on a portion of the energy required to grow the grain and produce the
ethanol being allocated to the co-product called distillers dried grains, and use
of lower input rates for corn production. Ethanol from wheat was found to be 6%
less energy efficient than from corn.
The energy balance for biodiesel also depends on the feedstock source. Waste
oils and fats will obviously have a large positive energy balance. Biodiesel
production from first-time oils from soybean and canola produces about twice
as much energy as the energy that goes into producing and processing the oil.
While canola production requires more energy inputs than soybean for crop
production, the oil yield of canola is higher than soybean, which means that the
two crops net about the same ratio of energy output per unit of energy input. Efficiency gains in the past decade include higher yielding crops, improvements to
the industrial oil extraction process and better trans-esterification processes that
produce more methyl ester and less glycerine.
A profound effect on farming
Canada has about 40 million hectares of cropland. Some of the main crops
used in biofuel production are wheat, grain corn, canola and soybeans. Forages,
barley and oats also require cropland to produce feed for cattle, sheep, hogs and
other animals. Canada’s large domestic populations of cattle, hogs and poultry
will all be affected if more cropland is used for biofuel production.
Meanwhile, biofuel production in North America has increased the demand for
cereals and oilseeds, resulting in increased crop prices. For crop producers,
higher prices have increased the income from cropping, increased the value of
farmland and affected cropping decisions. Land use will change as producers
switch to the more profitable crops. In the case of corn, this will likely result in
increased mono cropping and contribute to soil erosion. Other environmental
risks will also increase as corn requires higher rates of fertilizers, herbicides and
insecticides than most other crops. Additional soil conservation efforts by producers may reduce, but likely not avoid, the negative impacts of increased annual
crop production on soil, water and air quality.
Beyond political, economical, energy or environmental considerations, the biofuel
industry raises an ethical question: Should agricultural land be used to grow
food for humans or fuel to power our vehicles? Given that North America has
historically produced surplus grain, ethanol production will not result in local food
shortages but will increase food prices. Globally, biofuel production could reduce
food aid to Less Developed Countries and exacerbate famines. Clearly, a complete assessment of the impacts of grain ethanol production requires a global
view. While ethanol production from grain is one of many options to manage the
energy crisis, is it viable in the long term?
120
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
FIGURE 50
Distribution of Current (2007) and Planned (post-2007)
Ethanol and Biodiesel Production Facilities Across Canada,
million litres per year
BIODIESEL
1
ETHANOL
12-33
2-66
33-95
67-114
95-150
115-375
150-208
208-375
Source: Supplemented and adapted from data obtained from the Canadian Renewable Fuels Association, available online at: http://www.greenfuels.org/,
Klein, 2007 and corporate news briefings.
A few producers have invested in biofuel processing plants, but most plants
are large and owned and operated by established biofuel companies. For
producers close to a biofuel facility, there is an incentive to plant the types of
crops demanded by the facility. For example, ethanol production from wheat
in western Canada requires wheat high in starch and low in protein. However,
the ideal growing conditions for these types of wheat might not correspond to
conditions near the facility. In time, crop-breeding programs will develop lines
of wheat and corn hybrids that are better feedstock for biofuel facilities than the
currently available lines.
As prices rise, livestock producers are experiencing higher feed costs. This is especially important in the case of corn and barley, which are major feed sources for
the industry. Some low-cost by-products of biofuel production can be used by the
livestock industry, but many questions remain about how much by-product can be
fed to animals without adversely affecting animal performance and meat quality.
Reducing GHG emission
Biofuels are made from plant matter of recent biological origin, which means
that the CO2 emitted when they are burnt is from recycled carbon recently
removed from the air, rather than from fossil fuels.
Recent analyses estimate that net GHG emissions for the production and combustion of corn ethanol are 18% lower than conventional gasoline, with uncertainty
ranging from 36% below this mean estimate to 29% above it. Research shows that
potential reductions may vary depending on such factors as the rate of tillage and
the application of nitrogen to crops. Further study is needed on the flow of carbon
and nitrogen through air, water and soil to improve our understanding of how we
can produce biofuels with a positive GHG budget.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
121
FIGURE 51
Overview of the Carbon Cycle
SOLAR ENERGY +
CARBON DIOXIDE
CARBON
DIOXIDE
BIOMASS
BIOFUELS
HARVESTING
MICROBES
FERMENT SUGARS
INTO ETHANOL
PRE-PROCESSING
CELLULOSE
SUGARS
ENZYMES BREAK
DOWN CELLULOSE
INTO SUGAR
Strengthening rural communities
In 2006, Canada provided commercial subsidies to build new biofuel processing plants and to advance biofuel research and technological development.
This included a new program to add five new ethanol processing plants that will
increase Canadian production to 1.4 billion litres annually by 2008. These plants
will produce sufficient ethanol that 35% of all gasoline in Canada could have a
10% ethanol blend.
The Biofuels Opportunities for Producers Initiative (BOPI), which helps to lower
processing infrastructure costs, extended funding to agricultural producers to
create and expand their ethanol production capacity. Sustainable Development
Technology Canada (SDTC) recently extended financial support for four biofuel
technology projects to process ethanol from cellulosic material and mustard
122
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
seed in support of accelerating biofuel research and technology. Research will
be conducted on the energy saving provided by the industrial and commercial
applications of co-products, on the development of improved processing technology, and on how we can better evaluate the environmental and societal costs
and benefits of biofuel production.
The outlook for biofuels in Canada
The Government of Canada is committed to reaching an average renewable
fuel content for gasoline of 5% by 2010 and 2% for diesel fuel and heating oil
by 2012. To support this goal, the government has allocated resources to help
develop a renewable fuels industry. Three noteworthy programs are Biofuels
Opportunities for Producers Initiative (BOPI), which helps farmers hire technical,
financial and business-planning advisors who can develop sound business
proposals and undertake feasibility and other supporting studies; the Agricultural
Bioproducts Innovation Program (ABIP), which aims to integrate resources to
build greater research capacity in agricultural bioproducts and bioprocesses; and
the ecoAgriculture Biofuels Capital (ecoABC), which has allowed some farmbased renewable fuel plants to proceed with development plans.
The long-term success of the renewable fuel industry will depend on many factors, including the price of petroleum fuel, the supply of agricultural products
used to produce renewable fuels and the cost of producing the renewable fuels.
In 2007, high petroleum prices were beneficial to the economics of renewable
fuels, but short supplies of agricultural products (corn, wheat, soybean, canola)
resulted in higher prices for the feedstock used to produce renewable fuels and
higher costs to produce renewable fuels.
FU RTHE R R E AD I NG
Farrell, A. E., et al. 2006. Ethanol can contribute to energy and environmental goals. Science 311:506–508.
Hill, J., E. Nelson, D. Tilman, S. Polasky, and D. Tiffany. 2006. Environmental, economic, and energetic costs
and benefits of biodiesel and ethanol biofuels. Proceedings of the National Academy of Sciences 103:11206–11210.
Klein, K., D.G. LeRoy. 2007. The biofuel frenzy: what‘s in it for Canadian agriculture? Alberta Institute of
Agrologists. Banff, Alberta, 44pp.Available online at: http://www.aia.ab.ca/index.cfm/ci_id/2077/la_id/1/
document/1/re_id/0. Accessed October 30, 2007.
Newlands, N. K., J. Foyle, and L. L. Yang. 2006. Potential net reductions in greenhouse gas emissions from farm
bioenergy production in Canada. ASABE Proceedings of the 4th World Congress of Computers in Agriculture
and Natural Resources: 770–774. Available online at: http://asae.frymulti.com/request.asp?JID=1&AID=21
971&CID=canr2006&T=2. Accessed October 30, 2007.
Smith, E. G., H. H. Janzen and N. K. Newlands. 2008. Energy balances of biodiesel production from
soybean and canola in Canada. Canadian Journal of Plant Science 87:793-801.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
123
the Air
eRejuvenating
Future
P O L I C I E S T O QUA N T I F Y A N D R E DU C E G R E E N H O U S E
GAS EMISSIONS
Climate change is a long-term, global problem, yet there is still considerable uncertainty concerning which changes are likely to take place, when, to what degree and
how climate change will affect our lives. The major effects may not be felt for decades or even centuries, yet we are reasonably certain that greenhouse gas (GHG)
emissions to the atmosphere will have long-lived, cumulative effects, which demands
that we act now. The absence of immediate impacts creates a significant policy challenge: how can decision makers encourage people to change their behaviours now
to prevent a future problem about which there is still such uncertainty?
More difficult still will be to find ways to achieve policy objectives internationally.
The atmosphere knows no boundaries—GHGs emitted in one country or region
flow freely across others. In fact, some of the greatest climate change impacts
are predicted to occur in regions with the lowest GHG emission levels. The far
northern latitudes, where the highest temperature increases are likely to occur,
are one such example. Small tropical islands are another; they could be completely inundated if sea levels rise.
To stabilize GHG concentrations at levels that will prevent serious climate change
will require widespread GHG mitigation efforts throughout the world. This chapter examines the evolution of international agreements and strategies aimed at
mitigating climate change—and how Canada has responded to that evolution. It
also highlights groundbreaking new agricultural GHG mitigation practices and the
determined efforts of individual Canadian farmers who have adopted strategies
for their own land.
Managing climate change on the world stage
The global effort to combat climate change began in 1979 at the First World
Climate Conference, an intergovernmental meeting held in Geneva that examined
how climate change might affect human activities, especially agriculture, fishing,
forestry, hydrology and urban planning. The participants issued a declaration for
world governments “to foresee and prevent potential man-made changes in climate that might harm the well-being of humanity” and identified that the leading
cause of global warming is increased atmospheric concentrations of CO2 resulting from the burning of fossil fuels, deforestation and changes in land use.
124
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
In 1988, the World Meteorological Organization and the United Nations Environment Programme established the Intergovernmental Panel on Climate Change
(IPCC). IPCC’s role is to assess available scientific, technical and socio-economic
information and report on the risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. The first climate change
assessment report by the IPCC, released in 1990, was an important step on the
road to the first international global climate change agreement, the United Nations Framework Convention on Climate Change.
The Climate Convention, which has been adopted by 192 counties, is based
on the precautionary principle. The precautionary principle is a “better safe than
sorry” approach. It states that if there is a risk of severe and irreversible damage
to human health or the environment, lack of complete scientific certainty about
all of the causes and effects should not be used as a reason to delay action.
By ratifying the Climate Convention, governments around the world recognized
that despite some uncertainty about how the greenhouse effect might change
climate, the potential impacts are so serious that the only responsible course is
to take action now.
The Convention aimed to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous climate change. It contained voluntary targets for GHG emission reductions and advocated reducing emissions
to 1990 levels. Developed countries are required to submit national reports on
GHG emissions and to support similar reporting by developing countries through
financial and technical assistance.
Governments and scientists recognized that the voluntary targets adopted
under the Convention would have to be strengthened to prevent serious climate
change. Governments involved in the Climate Convention continued to negotiate deeper and more legally binding emission reduction commitments. In 1997,
they reached agreement on the Kyoto Protocol, a set of emission targets aimed
at reducing global GHG emissions to 5% below 1990 levels between 2008 and
2012. The Kyoto Protocol became international law on February 16, 2005. The
countries, including Canada, that agreed to participate in the Protocol are part
of the first international agreement based on legally binding emissions reduction
targets and the first international environmental agreement that will try to achieve
its objectives using markets, such as a carbon trading market.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
125
EMISSIONS REDUCTION
AS CURRENCY
Emission trading is a promising tool to help reduce
the cost of achieving emission reductions. In a carbon
market, sellers such as farmers generate carbon credits
by reducing their emissions or enhancing removals;
buyers purchase credits to offset their own emissions.
A market system can provide buyers with relatively
low-cost credits and farmers and other businesses with
economic incentives for adopting and developing lowemission technologies and practices. The value of traded
carbon is not expected to be high enough, at least in the
short term, to cause farmers to shift the focus of their
production systems to carbon credits instead of food and
fibre, but emission trading might tip the balance in favour
of GHG-mitigating practices in certain cases.
Most parties to the Climate Convention have ratified their Kyoto Protocol commitments. In July 2006, 61% of emissions from developed countries were covered
by the Kyoto Protocol. Commitments vary among countries: compared to 1990
levels, Canada’s target is -6%; Denmark and Germany have a target of -21%;
and Greece has a target of +30%. The United States (which produces about
25% of the world’s emissions) and Australia are the two most significant developed countries that did not ratify the Kyoto Protocol—although both countries
have domestic programs aimed at reducing GHG emissions.
Developing countries do not have emission reduction targets under the
Kyoto Protocol. It was agreed that targets for developing countries would be
set in later agreements once developed countries—which have been responsible for most GHG emission increases thus far—had taken the first steps to
reduce their emissions.
Countries can meet their targets in two ways: by reducing emissions of GHGs
and by generating biological carbon sinks2 to offset their emissions. Sinks can be
created by planting new forests, reducing deforestation and through other activities related to the management of forests, croplands and grazing lands.
2
A biological carbon sink is a transfer of CO2 from the atmosphere into a reservoir, such as a forest or soil, through the process of
photosynthesis.
126
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
How the Kyoto Protocol affects agriculture
Under the Climate Convention and Kyoto Protocol, countries must report emissions from the agriculture sector, specifically the sources and gases shown in
Table 9. Agriculture produces about 8% of Canada’s GHG emissions, including
most of its emissions of N2O and CH4.
TABLE 9
GHGs and Sources of Emissions for the Agriculture Sector
that must be Reported Internationally
SOURCE
ACTIVITY
GHG
Enteric fermentation
Ruminant livestock
CH4
Manure management
Handling or storage of livestock
manure
CH4, N2O
Rice cultivation
Flooded paddy production
CH4
Synthetic N fertilizer
N2O
Animal manure applied to soils
N2O
Manure from grazing animals on
pasture
N2O
Crop residue decomposition
N2O
Cultivation of organic soils
N2O
Volatilization
N2O
Leaching, erosion and runoff
N2O
Agricultural soils
Field burning of agricultural
residues
CH4, N2O
Prescribed burning of savannahs
CH4, N2O
Agriculture is a biological production system. Emissions of CO2, CH4 and N2O are
a natural part of agricultural production and will never be completely eliminated. However, it is the goal of the international agreements to encourage the search for better
ways of managing inputs of nutrients and energy so they are used more efficiently by
the crops and animals rather than leaked away as gases or dissolved in water.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
127
Cropping systems can also be managed to remove CO2 from the atmosphere
through carbon sequestration in soils. Under the Kyoto Protocol, countries have
to account for all their GHG emissions and removals from the conversion of croplands to forest (afforestation and reforestation) and the conversion of forest to
agricultural land (deforestation). Countries also have the option to count changes
in carbon stocks resulting from improved management. This provision was, at
first, controversial because carbon storage in agricultural soils is reversible. For
example, the stored carbon could be lost if land managers change their management practices or climate change reduces crop production.
Canada’s climate change and GHG mitigation activities
Canada ratified the Kyoto Protocol in December 2002. Canada’s domestic climate
change and GHG mitigation activities include the agriculture sector. In Canada
GHG mitigation and climate change objectives are integrated within the country’s
overall environmental and sustainability agenda for the agriculture sector.
Farmers manage farmland to sustain crop production over the long term. They
make their decisions by weighing all factors involved in their production system
and deciding what combination of activities and practices will offer the best possible overall economic and environmental outcomes. Agriculture policy developed
by governments often has the aim of supporting farmers to achieve broader social or public goals, including environmental goals such as adaptation to climate
change and GHG mitigation.
Fortunately, GHG mitigation is largely a matter of good land management,
conservation of resources and careful management of the carbon and nitrogen
cycles. Many GHG mitigation practices provide other benefits, economic and
environmental. Thus, although it would be difficult to motivate people to reduce
emissions for environmental impacts that are not yet clearly defined, many farmers are adopting good practices quite willingly because of those other benefits.
When scientists began to look for ways to reduce GHGs associated with crop
and livestock production, they found that many recent changes and innovations
in cropping and livestock systems already reduce emissions. Therefore, GHG
mitigation provides a fresh new impetus for understanding and promoting the
use of these beneficial practices.
128
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
HOW CANADIAN FARMERS ARE RESPONDING
PORK PRODUCER RECEIVES PRESTIGIOUS EMERALD AWARD
Dennis McKerracher, a High River, Alberta pork producer couldn’t believe
his ears when he heard he had won the coveted emerald award in the
Research and Innovation category of the Alberta Emerald Foundation for
Environmental Excellence.
McKerracher won for a yearlong, on-farm research project to examine how
waste water and GHGs can be reduced in hog operations. Supported by the
Greenhouse Gas Mitigation Program for Canadian Agriculture, Climate Change
Central, the Canadian Pork Council and Alberta Pork, McKerracher’s project
measured and compared the impacts of using ball bite versus standard water
drinker systems in his 500-head, all-in, all-out grower operation.
His research found that over a one-year period the group of pigs selected to
drink from the ball bite system used 35% less drinking water than the group using
the standard drinkers. Ball bite drinker systems release water when the pig bites
down on a ball, pushing a leaver that releases water.
The study results are significant. Water savings on McKerracher’s operation
means that he has to pump less of it. Not only is this more cost effective, but
it also saves him time. And the less water used, the more efficient the farm’s
manure management—resulting in a lower production of GHGs.
“To leave as small an ecological footprint as possible is my responsibility as a
farmer. To be able to make a difference on my own hog operation is great. But to
see the potential far-reaching, positive effects that my project could have on the
environment and my industry is the best reward to me.”
Canadian Pork Council June 21, 2006
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
129
ZERO TILL DELIVERS A BIGGER BANG FOR FEWER BUCKS
Jim Halford is a strong advocate of zero-till farming and direct seeding. The
southeast Saskatchewan farmer retired his tillage equipment more than 20 years
ago and has been reaping the rewards ever since.
Halford says that on parts of his Indian Head-area farm hard red spring wheat yields have
increased by nearly 15 percent over conventionally farmed land, while nitrogen fertilizer
requirements have been cut by 40 percent. He attributes these somewhat surprising
and continuing benefits to long-time zero-till farming and precise fertilizer placement.
“It’s due to the higher levels of organic matter in the soil,” says Halford. “As the
organic matter increases, it increases the ability of the soil to mineralize nitrogen
and make it more available to the crop.”
On Halford’s sandy-loam, clay-type soil, no-till has meant about a 40 percent reduction
in current fertilizer rates, while harvesting a very respectable 45 to 50 bushel HRSW
crop. It’s the difference between applying 50 to 60 pounds of nitrogen versus a more
traditional 90 pounds per acre, which saves Halford $12 to $16 per acre.
The production and economic benefits of zero till fit well with a national objective to
reduce GHG emissions related to agriculture, says Doug McKell, executive director of
Soil Conservation Council of Canada. The council administered the soils and nutrient
management components of the national Greenhouse Gas Mitigation Program for
Canadian Agriculture. The program’s mandate was to promote awareness and adoption
of practices that benefit production and at the same time reduce GHG emissions.
Zero-till farming produces a wide range of production and economic benefits, says Halford,
who is well known across North America as the developer of the Conserva Pak Seeding
System. He notes that proper placement of seed and fertilizer is important to a successful
crop. And as soil quality improves, inputs are able to reach their fullest potential.
The benefits of zero-till cropping build with time, so the longer land is farmed without
tillage, the more soil quality improves. For example, soil organic matter increased
about one percent every five years of zero tillage. Over 13 years of zero tillage,
organic matter increased from 2.7 to 5.1%.
The increase in soil organic matter translates directly into higher rates of nutrients
being mineralized and made available to the crop, says Dr. Jeff Schoenau, a
University of Saskatchewan soil scientist. It’s not a sudden process that happens
the first year of zero-till farming. In the first three to five years of zero till, fertilizer
requirements may actually increase, he points out. But, as the organic matter
increases, the conversion begins.
Soil Conservation Council of Canada
130
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
GROUNDBREAKING IDEAS FROM THE SCIENTIFIC
COMMUNITY
N E T F E E D E F F I C I E N C Y H O L D S G R E AT P R O M I S E F O R C A N A D A’ S B E E F I N D U S T R Y
Canada’s beef industry stands to gain well over $200 million annually in feed savings by
adopting technology to select animals for net feed efficiency, says a leading beef scientist
with more than 25 years experience in beef cattle production and management.
“In all my years in the beef industry, I have never seen a trait come along with higher
potential than net feed efficiency,” says Dr. John Basarab of Alberta Agriculture, Food
and Rural Development (AAFRD). Net feed efficiency, also known as residual feed
intake, is a relatively new discovery, but it’s rapidly gaining recognition internationally
among scientists, private industry and innovative producers.
Australia was the first to develop commercial technology for measuring individual
animal feed intake in the mid 1990s, a key measure for calculating net feed
efficiency. But the technology was prohibitively costly to produce and operate.
Following an investigative trip to Australia, Basarab and colleagues Dr. Bob Kemp
and Dr. Warren Snelling approached Alberta-based GrowSafe Systems Ltd. about
developing a less costly and more efficient model.
The result was a new standard in feed intake measurement equipment produced at
one-tenth of the cost of the Australian model and operated with less than one-fifth
the labour. The scientists also established a proof of concept for net feed efficiency
as a valuable measurement tool in a series of studies funded in part by the Canada
Alberta Beef Industry Development Fund (CABIDF). In 2006, the technology and
approach have made great strides in commercial adoption. “More people are
testing commercial bulls, and those bulls are going into industry and in many cases
being sold at a higher price,” says Basarab.
“If we are to take advantage of net feed efficiency, one of the priorities for the beef
industry over the next three to five years will be to identify the best bulls that have
the trait,” he notes. “Right now in Alberta, the approximately five percent of industry
that represents the leading innovators is taking the lead, and we’d like see use of
the technology gradually broaden throughout the industry.”
Canadian Cattlemen’s Association
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
131
C AT T L E F E E D A N D R E D U C E D
EMISSIONS
A study was conducted by the University of Guelph
at Elora Dairy Research Farm and Mayhaven Farms in
Rockwood, Ontario to look at how feeding cows dryrolled corn and an extract of palm oil (myristic acid) could
reduce CH4 emissions.
The formation of CH4 by the cow is a loss of energy from
the feed, accounting for up to 12% of the feed energy.
Given that CH4 gas is not used by the cow for milk
production, it represents a loss of feed energy that could
increase feed costs. Dry-rolled corn and myristic acid
were incorporated separately into the total mixed rations
of the cows’ daily diet. The CH4 emissions were collected
and measured in the breath of the cows with the aid of
custom built head hoods. Experiments compared steamflaked and dryrolled corn to see which produced a higher
gaseous output of CH4. Dry-rolled corn produced 7% less
CH4 per day per kilogram of milk produced than steamflaked corn. Myristic acid did even better, lowering CH4
emissions by 28% per day per kilogram of milk produced.
Although myristic acid is the clear winner in terms of
CH4 reduction, dry-rolled corn is only a slight change
from standard diets. Incorporating dry-rolled corn into
the diet is therefore probably the easier and more
practical change for producers to make. And dryrolled corn would benefit not only the health of the
cow, but also the environment.
Dairy Farmers of Canada
132
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
IMPROVING THE BOTTOM
LINE THROUGH CROPLAND
MANAGEMENT
There is a long history of soil carbon research in Canada
and farmers have generally been aware that loss of soil
organic matter is linked to soil degradation. Canadian
farmers have been among the pioneers developing crop
production systems based on direct seeding, minimum
tillage and continuous cropping that maintain soil quality.
Farmers’ primary motive for using innovative practices is
financial—the practices provide better economic returns
under present market and farming conditions. However,
the practices are now recognized for the significant
environmental benefits they offer, especially maintaining
and enhancing soil organic matter with its rich store of
soil organic carbon and nitrogen. (See earlier chapters
on carbon and nitrogen for full descriptions of these
processes.) Under the Kyoto Protocol, increases in soil
organic carbon that result from changes in cropland and
grazing management can be used as carbon credits to
offset GHG emissions during the first commitment period.
Agriculture and Agri-Food Canada
FU RTHE R R E AD I NG
Environment Canada. 2007. National Inventory Report: 1990–2005, Greenhouse gas sources and sinks in Canada.
Environment Canada, Greenhouse gas division.
Janzen, H.H. 2001. Soil science on the Canadian prairies—Peering into the future from a century ago.
Canadian Journal of Soil Science. 81:489–503.
Paustian, K., J. Antle, J. Sheehan, and E.A. Paul. 2006. Agriculture’s role in greenhouse gas mitigation.
Prepared for the Pew Centre on Global Climate Change, Arlington, VA. September (www.pewclimate.org)
Wall, E. and B. Smit. 2005. Climate change adaptation in light of sustainable agriculture. Journal of
Sustainable Agriculture. 27:113–123.
WMO. 1979. Proceedings of the World Climate Conference: a conference of experts on climate and
mankind. Geneva, 12–32 February 1979. WMO - No. 537. ISBN 92-63-10537-5.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
133
e Future
GREENHOUSE GAS EMISSIONS UNDER FUTURE
CONDITIONS
While there are plenty of opportunities to make agriculture more efficient in terms
of its GHG emissions, a rapidly growing world population and increasing demand
for food and improved diets means that GHG emissions from agriculture will
continue to grow. The United Nations has predicted that the world’s population
will grow from 6.5 billion in 2005 to 9.1 billion in 2050.
Population growth is expected to be higher in developing than developed
countries. If food production in developing countries increases to meet the
rising demand, it is likely that GHG emissions from agriculture will also rise in
those countries. Incomes are also expected to grow, which means that food
preferences and demand for improved diets (i.e., more livestock products) could
further increase GHG emissions from food production.
To feed the increasing population, global livestock production is projected to
more than double from 229 million tonnes in 2001 to 465 million tonnes in 2050.
Milk production is also expected rise from current levels of 580 million tonnes
to 1,043 million tonnes by 2050. The U.S. Environmental Protection Agency
projects that under business-as-usual conditions and rates of population growth,
global emissions from agriculture will increase by 25% between 2000 and 2020,
with an increasing share of emissions coming from developing countries.
I N T E R N AT I O N A L A N D
GLOBAL TRENDS
On a global scale, agriculture accounts for about
40% of total land use and about 70% of water use. It
has changed major nutrient cycles. It has more than
doubled the size of the nitrogen cycle—and contributes
about 10-12% of global GHGs, including most of the
world’s CH4 and N2O.
134
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Our changing use of land
Globally in 2000 there were about 5,000 million hectares of agricultural land compared to about 4,500 million hectares in 1960. An increase in agricultural land
area and new crop production technologies has allowed food production to keep
pace with increasing food demand and global population growth. However, this
has not occurred without cost to the environment.
Every year for the past 40 years, on average, 6 million hectares of forest and 7 million hectares of other land types have been converted to agriculture, mainly in the
developing world. Expansion of livestock production is a key driver of deforestation,
especially in Latin and South America where it is estimated that 70% of the forested land in the Amazon has been converted to pastures and croplands. Scientists
have said that tropical deforestation might be the key determinant in whether or
not GHG emissions are stabilized at a level that will prevent climate change. They
report that up to one quarter of global, human-induced emissions result from tropical deforestation; the emissions from deforestation in Brazil and Indonesia almost
equal the total emission reduction targets of the Kyoto Protocol.
Outside the tropics, emissions from land use and land-use change activities
have shifted from a source of GHGs in the 1980s to a small sink in the 1990s, as
some agricultural lands are returned to forest, forest fire-fighting efforts increased
and cropland soils gain carbon due to changes in land management. However,
whether terrestrial sinks in the temperate region can survive in the face of longterm climate change is uncertain.
Non-CO2 GHG emissions from agriculture are also expected to increase over
the next decades. Agriculture is the largest human-induced source of CH4 and
N2O and the Environmental Protection Agency in the United States indicates
that this is not likely to change. The main source of N2O emissions is agricultural soils; the main source of CH4 is livestock.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
135
Agricultural production is expected to increase to meet demand in Asia, Latin
America and Africa. In 1990, developed countries contributed about one third of
emissions of N2O from soils, but by 2020, projections indicate that will drop to 23%
with emissions from China and Asia up by 50% and Africa, Latin America and the
Middle East up by more than 100%. The growth in global CH4 emissions will come
mainly from China, Latin America, Africa and Asia, where urbanization and per capita income are expected to generate increased demand for livestock products. In
contrast, emissions in developed countries are expected to decline over time due
to increased production efficiency and lower export demand.
Our changing climate
Scientists make projections about the future of our climate by running global
climate models—generally referred to as global circulation models—based on
scenarios that represent a range of possible future conditions, including atmospheric GHG concentration, population size, socio-economic development and
technology change. These projections are heavily dependent on assumptions
about future conditions and the path that will likely lead us there. However, there
is growing agreement that our future climate will be warmer with more extreme
climate and weather events.
The climate scenarios of the Intergovernmental Panel on Climate Change project
that mean global temperatures are likely to increase by 0.2ºC per decade for
the next two decades, as illustrated in Figure 52. Projections at the high end of
the range reflect scenarios with high rates of population growth and emissions
of GHG continuing at current rates into the future (A1B). Low-range projections
are based on assumptions of slowing population growth and significant effort to
mitigate GHG emissions over the next decades (B1). The global estimates do not
provide good information about temperature changes at regional and local levels.
There is increasing effort to learn how to use the information from global circulation models to predict future climate in local regions.
FIGURE 52
GLOBAL SURFACE WARMING (˚C)
Global Warming Projections for a Range of Possible Paths to the Future
A2
A1B
B1
CONSTANT
COMPOSITION
COMMITMENT
20TH CENTURY
4.0
3.0
2.0
Solid lines are multi-model global averages of surface
warming (relative to 1980–1999) for the scenarios A2,
A1B and B1, shown as continuations of the 20th century simulations.Values beyond 2100 are for stabilisation
scenarios. The number of models that were run for a given
scenario are indicated by the coloured numbers given for
each period and scenario at the bottom of the panel.
1.0
0.0
-1.0
17
21
21
16
23
1990
2000
17
16
2100
12
10
2200
Source: IPCC AR4 WG1 Chapter 10, Global Climate Projections. Available online at: http://www.ipcc.
ch/graphics/graphics/ar4-wg1/ppt/figure10.ppt, accessed January 22, 2008.
2300
YEAR
136
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
C L I M AT E C H A N G E I N C A N A D A
Scientists have applied climate information produced by the Canadian Centre
for Climate Modelling and Analysis global circulation model (Canadian Coupled
GCM with aerosol) to the three Prairie provinces under two conditions: current
climate and future climate associated with a doubling of atmospheric CO2. The
model predicted that under a future climate, on average, high temperatures
would increase by 2ºC to 3ºC and low temperatures increase by about 3ºC.
Compared to current climate, precipitation was predicted to increase by 3%
to 7%. The results suggest that Alberta will benefit the most from increased
summer and winter precipitation, whereas eastern Saskatchewan and Manitoba
will experience little change or smaller increases. It is important to note that
projected changes in precipitation are more uncertain than estimates about
temperature change. Since there is a growing-season moisture deficit in much
of the Prairie region, even slight declines in the availability of moisture could
significantly harm crop production.
There is considerable evidence that climate is already changing:
• The global mean surface temperature has increased by 0.6 ± 0.2ºC
over the past century.
• The 1990s was the warmest decade of the past 1,000 years.
• The daily surface temperature range has decreased between 1950 and 2000
over land, with nighttime minimum temperatures increasing at twice the rate
of daytime maximum temperatures.
• There have been more hot days and fewer cold or frost days over the
past several decades.
• Continental precipitation has increased by 5 to 10% over the 20th
century in the northern hemisphere and declined in parts of Africa
and the Mediterranean.
• The number of heavy precipitation events have increased at mid and high
northern latitudes and the frequency and severity of drought has increased.
• Sea-ice cover has decreased.
• Shifts in species distributions have been observed.
• The global average sea level has increased.
For Canada, a high-latitude country, warming is expected to be more pronounced than the global average, with the north and southern and central
Prairies warming more than other regions. Most regions will likely be warmer with
longer frost-free seasons and increased evapotranspiration.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
137
Climate change could alter our agricultural landscape
Agriculture is both extremely important to the Canadian economy and inherently
sensitive to climate change. Climate controls the geographical distribution of
agricultural systems in Canada and exerts strong control over year-to-year variation in cropping success through drought, flooding, pest problems and storms.
Climate affects agriculture, positively and negatively, at scales ranging from individual plants and animals to global networks.
Our crops
Climate change will influence Canadian crop production, but projections show
great variation and a new set of risks and opportunities. For example, some
modeling exercises suggest that farmers may be able to plant their crops earlier
so crop growth will be complete before the hot, dry conditions in the late summer. If farmers are able to adapt to climate change in that way, yields of canola,
corn and wheat might not suffer and the range of crops that can be produced in
Canada might expand.
On the other hand, increased moisture stress and drought are concerns for irrigated and non-irrigated crops across the country. While climate change is expected to cause shifts in moisture patterns and rates of potential evapotranspiration,
there is still considerable uncertainty about the magnitude and direction of the
changes. Longer growing seasons and higher temperatures could increase water
demand. Drought could be become more frequent.
Climate models suggest that climate warming will be greatest in winter months,
which could reduce the risk of winter damage to sensitive crops, such as fruit
trees and grapes. However, the absence of extreme cold in the winter could
allow crop pests to survive. An increased frequency of extreme events, such as
high temperatures, floods, droughts and storms, could also negatively impact
future crop production in Canada.
Our livestock
Climate warming could benefit and harm livestock production. Benefits would be
especially evident in the winter in the form of lower feed requirements, increased
survival of the young and lower energy costs. Warmer summers, however, could
cause problems related to heat-wave deaths—especially in poultry operations—
reduced milk production and reduced reproduction in the dairy industry, as well
as reduced weight gain in beef cattle.
Droughts and floods could reduce pasture availability and forage production,
forcing producers to find alternative feed or reduce herd size.
138
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Our soils
Climate change could negatively affect agricultural soil quality by influencing the
quantity of soil organic matter, nutrient cycling and leaching, wind and water erosion and runoff, all of which could lead to an increase in emissions of CO2 and N2O
from soils. On the other hand, climate change could improve soil quality, enhance
carbon sequestration and reduce emissions of greenhouse gases if it were severe
enough to force a land-use change from annual crop production to perennial crops
and grazing lands.
Pests and disease
Scientists have reported a list of possible effects of climate change on crop pests
and disease. These include increased weed growth due to elevated atmospheric
CO2; increased prevalence of livestock and crop pests and pathogens; and
increased range, frequency and severity of insect and disease infestations. These
changes will not have large effects on GHG emissions from crop production
systems, although they could cause an increase in energy use associated with the
manufacture, transportation and application of pesticides.
GHG mitigation offers opportunities for agriculture
GHG emissions are a natural part of the carbon and nitrogen cycles. Therefore,
a certain level of emissions from any biological system is inevitable: CH4 emissions from ruminant animals cannot be reduced to zero; N2O emissions from
decomposing crop residues cannot be avoided; emissions of N2O and CH4 from
livestock manure cannot be eliminated.
However, some GHG emissions from crop and livestock production are avoidable; these represent leakage or inefficiency in the system of which both have environmental and economic consequences. For example, emissions of N2O imply
inefficient use of nitrogen fertilizer and CH4 emissions from ruminant livestock
indicate that feed is not being efficiently converted to milk or meat products.
There is a considerable body of literature about plant and animal production
systems that can reduce GHG emissions and offer positive economic benefits.
Examples include:
1. Use inputs—such as fertilizers and machinery—associated with large
emissions of fossil fuels as efficiently as possible.
2. Use some of the biomass produced on agricultural land to produce bioenergy
so as to partly replace fossil fuels. (The chapter on biofuels provides a detailed
examination of biofuel production in Canada and in other countries.)
3. Use agricultural wastes to generate energy.
4. Adopt management practices that increase the amount of carbon stored in soils.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
139
Adapting to climate change
Climate change has the potential to benefit and harm agriculture. Warmer temperatures, longer growing seasons and elevated CO2 concentration may improve
agricultural production; on the other hand, reduced soil moisture, more frequent
extreme weather and storms and new crop pests could hurt production potential. Appropriate adaptations can reduce the effects, especially if they are part of
an overall decision-making process at the farm and policy levels.
Developing countries are likely to face more difficulty adapting to climate change
than developed countries such as Canada because of limited resources. Damage to land and water resources will strain financial and technological capacities
and produce local consequences for food production. The capacity of a farming
system to adapt to climate change is determined by the quality of its natural resources and associated economic, social, cultural and political conditions. Global
projections indicate crop yield declines will be most severe in tropical, semi-arid
developing countries, and least severe in high latitude developed countries—although scientists caution that the exact projections are still uncertain.
In Canada, it is unlikely that climate change will drive the adaptation process by
itself. Farmers will continue to adapt to the wide range of conditions they face
each year: climate, markets, and policies, etc. Climate change, therefore, is likely
to be considered one more element of an overall risk-management strategy.
Meanwhile, options for climate-change adaptation are expected to fall under the
following four categories:
1. Technological development
• new crop varieties such as new species and hybrids that are more heat tolerant
and drought resistant or more adapted to climate extremes and pests
• water management innovations such as snow management in semiarid climates
to increase water storage or zero tillage to reduce water loss from the soil
• seeding earlier to take advantage of longer, warmer growing seasons and to
avoid a dry late-summer period
2. Government programs and insurance
•
•
•
•
140
subsidies and private insurance
water transfers and changes to crop insurance programs
research on development of new species and hybrids
carbon trading
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
3. Farm production practices
•
•
•
•
•
•
crop diversification
water conserving irrigation systems
reduced tillage and chemicals
adjusting shading and air conditioning for livestock
use of sprinklers to cool livestock during heat waves
increasing early-season grazing to avoid summer dry periods
4. Farm financial management
• income stabilization programs
In Canada and globally, agriculture is highly adaptive; but how well it can adapt
outside the normal range of climate conditions is uncertain. Indeed, there are climate thresholds beyond which farms and crops could never adapt. Understanding
where those thresholds lie—and how agriculture can be sustained within them—is
an important challenge for the research community in Canada and around the
world. Only through such understanding will our food sources remain secure.
FU RTHE R R E AD I NG
Gitay, H, S. Brown, W. Easterling, and B. Jallow. 2001. Ecosystems and their goods and services. Pp. 235342 In: J.J. McCarthy, O.F. Canziani, M.A. Leary, D.J. Dokken and K.S. White (eds.) Climate Change 2001:
impacts, adaptation and vulnerability; contribution of Working Group II to the Third Assessment Report on the
Intergovernmental Panel on Climate Change. Cambridge University Press. Available online at: http://www.grida.
no/climate/ipcc_tar/. Accessed December 2006.
Lemmen, D. S. and R. Warren (Eds.). 2004. Climate change impacts and adaptation: a Canadian perspective.
Climate Change Impacts and Adaptation Directorate. Natural Resources Canada: Ottawa. 175 pp.
McGinn, S. A. Toure, O. Akinremi, D. Major, and A. Barr. 1999. Agroclimate and crop response to climate
change in Alberta. Canada; Outlook on Agriculture, 28:19–28. Cited in Lemmen and Warren, 2004.
Powlson, D.S., A. Riche, and I. Shield. 2005. Biofuels and other approaches for decreasing fossil fuel
emissions from agriculture. Annals of Applied Biology 146:193–201.
Wall, E. and B. Smit. 2005. Climate change adaptation in light of sustainable agriculture. Journal of
Sustainable Agriculture 27:113–123.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
141
Restored
Restore
TheA Vision
Future
DREAMS OF FUTURE SOLUTIONS
Few of us see the future clearly. But we know with certainty that change is coming—and coming quickly—as there are more and more of us scrabbling about
on a planet whose resources are dwindling. How do we satisfy our spiralling
demands for energy and food without spewing more of the gases that imperil our
climate? Our farmlands are in the midst of these stresses; and they must be a
part of any solution.
In earlier chapters, we outlined emerging practices that might help avert unpleasant climate change; growing biofuels on farmland, for example, may help reduce
our dependency on fossil fuels. Other practices surely will emerge. The ones we
can foresee can be grouped under three categories.
Alternate energy sources
To wean ourselves from the fossil fuels that foul our air, we will need to find replacement energy sources to drive our societies. Many such sources have been
proposed: nuclear power, wind power, water power, energy from hydrogen and
solar energy. While these may seem unrelated to farming, many of them could
affect how we farm. Wind generators may be situated on farmland and the solar
panels of the future may also be sited there. What’s more, the transmission of
energy often occurs across farmlands. So while many energy systems may not
derive from farms, the sources we choose may well affect how we farm the land.
And if biofuels become important energy sources, demand for them will further
re-shape our farmlands.
More efficient use of energy
Farms, especially intensive ones, use a lot of energy. Just as we are doing for
other industries, we will need to look for ways to use energy more frugally on
farms. We will need more fuel-efficient vehicles, better-insulated buildings and
more efficient ways of transporting produce.
There are many opportunities for agriculture to increase its efficiency. Plant
breeders may develop new crop varieties with higher yields or varieties that
flourish with fewer inputs of irrigation water or energy-dependent chemicals.
Livestock scientists may develop practices or animals that produce more meat or
milk per unit of energy. Vaccines may emerge that suppress the release of CH4
from cattle, cutting down on potent GHGs and at the same time enabling cattle
to use feed energy more effectively.
142
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Another promising way to reduce energy use on farms is through better management of crop nutrients. Making fertilizer, especially nitrogen fertilizer, uses a lot of
energy (producing CO2 emissions). Maybe we can exploit better the biological fixation of atmospheric N, so plentiful, to replace some nitrogen fertilizer. Perhaps we can
genetically re-tool cereal crops to fix their own nitrogen; or at least, we can better use
the nitrogen fixed by legumes for other crops. Further, we can devise new fertilizer
forms and ways of delivering them to crops that avoid the leaks to the environment,
thereby saving energy and losses of N2O. For example, new sensors on satellites
or on the ground may allow farmers to measure exactly how much nitrogen a crop
needs as it grows, helping them to better match fertilizer rates to plant needs.
Another way to use nutrients more efficiently is to recycle them more cleanly.
Nutrients in manure could be more efficiently returned to the land, either by
new conveyance methods or, better, by placing livestock closer to where their
feed is grown. Perhaps, even, we can find safe ways to recycle nutrients in human wastes that now we flush away.
Reconnecting consumers to farmlands
Once, most consumers lived on the land that grew their food; now they may live
a continent away, with little thought about the ecosystems that sustain them.
That may change. We may once again learn that what we eat affects what happens to our lands. Through changing diets, consciously designed and chosen, it
may be possible for society to steer toward food-production systems that reduce
emissions from farmlands. Further, future consumers may opt to save energy and
emissions by using foods and other farm products grown close to home. In our
increasingly urban societies, the biggest advances in food production may come,
not in remote rural fields, but in the plots of urban farms.
These are just a few examples of how societies may increasingly acknowledge
again the link between consumers and the land, thereby reducing GHG emissions. Tomorrow’s innovators surely will envision more.
Closing thoughts
Many of the solutions to our current dilemmas are no doubt still beyond our purview. But the answers likely will emerge from a vision restored; from seeing our
farmlands—the soil, the trees, the crops, the sky—not as resources to be spent,
but as the home in which we live. For one way or another, wherever we may
reside, we do all live on the land, we and our descendants too.
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
143
144
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
145
146
Better Farming, Better Air | A scientific analysis of farming practice and greenhouse gases in Canada
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement