CROPPED SOILS WITH DENITRIFICATION LOSSES SUBSURFACE DRIP IRRIGATION by

CROPPED SOILS WITH DENITRIFICATION LOSSES SUBSURFACE DRIP IRRIGATION by
DENITRIFICATION LOSSES IN CROPPED SOILS WITH
SUBSURFACE DRIP IRRIGATION
by
Uriel Figueroa-Viramontes
Dissertation Submitted to the Faculty of the
DEPARTMENT OF SOIL, WATER AND ENVIRONMENTAL SCIENCE
In Partial Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
In the Graduate College
THE UNIVERSITY OF ARIZONA
1999
2
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
As members of the Final Examination Committee, we certify that we have
read the dissertation prepared byUriel Figueroa-Viramontes
entitled Denitrification losses in cropped soils with subsurface
drip irrigation.
and recommend that it be accepted as fulfilling the dissertation
requirement for the Degree of Doctor of Philosophy
)/S/9
Date
Date
/—
Date
Date
Steven P. McLaughlin
Final approval and acceptance of this dissertation is contingent upon
the candidate's submission of the final copy of the dissertation to the
Graduate College.
I hereby certify that I have read this dissertation prepared under my
direction and recommend that it be accepted as fulfilling the dissertation
requirement.
Dissertation Director D
ornas L. Thompson
Date
3
STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment of requirements for an
advanced degree at The University of Arizona and is deposited in the University Library to
be made available to borrowers under rules of the Library.
Brief quotations from this dissertation are allowable without special permission,
provided that accurate acknowledgment of source is made. Requests for permission for
extended quotation or reproduction of this manuscript in whole or in part may be granted
by the head of the major department or the Dean of the Graduate College when in his or
her judgement the proposed use of the material is in the interests of scholarship. In all
other instances, however, permission must be obtained from the author.
Signed:
4
ACKNOWLEDGMENTS
Thanks to Dr. Thomas L. Thompson, my advisor and dissertation director, for his
guidance to complete my degree. I really appreciate his way of teaching how to do the
field work by example.
Thanks to Dr. Janick F. Artiola, Dr, David M. Hendricks, Dr. James W.
O'Leary, and Dr. Steven P. McLaughlin for participating as members of my Committee.
I appreciate the suggestions to the manuscript. I also learned a lot from their courses.
Thanks to all the staff and students in the Soil Fertility Laboratory during the four
years that I spent here. Special thanks to Scott A. White for his help in many things in the
field and in the lab.
Thanks the staff in the main office of the SWES Department for their help.
Thanks to CONACYT and INIFAP in México for the scholarship that supported
my academic and living expenses.
5
DEDICATION
To my wife Koris, my daughter Mariel, and my son Alejandro.
To the memory of my Parents.
6
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS LIST OF TABLES ABSTRACT 1. INTRODUCTION 8
10
12
14
2. REVIEW OF LITERATURE the Process of Denitrification Methods to Evaluate Denitrifi cation in Soils ' 5N-Isotope Techniques Acetylene Inhibition Denitrifying Enzyme Activity (DEA) Main Factors Controlling Denitrification in Soils Organic Carbon Inorganic Nitrogen Oxygen and Soil Aeration Temperature Denitrification Rate in Different Irrigation Methods 17
17
19
19
20
22
23
23
25
27
28
29
3. MATERIALS AND METHODS Cauliflower Experiments Sweet Corn Experiment Evaluation of Denitrifi cation and Related Measurements Field Sampling and Core Incubation GC System Description Calculation of Denitrification Rate Cores with Nitrogen and Carbon Amendments Denitrifying Enzyme Activity Total and Soluble Organic Carbon Statistical Analysis 32
33
38
41
41
42
46
48
49
50
51
4. RESULTS AND DISCUSSION Cauliflower 1996-97 Denitrification Rate Yield Nitrogen Balance 52
52
52
59
60
7
TABLE OF CONTENTS Continued
Page
Cauliflower 1997-98 Denitrificati on Rate Carbon and Nitrogen Amendments Organic Carbon Denitrifying Enzyme Activity Yield Nitrogen Balance 62
63
70
74
75
77
77
Sweet corn 1997 81
81
88
89
91
93
Denitrification Rate
Organic Carbon Denitrifying Enzyme Activity Yield
Nitrogen Balance 5. CONCLUSIONS 96
APPENDIX 98
REFERENCES 123
8
LIST OF ILLUSTRATIONS
Figure
Page
Oxidative electron transport in bacterial respiration showing the aerobic
and the denitrification pathways 18
Maximum and minimum temperatures and precipitation during the 199697 cauliflower growing season 35
Maximum and minimum temperatures and precipitation during the 199697 cauliflower growing season 36
Maximum and minimum temperatures and precipitation during the 1997
sweet corn growing season 39
Diagram of the two Porapak columns and the two positions of 4-port
valve inside the GC oven 45
4-1
Denitrification rates during the 1996-97 cauliflower growing season 54
4-2
Relationship between WFPS and denitrification rate in cores taken 24 hr
after fertilization. Cauliflower 1996-97 56
Relationship between nitrate and denitrification rate in cores taken 24 hr
after fertilization. Cauliflower 1996-97 57
Denitrification losses of N in control and fertilized plots. Cauliflower
1996-97 61
Denitrification rate evaluated at ambient and room temperature.
Cauliflower 1997-98 65
Relationship between WFPS and denitrification rate in cores taken 24 hr
after fertilization. Cauliflower 1997-98 67
Regression analysis of denitrification rate evaluated at ambient versus
room temperature. Cauliflower 1997-98 69
2-1
3-1
3-2
3-3
3-4
4-3
4-4
4-5
4-6
4-7
4-8
Relationship between nitrate and denitrification rate in cores taken 24 hr
after fertilization. Cauliflower 1997-98 71
9
LIST OF ILLUSTRATIONS Continued
Page
Figure
Denitrification rate in soil cores amended with N and C. Cauliflower
1997-98 72
Denitrifying enzyme activity at the beginning and end of the 1997-98
cauliflower season 76
Denitrification losses of N in control and fertilized plots. Cauliflower
1997-98 80
4-12
Denitrification rates during the 1997 sweet corn season 83
4-13
Relationship between WFPS and denitrification rate in cores taken 24 hr
after fertilization for sweet corn, 1997 85
Relationship between nitrate and denitrification rate in cores taken 24 hr
after fertilization for sweet corn, 1997 87
Denitrifying enzyme activity at the beginning and end of the 1997 sweet
corn season 90
Residual ammonium and nitrate at the end of the 1997 sweet corn
season 92
Cumulative denitrification N losses during the 1997 sweet corn season 95
4-9
4-10
4-11
4-14
4-15
4-16
4-17
10
LIST OF TABLES
Page
Tables
2-1
Reduction reactions involved in denitrification 17
3-1
Target and average SWT, water applied, and rainfall in the 1996-98
cauliflower growing seasons 33
3-2
Schedule of N fertilizer applications for Cauliflower 34
3-3
Particle size distribution, bulk density, organic C, and N for the Casa
Grande soil, 0-30 cm of depth 37
Target and average SWT, water applied, and rainfall in the 1997 sweet
corn growing season 40
3-5
Schedule of N fertilizer applications according to crop growth stage 40
3-6
Particle size distribution, bulk density, organic C, and N for the Gila
soil 41
Sampling dates for the evaluation of denitrification and extreme temperatures during the soil incubation in cauliflower 1996-97 and 1997-98
seasons 43
Sampling dates for the evaluation of denitrification and extreme
temperatures during the soil incubation in sweet corn 1997 44
3-9
Concentration of N and C in solutions applied to soil cores 49
4-1
Distribution and coefficients of variation in the different sampling dates in
cauliflower 1996-97 53
Total biomass, marketable yield , and head diameter in cauliflower
1996-97 59
4-3
Nitrogen balance and unaccounted for N in cauliflower 1996-97 60
4-4
Frequency distribution, coefficients ofvariation, and statistical significance
in the cauliflower 1997-98 experiment 64
3-4
3-7
3-8
4-2
11
LIST OF TABLES Continued
Page
Tables
Concentrations of total (TOC) and soluble (SOC) organic carbon.
Cauliflower 1997-98 74
4-6
Marketable yield and above ground biomass. Cauliflower 1997-98 78
4-7
Nitrogen balance and unaccounted for N. Cauliflower 1997-98 78
4-8
Frequency distribution, coefficients ofvariation, and statistical significance
in the sweet corn experiment, 1997 82
Concentrations of total (TOC) and soluble (SOC) organic carbon. Sweet
corn 1997 89
4-10
Total biomass, marketable yield, and plant height in sweet corn, 1997 93
4-11
Nitrogen balance and unaccounted N for sweet corn, 1997 94
A-1
Corrected tensiometer readings. Cauliflower 1996-97 99
A-2
Corrected tensiometer readings. Cauliflower 1997-98 99
A-3
Corrected tensiometer readings. Sweet corn 1997 A-4
Meter readings and calculation of water applied. Cauliflower 1996-97 . . . . 101
A-5
Meter readings and calculation of water applied. Cauliflower 1997-98 101
A-6
Meter readings and calculation of water applied. Sweet corn 1997 102
A-7
Denitrification rate and related data. Cauliflower 1996-97 103
A-8
Denitrification rate and related data. Cauliflower 1997-98 107
A-9
Denitrification rate and related data. Sweet corn 1997 115
A-10
Cumulative N lost by denitrification. Cauliflower 1996-97 120
A-11
Cumulative N lost by denitrification. Cauliflower 1997-98 121
4-5
4-9
A-12
Cumulative N lost by denitrification. Sweet corn 1997 100
122
12
ABSTRACT
Denitrification is a microbial process of anaerobic respiration in which nitrate
(NO 3-) is chemically reduced to gaseous nitrous oxide (N2 0) and molecular N2. Fertilizer
N can be lost to the atmosphere through this process. Subsurface drip irrigation may
create favorable conditions for denitrification, such as high moisture and NO 3- content.
The objectives of this research were to: 1) determine the denitrification rate in drip-.
irrigated cauliflower and sweet corn crops; 2) evaluate the effect of soil water tension on
the denitrification rate, and; 3) estimate an N balance under subsurface drip irrigation,
including denitrification losses. Two field experiments with subsurface drip-irrigated
cauliflower were conducted during the 1996-98 winter growing seasons at the Maricopa
Agricultural Center, in Maricopa, AZ. An additional study with subsurface drip-irrigated
sweet corn was conducted at the Campus Agricultural Center in Tucson, AZ. All the
experiments were complete factorial designs with two soil water tension levels (low, high),
two levels of N fertilizer (zero, adequate), and three replications. The denitrification rates
evaluated at ambient temperature were <12 g N ha-1 d-1 during the cauliflower winter
seasons. When soil cores taken during the 1997-98 winter season were incubated at room
temperature (24 ±2°C), denitrification rates were five to 50 times higher than the rates
evaluated at ambient temperature. The denitrification rate measured at room temperature
in the cauliflower winter season was similar to the rate observed in the sweet corn during
summer. Soil cores from the cauliflower 1997-98 season that received 100 kg N ha-1 had
denitrification rates from 10 to 45 g N ha-1 d-1 ; when these cores were amended with
additional soluble carbon, the denitrification rate increased to 800 to 3500 g N ha-1 d-1.
13
All of the three experiments showed higher denitrification rates at the end of the season.
This trend coincided with increases in denitrifying enzyme activity and soluble organic
carbon. The denitrification loss of fertilizer N was <1% in cauliflower and almost 2% in
summer sweet corn, when irrigated at the higher soil water tension. Lower soil water
tension did not increase the denitrification rate in the winter, but in the summer the loss of
N due to denitrification increased to almost 6% of the applied N.
14
CHAPTER 1
INTRODUCTION
Vegetable crops are important in Arizona agriculture, and are grown on approximately 57,000 ha, representing about 15% of the total cropped area in 1996. The main
vegetable crop is lettuce, followed by melons, broccoli, and cauliflower. In the 1995-96
season, cauliflower was harvested on 1780 ha in Arizona; the average yield was 19.8 Mg
ha4 with a value of over 25 million dollars. The production of cauliflower in Arizona
represents almost 12% of the total production in the USA. Approximately 95% of
Arizona cauliflower is grown in Yuma county. Sweet corn is planted in a smaller area.
Only 730 ha of sweet corn were harvested in Arizona in 1996, with an average yield of 7.8
Mg ha"' and more than $2 million in total value (Sherman and Erwin, 1997).
Vegetable crops are commonly irrigated with pressurized irrigation systems. In
1997, there were 44718 ha irrigated with pressurized systems in Arizona, representing
almost 11% of the irrigated area. Of this total, 3238 ha were irrigated with surface drip
irrigation and 3642 ha with subsurface drip irrigation systems (Anonymous, 1998). Low
flow pressrized systems, such as subsurface drip irrigation, have the advantage of greater
efficiency in the application of water and nitrogen (N) fertilizers to the crop root zone.
The present situation of increasing cost of water and governmental regulations to reduce
groundwater contamination with nitrate demands increased efficiency of water and N use.
Pressurized irrigation can be a viable alternative to flood irrigation.
15
Losses of N from cropping systems are inevitable. Nitrogen can be lost from the
crop root zone through several processes, including nitrate (NO 3 ) leaching and denitrifica-
tion. Denitrification is a bacterial process of anaerobic respiration in which NO 3 is
-
chemically reduced to molecular N (N 2), thereby releasing energy from organic carbon
compounds. This process involves sequential reduction reactions from NO 3 to nitrite
-
(NO 2 ), then to nitrous oxide (N 2 0 t), and finally to dinitrogen (N 2 1 ). Each form of
-
nitrogen is used as the terminal electron acceptor in the reductive electron transport of
respiration. Since the end product of denitrification is gaseous N 2 , this process is important in the global N cycle because it balances the input of N 2 into terrestrial ecosystems
(Iserman, 1994). However, denitrification is responsible for substantial losses, up to 40%
under favorable conditions, of applied N-fertilizer in agricultural soils (Rolston et al.,
1982; Sextone et al., 1985). The main factors controlling denitrification are the concentration of 0 2 in the soil atmosphere, organic C substrate, available NO 3 , and temperature.
-
Subsurface drip irrigation may create favorable conditions for denitrification,
because of a localized soil zone of high moisture and high NO 3 content. In addition,
-
plant roots may contribute organic C in the form of root exudates. Crops irrigated with
subsurface drip systems may have up to 40% unaccounted fertilizer N when high rates of
water and N are applied (Thompson and Doerge, 1996). This unaccounted N is assumed
to include N fertilizer losses due to both NO 3 leaching and denitrification. However, the
-
magnitude of N losses specifically due to denitrification in subsurface drip irrigation
systems has not been quantified.
16
Therefore, the objectives of this research are to: 1) determine the denitrification
rate in drip irrigated cauliflower and sweet corn crops, using the acetylene inhibition
technique; 2) evaluate the effect of soil water tension on denitrification rate, and; 3)
estimate an N balance under sub-surface drip irrigation, including denitrification losses.
17
CHAPTER 2
LITERATURE REVIEW
The Process of Denitrification
Denitrification is a mechanism of anaerobic respiration, in which NO 3 is chemically
-
reduced to N 2 0 and N2 . The reduction steps as well as the N compounds involved in this
process are presented in Table 2-1.
Table 2-1.
Reduction steps involved in denitrification. (T) indicates that the compound can escape to the atmosphere in gaseous form. (Adapted from
Aulakh, et al., 1992)
Nitrogen compound
Nitrite
Nitric oxide
Nitrous oxide
Dinitrogen
NO 2 -
NO - (1)
N20 - (1)
N2 (1)
5+
3+
2+
1+
o
+2e-
+e
+e
+e-
Nitrate
-
N oxidation state:
Electrons involved:
Most denitrifying microorganisms are heterotrophs, which require organic C
compounds as electron donors to obtain energy. There are 21 genera of bacteria known to
be denitrifiers. Some common denitrifying species are Alcaligenes spp., Bacillus spp. and
Pseudomonas spp. (Knowles, 1981).
The overall reaction of respiration in bacteria, as summarized in Figure 2-1,
consists of the oxidation of organic compounds, coupled to the reduction of nicotinamide
adenosine dinucleotide (NAD) to form NADH + H. The electrons (e ) gained in the
-
18
Substrate
,
Reduced state/1' \ Oxidized state
Cytoplasm
CO
2e,2e
NAD+ NADH +
Cytoplasmic
MembraneL
(
.J2
ik
Transport
Chain
i
•
No 02 Available
0 2 Available
2e
-
2 Fr + 1 /202 IH20
-
P
eriplasm 40 NO3 2N 0 ;
-
'
2N 0
it`
2N20
2N2
itk
!i 141
0
f
2
NO3-
NO 2 NO
-
N20
N2
External ambient
Figure 2-1 Oxidative electron transport in bacterial respiration showing the aerobic and
the denitrification pathways (adapted from Paul and Clark, 1989; Singleton,
1992; and Tiedje, 1994).
19
reaction are then transported down a gradient of redox potential by an electron transport
chain bonded to the cytoplasmic membrane. Finally, the electrons flow to an external
oxidizing agent that also functions as a terminal electron acceptor. Oxygen is the terminal
acceptor in aerobic conditions and forms water as final product. However, when 0 2 is
not available in the environment, several oxidizing agents can be used instead. If N oxides
are utilized, denitrification occurs (Paul and Clark, 1989; Singleton, 1992).
Methods to Evaluate Denitrification in Soils
' 5N Isotope Techniques.
The two most common approaches to measure denitrification in soils are the
isotope and acetylene inhibition techniques. The isotope method usually consists of
applying a certain amount of ' 5N-enriched fertilizer. An ' 5N balance is calculated from soil
and plant analysis. Denitrification is supposed to be the unrecovered 15N, assuming that
NO; leaching and NH3 volatilization are negligible (Aulakh et al., 1992; Rolston et al.,
1976). Another N-isotope method involves the use of a closed chamber placed over a
microplot fertilized with an 15N-enriched fertilizer. The evolution of 15N2 0 and ' 5N from
the soil is monitored in the entrapped chamber atmosphere with mass spectrometry
(Aulakh et al., 1991a). This method requires very high 15N enrichment and specialized
equipment. The main disadvantage of the ' 5N balance method is the lack of precision
because NO; leaching and NH3 volatilization are not accounted for. (Tiedje et al., 1989).
20
Acetylene Inhibition.
Acetylene (C 2H2 ) can be used to prevent the reduction of N2 0 to N2, and the
accumulated N2 0 inside chambers or incubation jars is collected and expressed as
denitrification rate. The analytical advantage of this method is that small changes in the
ambient concentration of N2 0 are easier to detect than changes in N2 , since the natural
atmospheric concentration of N2 0 is very low (320 ppb) compared to N2 (78%). Soil
core incubation and in situ chambers, combined with C 2H2 inhibition, are two common
methods of measuring denitrification.
Chambers. Chambers are open-bottom enclosures that can be driven directly into the soil
or fitted over a base previously installed in the soil. The dimensions of chambers vary
widely. Mosier and Klemedtson (1994) recommended cylinders 15-30 cm in diameter by
10-60 cm in length. However, they also mention that the dimensions can be adjusted to
meet specific needs. Matthias et al. (1980) used a cylindrical chamber 88 cm in diameter
and 17 cm in height to measure N2 0 flux. Acetylene may be added into holes around the
chamber as calcium carbide (CaC 2), which reacts with water to form calcium hydroxide
[Ca(OH) 2] and C2H2 (Mosier and Klemedtson, 1994). Also, C 2H2 can be incorporated in
gaseous form through perforated tubes or dissolved in the irrigation water (Tiedje et al.,
1989). In subsurface drip irrigation systems, it is possible to inject C 2H2 through the
buried drip tape (Thompson et al., 1995).
Acetylene concentrations as low as 0.1% (v/v) in the soil atmosphere have been
found to effectively inhibit the reduction of N2 0 (Ryden et al., 1979). The atmosphere
21
inside the chamber is sampled through a septum after an accumulation period (usually 30
min to 2 hr), or multiple samples can be taken over the accumulation period (Tiedje et al.,
1989). Some advantages of chamber methods are the simplicity, low cost, and high
sensitivity (Aulakh et al., 1992). The detection limit is about 1 g N ha."' day', compared to
5 g N ha' d"' reported by Siegel et al. (1982) for an 15N chamber method. On the other
hand, chambers may influence the measurement of denitrification by increasing the soil
temperature inside the chamber; this in turn controls the solubility and diffusion of N2 0,
and markedly affects the rate of microbial processes. Also, when the N2 0 flux is high, a
pressure buildup inside the chamber may inhibit further diffusion of gases out of the soil
(Tiedje et al., 1989). Since the chamber methodology yields denitrification values relative
to the unit area of soil, this method is useful to evaluate the instantaneous flux of N20
from the soil to the atmosphere (Tiedje et al., 1989).
Core Incubation. In the soil core methodology, an undisturbed (or minimally disturbed)
soil core is incubated for 6 to 24 h in an air tight flask or jar with 5% to 10% (v/v)
acetylene. (Ryden et al., 1987; Tiedje et al., 1989). Some problems of this method are the
disturbance of the soil structure, and the diffusion of gases may be not as efficient as in
chambers. The advantages of soil core techniques are the simplicity of the field work and,
when the incubation is for 24 hr, the denitrification rate is integrated over a day, avoiding
the daily variability caused by temperature fluctuations. Additionally, this method
performs better than chambers in very wet soils, because of the small volume of soil the
gases have to diffuse into and out of (Aulakh et al., 1992). Long term incubations may
22
overestimate denitrification rates because C 2H2 can be metabolized by soil microorganisms
after seven days of continuous exposure (Terry and Duxbury, 1985).
Ryden et al. (1987) compared a chamber method and a core incubation method to
measure denitrification rate. The regression analysis for log-transformed rates showed
that the slope was 1.02 with a 95% confidence interval of 0.95-1.11. Therefore, the
denitrification rate was statistically the same with both methods. Higher rates of
denitrification using the core incubation method have been reported by Aulalch et al.
(1991a). During a period of four days, they found denitrification rates five to seven times
higher with the core method than with 15N-chamber or C 2H2-chamber methods. However,
the denitrification rates obtained from both methods were similar on the second day, when
the water-filled pore space (WFPS) in the soil cores was the similar to that in the chambers.
With the soil core methodology, the denitrification rate obtained involves the total
production of N20-N per unit mass of soil. Hence, this method can effectively be used to
evaluate denitrification as a part of an N balance. In this research, I used a soil coreacetylene inhibition technique to measure denitrification because it is more specific for
assessing N losses from fertilizer in agricultural systems.
Denitrifying Enzyme Activity
Denitrifying enzyme activity (DEA) is a laboratory assay that measures the
concentration of functional denitrifying enzymes in soil samples. The principle of the
method is that the rate of denitrification is proportional to the enzyme concentration when
23
there are no limiting factors; so the soil sample is supplied with excess of organic C and
NO 3 . An anaerobic environment is created by flushing the flask headspace with an inert
-
gas such as N2 or He, and a condition of no diffusion restriction is achieved by shaking the
slurry during the incubation. Acetylene is added to quantify the rate of N2 0 production
over a short period of time (usually 2 to 3 hr), before de novo enzyme synthesis occurs
(Tiedje, 1994). This assay reflects the concentration of denitrifying enzymes at the time of
sampling, and it can be helpful in characterization of soils, in comparative studies between
different soils or soil management practices, or to evaluate the effect of C, N, 0 2 , or other
factors on denitrification (Tiedje et al., 1989).
Main Factors Controlling Denitrification in Soils
Organic Carbon
The organic C content of the soil, derived from organic matter, may control the
rate of denitrification because it is the substrate in the respiration reaction. The decompo-
sition of soil organic matter is important for supplying simple organic molecules to
denitrifiers. Simple molecules, such as soluble carbohydrates and some organic acids, can
be used directly by denitrifiers. On the other hand, complex molecules such as
polysacharides, proteins, lipids, and lignin, need to be decomposed into simpler molecules
such as amino acids, fatty acids, and phenolic acids, before denitrifiers can use them
(Beauchamp et al., 1989).
Crop residues represent the most abundant organic C source in agricultural soils.
Carbon from these residues is available to denitrifiers only after decomposition. Therefore,
24
the nature and the rate of C supply depend on the specific composition of the residue, the
climate of the region, and the soil microbial activity. Aulakh et al. (1984) found that the
addition of 3000 kg ha' of wheat (Triticum aestivum, L.) residue to conventional tilled
plots that received 100 kg N ha-1 [as NH4 (SO 4 ) 2], resulted in 70% more denitrification loss
than fertilized plots without added residue. When the plant residue was applied as mulch
in zero-tillage plots, the accumulated gaseous-N loss increased 90%. However, this
increased denitrification was attributed by the authors to higher water retention (more
WFPS) due to a mulch effect.
The C:N ratio is commonly used to predict the decomposition rate of plant
residues, and in general it is inversely related to denitrification. At high C:N values,
decomposers compete with denitrifiers for NO 3 , while low ratios can result in immediate
-
mineralization-nitrification and more available NO; for denitrifiers. Aulakh et al. (1991b),
found that the denitrification rate in a soil amended with hairy vetch (Vicia villosa, Roth.)
having a C:N= 8, was 102 mg N kg -1 (accumulated over 35 days), whereas in the soil
amended with wheat (C:N= 82) the gaseous-N loss was 70 mg N kg-1 .
In general, there is a direct relationship between soil organic matter concentration
(SOM) and the denitrification rate. However, Burford and Bremner (1975) have shown
that denitrification is significantly more correlated to simpler C forms than to the total
organic C content of the soil. These authors obtained a correlation coefficient (e) of 0.77
between denitrification and total organic C (TOC), while thee with water-soluble organic
C (SOC) was 0.99. McCarty and Bremner (1992) studied the availability of organic C for
denitrification in several soils. A Clarion soil had 1.42% TOC and 21.7 ppm SOC,
25
whereas a Nicollet soil had 2.12% TOC and only 13.0 ppm SOC. When 20 mL of water
extracts from these soils were added to a subsoil sample from the same soil and treated
with 100 jig N-KNO 3 g soit i , the production of N2 0 during 10 days of incubation was
3.40 ps N2 0 g-1 of soil in the Clarion and 1.26 jig N2 0
in the Nicolette. These results
suggested that the denitrification rate was proportional to the soluble organic C, but not to
the total organic C.
The plant root system may influence the denitrification process by stimulating
microbial activity with organic C from root materials and exudates, and also by consuming 0 2 , NO 3 , and water. As a result, a net increase in the denitrification rate due to the
-
presence of plants is commonly reported in the literature (Woldendorp, 1962; Stefanson,
1972; Klemedtsson et al., 1987). For instance, Hojberg et al. (1996) observed a range of
DEA values from 0.05 to 0.39 jig N g -1 11-1 , and the DEA was two times higher in the
rhizosphere of barley (Hordeum vulgare) than in the bulk soil. On the other hand, Haider
et al. (1985) found in corn (Zea mays, L.) and wheat that only 5 to 7% of the root
biomass C was in the soluble fraction. They suggested that the root biomass C was not
available to the denitrifying bacteria, because the denitrification rate was the same in pots
with and without plants.
Inorganic Nitrogen.
The NO 3" content in the soil may control denitrification rate when 0 2 is not
available. The rate of this process follows a substrate dependent or first order reaction if
soil NO 3- is lower than a threshold value of 20 to 25 mg NO 3- -N kg'. That is, NO; will
26
control the denitrification rate when the supply of electron acceptors (e.g., N oxides) is
smaller than the rate of electron production. Conversely, at concentrations of soil NO 3 "
higher than the threshold value, the denitrification rate follows a zero order reaction,
implying that denitrifi cation will be independent of soil NO; content until other factors
limit its rate (Linuner and Steele, 1982; Paul and Clark, 1989).
Weier et al. (1993) reported that at 75% water-filled pore space (WFPS) and no
addition of glucose, denitrification increased from 44 g N ha" c1-1 in unfertilized soil to 124
g N ha" d"' in soil fertilized with 50 kg N ha', and to 87 g N ha"' d"' when 100 kg N ha'
were added. Denitrification in cores with 100 kg N ha" as KNO 3 was limited by the low
availability of organic C, since the addition of 180 kg C ha" increased the denitrification
rate in this soil to almost 9,000 g N ha" d". Similarly, de Klein and van Logtestijn (1996)
reported denitrification rates of 3.0 kg N ha-1 cl-1 when 40 kg N ha" was added to the soil,
and only 2.7 kg N ha4 c1-1 when 80 kg N ha" were applied. According to Myrold and
Tiedje (1985), the effect of added NO 3--N on denitrification rate may be masked by the
native N in the soil; these authors did not find significant increases in denitrification when
100 mg NO;-N kg' was applied to a soil containing more than 20 mg NO;-N
The interactions between the factors influencing denitrification may be responsible
for the wide variability of gaseous losses of N from fertilizer reported in the literature.
Malunood et al. (1998) estimated total denitrification losses of N from fertilizer of 2-3%
from 100 to 200 kg N-urea ha-i applied over a year in a maize-wheat cropping system.
Ryden et al. (1979) reported 15% gaseous losses of 335 kg N ha' applied to celery
(Apium graveolens, var.. dulce). Ryden and Lund (1980) found denitrification N losses in
27
fin-row-irrigated vegetable crops of 14 to 52% of the applied N, when the added fertilizer
was 290 to 660 kg N ha-1 .
Oxygen and Soil Aeration.
When 0 2 becomes limited and cannot be used in microbial respiration, NO 3- is the
main electron acceptor. Lack of 0 2 in the soil atmosphere is mainly related to the water
content. Higher water-filled pore space leads to slower 02 diffusion in the soil because of
the displacement of air from the pores, and because the diffusion of 0 2 in water is 10,000
times slower in water than in air (Aulakh et al., 1992). Sixty percent WFPS has been
reported as a threshold value above which denitrification begins to be detectable (Groffman and Tiedje, 1988). Weier et al. (1993) found denitrification values of 5 g ha-1 d'' in a
sandy soil with 60% WFPS; this rate increased to 210 g ha-1 d-1 in the same soil with a
WFPS of 90%.
When a soil is exposed to periods of dryness and wetness, the denitrification rate
follows the pattern of the water content in the soil. Gro man and Tiedje (1988) reported
that when a soil was being dried, the denitrification rate dropped sharply from saturation
to field capacity, and if the soil was being wetted, the production of N2-N2 0 increased
rapidly when the WFPS was raised from 20 to 60%.
Denitrification in relatively dry soils (less than field capacity) may occur in small
aggregates, which can hold water in small pores, creating anaerobic microsites. In such
conditions, root respiration, microbial respiration, low 0 2 diffusion, and rhizo sphere C
compounds may support the process of denitrification (Knowles, 1981). Lensi et al.
28
(1995) found that 62% of the organic C was accumulated in soil aggregates smaller than
20 pm; the DEA in this soil fraction was 960 ng N2 0-N g -1 h-1 , which is about 20 times
higher than the DEA evaluated in soil fractions of 250 p.m and above.
Temperature
Denitrification is a microbial process involving biochemical reactions, therefore it
increases with temperature above a threshold value. Significant denitrification values are
usually detected above 5°C, and the optimum range can vary from 30 to 67°C, depending
on the temperature regime of the soil (Aulalch et al., 1992). The relationship between
temperature and rates of biochemical processes is commonly expressed as Q 10 values,
which is the proportional change in the rate of the process per 10°C of temperature
increase. A review by Granli and Bockman (1994) indicates that Q 10 values were variable
in different experiments, from 0.1 to 19.5; they also mention that a Q 10 around 2 is
commonly found in biochemical reactions. Very high values of Q 10 may indicate the
influence of other factors, such as increased microbial population with temperature. Maag
et al. (1997) observed Q 10 values from 1.9 to 3.4 for potential denitrification (denitrification rate in soil incubated with N and no C) in a riparian meadow, when evaluated from 5
to 35°C, in 10°C increments. De Klein and van Logtestijn (1996) found an average
denitrification rate in a grassland sandy soil of 811 g N ha-1 d -1 at 10°C, 24 h after adding
10 mm of irrigation water and 80 kg NO 3 -N ha.-1 . When the incubation temperature was
increased to 20°C, the denitrification rate was 3.3 times higher than at 10°C.
29
Denitrification is a complex process influenced by several soil factors. The main
soil controlling factors discussed before are interrelated, and the effect of one will depend
on the status of others. This might be the reason most researchers do not agree on a
single factor controlling denitrification. Instead, the major controlling factor varies
according to specific conditions.
Denitrification Rates with Different Irrigation Methods
The irrigation method influences the denitrification rate by modifying the aeration
status of the soil. When a soil is exposed to periods of extreme wetness and dryness, as in
flood irrigation, the denitrification rate follows the pattern of the water content in the soil.
That is, the denitrification rate increases as the soil changes from dry to saturation after
irrigation; afterwards, the rate decreases as the soil water content declines from saturation
to field capacity (Groffman and Tiedje, 1988). Mahmood et al. (1998) observed bursts of
denitrification up to 600 g N ha' day' in wheat and up to 2500 g N ha' day' in maize,
coinciding with irrigation events.
With pressurized irrigation systems, on the other hand, water is delivered more
efficiently, and crops are usually irrigated more often, thereby reducing the fluctuation
between wet and dry periods. Consequently, lower denitrification rates have been reported
with pressurized irrigation. For instance, Terry et al. (1986) reported denitrification losses
of 16 kg N ha", during a period of 42 days in flood-irrigated plots fertilized with 200 kg N
ha", compared to 3 kg N ha" lost in sprinlder-irrigated plots. Sextone et al. (1985)
evaluated the denitrification rate in N-amended, sprinkler-irrigated fallow soils. The
30
denitrification rate in a sandy loam soil prior to applying 20 mm of irrigation water was 32
ng N g"' d 4 , then increased to 209 ng N g"' 03 4 one hr after irrigation, and 12 hr after the
rate went back to the pre-irrigation value. A similar trend was observed in a clay loam
soil.
Although subsurface drip irrigation has the advantage of greater efficiency than
flooding methods in delivering water and fertilizers to crops, this irrigation system may
enhance soil conditions that promote denitrification. For instance, high soil moisture and
high N occur simultaneously when soluble N-fertilizer is applied through the irrigation
system, and C may be available through plant root exudation and crop residues. Stark et
al. (1983) evaluated N use efficiency in a subsurface trickle-irrigated tomato (Licoper-
sicon esculentum, L.) crop when N rates of 1.8, 3.6, and 5.4 mol N le were continuously
injected at two irrigation rates, 10 and 30 kPa of soil water tension (SWT). Denitrifica-
tion was evaluated only during a four day period at the end of the season. The denitrification rate was low, around 1 mg ni2 s" 1 , in the two lower N treatments, while in the plots
receiving the highest rate of N and water, the rate increased to 6.1 jig ni2 s4 . However,
the unaccounted for N, excluding denitrification losses, varied from 40 kg N ha' (16% of
the applied N) in the 3.6 mol N ni3 and 10 kPa SWT treatment, to 213 kg N ha."' (40% of
the applied N) in the plots with the highest rate of N and water. According to the authors,
most of the unaccounted N may have been lost by denitrification.
Similar results were reported by Thompson and Doerge (1996) in subsurface dripirrigated lettuce. In their study, approximately 40% of the applied N was unaccounted for
when high N and high water levels were applied. This unaccounted amount of N repre-
31
sents losses out of the crop system, caused mainly by NO; leaching and denitrification.
However, the magnitude of N loss from fertilizer specifically due to denitrification with
subsurface drip irrigation has not been quantified.
32
CHAPTER 3
MATERIALS AND METHODS
Field experiments with subsurface-irrigated cauliflower were conducted at the
University of Arizona Maricopa Agricultural Center (MAC) during the 1996-97 and 199798 winter seasons. A similar experiment was conducted during summer 1997 with sweet
corn at the University of Arizona Campus Agricultural Center. In each of the experiments,
drip tubing (Turbulent Twin-wall, outlets every 23 cm, delivering 0.001 L s' rri l at 70
IcPa; Chapin Watermatics Inc., Watertown, NY) was buried 0.15 m deep under the
midline of north-south oriented raised beds. Uniform irrigation was applied until the plant
stands were established (1-2 leaf stage). A tensiometer was installed within each plot at
0.3 m depth to monitor the SWT with a Tensicorder (Soil Measurement Systems, Tucson,
AZ). Water was applied daily to the plots and the irrigation time was programmed with
an automatic controller (Irritrol MC-6, Garden America, Carson City, NV) connected to
solenoid operated valves (UltraFlow 700 series, Hardie Irrigation, El Cajon, CA). The
volume of water applied to each treatment was measured by propeller-type flow meters.
Nitrogen was applied as a solution of calcium ammonium nitrate (CAN-17, 11% NO 3INT
and 6% NH4+-N), injected directly into the irrigation water through venturi-type chemigators (Performance Products, Inc., Coolidge, AZ). Prior to planting each of the experiments, 120 kg P ha-1 as triple superphosphate, was incorporated into the soil.
33
Cauliflower (Brassica oleracea, L. botrytis group) Experiments
Cauliflower (cv. Candid Charm) was grown during the 1996-97 and 1997-98
winter growing seasons at MAC. The experiments were complete factorial experiments
with two SWT levels (low, high), two levels of N fertilizer (zero, adequate) and three
replications in a randomized complete block design. The target SWT levels were designated to provide adequate and excessive water, according to previous research with
cauliflower (Thompson et al., 1998). Average SWT and water applied after stand
establishment are presented in Table 3-1. Water applied for stand establishment was 24
mm in 1996-97 and 173 mm in 1997-98. The 1996-97 experiment had to be re-seeded on
wet beds, so less water was required water for establishment. The N fertilizer was split
into four applications, according to crop growth stage (Table 3-2). Daily extreme
temperatures and precipitation for each of the seasons are illustrated in Figs. 3-1 and 3-2.
Target and average SWT, water applied, and rainfall in the 1996-98
cauliflower growing seasons.
Table 3-1.
Season
Average
SWT
Target
SWT
1996-97
1997-98
Water
applied
Rainfall
mm 1cPa 10
5.2
218
4
4.0
529
10
7.6
322
4
4.0
712
62
121
34
Table 3-2.
Fertilization
Schedule of N fertilizer applications for Cauliflower.
Growth stage
1
1-2
2
4-6
3
10-12
4
Total
leaves
17
First buds
,,
Days after planting (DAP)
Nitrogen
1996-97
1997-98
kg/ha
24
19
40
64
42
60
90
84
110
116
127
90
300
The soil is mapped as a Casa Grande sandy loam [fine-loamy, mixed, hyperthermic,
typic Natriargid (reclaimed)]. This soil is deep and well drained, with accumulation of
calcium carbonate in the subsoil (Post et al., 1988). Some of the soil characteristics are
presented in Table 3-3. Before planting the cauliflower, the experimental field was
cropped with sudangrass (Sorgum sudaneses, L.) for five months without N fertilizer and
under flood irrigation to lower amounts of available N. Cauliflower was direct-seeded on
November 21, 1996 and October 23, 1997 in one row per bed. Plants were thinned to a
final population of 30,000 plants ha- ' at the 2-3 leaf stage. Each experimental plot
consisted of four raised beds, 1.02 m apart by 6.1 m long for a total area of 18.7 m 2 per
plot.
35
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or,
=
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<-
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Mae
kr,
I
I
0
rel
o
N
o
—
(stusTaD) anutiodwai
36
(unu) uoutYncIpaid
trl
tr)
1111••••••••1111111n11•1110....
=NEW
-
---------;-n
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37
Selected properties of the Casa Grande soil, 0-30 cm depth.l.
Table 3-3.
Organic C
Sandi.
Clayt
Bulk densityt
Total
15-22
1.4-1.6
NO3'.
mg kg'mg kg-1
g cm'
55-65
Soluble
0.23
21
1.4
tFrom Post et al. 1988.
At the end of each season, cauliflower marketable yield and total above ground
biomass were measured in 2 in 2 areas from each plot. Individual heads were trimmed and
graded for weight, size, and appearance. The above ground dry matter was determined
after drying the plant samples at 65°C. Subsamples of the dried plants were ground to
pass a 40 mesh sieve for total N analysis (Bremner and Mulvaney, 1982).
After harvest, soil residual inorganic N (NA + and NO 3-) was analyzed in 1M KC1
extracts (Keeney and Nelson, 1982) from samples taken at 0-30, 30-60 and 60-90 cm
depths. A nitrogen balance was calculated using the difference method (Thompson and
Doerge, 1996), according to equation 9:
UN = FN; + WN; - (SINT - SN,,) - (PN; - PN0) - (DN; - DNo)
;
;
(9)
where LTINT; is unaccounted for N in plot i, FN; is fertilizer N applied to plot i, WN; is N
applied in irrigation water to plot i, SN; is residual soil inorganic N (NH4+ + NO 3-) to a
depth of 0.9 m in plot i, SN o is residual soil inorganic N (NH4+ + NO;) in control plots
with no N fertilizer, PN; is N in crop biomass from plot i, PNo is N in crop biomass from
38
control plots, DN is N lost by denitrification in plot i, and DN,, is N lost by denitrification
;
in control plots.
Sweet Corn Experiment
Sweet corn (cv. Sweetie 82) was planted in the summer of 1997 at the Campus
Agricultural Center. The extreme temperatures and precipitation are illustrated in Figure
3-3. Sweet corn seeds were planted in March 21, 1997 directly on the top of raised beds.
Plants were thinned to a final population of 65,000 plants ha"' at the 2 leaf growth stage.
This study was also a complete factorial experiment with two SWT levels (low, high), two
levels of N fertilizer (zero, adequate) and three replications in a randomized complete
block design. Each experimental plot was four beds, 1.02 m apart by 12.2 m long, for an
area of 50.0 ni 2 per plot.
The accumulated water applied and the actual SWT during the sweet corn season
are presented in Table 3-4. The mean actual water tensions were 48 and 30 kPa in the low
and high water treatments, respectively. The soil in this experimental site had characte-
ristics of water repellency (hydrophobic soil). Unlike normal soils, the infiltration rate in
water repellent soils is very slow right after irrigation, and then the rate increases with time
(Wallis and Horne, 1992). We observed in this soil that irrigation times longer than 10 to
12 minutes produced a movement and accumulation of water on the soil surface. It is
possible that the hydrophobic property of this soil repelled the water away from the
ceramic cups in the tensiometers, creating the high SWT registered in this experiment,
without water-stressing the plants.
39
(tuw) uopreTdpaid
o
00
V")
N
V')
o
•••••n
O
en
cs1
(sn!spD) anneiadulai
o
40
Target and average SWT, water applied, and rainfall in the 1997 sweet
corn growing season.
Table 3-4.
Target
Average
SWT
SWT
lcPa
10
4
Water applied
Rainfall
mm
48
379
30
460
22
The N fertilizer was split to in four applications, according to the crop growth
stage (Table 3-5). An extra fertilization with 70 kg ha ' was applied two days after harvest
-
so that we could measure denitrification rates at the end of the season. The soil in this
experimental site has a fine sandy loam texture and is classified as the Gila series (loamy,
calcareous, thermic, Typic Torrifluvent). Some properties of this soil are shown in Table
3-6 (Al-Jabri, 1995).
Schedule of N fertilizer applications according to crop growth stage.
Table 3-5.
Fertilization
Growth stage
DAP
Nitrogen
kg/ha
1
Emergence
16
30
2
4-leaf
31
30
3
9-leaf
57
70
4
tassel
68
70
Total
200
41
Table 3-6.
Selected properties of the Gila soil.
Organic C
Bulk
Sandt
g
Silft
Clayt
38
Total
cm-3%
%
52
density
10
1.48
0.61
Soluble
NO 3"--N
mg kg-1mg kg- '
47
5.7
IFrom Al-Jabri, 1995.
At the end of the season, marketable yield was evaluated in 2 m2 areas and above
ground biomass was evaluated in 4 m2 areas from each plot. Individual ears were graded
for weight, size, and appearance. The above ground plant samples were dried at 65°C to
evaluate dry matter accumulation. Subsamples of the dried plants were ground to pass a
40 mesh sieve for total N analysis (Bremner and Mulvaney, 1982).
Soil residual inorganic N (N114+ and NO 3-) was analyzed after harvest in 1M KC1
extracts (Keeney and Nelson, 1982) from samples taken at 0-30, 30-60 and 60-90 cm
depth. A nitrogen balance was calculated using the difference method (Thompson and
Doerge, 1996), as described previously.
Evaluation of Denitrification and Related Measurements
Field Sampling and Core Incubation.
The denitrification rate was evaluated by the acetylene inhibition technique in soil
cores, as described by Ryden et al. (1987), and Mosier and Klemedtsson (1994). Two
soil cores from the top of beds were taken in each plot with a split core sampler (Art's
Manufacturing and Supply, Inc. American Falls, ID) on the sampling dates shown in
42
Tables 3-7 and 3-8. In the 1996-97 cauliflower season and in the sweet corn experiment,
the cores were taken from the top 15 cm of soil. In the 1997-98 cauliflower season, the
soil cores were taken from a depth of 8 to 23 cm, discarding the top 8 cm of soil. A
plastic sleeve (15.2 cm long by 5.1 cm in diameter) fitted inside the auger was used to
keep the soil core minimally disturbed during the incubation. The intact soil cores were
individually placed in 1 L incubation jars with two rubber septa fitted in the lid. Forty rnL
of air were drawn out each jar and replaced with 40 mL of acetylene to reach a final
concentration of 7 to 10% (v/v), depending on the actual size of the core and the moisture
content. The second septum was used to check for leaks with a Tensicorder (Soil Mea-
surement Systems, Tucson, AZ) while drawing out 40 mL of air. The jars were incubated
at ambient temperatures inside cardboard boxes for 24 hours. At the end of the incubation
a 40 mL gas sample was taken and analyzed for N 2 0 by gas chromatography (GC).
During the 1997-98 cauliflower season, four cores per plot were taken to evaluate the
effect of incubation temperature on denitrification rate. Two of the cores were incubated
at ambient temperature and the other two at room temperature (24 ±2 °C).
GC System Description.
Nitrous oxide concentration in gas samples from the 1996-97 cauliflower experiment and from the sweet corn experiment were determined using a Varian 3400 GC
(Varian Instruments, Palo Alto, CA). Samples from the cauliflower 1997/98 season were
43
Sampling dates for the evaluation of denitrification and extreme temperatures during the soil incubation in cauliflower 1996-97 and 1997-98 seasons.
Table 3-7.
Days
after
planting
Date
Daily
Daily
Maxim.
Minim.
temp.
temp.
- - -
°C
Fert. no.
Sampling
time
- - -
1996-97
12-18-96
24
17.7
-2.7
12-19-96
25
12.5
-4.4
01-27-97
64
20.2
3.9
01-28-97
65
20.4
3.0
02-22-97
90
21.7
-2.0
02-23-97
91
22.0
-0.7
03-20-97
116
35.2
8.7
03-21-97
117
34.5
11.0
11-11-97
19
23.0
13.6
11-22-97
30
24.6
3.2
12-04-97
42
18.8
1.6
12-18-97
56
21.1
-0.4
01-16-98
84
20.9
7.9
02-20-98
119
12.1
6.7
02-28-98
127
16.6
1.6
1
3h
24 h
2
3h
24h
3
3h
24h
4
3h
24h
1997-98
23.3
145
03-18-98
THours (h) or days (d) after the previous fertilization.
7.4
1
3h
24 d
2
3h
11 d
3
3h
35d
4
3h
18 d
44
Table 3-8. Sampling dates for the evaluation of denitrification and extreme temperatures
during the soil incubation in sweet corn 1997.
Date
Days
after
planting
Daily
Maxim.
temp.
Daily
Minim.
temp.
Fert. no.
Sampling
time'
---°C--04-09-97
17
20.6
9.3
1
24 h
04-24-97
32
21.0
4.4
2
24 h
04-25-97
33
25.1
10.3
05-20-97
58
32.4
14.2
3
24 h
05-31-97
69
40.0
14.6
4
24 h
06-02-97
71
38.7
16.8
38.5
19.5
95
06-26-97
THours after the previous fertilization
48 h
72 h
5
24 h
analyzed using a Shimadzu 14A GC (Shimadzu Corporation, Tokyo, Japan). In both
cases, a 'Ni-electron capture detector (ECD) heated to 300°C was used to quantify N2 0
in the samples. Ultra high pure nitrogen was used as carrier gas at a flow rate of 50 mL
mind . Two stainless steel columns (2nun i.d. x 3.05m) packed with Porapak Q, 80/100
mesh (Supelco , Bellefonte, PA) were fitted inside the GC oven and kept at a constant
temperature of 70°C (Figure 3-4). The inlet end of the first column was connected to a 6port electrically actuated sampling valve (Valco Instruments Co. Inc. Houston, TX)
fitted with a 1 mL sample loop, and the outlet end was attached to a 4-port electrically
actuated valve. The second column was plumbed at the inlet to the 4-port valve, with the
outlet end connected to the ECD. A second line of carrier gas was connected to the third
port in the 4-port valve, while the last port was vented out of the GC. When a sample was
injected, the carrier line 1 pushed the sample to the first column, which is vented out of the
45
Carrier # I
Position A
Position B
Figure 3-4. Diagram of the two porapak columns and the two position of the
4-port valve inside the GC oven.
46
GC with the 4-port valve in position A. At the same time, the carrier line 2 was flowing
through the second column and then to the ECD. When oxygen (0 2) and carbon dioxide
(CO 2) were separated and vented out of the first column (approximately 1.7 min), the 4port valve was actuated to position B to send the N 2 0 to the second column and then to
the ECD; in position B, the carrier line 2 was vented out in the 4-port valve. After all the
N2 0 passed to column 2 (in approximately 35 seconds), the 4-port valve was switched
back to position A to vent all the components in the sample separated after N 2 0, including
C 2H2 , and to be ready for the next sample. The N2 0 retention time was around 3.4 min
and samples were injected every 10 to 12 minutes.
The concentration of N2 0 was calculated from certified standards containing 100,
500, and 1000 ppb (v/v) N2 0 in N2 (Scotty Specialty Gasses, Inc. Plumbsteadville, PA).
For samples with high concentrations of N 2 0, a standard curve between 10 and 1000 ppm
(v/v) N20 was made by diluting a standard concentration of 1000 ppm (v/v) of N2 0 in N2 .
Calculation of Denitrification Rate.
The mass of N2 0 produced from denitrification was calculated by subtracting the
ambient concentration of N2 0 (ppb) from the N2 0 in the jar after 24 hr of incubation,
according to equation 1:
N2 O h = (N 2 0 N20 ainh) * 10 -9 * HSV * DN2o
(1)
where N 2 O h is mass of N2 0 in the headspace, produced from denitrification (g), N 2 0i is
concentration of N2 0 in the incubation jar (ppb), N 2 0 ainh is ambient concentration in
samples from the experimental field (ppb), HSV is headspace volume in the incubation jar
47
(L), and DN20 is density of N2 0 (1.931 g L-1 at 25°C; Lide, 1998). Headspace volume was
calculated by equation 2:
(2)
HSV = 1 - (SV + SWV)
where SV is soil volume (L) and SWV is soil water volume (L), evaluated gravimetricaly.
The N2 0 produced by denitrification was corrected for the amount of N2 0
dissolved in the soil solution, calculated by the Bunsen coefficient (Tiedje, 1994):
N 2O w = N 2O h * b *
SW"
HSV
(3
)
where N2 0„ is mass of N2 0 (g) dissolved in the soil solution, and b is solubility of N2 0 in
water (mL N 2 0 mL water-1 ): 0.63 at 20°C for cauliflower and 0.41 at 35°C for sweet corn.
Finally, the total N2 0 from denitrification (N2 0 d = N2Oh + N2 0) was transformed
to molar N fraction (N2 0-N) and expressed on a gravimetric basis using equation 4:
N 2 0 d (g N 2 0 - N g
N20d (g N 2 0 g soil -1 ) * 0.635
wg of dry soil
(4)
The denitrification rate was then converted to g N20-N ha-1 day' by using the weight of
soil in a hectare to 0.15 m depth with an assumed bulk density of 1.5 Mg nf3 :
N20d
(g N2 0-N ha-1 d -1 ) = N2 0 d (g N20-N g soil -1 ) * 2.25x10 9 g soil ha- '
(5)
After incubation and gas sampling, the soil cores were oven dried at 65°C and
ground. Inorganic N (NH4+ and NO 3-) was extracted with 1 M KC1 (Keeney and Nelson,
1982). The water filled pore space in the soil cores was estimated by:
48
WFPS
eg * Db
(6)
where Ei g is gravimetric water content (gig), Db is soil bulk density (g cm-3 ), D p is soil
particle density (2.65 g cm-3 ).
Denitrification losses of N throughout the season were estimated by multiplying
the denitrification rate (g N2 0-N ha' d ') times half the number of days between two
-
subsequent sampling dates. The total N lost per season due to denitrification in control
plots was subtracted from the values obtained in fertilized plots to obtain the denitrifica-
tion losses of N from fertilizer.
Cores with Nitrogen and Carbon Amendments
At the end of the 1997-98 cauliflower season, 18 days after the last fertilization,
four cores per plot were taken from each plot to evaluate the denitrification rate when N
and/or C were added directly to the soil cores. Each of the cores received 10 mL of a
solution containing either N, C, or both, according to the treatments shown in Table 3-9,
plus 7% (v/v) C 2H2 . The amount of N added was calculated to simulate a fertilization of
100 kg ha-1 (assuming 0.15 m depth and 1.5 Mg In 3 of bulk density), with the same N
-
source used in the field experiment. The denitrification rate in the cores amended with N
represented the potential denitrification for the actual soil conditions of organic C content
and temperature regime (Maag et al., 1997). The concentration of C was that recommended for the DEA assay, which is supposed to be non-limiting for denitrification. The
49
cores were incubated and sampled following the same procedure described for quantifying
denitrification rate under field conditions.
Concentration of N and C in solutions applied to soil cores.
Table 3-9.
Core
Concentration in solution
Approximate concentration in soil
(avg. wg. of soil core= 300 g)
1
DI water
Control
2
9 g C-Glucose L"
675 kg C ha' (300 ps C g soil")
3
1.5 g N-CAN17 L-1
112 kg N ha" (50 jig N g soil")
4
(9 g C+1.5 g N) L 4
Denitrifying Enzyme Activity
The DEA assay provides an estimate of functional denitrifying enzyme concentration. The principle of the method is to provide all requirements for enzymatic activity
saturation (NO 3-, a carbon source, no oxygen, and no diffusion limitation), so that the rate
of N2 0 production is proportional to the denitrifying enzyme content. The procedure
described by Luo et al. (1996) was followed. Air dry soil samples taken at the beginning
and at the end of the season from the sweet corn and cauliflower (1997/98 season) field
plots were used to evaluate DEA. Twenty grams of air dried soil were placed in 125 mL
Erlenmeyer flasks, with 20 mL of a solution containing KNO 3 and glucose to give
concentrations of 50 gg NO 3 "-N g" soil, and 300 1.1.g glucose-C g" soil. The flasks were
capped with a rubber stopper fitted with two glass tubes. Through these tubes, the air
inside the flasks was flushed and replaced with pure N2 and 5% (v/v) acetylene. The
slurries were incubated at room temperature (24 °C) on a rotary shaker for two hours and
50
the headspace was sampled every 40 min and analyzed for N2 0. The DEA (ng N2 0-N g
11- ') was calculated as the slope of the regression between N2 0 production (ng N2 0N g soil -1 ) and incubation time (hr).
Total and Soluble Organic Carbon
The total (TOC) and soluble organic carbon (SOC) were quantified in the same
samples analyzed for DEA, according to the wet oxidation-0O 2 trap method described by
Snyder and Trofymow (1984). For SOC, 25 g of soil plus 50 mL of water were shaken
gently for 30 minutes in stoppered 125 Erlenmeyer flasks. The extract was filtered with
Whatman paper no. 40, and 20 rnL of each extract were evaporated to about 5 mL and
then vacuum-filtered through a 0.45 gm membrane filter. For TOC, 1 g of air dry soil was
placed directly in oxidation-diffusion tubes. Before the wet oxidation, inorganic CO 32- was
removed by adding 3 mL of 2N H2 SO 4 to the samples and agitating them uncapped in a
reciprocal shaker for 60 min. Wet oxidation was then achieved with 1 g of potassium
dichromate (K2Cr2 0 7) plus 25 mL of a 3:2 mixture of concentrated H2 SO 4 :85% H 3PO 4 .
The oxidation-diffusion tubes were screw-cap culture tubes (25 x 200 mm) modified with
two indentations near the top to hold a vial (1 dram, 15 x 45 mm) containing the CO 2 trap
(1 mL of 2 N NaOH.) After inserting the CO 2 trap, the tubes were placed in a digestion
block for two hours, but the traps were removed and titrated after 12 hr to allow complete
diffusion of CO 2 . Once removed, the NaOH from the trap was diluted to 50 mL in an
Erlenmeyer flask; then four drops of carbonic anhydrase enzyme (1 mg mL-1 of pure
enzyme, Sigma Chemical, Co. St. Louis, Mo) were added to ensure that all the CO2
51
trapped was converted to CO 3 2- . Immediately after, the pH was adjusted to 10 by slowly
adding 1N H 2 SO 4 , then the pH was lowered to 8.3 with 0.05 N H 2 SO 4 while stirring the
solution. Finally, the solution was titrated to pH 3.7 with 0.025 M (for TOC) or 0.0025
M (for SOC) H2 SO 4 . The volume of acid in this last titration step, corrected by the
average volume to titrate blanks, was used to calculate the CO 2 trapped. The TOC and
SOC were calculated using equations 7 and 8 respectively:
TOC (%) = (mL H2SO4— Blank)* N H2SO4*12.01
*100
Sample wg
SOC (mg kg -1 ) = (inL H2SO4— Blank)* N H2SO4*12.01 * 2.5
*1000
Sample wg
(7)
(8)
Statistical Analysis
Most of the variables evaluated were analyzed for statistical significance with SAS
(SAS Institute, 1988) using ANOVA. DEA regression analyses were adjusted to zero
intercept. Denitrification rates per sampling date and accumulated denitrification losses of
N were analyzed for normal distribution with the Shapiro-Wilk's W test (Parkin and
Robinson, 1992; SAS Institute, 1988). The data from sampling dates not showing a
normal distribution were log-transformed (log [1+denitrification] was used if values < 1.0
were present). The Shapiro-Wilk's W test was applied to the log-transformed data to
check for lognormal distribution. When lognormal distribution was significant, the logtransformed data was used for analysis of variance and the averages per treatment of the
actual data were used as the estimated parameter.
52
CHAPTER 4
RESULTS AND DISCUSSION
Cauliflower 1996-97
Denitrification Rate
The denitrification rate was evaluated 11 times during the season in this experiment. The data from five of the sampling dates, most of them in the first half of the
season, followed a normal distribution with coefficients of variation (CVs) in the ANOVA
between 41 and 60%. Only one of the sampling dates had a log-normal distribution, while
the other five sampling dates did not have a normal nor log-normal distribution. The Cvs
of the dates without a defined distribution ranged from 132 to 270% (Table 4-1).
Denitrification is commonly reported as a highly variable process that follows a log-normal
distribution (Parkin, 1987; de Klein and van Logtestjn, 1996; Loro et al., 1997). This
distribution is characterized by a positively skewed frequency due to a large number of
low values and few samples exhibiting high values of denitrification. Statistically, a
lognormal distribution occurs when the logarithm of the variable follows a normal
distribution (Parkin and Robinson, 1992). Parkin (1987) found coefficients of variation
up to 400% in denitrification rate measurements with the soil core incubation methodology; he suggested that the lognormality of denitrification is caused by a patchy distribution
of "hot spots" containing organic residues and high denitrifying activity.
53
Table 4-1.
Distribution and coefficients of variation in the different sampling dates in
cauliflower 1996-97.
Sampling
timet
Sampling
date
Coefficient of
variation 1
Distribution
After
Before
%
12-18-96
-3 h
Normal
51
12-18-96
3h
Normal
46
12-19-96
24h
Normal
57
1-27-97
-3 h
Log-normal
75
1-28-97
24 h
Normal
59
2-22-97
-3 h
None
132
2-22-97
3h
Normal
41
2-23-97
24 h
None
268
3-5-97
10 d
None
162
3-20-97
-3 h
None
203
3-21-97
24h
None
270
52
(h) or days (d) before (-) and after the previous fertilization.
CV before and after log-transformation of data.
T Hours
The effects of N and irrigation levels on denitrification rate were not significant for
any of the sampling dates. The actual values of denitrification were in the range of 0.21 to
18.5 g N2 0-N ha ' d', with 65% of the treatment averages below 1.0 g N20-N ha' d -1
-
(Figure 4-1). The overall mean denitrification per sampling date increased from 0.49
54
100 _
_
_
O 5.2 kPa, 0 kg N
O 5.2 kPa, 300 kg N
L 4.0 kPa, 0 kg N
O 4.0 kPa, 300 kg N
,
•
•
10—
0
-
1 ...
...
0.1
0
20
40
60
80
100
120
140
Days after planting
Figure 4-1. Denitrification rates during the 1996-97 cauliflower growing season.
Open symbols are samples taken three hr after fertilization; solid symbols
are samples taken 24 hr after fertilization.
55
g N2 0-N ha-2 d4 after the first fertilization event to 5.2 g N2 0-N ha-2 d-1 after the last
fertilization, although this difference was not significant.
The denitrification rate was not correlated with WFPS (Figure 4-2B). While
denitrification tended to increase at the end of the season, WFPS decreased from 0.50
after the first sampling date to 0.37 after the last fertilization (Figure 4-2A). There were
no significant differences between water levels; average WFPS in cores taken 24 hr after
fertilization were 0.44 and 0.42 in the low and high water levels, respectively. The
application of N significantly reduced the WFPS of soil cores sampled 24 hr after fertilization. Mean WFPS values were 0.46 and 0.40 in control and fertilized plots. In these
plots, the greater canopy induced by the added N might have depleted the water in the top
soil. The WFPS values in this experiment are lower than threshold values reported
elsewhere, such as 82% for sandy soils (de Klein and van Logtestijn, 1996) and 60% for
clay loam soils (Sextone et al., 1988). Values of 42-55% WFPS were also proposed as a
threshold value in loamy soils (Klemedtsson et al., 1991). The WFPS in this experiment
was low because the cores were taken from the top 15 cm of soil and, since the water was
delivered at 15 cm depth, the top 2-3 cm of soil were always drier than the soil closer to
the drip tubing.
Nitrate concentration was significantly higher in the fertilized plots, and the
highest values were obtained after the third fertilization, with mean concentrations of 15.6
and 7.8 mg NO 3"--N kg-1 in the fertilized and control plots, respectively. Nitrate concentrations after the fourth fertilization were very low in all treatments (Figure 4-3A). The NO 3 -N concentrations in the soil cores did not correlate with denitrification rate (Figure 4-3B).
56
4.0 kPa, 0 kg N
5.2 kPa, 0 kg N
4.0 kPa, 300 kg N
5.21(13 a, 300 kg N
100 _
B
O 5.2 kPa, 0 kg N
O 5.2 kPa, 300 kg N
,L, 4.0 kPa, 0 kg N
O 4.0 kPa, 300 kg N
10 .7--
A
0
A
Oa
o
0
0.1
0.25
o
a
0L\
E
A
0.3
0.35
0.4
O
o
0
0.45
0.5
WFPS
Figure 4-2. Relationship between WFPS and denitrification rate in cores
taken 24 hr after fertilization. Cauliflower 1996-97.
0.55
57
15
4.0 kPa, 0 kg N
5.2 kPa, 0 kg N
4.0 kPa, 300 kg N
5.2 kPa, 300 kg N 100 .
A
3
k- - •
B
E 5.2 kPa, 0 kg N
O 5.2 Oa, 300 kg N
A 4.0 kPa, 0 kg N
<> 4.0 kPa, 300 kg N
0
A
0 A
<> 0
0 <>
<> E 0
O
0
O A
0.1
0
I
1
I
2
I
3
I
4
5
6
7
NO3-N (mg/kg soil)
Figure 4-3. Relationship between nitrate and denitrification rate in cores
taken 24 hr after fertilization. Cauliflower 1996-97.
8
58
Lack of response of denitrification to additions of N have been reported in the literature.
For instance, Weier et al. (1993) observed denitrification values between 7 and 13
g N ha-1 d -1 in different soils incubated with no added N and 60% WFPS, while the
addition of 100 kg N ha-1 resulted in denitrification rates from 2 to 5 g N ha-1 d-1 .
Similarly, Myrold and Tiedje (1985) found no differences in denitrification rate of
incubated soils with and without the addition of 100 mg NO;-N kg-1 . Lack of response of
denitrification rate to NO; suggests that some other factor may have been limiting the
process.
One factor responsible for the low rates of denitrification was temperature. The
minimum temperature during the incubations after the first and third fertilizations was
<0°C, and only at the fourth fertilization was the minimum temperature above 5°C (Table
3-5). The effect of temperature on denitrification has been documented in laboratory
incubations as well as in field experiments. De Klein and van Logtestijn (1996) reported a
ten fold increase in denitrification rate, from about 70 to 700 g N ha-1 d-1 , in soil cores
incubated at 10 and 20°C, respectively. Under field conditions, Mahmood et al. (1998)
found denitrification rates below 20 g N ha-1 d-1 most of the season (from November to
April) in a wheat crop; maximum denitrification peaks in this season were up to 600 g N
ha-1 d-1 . The same site was cropped with maize after wheat (from August to October), and
the denitrification rate was above 100 g N ha-1 (14 at most of the sampling dates, with
maximum peaks up to 2400 g N ha-1 d-1 . The mean soil temperature was < 20°C most of
the wheat season and > 30°C most of the maize season.
59
Yield
The unfertilized plots had no marketable yield. The fertilized plots, on the other
hand, yielded 9.8 and 10.7 Mg ha-i in plots receiving low and high water. The head
diameter was not affected by irrigation treatment; the average head diameter in the low
water level was 9.7 cm and 10.1 cm in the plots with high water. The above ground
biomass was higher in the fertilized plots with an average of 7.3 Mg ha-1 , while the
unfertilized plots yielded 1.6 Mg ha'. The effect of water level on biomass production
was not significant (Table 4-2). The cauliflower marketable yield was lower than the state
average for the same season (20 Mg ha') and than previous experiments with subsurface
cauliflower in the same soil (Thompson et al., 1998). They reported 17 to 24 Mg ha.'
during the 1994-96 growing seasons, in plots receiving 300 kg N ha4 and optimum to
excessive water. The low yield in our experiment was possibly caused by a delay in crop
growth and development, since the cauliflower had to be re-seeded on November 21.
Table 4-2.
Total biomass, marketable yield, and head diameter in cauliflower 1996-97.
Average
SWT
fertilizer
Total dry biomass
Marketable yield
Head diameter
kPa
kg ha- '
Mg haT 1
Mg ha- '
cm
5.2
0
1.62b
0
5.2
300
6.66 a
9.82 NS
4.0
0
1.56b
0
9.7 NS
10.1 NS
10.73 NS
8.02 a
4.0
300
Within columns, values followed by the same letter are not significantly different at P<0.05 (Tukey's
HSD). NS, not significant.
60
Nitrogen Balance
The total N concentration in plant tissue samples was affected by the N fertilizer
rate. In the unfertilized plots, plant total N was not different between water levels and the
average was 1.1%. Plants with N fertilizer and low water showed a significantly higher
plant total N than the high water treatment (Table 4-3). The total residual N (NO 3 - +
NH4 ) to a depth of 0.9 m was higher in the fertilized plots with low water, averaging 131
kg N ha- ', than in the plots with high water (Table 4-3).
Table 4-3.
Average
SWT
kPa
Nitrogen balance and unaccounted for N in cauliflower 1996-97
N
fertilizer
Residual
soil N
Crop N
kg ha-1%
N lost by Unaccounted
denitrif.
N
kg ha-1kg ha."'
kg ha- '
5.2
0
1.01 c
16.3 b
67.0 c
0.09 NS
5.2
300
3.30a
216.0 a
131.2a
0.36
4.0
0
1.15 c
17.9 b
61.3 c
0.55
kg he
35.9 NS
60.4
0.09
106.9 b
212.4 a
300
2.63 b
4.0
Within columns, values followed by the same letter are not significantly different at P<0.05 (T'ukey's
HSD). NS, not significant.
The total amount of N lost during the season by denitrification was not significantly affected by N-fertilizer or soil water tension. The overall mean was 0.27 kg ha.-1
(Table 4-3, Figure 4-4). Denitrification losses of N were very low as a result of the low
denitrification rates during the season. These losses represented <1% of the applied N.
Similar values of denitrification N losses were reported by Terry et al. (1986).
61
0.6 SWT: 5.2 KPa
ri 0 kg N/ha
o
Q
E3 300 kg N/ha
0.4 -
.4-o
E.)
o
z 0.2 .174
64
24
90
116
139
Days after planting
SWT: 4.0 KPa
7 0 kg N/ha
0 300 kg N/ha
FT77:0777i
-
64
90
116
139
Days after planting
Figure 4-4. Denitrification losses ofN in control and fertilized plots. Caulflower 1996-97
62
They found 0.6 to 1.5% of N fertilizer was lost by denitrification in bare sprinkler-irrigated
soils during a 42 day period between June and August.
The unaccounted N was not different between water levels (Table 4-3). The mean
values were 36 and 60 kg N ha:' in the fertilized plots with low and high water, respectively. The unaccounted N in this experiment was lower than the values reported by Pier
and Doerge (1995) in watermelon. Using the same irrigation method in the same soil,
they found approximately 70 and 100 kg ha' of unaccounted N in plots subjected to 4 and
7 kPa of soil water tension, respectively, both receiving 300 kg N ha-l .
Cauliflower 1997-98
In this experiment, the soil cores for denitrification were taken from a depth of 8 to
23 cm, approximately, with the drip tubing buried at 15 cm deep. This procedure was
followed in order to sample that part of the root zone where denitrification would be most
important. To evaluate the effect of incubation temperature on the denitrification rate, this
season we compared the denitrification rate in cores incubated at ambient versus room
temperature. At the end of this season, the denitrification rate was measured when 100 kg
N ha- ', with or without additional organic C, was added directly to soil cores. With this
procedure, the potential denitrification for this soil was estimated. Also, organic C and
denitrifying enzyme activity were evaluated at the beginning and end of this season.
63
Denitrification Rate.
In this experiment there were eight sampling events. In four of the dates, the
samples were taken approximately 3 hr after each fertilization event, and the other four
dates were between two fertilization events. Denitrification in field-incubated cores
followed a normal distribution in four of the sampling dates, with CVs between 33 and
82%. Three sampling dates showed a lognormal distribution and the denitrification rate
was transformed by log(l+denitrification) prior to analysis of variance. The Cvs of the
original data ranged from 100 to 133%, and decreased to 41 to 55% after log-transforma-
tion (Table 4-4). The data from room-temperature incubated cores had a normal distribution on three of the sampling dates, with CVs between 22 and 46%. Log-normal distribution was observed in four sampling dates with CVs from 27 to 61 after log transformation.
In general, the CVs found in this season were smaller than in the previous one. An
increase in WFPS of the cores taken during the 1997-98 season may be the cause of the
reduced variability. Loro et al. (1997) found CVs of 121% for denitrification rate
evaluated in the fall, and 419% in spring. Volumetric water content was 26.6 to 29.6% in
the fall, and 14.6 to 25.5% in the spring.
The denitrification rate in cores incubated at ambient temperature averaged less
than 2.0 g ha."' d"' during the first half of the season. After the third fertilization, the
denitrification rate increased in all the treatments but was more noticeable in the fertilized
plots (Figure 4-5A). The fertilized plots averaged 7.2 and 11.6 g N ha' d"' for low and
high water treatments, respectively, during the second half of the season. The mean
denitrification in the unfertilized plots was 2.9 g N ha"' (1 4 . However, these differences
64
Table 4-4.
Sampling
date
Frequency distribution, coefficients of variation, and statistical significance
in the cauliflower 1997-98 experiment.
Sampling
time
Coefficient of
variation
Distribution
Before
After
Statistical significance
Water
Nitrogen
%
Field incubation
11-11-97
3 h
Normal
82
NS
NS
11-22-97
11 d
Normal
39
*
NS
12-04-97
3 h
Lognormal
100
NS
NS
12-18-97
14 d
Normal
33
NS
NS
01-16-98
3 h
Normal
44
NS
NS
02-20-98
35 d
Lognormal
133
41
NS
NS
02-28-98
3 h
Lognormal
126
46
NS
NS
134
62
NS
NS
NS
*
03-18-98
18dNone
55
Room incubation
11-11-97
3 h
Normal
46
11-22-97
11 d
Lognormal
127
61
NS
NS
12-04-97
3 h
Lognormal
94
30
NS
NS
12-18-97
14 d
Normal
22
NS
*
01-16-98
3 h
Normal
38
NS
**
02-20-98
35 d
Lognormal
70
27
NS
*
02-28-98
3 h
None
142
37
NS
*
35
213
Lognormal
18d
03-18-98
THours (h) or days (d) after the previous fertilization.
CV before and after log transformation of data.
** Significant at Ps 0.05 and 0.01, respectively; NS, not significant.
NS
NS
65
(Wetittsl OzN 3) ow uope3 T-Illuga
-
66
between N levels were not significant because of the high variability. The effect of water
level was significant only on the second sampling date at ambient temperature.
Denitrification during this season followed the same trend as the previous season,
with lower rates at the beginning and increasingly higher toward the end of the season.
However, denitrification was higher in the 1997-98 experiment (Figures 4-1 and 4-5A).
Two main factors causing this increased denitrification were the ambient temperature
during incubation periods and the WFPS in the incubated soil cores. During the 1997-98
study, the minimum ambient temperature during the incubation of soil cores was < 0°C
only in one of the sampling dates, and half of the sampling dates had minimum temperatures > 5°C (Table 3-6). During the 1996-97 experiment, half of the sampling dates had
minimum incubation temperatures < 0°C, and only the last two sampling dates had
minimum temperatures above 5°C (Table 3-5).
The water-filled pore space in the soil cores was also higher in the 1997-98
experiment. The main reason for this was that the drier top 8 cm of soil in each sampling
point was discarded before taking the core for denitrification measurement. The soil core
was then taken from 8-23 cm deep, while the drip tubing delivered the water at 15 cm.
The average value of WFPS ranged from 0.60 to 0.63 in the low water treatment and from
0.59 to 0.69 in the high water treatment (Figure 4-6A). However, these differences
between irrigation levels were not significant. Water-filled pore space did not correlate
with denitrification rate (Figure 4-6B). Most of the VVFPS values were above the 0.60
67
i
7.6 kPa, 0 kg N
4.0IcPa, 0 kg N
4.0 kPa, 300 kg N
7.6 kPa, 300 kg N
7
E 7.6 kPa, 0 kg N
B
0 7.6 kPa, 300 kg N
A 4.0 kPa, 0 kg N
0 4.0 kPa, 300 kg tn
0
0
0
0
0
A
A
0
_I
0
A
0
1
0.55
0.6
0.65
WFPS
Figure 4-6. Relationship between WFPS and denitrification rate in cores
taken 3 hr after fertilization. Cauliflower 1997-98.
0.7
68
threshold cited by some authors (Sextone et al., 1988; Granli and Bocicman, 1994),
nevertheless, the denitrifi cation rate remained very low, probably limited by temperature.
When the cores were incubated at room temperature (24°C), the denitrification
followed the same trend as the field incubation but the rates were significantly higher
(Figure 4-5B). The mean rate during the first half of the season was 10.1 g N ha"' d -1 ,
which was 5 times higher than the denitrification evaluated at ambient temperature for the
same period. During the second half of the season, the fertilized plots had significantly
higher rates in most of the sampling dates. Maximum values of denitrification were
observed in the last sampling date, with average values in the fertilized plots of 686 g N
ha"' d'' compared to 32 g N ha.' d'' in the control plots (Figure 4-5B). The effect of water
level was not significant at any of the sampling dates. On the other hand, the effect of N
was significant in five of the eight sampling dates (Table 4-4).
The transformed values of denitrification obtained at ambient and room tempera-
ture were significantly correlated by the linear equation:
log(l+denitrification),.= 1.34 * log(l+denitrification) fied + 0.28;
(9)
Although the correlation was significant according to the F test for the regression analysis,
the r2 was only 0.51 (Figure 4-7). These results indicate that denitrification was limited by
the low temperatures typical of the winter season in southern Arizona. Also, the effect of
added N was evident when incubation was done at room temperature and the limiting
effect of colder ambient temperatures was eliminated. The response of denitrification to
incubation temperature in this experiment is similar to that reported by Colbourn
69
3
D
O
•
O
7.61cPa, 0 kg N
7.6 kPa, 300 kg N
4.0 kPa, 0 kg N
4.0 kPa, 300 kg N
-
0
0.0
I
0.5
I
1.0
1.5
Log(l+den. rate in g N20-N/ha/d) Ambient incubation
Figure- 4-7.
Regression analysis of denitrification rate evaluated at ambient
versus room temperature. Cauliflower 1997-98.
70
(1993) who also found a five-fold increase in denitrification rate when cores were
incubated at room temperature.
The nitrate content in the soil cores colleted 3 hr after fertilization was correlated
with the denitrification rate (Figure 4-8B). However, the range of NO 3- concentration
was very wide, from 1.5 to 87 mg NO 3- -N kg-1 , whereas the range of denitrification was
from 1.5 to less than 6 g N2 0-N ha"' c1 -1 . The NO 3" concentration was low after the first
fertilization, averaging 2.0 mg NO 3--N kg' in the fertilized plots. Nitrate in the soil cores
increased to 41 and 55 mg NO 3--N kg' after fertilizations two and three, respectively
(Figure 4-8A). However, these averages were not statistically different from the unfertilized plots.
Carbon and Nitrogen Amendments
Denitrification rates in cores collected at the end of the season and amended with
N and C are shown in Figure 4-9. Denitrification was affected by the amendment solution,
by the field water treatment, and by the amendment x water interaction. Denitrification in
cores amended with C or N only did not differ significantly from control cores. The
average rate in control cores and in C-treated cores was 9.7 g N 20-N ha' d- ', while the N-
treated cores averaged 13 and 44 g N2 0-N ha."' d -1 in cores with low and high water levels,
respectively. The denitrification rate in cores amended with N and incubated at ambient
temperature represented the potential denitrification for the actual soil conditions of
organic C and temperature. The potential denitrification was 2 to 4 times higher than the
average denitrification rate measured at ambient temperature during the second half of the
71
100
4.010a, 0 kg N
7.6 kPa, 0 kg N
4.0 kPa, 300 kg N
7.610a, 300 kg N
Y = 0.039*X + 2.21; rA2 = 0.62
E 7.6 kPa, 0 kg N
O 7.6 kPa, 300 kg N
,L 4.0 kPa, 0 kg N
O 4.0 kPa, 300 kg N
0
20
40
60
80
NO3-N (mg/kg soil)
Figure 4-8. Relationship between nitrate and denitrification rate in cores
taken 3 hr after fertili7ation. Cauliflower 1997-98.
100
72
Control
Carbon
Pir Nitrogen (Potential denitrification)
•C+N
7.6 kPa, 0 kg N
4.0 kPa, 0 kg N
4.0 kPa, 300 kg N
7.6 1cPa, 300 kg N
Field treatments
Figure 4-9. Denitrification rate in soil cores amended with N and C
Cauliflower 1997-98
73
season. However, the potential denitrification was < 10% of the denitrification rate
measured at room temperature in the second half of the season. Therefore, temperature
limited the potential denitrification in this soil during the winter season.
When the cores were amended with C+N, the average denitrifi cation rate was 950
g N2 0-N ha4 cr' in cores with the low water level, and 3500 g N2 0-N ha"' d"' in the cores
with high water. Similar results were found by Weier et al. (1993) and Artiola and Pepper
(1992). This response indicates that both C and N limited denitrification. However, under
field conditions and after applying N fertilizer to the soil, organic C would be the limiting
factor. Burton and Beauchamp (1985) found that concentrations of soluble organic C
higher than 60-80 .tg C g soir l are necessary to maintain denitrifier activity. Nitrogen
addition did not increase the denitrification rate significantly because the soil used in this
experiment had only 25 fig C g soir' in soluble form at the end of the 1997-98 season. On
the other hand, C alone did not increase the denitrification rate over the control cores
treated with water only, not even in cores from fertilized plots, which had a mean NO;
concentration of 3.0 fig N g soir'. Some authors mention a threshold value of 20-25 .tg
N-NO; g soir l (Limmer and Steele, 1982; Paul and Clark, 1989) below which the
denitrification rate depends on NO; concentration. The low NO; in cores from fertilized
plots was probably caused by a leaching effect of the amendment solution, since 10 mL of
each solution were added over an area of 20 cm' and most of the cores drained some
excess water. Also, the samples for the amendment study were taken 18 days after the
last fertilization of 90 kg ha-1.
74
The denitrification rate was significantly higher in cores from the high water
treatment (Figure 4-9). These cores had higher WFPS, with an average of 0.57 compared
to 0.49 in the low water level.
Organic Carbon
Total and soluble organic C concentration were analyzed in samples at the
beginning and at the end of the season. All the plots had the same TOC irrespective of the
water and N treatments, and it did not increase at the end of the season. The mean TOC
was 0.23% at the beginning of the season and 0.24% at the end. Soluble organic C was
not different between treatments, but it significantly increased at the end of the season
from 21 to 25 gg C g soil' (Table 4-5). The SOC values in this experiment were in the
range of 9 to 259 gg C g soil' reported by Burford and Bremner (1975) in 17 soils from
Table 4-5. Concentrations of total (TOC) and soluble (SOC) organic carbon.
Cauliflower 1997/98.
TOC
Average
SWT
fertilizer
kPa
kg ha'
7.6
0
7.6
beginning
of season
end
of season
SOC
beginning
of season
end
of season
gg C g soil -1
%
0.23 NS
0.24 NS
19.9 NS
23.7 NS
300
0.23
0.26
22.4
25.1
4.0
0
0.23
0.22
22.0
24.6
4.0
300
0.22
0.24
20.4
26.1
Within columns, values followed by the same letter are not significantly different at P<0.05 (Tukey's
HSD). NS, not significant.
75
Iowa. However, all SOC concentrations were lower than the minimum value of 60-80 pg
C g soil -1 , reported by Burton and Beauchamp (1985), required to maintain a measurable
denitrification rate.
Denitrifying Enzyme Activity
This laboratory assay was performed to compare the concentration of functional
denitrifying enzymes in soil samples taken at the beginning and at the end of the season.
The principle of the method is to provide a soil sample with excess of C and N, anaerobic
headspace, and adequate temperature, so that the denitrification rate is proportional to the
enzyme concentration without limiting factors.
The DEA evaluated at the beginning of the season was the same in all the plots,
with an average of 5.8 ng N2 0-N g soil-1 114 (314 g N2 0-N ha-1 d-1 ). At the end of the
season, however, the DEA was significantly higher and was affected by the field N
treatment. The soil samples from fertilized plots had a mean DEA of 20 ng N 2 0-N g soil -1
hi' (1105 g N20-N ha-1 d-1 ), whereas the DEA in unfertilized plots was 7.6 ng N 2 0-N g
soil' hr-1 (Figure 4-10). The increase in DEA at the end of the season might be caused by
the presence of plant roots; the same effect has been reported by Woldendorp (1962), and
Stefanson (1972). The DEA values in our experiment were very low compared to the
results of Lensi et al. (1995). In a Mollisol, they found DEA values of 144 ng N 2 0-N g
soil -1 lir-1 in cultivated areas and 700 ng N 2 0-N g soil -1 hr-1 in areas with permanent
pasture. Sotomayor and Rice (1996) found lower DEA values in an Entisol. When
measured in spring, the DEA was 0.06 ng N2 0-N g soil -1 hr-1 and increased to 5.38 ng
76
Before fert. 1
60-
O 7.6 kPa, 0 kg N
O 7.6 kPa, 300 kg N
,L 4.0kPa, 0 kg N
O 4.0 kPa, 300 kg N
MI
0
1
2
Incubation time (hr)
1
2
Incubation time (hr)
Figure 4-10. Denitrifying enzyme activity at the beginning and end of
the 1997-98 cauliflower season.
77
N 2 0-N g soil -1 hr"' in samples taken in the fall. In our experiment, the higher values of
DEA and SOC at the end of the season might be responsible for the increased denitrification rate toward the end of the season.
Yield
The fertilized plots yielded 9.8 and 15.0 Mg ha"' in plots with low and high water
treatments, respectively. This difference was significant only at a 90% probability level.
The unfertilized plots did not have any marketable yield. The average head diameter was
13.1 cm and was not affected by irrigation treatment. The above ground biomass was
higher in the fertilized plots with an average of 5.4 ton ha-1 , while the unfertilized plants
yielded 1.8 ton ha'. The effect of water level on biomass production was significant with
a confidence level of a= 0.07. In both of the N levels, the above ground biomass was
higher in the plots under low water than in the plots with high water (Table 4-6). The
marketable yield obtained this season in the fertilized plots and high water level was
similar to that obtained during the previous season. The plots with low and high water
levels received approximately 100 and 200 mm more water this season than during 199697, because the planting date was one month earlier.
Nitrogen Balance
Table 4-7 summarizes the N balance in the 1997-98 cauliflower experiment. The
differences in N removed by the crop were caused by higher biomass production (Table 46) and higher percentage of total N in the plants receiving the low water treatment (Table
4-7).
78
The total N concentration in plant tissue was affected by irrigation treatment, by N
fertilizer, and by the irrigation x N interaction. In the unfertilized plots, plant N content
was 1.3%. Plant N content in fertilized plots was higher, and was significantly affected by
irrigation treatment. (Table 4-7).
Table 4-6. Marketable yield and above ground biomass. Cauliflower 1997-98.
Average
SWT
N
fertilizer
Total dry
biomass
Marketable
yield
Head
diameter
kPa
kg ha-1
Mg ha"'
Mg ha: I
cm
7.6
0
2.0 b
0.0
7.6
300
5.8 a
9.8 NS
4.0
0
1.6b
0.0
NO
12.4 NS
13.8
300
5.0 a
15.0
4.0
Within columns, values followed by the same letter are not significantly different at P<0.05 (Tukey's
HSD). NS, not significant.
Table 4-7. Nitrogen balance and unaccounted for N. Cauliflower 1997-98.
Average
SWT
kPa
N
fertilizer
N in dry biomass
kg N ha-i%
UnacResidual N lost by counted
for N
N
denitrif
kg N ha' kg N ha."' kg N ha' kg N ha-1
7.6
0
1.23 c
24.4c
40.8 NS
0.39 NS
7.6
300
3.32 a
193.1 a
47.5
0.79
4.0
0
1.37 c
21.4 c
41.5
0.38
124.2 NS
187.5
1.22
132.8b
41.8
300
2.65b
4.0
Within columns, values followed by the same letter are not significantly different at P<0.05 (Tukey's
HSD). NS, not significant.
79
Residual soil NH4 and NO 3- to a depth of 0.9 m at the end of the season was not
influenced by irrigation or N treatments. The average over all the treatments was 43 kg N
ha'. The residual soil N in this experiment was lower than the values reported by
Thompson and Doerge (1996) in the same soil with a leaf lettuce crop. When 300 kg N
ha-I were applied as fertilizer, they found approximately 120 kg ha-1 of residual inorganic
N in the plots with 9 kPa average SWT and 80 kg ha' in plots with 5 kPa average SWT.
They evaluated the residual N to a depth of 1.2 m, while in this experiment the residual N
was measured to 0.9 m.
The average amount of N lost by denitrification in the unfertilized plots was 0.4 kg
ha-I . Plots receiving 300 kg ha-I and low water level lost only 0.8 kg ha' of N. The high
water treatment resulted in 1.2 kg N ha-I lost by denitrification (Figure 4-11). After
correcting the losses of N in fertilized plots by subtracting the N2 0-N lost in control plots,
the fertilizer N lost by denitrification was only 0.1 to 0.3% in the low and high water
treatments, respectively. These percentages are very low but might be reasonable for a
winter season with a subsurface drip-irrigated crop. Malunood et al. (1998) found
denitrification losses around 2% of 100 kg ha.-1 of N fertilizer in a flood-irrigated winter
wheat crop. Terry et al. (1986) mention that the crust formed on the surface of floodirrigated soils might retard water percolation, thereby reducing oxygen diffusion into the
soil and enhancing denitrification. They found that 8% of N fertilizer was lost by
denitrification in flood-irrigated soils during a 42 day period between June and August,
compared to 0.6 to 1.5% in sprinkler-irrigated plots during the same period.
80
SWT: 7.6 KPa
D
0 kg N/ha
300 kg N/ha
32
21
44
i
58
1
74
78
117
135
78
117
135
Days after planting
SWT: 4.0 KPa
ri 0 kg N/ha
0
21
300 kg N/ha
I
I
32
44
1
58
I
74
Days after planting
Figure 4-11. Denitrification losses of N in control and fertilized plots. Cauliflower 1997-98
81
According to the ANOVA for unaccounted N, the effect of SWT was significant
with an a= 0.07. The unaccounted N with low water was 124 kg N ha', and 187 kg N
ha.-1 with high water. These values are higher than those reported by Thompson and
Doerge (1996). In a leaf lettuce experiment in the same soil, they found 101 and 149 kg
ha' of unaccounted N in plots subjected to optimum and excessive water treatments,
respectively, that received 300 kg N ha'.
Sweet Corn 1996/97
This experiment was done to evaluate denitrification at higher ambient temperatures in a summer crop. The soil cores were taken from the top 15 cm of soil, because
most of the time there was some excess of water on the soil surface. Organic C and DEA
were also evaluated in soil cores taken at the beginning and the end of the season.
Denitrification Rate.
This experiment was sampled ten times during the season. Denitrification rate
followed a log-normal distribution in five of the sampling dates, with Cvs between 10 and
78% after log-transformation. A normal distribution was observed only in one of the
sampling dates with CV of 64%. The other four dates did not show a normal nor lognormal distribution and the CVs ranged from 109 to 221% (Table 4-8).
The denitrification rate was not affected by water or N levels, except in the last
two sampling dates. Average denitrification rates fluctuated between 5 and 22 g N2 0-N
ha"' d'', with a range from 2 to 59 g N2 0-N ha-I c1-1 through the sampling date 24 hr after
82
Table 4-8.
Date
Frequency distribution, coefficients of variation, and statistical significance
in the sweet corn experiment, 1997.
Sampling
timet
Coefficient of
variations
Distribution
Before
After
Statistical significance
Water
Nitrogen
%
04-09-97
1
None
109
NS
NS
04-16-97
7
None
139
NS
NS
04-24-97
1
Log-normal
105
52
NS
NS
04-25-97
2
Log-normal
137
78
NS
NS
05-18-97
-1
None
221
NS
NS
05-20-97
1
Log-normal
68
NS
NS
05-29-97
-1
Normal
64
NS
NS
05-31-97
1
None
208
NS
NS
06-02-97
3
Log-normal
124
18
*
**
06-26-97
1
Log-normal
88
10
NS
*
30
'bays before (-) and after the previous fertilization.
CV before and after log transformation of data.
*, ** Significant at P 0.05 and 0.01, respectively; NS, not significant.
the fourth fertilization or 68 DAP (Figure 4-12). Three days after the fourth fertilization
the denitrification rate was significantly higher in the fertilized plots (594 g N2 0-N ha"' d'')
than in the control plots (70 g N2 0-N ha' d-1 ). At this sampling date, the plots with high
water level had significantly higher denitrification rates. At the last sampling date, only N
had a significant effect on denitrification (Table 4-8). The mean rate on the last date was
83
1,000
-
48 kPa, 0 kg N
e 48 kPa, 270 kg N
30 kPa, 0 kg N
30 kPa, 270 kg N
-
100
10
1
10
20
30
40
50
60
70
80
90
Days After Planting
Figure 4-12. Denitrification rates during the 1997 sweet corn season.
100
84
390 g N2 0-N ha-1 d' i in fertilized plots, compared to 133 g N2 0-N ha"' cl- ' in control plots
(Figure 4-12).
The denitrification rates for sweet corn were 2 to 30 times higher than those
obtained in the 1997-98 cauliflower experiment at ambient temperatures. However, the
denitrification rates found in sweet corn were very similar to the rates obtained at roomtemperature incubation in the 1997-98 cauliflower study. In that case, the mean
denitrification rate through the fourth fertilization varied from 2 to 39 g N2 0-N ha' d - ',
compared to 5 to 22 in sweet corn. In both cases, the highest mean denitrification was
obtained in the fertilized plots with high water; the means were 1022 and 1075 g N2 0-N
ha"' d', recorded three and nine days after the fourth fertilization in sweet corn and
cauliflower, respectively. The mean temperature of incubation in the sweet corn experiment increased from 16°C after the first fertilization to 30°C after the last fertilization. In
the 1997-98 cauliflower season, the mean ambient temperature during the field incubations
was between 9 and 18°C, while the room incubation temperature was 24±2°C.
Although the sweet corn experiment was established in a different soil, these results
demonstrate that temperature was the main factor limiting the potential denitrification
during the winter cauliflower season.
The effect of soil water tension on the WFPS was significant only in the sampling
date 24 hours after the first fertilization, with mean values of 0.52 for the high water and
0.46 for the low water treatment. The average WFPS after the third and fourth fertilizations were significantly lower than all the other sampling dates (Figure 4-13A). The
85
Fert. 1
• Fert. 2
• Fert. 3
• Fert. 4
30 kPa, 0 kg N
48kPa, 0 kg N
30 kPa, 300 kg N
48 kPa, 300 kg N
80
60 -
48 kPa, 0 kg N
48 kPa, 270 kg N
30 kPa, 0 kg N
30 kPa, 270 kg N
E
O
•
O
40-
20-
o
0.25
I
I
I
1
I
0.3
0.35
0.4
0.45
0.5
i
0.55
WFPS
Figure 4-13. Relationship between WFPS and denitrification rate in cores
taken 24 hr after fertilization for sweet corn, 1997.
06
86
regression analysis between denitrification rate 24 hr after fertilization and WFPS was
significant according to the F test, although the r2 coefficient of determination was low
(Figure 4-13B). A similar relationship was described by de Klein and van Logtestijn
(1996). They used denitrification data from soils of three different textures to obtain the
equation:
Denitrification [kg N ha."' d 1 J = 0.046 * %WFPS - 1.1; r 2 = 0.65
(10)
This equation yields higher denitrification rates than were observed in this experiment
(Figure 4-12B). The reason may be that de Klein and van Logtestijn (1996) developed
their equation from laboratory incubations at 20°C. Weier et al. (1993) and Mahmood et
al. (1998) also reported increasing denitrification rates with increasing values of WFPS,
although these authors did not present a regression relationship.
The mean NO; concentration in the cores taken 24 hr after fertilization fluctuated
from 5.4 to 13.7 mg No, -N kg' and from 2.7 to 5.6 mg NO;-N kg' in the control plots
-
(Figure 4-14A). The difference in NO; between the N treatments was significant after
the second and fourth sampling dates. However, the regression analysis between
denitrification rate and NO; content was not significant at any sampling date (Figure 414B). Limited response of denitrification to N fertilizer has been observed by Ryden and
Lund (1980), Weier et al. (1993), and de Klein and van Logtestijn (1996). Ryden and
Lund (1980) mentioned that NO; did not limit denitrification when other conditions were
favorable. They found denitrification rates between 100 and 2100 g N 20-N ha"' d -1 when
the range of NO;-N was approximately 1 to 40 mg kg', although three of the four
highest denitrification values were obtained with less than 10 mg NO;-N kg'. In the
87
15
0
30 kPa, 0 kg N
48 kPa, 0 kg N
48 kPa, 270 kg N
30 kPa, 270 kg N
80
48kPa,OkgN
60
0 48 kPa, 270 kg N
A 30 kPa, 0 kg N
0 30 kPa, 270 kg N
0
0
40
A
20
O
0
0
0
Figure 4-14.
5
10
NO3-N (mg/kg soil)
15
Relationship between nitrate and denitrification rate in cores
taken 24 hr after fertilization. Sweet corn 1997.
20
88
sweet corn experiment the denitrification rate was lower than the values reported by
Ryden and Lund (1980). It is possible that NO 3- did not increase the denitrification rate
most of the season because of a limited availability of organic C, as discussed in the next
section.
Organic Carbon
The total and soluble organic C concentrations were analyzed in core samples at
the beginning and at the end of the season. All the plots had the same TOC irrespective of
the water and N treatments, and it did not increase at the end of the season. The mean
TOC was 0.63% at the beginning of the season and 0.65% at the end. Soluble organic C
was also not different between treatments. However, the average concentration significantly increased from 45.7 .tg C g soil' at the beginning of the season to 47.5 1.1g C g soil'
1
at the end (Table 4-9). Burford and Bremner, (1975) reported that denitrification rate
was more correlated to SOC than to TOC. The regression was evaluated in 17 soils from
Iowa with a range of 9 to 259 pig SOC g soil'. However, 82% of the soils had SOC
values higher than the 48 .tg C g soil -1 found in our study. Although the SOC concentra-
tion in sweet corn was higher than the values found in the 1997-98 cauliflower experiment, it was also lower than the 60-80 lis SOC g soil' range required to have measurable
denitrification rates (Burton and Beauchamp, 1985).
89
Table 4-9.
Concentrations of total (TOC) and soluble (SOC) organic carbon.
Sweet corn 1997.
SOC
TOC
Average
SWT
N
fertilizer
kPa
kg ha"'
48
0
0.61 NS
0.65 NS
46.7 NS
47.9 NS
48
270
0.61
0.62
45.6
48.0
30
0
0.64
0.68
44.9
46.9
30
270
0.64
0.63
45.9
47.2
end
of season
beginning
of season
%
beginning
of season
end
of season
- - - fig C kg soil -1 - - -
NS, not significant.
Denitrifying Enzyme Activity
The DEA was evaluated only in one plot per treatment because of problems with
the GC. Therefore, this data was not analyzed for statistical significance and the mean and
standard deviation are presented in Figure 4-15. The initial DEA in this soil was 23 ng
N20-N g soit' hr4 (approximately 1.2 kg he day', assuming a depth of 0.15 m and 1.5 g
cm' of bulk density). At the end of the season, the fertilized plots had an average DEA
of 50 ng N2 0-N g soil-1 hr-1 (2.7 kg ha4 day'), which was higher than the DEA of 39 ng
N2 0-N g soil -1 hr4 in unfertilized plots. These DEA values showed a similar trend as with
cauliflower, with low values at the beginning of the season followed by a doubling. This
trend might be responsible in part for the low denitrification rates during the first part of
the season, and higher values at the end. Also, DEA rates in the sweet corn site were
90
120
100 —
23.0 (11.0)
• Initial:
— End of season:
38.5 (1.3)
O 48 kPa, 0 kg N:
L 48 kPa, 270 kg N: 56.1 (19.9)
30 kPa, 270 kg N: 45.0 (26.9)
,
80 —
60 —
40 —
20 7
0
0.0
I
I
I
0.5
1.0
1.5
2.0
Incubation time (hr)
Figure 4-15. Denitrifying enzyme activity at the beginning and end of the 1997
sweet corn season. Numbers in legend are DEA in ng N20-N/g
soil/hr (standard deviation).
91
more than double the values found in the cauliflower experiments. The difference in DEA
values might be due to the higher organic C content in the sweet corn plots. In the
literature, higher DEA has been reported for Mollisols (Lensi et al., 1995) compared to
Entisols (Sotomayor and Rice, 1996).
Yield.
The high water treatment significantly increased the marketable yield, above
ground biomass, and plant height. Plots with high water had 13 Mg ha' of marketable
yield and 8.4 Mg ha-1 of above ground biomass, compared to 10 and 6.7 Mg ha4 of
marketable yield and biomass, respectively, produced with the low water treatment. The
average plant height in the plots in the high water treatment was 198 cm, while in the plots
with low water the plants averaged 167 cm tall. The effect of N on marketable yield,
biomass, and plant height was not significant (Table 4-10). The marketable yield in this
experiment was higher than the state average of 7.8 Mg ha' for the 1996 growing season
(Sherman and Erwin, 1997). The lack of response of sweet corn to N fertilization was
probably due to the high concentration of N in the soil. The initial N content in the soil
was 54 kg N ha' (in the top 30 cm of soil) and the control plots accidentally received 20
kg N ha' at the beginning of the season. Also, some N was already present deeper in the
soil, because at the end of the season there were 193 kg N ha-I at 60-90 cm depth (Figure
4-16).
92
N concentration (mg N/kg soil)
150
100
50
200
Ell Ammonium-N
Nitrate-N
15
0 kg N/ha
75
0
200
Figure4-16. Residual ammonium and nitrate at the end of the 1997 sweet corn
season..
93
Table 4-10.
Total biomass, marketable yield, and plant height in sweet corn, 1997.
Average
SWT
N
fertilizer
Total
dry biomass
Marketable
yield
Plant
height
kPa
kg ha '
Mg ha '
Mg ha"'
m
48
0
6.54c
10.39 NS
1.64c
48
270
6.79 bc
9.78
1.70 bc
30
0
8.41 a
12.08
1.92 ab
-
-
13.86
2.03 a
270
8.34 ab
30
Within columns, values followed by the same letter are not significantly different at P<0.05 (Tukey's
HSD). NS, not significant.
Nitrogen Balance
A summary of the N balance in the sweet corn experiment is shown in Table 4-11.
Total N concentration in plant tissue was affected by the N fertilizer rate only. The mean
N content in plants from fertilized plots was 1.75% (w/w), and unfertilized plots averaged
1.55%. At both N rates, the plots with higher water had lower plant N, but the differences
were not significant (Table 4-11). The total residual soil inorganic N was significantly
higher in the fertilized plots, with an average of 411 kg N ha-1 , whereas the control plots
had a mean residual N of 226 kg N ha' (Table 4-11). The very high residual N in this
experiment was caused by high initial N content in the soil (54 kg N ha"' in the top 30 cm
of soil), since no crop was grown to remove the residual N from the previous season.
Also, the control plots accidentally received 20 kg N ha-1 at the beginning of the season.
The accumulated amount of N lost by denitrification followed a log-normal
distribution and the data was transformed before statistical analysis. It was significantly
94
Table 4-11. Nitrogen balance and unaccounted N for sweet corn 1997.
UnacN
Residual
SWT
fertilizer
N
N lost by
denitrif.
counted
for N
kPa
kg N ha'
kg N ha-1
kg N ha'
kg N ha'
kg N ha'
48
0
1.59 ab
104.3 NS
227b
1.32b
48
270
1.81a
123.6
434a
5.90a
30
0
1.50b
127.5
225b
3.88 ab
Average
N in dry biomass
%
41.0 NS
18.35a
79.5
388a
Within columns, values followed by the same letter are not significantly different at P<0.05 (Tukey's
HSD). NS, not significant.
30
270
1.68 ab
140.3
affected by the N fertilizer and the irrigation levels. The average N lost by denitrification
in the control plots was 2.6 kg ha', while the plots that received 270 kg ha-1 of N-fertilizer
and low water lost 5.9 kg ha-1 N. With high water, the amount of N lost by denitrification
increased to 18.4 kg ha' (Figure 4-17). The losses of N fertilizer due to denitrification
represented 1.7% and 5.7% of total applied with low and high water, respectively.
Mahmood et al. (1998) reported similar denitrification losses of N from fertilizer in a
maize crop. They applied 100 kg N ha' as fertilizer and recorded losses of 7.9 kg N ha'
due to denitrification. Since the control plots showed denitrification losses of 4.3 kg N ha
1, the corrected percentage of N-fertilizer lost through denitrification was 3.6%. In the
sweet corn experiment, the denitrification losses of N represented 10 and 15% of the
unaccounted for N in the low and high water levels, respectively (Table 4-11).
95
SWT: 48 kPa
I 1 Control
.
Ej 270 kg N/ha
I
24
17
I
32
I
58
71
85
71
85
Days after planting
SWT: 30 kPa
Figure 4-17. Cummulative denitrification N losses during the 1997 sweet corn
season.
96
CHAPTER 5
CONCLUSIONS
Denitrification losses of N in subsurface drip-irrigated cauliflower and sweet corn
represented a small percentage of the applied fertilizer. The main factors limiting
denitrification were low organic C availability and low WFPS. During the winter cauliflower season, low temperature was a limiting factor. Although the denitrification rates
were usually higher in the fertilized plots, differences were not statistically significant
because of the low temperature and high variability. When denitrification was evaluated at
room temperature, the increased rates caused by the N fertilizer were significant. The
values of WFPS obtained with the low and high water levels with subsurface drip irrigation were generally around or lower than 60%, which is a commonly reported threshold
for denitrification.
In both seasons, denitrification rates were higher at the end of the season. It
seemed that the growth and development of the crop favored an increase in soluble
organic C and a higher denitrifying enzyme activity. Both characteristics might be
responsible for the higher denitrification rates toward the end of the season.
The estimated denitrification losses of N from fertilizer throughout the season
were less than 1% in the winter cauliflower season and almost 2% in summer sweet corn,
when irrigated with the low level of water. Excessive irrigation did not increase the
denitrification rate in the winter, but in the summer the losses of N due to denitrification
97
increased to almost 6% of the applied N. When the denitrification losses of N were
included in the N balance, it did not make a significant difference in the cauliflower, since
denitrification was again less than 1% of the unaccounted for N. In the summer sweet
corn, however, the denitrification losses represented 10 and 15% of the unaccounted for
N, when the applied irrigation water was low and high, respectively. Therefore, most of
the unaccounted for N with subsurface drip irrigation, in both summer and winter seasons,
was probably lost through leaching of NO3".
98
APENDIX
Experimental data
99
00
".
co
00
es'
00 ..,tt Q eq OS
.0 t--
trn
s cN
'''
-- 1"-r-
00 'et
tr) 'Tt eN1 r--
141 C"
kr)
WI et In
sO 00 tri
C)
CNI
00 ten
n.0 c7s 0 ,"•-n 0 CP, CrN v:S
css
es1
Ln
-eh
Os en 00
en 1,1 N
en 00 tn
NV-1c
00
eN1 WINeeNOONINMONtel
sc
et et e1. el'
tn et.
N
N
CZN
C)
,
N N Os ••-_,
\ C' 00 N 4"),1.11
Cn
sO en en 00 C" ", 00 C" en Ir.- s'ID SO
00 00 00 00 C)N C)C)
sC>
ON
un en Len
N
Cri •
9
t"--
-;r en
NN
cc
if)
en Os '000 en en en Os
N
so in tri in Os kri "0 00 et- Os le)
et- N
00N
s0 en 00
tri
'
en 0 tr)
et et
sO
•
N NO VO
N
est N IN CD et
trl NO ON
o
1m.
1n1
--
ON
In1
o
00
it)
Nesi
VD *et trs
•iir
0 et
cc.)
',JO o0 sO en
00 00
r-
in
hl
in
N
00 LC N
ktn 00 eq trl tin en esi Os
o
,;)
o
ect
"7.
el
es)
-et
vl CD VD hl
N 00 cs1 et
sCi
er el In en Len n.0 .4*
en yen sLO un
en
07, en
tr1
tri en 0 DO
C
sf's -cr
1,1
00 00 00 N
N
sO
et- en CC eV
in en
en en -I-
*.zr 00
en
st)
CD r-
r- 00
Crs N 00 in 0 en N. in 1/40
N
in et er en Len
en Le's . t•
•
N 00 tn et le) ee
O
hi
•
•iifr 1/40
sO r-- en en NI
ir)
VI c".1
,-,
un csl CD C:sn en
1.r)
sO vO
Os
•itt
tri
.4")
".1
in
\ ,4
in
,
0 1/400 en -71- 00 -cp
tri -it
Ifs
in
N ON 0 00
trs
Os N
r-- r--
ess
NenN '0Q
.er
en -1- un
ten r-
oo o.
•Iti• .1.
o
•
o
tin
CO es1 en
hi -4" ••7• et en un
rn
0 s.0
hl
er In
.st
"0
Un
oo
rn
en in
.o
In
tr)
irs trl
CNI
rn
os t-ss
ezt
= 0 0 0 0 0 0
•
0 0 0 0 0 0 0 0 0 0 0 0
en
en en
en
NOONNN CD OCDNON
or;
•Tr:
tri
tri
tc;
4 4
<IC
.o
ct
E-4
4 4
Ff.(
r- 00 Cs
co 0 CD
0
=
0 0 0 0 0 CD 0 0 0 0 0 0
000
gAi
.W
en en
r-:
o cs ns0
r-:
en en en
en
.f0
o o vD cs
r-:
t-: r-:
▪
100
cn 00 On
Tte 00
00 en tin
-4" VD in vD VD ten
000 t-- I-- I--
00
• —n
Ni en ON en NI
%.0
VD tin In
(--4 NI 000N0
NvD 00 tlf-- r 00
N N N vtD e--
N vD
N
tin et
S 00 0 r- U NN00 0
00 N NO0 en
N
Nt VD
VD VD el VD en
N 0 in en
N
CIN t-- N
ON a% 0
tr- en en vD
VD 00
tn
0 en tn 0, 0 0 as VD el VD
00
VD NI ttl• in 00
0 In In ten
en en VD
N t-tr,
vD 1/40 NI
00
.11
o
Os S. 0 N
00
-
wnI r•--
o
2
ea „A
C1N
•
•
o
5
en
00
N 1/410
".1
N N
ss0
,st) VD 0 S S M
Nt
t.0 N D en en 00 00
VDen ,-INNNINI ,--IN
N
N
00
bet Fri 00
-
N
1n4
a
(-4 esi
rq •—n
onI —
d-
a,• °°
oo
1n1 1n4
o
00
CA
ccN Crs
000 en
4
‘71- •ttt Ch en n.rD
eneno0
1n.1 v1 n•n.4
o
0 00 00 CA
ten el
•
nnI In1
0 tin
N
4
un 00 t:/%
N 00 0
--0 •-• •••n el
.......
N
VD In el - CO N
en el
N
-01'
o
Ces
o
NI en 0 in in On CO N N ON 0
teten•-t--1•NOenc-4 n-4 NN-01-
o
03
0 000 0 0
NONOONNONONO
N N N N
NI N4
03 0 0 0 0 0 0 0 0 0 0 0 0
6 6 00 00 6 ec; 6 cc; a; 6 6 oe;
en en
•I•
en
•I•
en et
,er
en cn
1 01
Table A-4.
Meter readings and calculation of water applied. Cauliflower 1996-97.
Date
Days
after
planting
5.2 kPa
11-24
11-27
12-10
12-20
12-31
01-07
01-17
01-28
02-05
02-22
03-09
03-18
0
3
16
26
37
44
54
65
73
90
105
114
119896
120531
121860
122300
123008
123130
123140
123246
123282
123907
124421
125007
115909
116449
117691
118473
118903
119190
119510
119749
120043
120494
124012
126216
0
635
1330
440
708
123
10
105
37
624
515
586
0
539
1242
782
430
288
319
240
294
450
3519
2204
L
0
2402
7435
9099
11778
12242
12280
12678
12818
15180
17128
19345
0
2042
6744
9705
11331
12419
13628
14535
15648
17352
30670
39011
0
22
68
83
107
111
112
115
117
138
156
176
0
19
61
88
103
113
124
132
143
158
279
355
04-12
139
126210
131268
1203
5052
23897
58135
218
529
4.0 kPa
gal
Table A-5.
10-23
10-26
10-31
11434
11-11
11-22
11-29
12434
12-10
12-18
12-23
12-30
01-06
01-14
01-21
01-28
02 405
02-17
02-25
03-25
Cumulative liters
Depth of water
5.2 kPa 4.0 kPa
5.2 kPa 4.0 kPa
Meter readings and calculation of water applied. Cauliflower 1997-98.
Days
after
Date
Gallons
5.2 kPa 4.0 kPa
Meter reading
planting
Gallons
Meter reading
7.6
kPa
4.0 kPa
4.0
kPa
7.6 kPa
gal Cumulative liters
Depth of water
7.6 kPa 4.0 kPa
7.6 kPa 4.0 kPa
L
0
3
8
12
19
30
37
42
48
56
61
68
74
82
89
96
104
116
124
136367
137664
139297
139780
140505
140939
141449
141501
141677
141883
141931
141965
142072
142139
142607
143021
143401
143781
143867
131629
133010
134748
135262
136060
137231
138077
138540
139002
139420
139638
139791
140321
140766
142207
144490
146372
148213
148522
0
2162
1633
483
725
434
509
53
176
205
48
34
107
67
468
414
380
380
86
0
2301
1738
514
798
1170
847
463
462
418
218
153
530
445
1441
2283
1882
1841
308
0
8184
14366
16195
18937
20581
22509
22709
23375
24152
24333
24463
24869
25123
26894
28462
29899
31337
31663
0
8708
15287
17234
20254
24683
27888
29641
31389
32969
33796
34375
36382
38065
43518
52160
59284
66253
67420
0
73
128
145
169
184
201
203
209
216
217
218
222
224
240
254
267
280
283
0
78
136
154
181
220
249
265
280
294
302
307
325
340
389
466
529
592
602
152
145038
151783
1171
3261
36096
79764
322
712
102
Table A-6.
Date
Meter readings and calculation of water applied. Sweety corn 1998.
Days
after
planting
Meter reading
#1
#2
Volume
# 1
#2
Average Cumulat. Depth
volume volume of water
Cubic feet mm
SWT: 48 kPa
0
03-23
04-09
17
23
04-15
04-18
26
34
04-26
05-06
44
46
05-08
57
05-19
05-22
60
70
06-01
06-18
87
25991
27839
28076
28194
28501
28868
28941
29671
30011
30925
32853
32404
34287
34528
34648
34962
35335
35409
36154
36500
37432
39393
0
1072
138
68
178
212
42
424
197
530
1118
0
1092
140
70
182
216
43
432
201
541
1137
0
1082
139
69
180
214
43
428
199
536
1128
0
1082
1221
1290
1470
1684
1727
2155
2354
2889
4017
0
102
115
122
139
159
163
203
222
273
379
SWT: 30 kPa
0
03-23
17
04-09
04-15
23
04-18
26
34
04-26
05-06
44
05-08
46
57
05-19
60
05-22
70
06-01
87
06-18
36542
37423
37628
37726
37999
38339
38415
38915
39124
39647
40830
69428
70569
70836
70963
71318
71762
71860
72508
72729
73454
74896
0
881.24
204.98
97.87
272.31
340.56
75.92
499.95
209.36
522.18
1183.5
0
1142
267
127
355
444
98
647
222
724
1442
0
1012
236
113
313
392
87
574
215
623
1313
0
1012
1247
1360
1673
2066
2153
2726
2942
3565
4878
0
95
118
128
158
195
203
257
278
337
460
103
Table A-7.
Denitrification rate and related data. Cauliflower 1996-97.
N20
jar
Target
water
tension
kPa
N
kg/ha
N20 in N20
jar
disolved
core
weight of water
PLOT concentr. dry core content
rnL
#
ppb
g
N20
total
Denitrif
rate
WFPS headspac in water fidenitr N20-N
g
g
g
g/ha/d
Sampling date: 12-18-96, 3 hr before fertilization
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
364
393
367
396
338
351
412
347
335
313
309
302
357
374
363
260
227
217
235
274
366
305
314
271
42.8
39.8
41.6
35.7
31.4
23.1
29.5
37.2
48.1
35.0
37.4
41.1
0.41
0.37
0.40
0.47
0.48
0.37
0.43
0.47
0.45
0.40
0.41
0.52
1.2E-07
1.6E-07
1.2E-07
1.8E-07
8.1E-08
1.1E-07
2.1E-07
9.4E-08
7.0E-08
3.7E-08
2.9E-08
1.7E-08
8.1E-12
1.0E-11
8.0E-12
1.3E-11
6.0E-12
5.9E-12
1.4E-11
7.0E-12
5.3E-12
2.3E-12
1.9E-12
1.4E-12
1.2E-07
1.6E-07
1.2E-07
1.8E-07
8.1E-08
1.1E-07
2.1E-07
9.4E-08
7.0E-08
3.7E-08
2.9E-08
1.7E-08
0.47
0.63
0.48
0.98
0.51
0.69
1.27
0.49
0.27
0.17
0.13
0.09
43.9
42.4
50.5
47.7
48.8
44.4
51.6
46.2
28.9
37.5
41.5
45.0
0.48
0.43
0.50
0.51
0.55
0.45
0.46
0.45
0.45
0.45
0.49
0.60
3.1E-07
3.4E-07
2.5E-07
1.4E-07
5.0E-08
4.8E-08
1.2E-07
4.2E-08
7.4E-08
4.7E-08
1.7E-07
1.1E-07
2.4E-11
2.4E-11
2.1E-11
1.2E-11
4.5E-12
3.5E-12
9.8E-12
3.2E-12
5.1E-12
3.3E-12
1.3E-11
1.1E-11
3.1E-07
3.4E-07
2.5E-07
1.4E-07
5.0E-08
4.8E-08
1.2E-07
4.2E-08
7.4E-08
4.7E-08
1.7E-07
1.1E-07
1.41
1.45
1.03
0.61
0.24
0.20
0.46
0.17
0.47
0.23
0.81
0.63
40.3
35.7
35.0
36.8
32.5
31.1
31.5
19.4
44.2
51.8
30.4
44.9
0.50
0.49
0.50
0.58
0.55
0.49
0.45
0.47
0.50
0.46
0.44
0.53
2.0E-09
2.7E-08
5.8E-08
9.1E-08
4.2E-08
8.4E-08
1.2E-07
1.2E-07
6.5E-08
8.3E-08
7.7E-08
2.0E-07
1.6E-13
2.1E-12
4.5E-12
8.2E-12
3.6E-12
6.3E-12
8.2E-12
8.0E-12
5.3E-12
6.6E-12
5.2E-12
1.7E-11
2.0E-09
2.7E-08
5.8E-08
9.1E-08
4.2E-08
8.4E-08
1.2E-07
1.2E-07
6.5E-08
8.3E-08
7.7E-08
2.0E-07
0.01
0.15
0.34
0.59
0.30
0.55
0.69
1.15
0.30
0.31
0.46
0.97
Sampling date: 12-18-96, 3 hr after fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
454
475
421
351
296
295
345
292
308
294
365
333
316
337
346
324
305
343
384
352
224
291
293
258
Sampling date: 12-19-96, 24 hr after fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
201
216
234
253
224
248
267
264
240
253
244
319
277
250
240
220
203
218
240
144
308
387
239
291
104
Table A-7.
Continued
Target
water
tension
kPa
N
kg/ha
core
N20
weight of water
jar
PLOT concentr. dry core content
mL
ppb
#
g
N20 Denitrif.
N20 in N20
rate
jar
disolved total
WFPS headspac in water f/denitr N20-N
g/ha/d
g
g
g
Sampling date: 01-27-97, 3 hr before fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
320
343
419
309
273
309
405
511
274
286
325
334
248
244
169
208
267
306
326
352
295
264
356
306
37.9
36.1
26.2
32.9
43.9
38.7
40.3
50.3
40.0
31.4
43.5
48.0
0.46
0.45
0.46
0.47
0.49
0.39
0.38
0.43
0.41
0.37
0.38
0.47
1.2E-07
1.6E-07
3.0E-07
1.0E-07
4.0E-08
1.0E-07
2.6E-07
4.2E-07
4.2E-08
6.3E-08
1.2E-07
1.4E-07
2.5E-09
3.1E-09
4.1E-09
1.8E-09
9.8E-10
2.2E-09
5.8E-09
1.2E-08
9.4E-10
1.1E-09
3.0E-09
3.8E-09
1.2E-07
1.6E-07
3.1E-07
1.1E-07
4.1E-08
1.0E-07
2.6E-07
4.3E-07
4.3E-08
6.5E-08
1.3E-07
1.4E-07
0.71
0.96
2.61
0.73
0.22
0.48
1.15
1.75
0.21
0.35
0.50
0.67
48.3
48.8
52.4
35.1
52.9
34.7
38.9
52.9
48.2
44.9
50.7
52.2
0.44
0.38
0.45
0.46
0.44
0.40
0.39
0.40
0.43
0.36
0.42
0.50
9.3E-08
1.0E-07
2.2E-07
5.1E-08
2.4E-07
7.7E-08
6.1E-08
5.5E-08
1.7E-07
9.5E-08
4.0E-08
1.0E-07
2.6E-09
2.9E-09
6.5E-09
9.5E-10
7.5E-09
1.5E-09
1.3E-09
1.7E-09
4.6E-09
2.5E-09
1.2E-09
3.0E-09
9.5E-08
1.0E-07
2.2E-07
5.2E-08
2.5E-07
7.8E-08
6.2E-08
5.7E-08
1.7E-07
9.8E-08
4.1E-08
1.0E-07
0.41
0.38
0.90
0.33
0.99
0.42
0.29
0.20
0.72
0.36
0.16
0.48
48.3
48.8
52.4
35.1
52.9
34.7
38.9
52.9
48.2
44.9
50.7
52.2
0.44
0.38
0.45
0.46
0.44
0.40
0.39
0.40
0.43
0.36
0.42
0.50
2.5E-08
3.0E-08
6.0E-07
1.5E-07
1.3E-06
3.1E-08
1.0E-07
3.0E-08
1.2E-07
2.7E-08
1.9E-07
2.8E-08
7.0E-10
8.7E-10
1.8E-08
2.9E-09
3.9E-08
5.8E-10
2.2E-09
9.4E-10
3.3E-09
7.0E-10
5.5E-09
8.2E-10
2.6E-08
3.1E-08
6.1E-07
1.6E-07
1.3E-06
3.1E-08
1.0E-07
3.1E-08
1.2E-07
2.7E-08
1.9E-07
2.8E-08
0.11
0.11
2.50
0.99
5.14
0.17
0.48
0.11
0.51
0.10
0.75
0.13
Sampling date: 01-28-97, 24 hr after fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
296
304
374
269
392
285
276
274
343
299
264
301
331
389
351
226
361
268
302
399
341
386
367
308
Sampling date: 02-22-97, 3 hr before fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
255
258
612
328
1029
257
299
258
312
256
357
256
331
389
351
226
361
268
302
399
341
386
367
308
105
Table A-7.
Continued
tension
kPa
N20 Denitrif.
N20 in N20
core
rate
jar
disolved total
weight of water
PLOT concentr. dry core content WFPS headspac in water Vdenitr N20-N
N20
jar
Target
water
N
kg/ha
14
ppb
g
mL
g
g
g
g/ha/d
Sampling date: 02-22-97, 3 hr after fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
412
463
463
364
424
545
377
587
548
434
487
424
318
341
375
365
373
295
317
377
421
342
372
369
47.8
35.8
33.9
52.9
50.1
36.5
26.0
42.7
47.0
40.7
49.1
56.6
0.52
0.36
0.31
0.50
0.46
0.43
0.28
0.39
0.39
0.41
0.46
0.53
2.3E-07
3.2E-07
3.1E-07
1.5E-07
2.5E-07
4.6E-07
1.8E-07
5.1E-07
4.3E-07
2.7E-07
3.5E-07
2.4E-07
6.3E-09
6.4E-09
6.1E-09
4.6E-09
7.2E-09
9.3E-09
2.6E-09
1.3E-08
1.2E-08
6.2E-09
9.9E-09
8.1E-09
2.4E-07
3.2E-07
3.2E-07
1.6E-07
15E-07
4.7E-07
1.8E-07
5.2E-07
4.5E-07
2.7E-07
3.6E-07
2.5E-07
1.08
1.36
1.22
0.61
0.97
2.28
0.83
1.98
1.51
1.15
1.37
0.98
53.4
32.7
42.7
44.6
38.1
42.0
28.0
51.1
37.2
38.2
50.0
41.8
0.60
0.42
0.39
0.51
0.38
0.46
0.32
0.49
0.36
0.37
0.48
0.49
7.6E-06
3.3E-07
1.6E-07
5.3E-08
2.4E-09
4.8E-07
1.9E-07
7.6E-07
3.3E-08
8.5E-08
4.1E-07
2.4E-08
2.3E-07
5.9E-09
4.0E-09
1.3E-09
5.1E-11
1.1E-08
3.0E-09
2.2E-08
7.0E-10
1.9E-09
1.2E-08
5.7E-10
7.9E-06
3.4E-07
1.7E-07
5.4E-08
2.4E-09
4.9E-07
1.9E-07
7.8E-07
3.4E-08
8.7E-08
4.2E-07
2.5E-08
36.54
1.81
0.63
0.26
0.01
2.20
0.92
3.09
0.14
0.35
1.67
0.12
0.60
0.42
0.39
0.51
0.38
0.46
0.32
0.49
0.36
0.37
0.48
0.49
7.6E-06
3.3E-07
1.6E-07
5.3E-08
2.4E-09
4.8E-07
1.9E-07
7.6E-07
3.3E-08
8.5E-08
4.1E-07
2.4E-08
2.3E-07
5.9E-09
4.0E-09
1.3E-09
5.1E-11
1.1E-08
3.0E-09
2.2E-08
7.0E-10
1.9E-09
1.2E-08
5.7E-10
7.9E-06
3.4E-07
1.7E-07
5.4E-08
2.4E-09
4.9E-07
1.9E-07
7.8E-07
3.4E-08
8.7E-08
4.2E-07
2.5E-08
16.24
0.81
0.28
0.11
0.00
0.98
0.41
1.37
0.06
0.15
0.74
0.05
Sampling date: 02-23-97, 24 hr after fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
4959
466
373
303
272
560
385
743
291
323
525
285
308
267
381
301
346
316
303
360
356
360
357
298
Sampling date: 03-05-97, 10 days after fertilization.
5.2
4.0
4.0
5.2
5.2
5.2
4.0
4.0
4.0
5.2
4.0
5.2
300
0
300
0
300
0
300
0
300
300
0
0
1
2
3
4
5
6
7
8
9
10
11
12
4959
466
373
303
272
560
385
743
291
323
525
285
308
267
381
301
346
316
303
360
356
360
357
298
53.4
32.7
42.7
44.6
38.1
42.0
28.0
51.1
37.2
38.2
50.0
41.8
106
Table A-7. Continued
Target
water
tension
kPa
N
kg/ha
N20
N20 in
jar
jar
core
weight of water
PLOT concentr. dry core content
mL
#
ppb
g
N20
disolved
N20
Denitrif
total
rate
WFPS headspac in water fdenitr N20-N
g
g
g
g/ha/d
Sampling date: 03-20-97, 3 hr before fertilization
34.7
307
2077
1
300
5.2
43.2
381
377
2
0
4.0
39.2
322
730
3
300
4.0
32.0
356
346
4
0
5.2
27.8
355
5
339
300
5.2
35.0
353
317
6
0
5.2
26.7
319
321
7
300
4.0
48.1
397
524
8
0
4.0
29.9
299
386
9
300
4.0
19.1
345
321
10
300
5.2
49.3
353
350
11
0
4.0
36.8
381
335
12
0
5.2
0.39
0.39
0.42
0.31
0.27
0.34
0.29
0.42
0.34
0.19
0.48
0.33
3.0E-06
1.5E-07
7.4E-07
1.0E-07
9.4E-08
5.6E-08
6.5E-08
3.8E-07
1.8E-07
6.5E-08
1.1E-07
8.5E-08
5.8E-08
3.8E-09
1.6E-08
1.9E-09
1.5E-09
1.1E-09
9.6E-10
1.1E-08
2.9E-09
6.9E-10
3.1E-09
1.8E-09
3.1E-06
1.6E-07
7.5E-07
1.1E-07
9.6E-08
5.7E-08
6.6E-08
3.9E-07
1.8E-07
6.6E-08
1.1E-07
8.6E-08
6.32
0.26
1.49
0.19
0.17
0.10
0.13
0.63
0.38
0.12
0.20
0.14
Sampling date: 03-21-97, 24 hr after fertilization.
37.0
354
353
1
300
5.2
55.3
360
8186
2
0
4.0
36.7
347
404
3
300
4.0
52.6
359
633
4
0
5.2
27.4
348
362
5
300
5.2
44.5
397
368
6
0
5.2
28.5
333
540
7
300
4.0
47.8
357
767
8
0
4.0
35.8
387
326
9
300
4.0
20.3
377
291
10
300
5.2
48.1
377
438
11
0
4.0
29.4
330
294
12
0
5.2
0.36
0.53
0.37
0.51
0.27
0.39
0.30
0.46
0.32
0.19
0.44
0.31
1.2E-07
1.3E-05
2.0E-07
5.6E-07
1.3E-07
1.4E-07
4.3E-07
7.8E-07
7.0E-08
1.5E-08
2.5E-07
1.9E-08
2.5E-09
4.1E-07
4.2E-09
1.7E-08
2.0E-09
3.5E-09
6.8E-09
2.1E-08
1.4E-09
1.7E-10
6.9E-09
3.1E-10
1.2E-07
1.3E-05
2.0E-07
5.8E-07
1.3E-07
1.4E-07
4.4E-07
8.0E-07
7.1E-08
1.5E-08
2.5E-07
1.9E-08
0.22
22.87
0.37
1.02
0.25
0.22
0.83
1.42
0.12
0.03
0.43
0.04
107
Table A-8.
Denitrification rate and related data. Cauliflower 1998-98.
N20 Denitrif.
N20 in N20
core
N20
Target
rate
disolved total
jar
Incu- jar weight of water
water
tension N Plot bation concentr. dry core content WFPS headspaa in water f/denitr N20-N
g/ha/d
g
tnL
ppb
kPa kg/ha /I
g
g
g
Sampling date: 11-11-97, 3 hr after fertilization.
572
299
1
R
300
7.6
313
R
2778
341
F
191
178
260
F
366
4796
2
R
4.0
300
800
339
R
1030
397
F
406
286
F
290
R
1514
0
3
4.0
310
362
R
337
F
617
241
349
F
252
R
2633
0
4
7.6
336
R
1151
323
F
579
315
2003
F
330
1134
0
5
R
7.6
272
284
R
204
327
F
338
1087
F
319
311
6
R
4.0
0
426
321
R
385
138
F
284
348
F
2018
375
7
R
4.0
300
-16
384
R
528
394
F
407
218
F
340
2192
8
R
7.6
300
325
226
R
546
376
F
377
F
390
338
4.0
300
9
1276
R
377
7516
R
374
409
F
1463
369
F
370
7.6
0
10
R
1215
356
272
R
367
827
F
332
307
F
266
7.6
866
300
11
R
58.0
61.2
67.1
52.2
70.0
64.8
77.1
81.3
65.9
72.9
70.9
70.4
62.7
81.2
77.9
73.6
80.7
63.9
78.3
80.5
62.3
66.8
77.3
67.4
67.8
69.4
70.5
71.4
69.9
60.5
75.2
78.4
72.2
77.0
79.7
81.9
74.2
66.6
71.0
64.0
50.7
0.56 6.3E-07 2.1E-08 6.5E-07
0.56 4.2E-06 1.5E-07 4.3E-06
0.57 9.5E-09 3.7E-10 9.8E-09
0.58 -1.2E-08 -3.6E-10 -1.3E-08
0.55 7.2E-06 3.0E-07 7.5E-06
0.56 9.8E-07 3.7E-08 1.0E-06
0.56 1.3E-06 6.0E-08 1.3E-06
0.58 1.5E-07 7.6E-09 1.6E-07
0.64 2.2E-06 8.1E-08 2.2E-06
0.58 1.9E-07 8.4E-09 2.0E-07
0.60 6.8E-07 2.8E-08 7.1E-07
0.58 8.7E-08 3.6E-09 9.1E-08
0.69 4.1E-06 1.4E-07 4.2E-06
0.67 1.5E-06 7.3E-08 1.6E-06
0.67 6.2E-07 2.8E-08 6.5E-07
0.65 2.9E-06 1.2E-07 3.0E-06
0.68 1.5E-06 7.1E-08 1.6E-06
0.66 1.6E-07 5.9E-09 1.7E-07
0.67 3.0E-08 1.4E-09 3.2E-08
0.66 1.4E-06 6.7E-08 1.5E-06
0.58 2.2E-07 7.7E-09 2.2E-07
0.60 3.8E-07 1.5E-08 4.0E-07
0.58 -7.2E-08 -3.4E-09 -7.6E-08
0.56 1.6E-07 6.2E-09 1.6E-07
0.53 2.8E-06 1.2E-07 3.0E-06
0.53 -2.9E-07 -1.2E-08 -3.0E-07
0.52 5.3E-07 2.2E-08 5.5E-07
0.52 5.0E-08 2.2E-09 5.2E-08
0.59 3.2E-06 1.3E-07 3.3E-06
0.54 6.6E-08 2.3E-09 6.8E-08
0.58 5.6E-07 2.5E-08 5.8E-07
0.60 3.1E-07 1.5E-08 3.3E-07
0.61 1.7E-06 7.3E-08 1.8E-06
0.59 1.1E-05 5.2E-07 1.2E-05
0.61 3.4E-07 1.7E-08 3.6E-07
0.63 2.0E-06 9.7E-08 2.1E-06
0.58 1.6E-06 7.1E-08 1.7E-06
0.54 1.4E-07 5.4E-09 1.4E-07
0.56 1.0E-06 4.2E-08 1.0E-06
0.56 1.9E-07 7.3E-09 2.0E-07
0.55 1.1E-06 3.2E-08 1.2E-06
3.11
19.73
0.04
0.00
29.16
4.27
4.84
0.56
11.01
0.80
3.00
0.37
23.73
6.70
2.87
13.63
6.72
0.88
0.14
6.21
1.03
1.78
0.00
0.67
11.28
0.00
1.99
0.18
13.84
0.30
2.21
1.25
7.57
44.66
1.38
7.95
6.41
0.57
4.05
0.87
6.28
108
Table A-8. Continued
N20 Denitrif.
N20
N20 in
core
disolved
total
rate
jar
weight of water
jar
Incu-
N20-N
f/denitr
tensionNPlot bation concentr. thy core content WFPS headspact in water
g/ha/d
g
g
ppbgmLg
kPa kg/ha #
N20
Target
water
4.0
0
12
R
F
F
R
R
F
F
4939
455
512
1067
1220
701
818
366
295
349
294
362
262
283
72.1
59.2
75.0
70.0
80.4
61.2
68.3
0.57
0.58
0.61
0.66
0.63
0.65
0.67
7.4E-06
4.4E-07
5.1E-07
1.4E-06
1.6E-06
8.5E-07
1.0E-06
3.2E-07
1.5E-08
2.3E-08
5.7E-08
7.7E-08
2.9E-08
4.0E-08
7.7E-06
4.5E-07
5.3E-07
1.5E-06
1.7E-06
8.8E-07
1.1E-06
30.06
2.20
2.18
7.17
6.58
4.81
5.39
0.48
0.53
0.56
0.54
0.56
0.55
0.53
0.55
0.62
0.60
0.59
0.58
0.60
0.61
0.62
0.60
0.59
0.59
0.60
0.58
0.55
0.54
0.56
0.53
0.52
0.54
0.57
0.52
0.53
0.54
0.52
0.55
0.56
1.4E-05
6.5E-07
4.0E-08
1.6E-07
2.5E-06
1.6E-07
4.5E-07
3.2E-07
2.1E-06
2.8E-07
4.1E-07
1.0E-07
7.1E-07
5.9E-06
2.7E-07
3.8E-07
8.8E-08
1.4E-06
4.6E-07
9.3E-08
1.5E-08
4.9E-07
1.9E-07
2.3E-07
1.7E-06
2.9E-07
1.0E-06
2.7E-07
2.9E-07
2.0E-07
2.6E-07
-3.2E-09
2.4E-07
4.6E-07
2.6E-08
1.6E-09
5.8E-09
7.6E-08
6.5E-09
1.7E-08
1.2E-08
8.5E-08
1.1E-08
1.6E-08
4.5E-09
2.3E-08
2.1E-07
9.3E-09
1.4E-08
3.4E-09
5.3E-08
1.5E-08
3.8E-09
4.9E-10
1.9E-08
6.4E-09
9.3E-09
6.5E-08
1.2E-08
4.1E-08
1.0E-08
9.2E-09
6.7E-09
9.0E-09
-1.4E-10
8.9E-09
1.4E-05
6.8E-07
4.1E-08
1.7E-07
2.6E-06
1.7E-07
4.6E-07
3.3E-07
2.2E-06
2.9E-07
4.3E-07
1.1E-07
7.3E-07
6.1E-06
2.8E-07
4.0E-07
9.1E-08
1.5E-06
4.7E-07
9.6E-08
1.5E-08
5.1E-07
1.9E-07
2.4E-07
1.7E-06
3.0E-07
1.1E-06
2.9E-07
3.0E-07
2.0E-07
2.6E-07
-3.3E-09
2.4E-07
59.17
2.61
0.17
0.75
13.40
0.65
1.81
1.41
9.65
1.24
1.85
0.43
3.85
29.99
1.45
1.90
0.41
6.81
2.38
0.40
0.07
2.14
0.88
0.89
6.66
1.19
4.53
1.13
1.41
0.91
1.10
-0.01
1.05
Sampling date: 11-22-97, 11 days after fertilization
7.6
300
1
4.0
300
2
4.0
0
3
7.6
0
4
7.6
0
5
4.0
0
6
4.0
300
7
7.6
300
8
4.0
300
9
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
8919
585
194
271
1685
271
454
372
1481
343
428
236
597
3793
335
405
224
1058
447
228
178
481
284
315
1230
355
829
344
347
291
329
167
317
348
370
354
326
276
365
366
339
321
331
330
360
271
291
277
298
321
311
284
347
306
343
311
380
369
365
342
362
304
322
342
385
333
56.1
66.6
68.3
60.9
53.7
68.5
65.6
64.2
69.9
68.9
67.5
73.0
56.9
61.8
60.3
62.3
65.9
63.9
59.6
69.6
57.5
64.1
59.6
68.7
66.0
67.3
67.3
64.5
55.6
59.0
60.7
73.1
65.0
109
Continued
Table A-8.
N20 Denitrif.
N20 in
N20
core
rate
total
disolved
jar
weight of water
tensionNPlot bation concentr. dly core content WFPS headspacc in water f/denitr N20-N
g/ha/d
g
g
ppbgmLg
kPa kg/ha #
N20
Target
water
7.6
0
10
7.6
300
11
4.0
0
12
Incu-
jar
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
8095
732
499
256
265
447
383
271
322
281
367
3594
378
521
724
325
363
325
372
370
363
357
299
372
286
346
316
319
327
331
71.9
77.8
82.8
62.2
63.9
65.0
61.4
51.1
64.9
49.7
61.5
72.5
72.9
78.3
71.8
0.63
0.61
0.70
0.50
0.51
0.52
0.51
0.50
0.51
0.51
0.52
0.65
0.64
0.67
0.62
1.3E-05
8.7E-07
5.2E-07
1.4E-07
1.5E-07
4.4E-07
3.4E-07
1.7E-07
2.4E-07
1.9E-07
3.1E-07
5.4E-06
3.3E-07
5.5E-07
8.8E-07
5.3E-07 1.3E-05
4.1E-08 9.1E-07
2.5E-08 5.4E-07
5.1E-09 1.4E-07
5.7E-09 1.6E-07
1.7E-08 4.5E-07
1.2E-08 3.5E-07
4.8E-09 1.7E-07
9.2E-09 2.5E-07
5.2E-09 1.9E-07
1.1E-08 3.3E-07
2.3E-07 5.7E-06
1.4E-08 3.5E-07
2.6E-08 5.8E-07
3.7E-08 9.1E-07
57.38
3.58
2.38
0.55
0.60
1.79
1.40
0.82
0.95
0.96
1.34
25.64
1.55
2.52
3.94
72.2
69.3
63.2
66.1
76.5
70.1
77.9
79.9
69.8
81.4
82.6
88.8
65.1
69.7
84.5
67.9
61.2
65.5
81.4
84.5
80.6
78.6
77.6
81.3
67.3
0.56
0.56
0.64
0.64
0.58
0.58
0.58
0.58
0.61
0.61
0.62
0.62
0.66
0.66
0.68
0.68
0.65
0.65
0.68
0.68
0.65
0.65
0.59
0.59
0.53
6.1E-06
1.7E-06
3.0E-07
2.5E-06
2.2E-06
3.5E-07
5.3E-07
4.1E-07
1.1E-06
4.6E-07
3.7E-07
4.1E-07
1.3E-05
4.1E-06
3.7E-07
6.1E-07
1.8E-06
2.2E-06
3.6E-07
3.8E-07
2.6E-06
2.3E-06
3.9E-07
3.0E-07
1.2E-05
2.7E-07
6.9E-08
1.1E-08
9.5E-08
1.0E-07
1.4E-08
2.5E-08
2.0E-08
4.6E-08
2.3E-08
1.9E-08
2.2E-08
4.7E-07
1.6E-07
1.9E-08
2.4E-08
6.0E-08
8.2E-08
1.8E-08
1.9E-08
1.3E-07
1.1E-07
1.8E-08
1.5E-08
4.8E-07
6.4E-06
1.8E-06
3.1E-07
2.6E-06
2.3E-06
3.6E-07
5.5E-07
4.3E-07
1.2E-06
4.9E-07
3.9E-07
4.3E-07
1.3E-05
4.2E-06
3.9E-07
6.3E-07
1.8E-06
2.3E-06
3.8E-07
4.0E-07
2.8E-06
2.4E-06
4.1E-07
3.2E-07
1.2E-05
24.57
6.98
1.58
12.79
8.48
1.48
2.05
1.54
5.18
1.83
1.48
1.52
68.76
20.50
1.61
3.23
9.72
11.37
1.63
1.63
11.34
9.97
1.55
1.16
47.73
Sampling date: 12-04-97, 3 hr after fertilization.
7.6
300
1
4.0
300
2
4.0
0
3
7.6
0
4
7.6
0
5
4.0
0
6
4.0
300
7
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
4158
1260
367
1737
1602
406
529
453
902
489
427
457
8010
2713
425
558
1247
1530
418
429
1896
1644
438
385
7855
373
358
278
291
382
350
384
394
326
380
375
403
275
295
347
279
266
285
334
347
350
341
375
393
372
110
Continued
Table A-8.
N20 in
N20
N20 Denitrif.
core
N20
Target
jar
disolved
total
rate
water
jar weight of
Incu-
water
in
water
Edenitr
N20-N
dry
core
content
WFPS
headspacx
tensionNPlot bation concentr.
kPa
kg/ha
#
7.6
300
8
4.0
300
9
7.6
0
10
7.6
300
11
4.0
0
12
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
ppb
g
mL
416
396
1574
1078
10317
239
297
2639
1314
621
245
912
831
362
295
4689
1556
214
559
644
1181
487
840
362
365
345
297
330
312
380
324
354
355
382
328
373
382
373
374
378
331
313
361
338
330
273
65.6
76.3
72.2
59.9
66.5
60.2
73.4
69.5
76.0
84.5
91.0
58.1
65.9
75.2
73.3
72.4
73.2
67.6
63.8
85.0
79.5
89.5
74.1
g
g
g
g/ha/d
0.53
0.60
0.60
0.58
0.58
0.56
0.56
0.61
0.61
0.67
0.67
0.52
0.52
0.57
0.57
0.56
0.56
0.59
0.59
0.66
0.66
0.74
0.74
3.6E-07
3.3E-07
2.2E-06
1.5E-06
1.6E-05
8.8E-08
1.7E-07
3.9E-06
1.8E-06
6.7E-07
9.0E-08
1.2E-06
1.0E-06
2.7E-07
1.7E-07
7.0E-06
2.1E-06
4.6E-08
6.0E-07
7.0E-07
1.6E-06
4.7E-07
1.1E-06
1.4E-08
1.5E-08
9.3E-08
5.0E-08
6.3E-07
3.1E-09
7.6E-09
1.6E-07
8.0E-08
3.4E-08
5.1E-09
3.9E-08
4.0E-08
1.2E-08
7.5E-09
3.0E-07
9.3E-08
1.8E-09
2.2E-08
3.6E-08
7.3E-08
2.5E-08
4.5E-08
3.8E-07
3.4E-07
2.3E-06
1.5E-06
1.7E-05
9.1E-08
1.8E-07
4.1E-06
1.8E-06
7.0E-07
9.5E-08
1.2E-06
1.0E-06
2.8E-07
1.8E-07
7.3E-06
2.2E-06
4.8E-08
6.2E-07
7.4E-07
1.6E-06
4.9E-07
1.1E-06
1.49
1.33
9.40
7.22
72.41
0.42
0.68
17.91
7.40
2.84
0.36
5.26
4.01
1.06
0.68
27.78
8.35
0.21
2.85
2.92
6.88
2.13
5.77
0.57
0.57
0.70
0.70
0.54
0.54
0.53
0.53
0.61
0.61
0.53
0.53
0.62
0.62
0.59
0.59
0.59
5.4E-07
3.3E-07
3.3E-07
3.0E-07
1.0E-06
1.5E-07
1.9E-07
2.4E-07
1.6E-06
3.0E-07
4.9E-07
3.6E-07
6.2E-07
5.3E-07
-8.6E-09
3.5E-07
9.1E-07
1.7E-08
9.9E-09
1.8E-08
1.2E-08
3.4E-08
5.6E-09
7.7E-09
8.7E-09
6.7E-08
1.5E-08
2.1E-08
1.2E-08
1.5E-08
1.6E-08
-3.4E-10
1.3E-08
3.2E-08
5.5E-07
3.4E-07
3.5E-07
3.1E-07
1.1E-06
1.5E-07
2.0E-07
2.4E-07
1.6E-06
3.2E-07
5.1E-07
3.7E-07
6.4E-07
5.4E-07
-9.0E-09
3.7E-07
9.4E-07
2.31
1.78
1.46
1.30
4.31
0.62
0.78
0.86
5.96
1.22
1.89
1.45
3.75
3.10
-0.04
1.39
3.80
Sampling date: 12-18-97, 14 days after fertilization.
7.6
300
1
4.0
300
2
4.0
0
3
7.6
0
4
7.6
0
5
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
517
381
400
372
836
275
307
335
1212
381
504
410
548
498
177
408
756
341
272
344
341
356
351
370
404
395
372
389
367
243
251
328
375
353
56.3
53.8
87.2
69.0
56.0
65.7
66.4
61.6
70.1
80.4
70.6
56.3
43.7
55.1
67.1
63.7
60.2
111
Continued
Table A-8.
Target
water
tension
kPa
N20 Denitrif
N20
N20 in
core
rate
total
jar
disolved
weight of water
N Plot bation concentr. dry core content WFPS headspau in water f/denitr N20-N
g/ha/d
g
g
ppbgmLg
kg/ha #
N20
4.0
0
6
4.0
300
7
7.6
300
8
4.0
300
9
7.6
0
10
7.6
300
11
4.0
0
12
Incu-
jar
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
342
338
253
330
376
336
358
498
830
427
314
365
358
398
321
323
516
248
223
169
1086
347
311
422
305
300
271
583
381
476
257
331
306
302
388
395
357
309
396
391
363
381
368
347
389
366
400
343
379
352
338
375
303
347
358
307
331
379
312
298
262
360
68.0
59.6
49.2
61.4
74.3
81.9
57.6
62.8
73.7
69.3
61.0
56.0
62.3
72.4
57.4
66.7
68.6
76.0
58.7
50.3
65.5
50.2
49.3
50.2
50.0
58.4
56.8
57.3
67.1
58.5
65.8
0.59
0.56
0.56
0.55
0.55
0.65
0.65
0.55
0.55
0.55
0.55
0.53
0.53
0.54
0.54
0.58
0.58
0.58
0.58
0.51
0.51
0.49
0.49
0.48
0.48
0.52
0.52
0.64
0.64
0.63
0.63
2.5E-07
2.5E-07
1.2E-07
2.3E-07
3.0E-07
2.4E-07
2.8E-07
4.9E-07
9.9E-07
3.8E-07
2.0E-07
2.9E-07
2.8E-07
3.3E-07
2.2E-07
2.2E-07
5.3E-07
1.0E-07
6.5E-08
-2.2E-08
1.4E-06
2.7E-07
2.1E-07
3.8E-07
2.0E-07
1.9E-07
1.4E-07
6.5E-07
3.2E-07
4.9E-07
1.2E-07
2.6E-07
2.6E-07
1.2E-07
2.4E-07
3.1E-07
2.5E-07
2.9E-07
5.1E-07
1.0E-06
4.0E-07
2.1E-07
3.0E-07
2.9E-07
3.5E-07
2.3E-07
2.2E-07
5.5E-07
1.1E-07
6.7E-08
-2.2E-08
1.5E-06
2.8E-07
2.1E-07
4.0E-07
2.1E-07
2.0E-07
1.4E-07
6.7E-07
3.3E-07
5.0E-07
1.2E-07
1.14
1.22
0.57
0.88
1.12
0.99
1.36
1.83
3.79
1.56
0.80
1.16
1.19
1.27
0.88
0.80
2.28
0.40
0.27
-0.09
5.57
1.31
0.88
1.58
0.96
0.84
0.54
3.07
1.59
2.74
0.48
56.0
80.0
55.7
57.6
71.1
82.8
69.6
84.4
75.0
0.61
0.61
0.59
0.59
0.64
0.64
0.71
0.71
0.73
1.4E-06 4.5E-08 1.4E-06
4.1E-06 2.0E-07 4.3E-06
1.1E-06 3.7E-08 1.2E-06
3.8E-07 1.2E-08 3.9E-07
9.8E-07 4.2E-08 1.0E-06
4.2E-06 2.1E-07 4.4E-06
9.9E-07 4.1E-08 1.0E-06
1.1E-06 5.6E-08 1.2E-06
3.7E-07 1.7E-08 3.9E-07
6.49
16.47
5.20
2.00
3.79
17.36
4.37
5.16
1.56
1.0E-08
8.6E-09
3.2E-09
8.4E-09
1.3E-08
1.2E-08
9.4E-09
1.8E-08
4.4E-08
1.6E-08
7.4E-09
9.5E-09
1.0E-08
1.4E-08
7.4E-09
8.7E-09
2.1E-08
4.6E-09
2.2E-09
-6.3E-10
5.5E-08
7.7E-09
5.9E-09
1.1E-08
5.7E-09
6.4E-09
4.6E-09
2.1E-08
1.2E-08
1.6E-08
4.5E-09
Sampling date: 01-16-98, 3 hr after fertilization.
7.6
300
1
4.0
300
2
4.0
0
3
R
R
F
F
R
R
F
F
R
1067
2883
918
436
842
2964
836
925
445
317
373
325
279
385
365
338
325
354
112
Table A-8.
Continued
N20 in
N20
N20 Denitrif.
core
N20
Target
jar
disolved
total
rate
jar
weight of water
Incu-
water
NPlot bation concentr. dry core content WFPS headspact in water f/denitr N20-N
tension
g/ha/d
inL
g
ppb
kPa kg/ha #
g
g
g
7.6
0
4
7.6
0
5
4.0
0
6
4.0
300
7
7.6
300
8
4.0
300
9
7.6
0
10
7.6
300
11
4.0
0
12
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
R
R
F
F
539
385
416
586
587
796
750
781
577
1668
542
250
648
418
506
1502
1115
587
849
211
1784
426
1269
798
2150
1392
672
569
990
552
772
827
810
450
456
925
676
529
685
357
370
351
260
293
320
265
334
322
323
308
364
375
398
350
342
352
341
379
377
324
307
272
308
285
302
317
344
258
292
308
343
336
338
341
323
302
311
337
95.9
76.7
91.5
55.1
78.6
65.9
68.8
70.0
85.3
64.0
75.9
69.1
87.9
69.3
73.7
66.6
85.0
63.0
85.8
58.3
59.1
53.0
56.8
60.4
69.5
62.7
83.1
67.4
63.0
48.0
60.6
65.0
78.6
59.7
73.1
67.3
79.4
67.6
93.5
0.73
0.72
0.72
0.73
0.73
0.71
0.71
0.72
0.72
0.68
0.68
0.66
0.66
0.60
0.60
0.67
0.67
0.64
0.64
0.53
0.53
0.60
0.60
0.68
0.68
0.72
0.72
0.68
0.68
0.57
0.57
0.65
0.65
0.61
0.61
0.72
0.72
0.75
0.75
5.0E-07
2.8E-07
3.2E-07
6.3E-07
6.1E-07
9.4E-07
8.9E-07
9.1E-07
5.8E-07
2.3E-06
5.3E-07
6.8E-08
6.7E-07
3.2E-07
4.7E-07
2.0E-06
1.4E-06
6.0E-07
9.7E-07
6.7E-09
2.5E-06
3.6E-07
1.8E-06
9.6E-07
3.1E-06
1.9E-06
7.3E-07
5.7E-07
1.3E-06
5.7E-07
9.1E-07
9.8E-07
9.4E-07
3.9E-07
3.9E-07
1.1E-06
7.4E-07
5.2E-07
7.3E-07
3.0E-08
1.3E-08
1.8E-08
1.9E-08
2.8E-08
3.6E-08
3.5E-08
3.7E-08
2.9E-08
8.7E-08
2.4E-08
2.8E-09
3.6E-08
1.4E-08
2.0E-08
8.0E-08
7.2E-08
2.2E-08
5.1E-08
2.3E-10
8.6E-08
1.1E-08
5.6E-08
3.3E-08
1.3E-07
6.9E-08
3.6E-08
2.3E-08
4.6E-08
1.5E-08
3.2E-08
3.7E-08
4.4E-08
1.3E-08
1.7E-08
4.5E-08
3.5E-08
2.0E-08
4.1E-08
5.3E-07
2.9E-07
3.4E-07
6.5E-07
6.3E-07
9.8E-07
9.2E-07
9.4E-07
6.1E-07
2.4E-06
5.6E-07
7.1E-08
7.0E-07
3.4E-07
4.9E-07
2.1E-06
1.5E-06
6.3E-07
1.0E-06
6.9E-09
2.6E-06
3.7E-07
1.8E-06
9.9E-07
3.3E-06
2.0E-06
7.7E-07
5.9E-07
1.3E-06
5.9E-07
9.5E-07
1.0E-06
9.9E-07
4.0E-07
4.1E-07
1.2E-06
7.8E-07
5.4E-07
7.7E-07
2.13
1.11
1.37
3.57
3.09
4.37
4.97
4.04
2.69
10.71
2.58
0.28
2.69
1.21
1.99
8.88
5.95
2.63
3.87
0.03
11.58
1.72
9.51
4.59
16.37
9.40
3.45
2.47
7.41
2.88
4.39
4.24
4.19
1.70
1.71
5.26
3.68
2.46
3.28
113
Table A-8.
Continued
N20
Target
water
Incu-
jar
N20 in
core
weight of water
jar
N20
disolved
N20
Denitrif.
total
rate
tensionNPlot bation concentr. dry core content WFPS headspacc in water f/denitr N20-N
kPa
kg/ha
#
ppb
g
mLg
g
g
g/ha/d
Sampling date: 02-20-98, 35 days after fertilization.
38.9
269
282
1
F
300
7.6
58.7
347
15452
R
65.7
367
21573
R
2
300
4.0
77.3
355
962
F
58.1
313
958
R
3
0
4.0
74.3
326
687
F
46.9
246
3263
4
R
0
7.6
54.5
232
554
F
62.6
351
422
F
5
0
7.6
59.0
272
482
R
64.2
346
613
F
6
0
4.0
77.8
342
2855
R
75.6
412
6834
R
7
300
4.0
83.8
373
6166
F
55.1
328
1251
F
8
300
7.6
58.5
289
6359
R
58.7
310
1070
F
300
9
4.0
85.4
365
6813
R
64.2
380
411
F
10
0
7.6
72.0
354
527
R
53.5
338
3810
R
11
300
7.6
72.4
386
835
F
60.0
295
3537
12
R
0
4.0
78.8
309
940
F
0.50
0.50
0.62
0.62
0.64
0.64
0.66
0.66
0.62
0.62
0.64
0.64
0.63
0.63
0.58
0.58
0.66
0.66
0.58
0.58
0.55
0.55
0.70
0.70
1.6E-07
2.4E-05
3.3E-05
1.2E-06
1.2E-06
7.9E-07
5.2E-06
6.2E-07
3.7E-07
4.9E-07
6.7E-07
4.2E-06
1.0E-05
9.1E-06
1.7E-06
1.0E-05
1.4E-06
1.0E-05
3.5E-07
5.3E-07
5.8E-06
1.0E-06
5.5E-06
1.2E-06
3.4E-09
8.3E-07
1.3E-06
5.6E-08
4.1E-08
3.4E-08
1.3E-07
1.9E-08
1.4E-08
1.6E-08
2.5E-08
1.9E-07
4.7E-07
4.6E-07
5.4E-08
3.3E-07
4.8E-08
5.2E-07
1.3E-08
2.3E-08
1.8E-07
4.4E-08
1.9E-07
5.5E-08
1.6E-07
2.5E-05
3.5E-05
1.3E-06
1.3E-06
8.2E-07
5.3E-06
6.4E-07
3.9E-07
5.0E-07
7.0E-07
4.4E-06
1.1E-05
9.6E-06
1.8E-06
1.0E-05
1.5E-06
1.1E-05
3.6E-07
5.5E-07
6.0E-06
1.0E-06
5.6E-06
1.2E-06
0.87
103.37
135.13
5.06
5.89
3.60
30.91
3.93
1.57
2.64
2.88
18.19
36.40
36.62
7.73
51.56
6.82
41.64
1.36
2.23
25.37
3.85
27.28
5.75
Sampling date: 02-28-98, 3 hr after fertilization.
323
5572
1
R
300
7.6
284
2663
F
312
1734
R
2
300
4.0
323
916
F
362
434
R
3
0
4.0
339
354
F
260
421
R
4
0
7.6
273
346
F
269
415
R
5
0
7.6
253
439
F
369
363
R
6
0
4.0
348
354
F
293
504
R
300
7
4.0
299
366
F
296
523
8
F
300
7.6
0.61
0.61
0.61
0.61
0.56
0.56
0.59
0.59
0.59
0.59
0.57
0.57
0.55
0.55
0.51
8.7E-06
4.0E-06
2.5E-06
1.2E-06
3.9E-07
2.6E-07
3.9E-07
2.6E-07
3.8E-07
4.2E-07
2.8E-07
2.6E-07
5.2E-07
2.9E-07
5.6E-07
2.8E-07
1.4E-07
7.9E-08
4.7E-08
1.3E-08
1.0E-08
9.6E-09
8.2E-09
9.8E-09
1.2E-08
9.9E-09
1.1E-08
1.4E-08
9.3E-09
1.4E-08
9.0E-06
4.2E-06
2.6E-06
1.2E-06
4.0E-07
2.7E-07
4.0E-07
2.7E-07
3.9E-07
4.3E-07
2.9E-07
2.7E-07
5.4E-07
3.0E-07
5.7E-07
39.74
21.10
11.88
5.33
1.59
1.15
2.22
1.41
2.08
2.45
1.11
1.12
2.63
1.43
2.75
57.0
60.9
55.3
69.6
58.8
65.7
44.2
55.9
46.3
52.7
60.7
68.4
46.4
56.3
43.7
114
Table A-8. Continued
N20 in
N20
core
N20
jar
disolved
Incujar weight of water
N Plot bation concentr. dry core content WFPS headspact in water
tension
g
ppbgmLg
kPa kg/ha #
N20
Denitrif.
total
f/denitr
g
rate
N20-N
g/ha/d
3.82
8.07
8.32
2.19
2.07
3.03
4.89
2.97
3.88
Target
water
4.0
300
9
7.6
0
10
7.6
300
11
4.0
0
12
R
R
F
F
R
F
R
R
F
538
1242
1150
470
513
534
890
607
692
230
313
280
310
365
281
340
336
312
39.7
53.6
57.9
48.9
68.3
39.0
54.9
47.3
51.1
0.51
0.59
0.59
0.55
0.55
0.48
0.48
0.49
0.49
6.0E-07
1.7E-06
1.6E-06
4.6E-07
5.1E-07
5.8E-07
1.1E-06
6.8E-07
8.2E-07
1.3E-08
5.2E-08
5.2E-08
1.3E-08
2.1E-08
1.3E-08
3.6E-08
1.8E-08
2.4E-08
6.1E-07
1.8E-06
1.6E-06
4.8E-07
5.3E-07
5.9E-07
1.2E-06
7.0E-07
8.5E-07
7.5E-06 31.93
4.2E-06 20.55
5.10
1.2E-06
0.88
1.7E-07
4.20
8.1E-07
3.11
7.3E-07
2.20
5.3E-07
1.96
3.9E-07
8.9E-06 37.72
2.02
4.8E-07
2.01
4.5E-07
0.70
1.5E-07
2.0E-04 863.65
5.7E-04 2942.73
1.3E-05 54.29
2.1E-06 11.25
5.5E-06 29.79
1.6E-05 70.97
2.1E-05 89.04
4.3E-06 22.57
4.3E-05 193.24
3.0E-06 13.00
4.40
9.4E-07
Sampling date: 02-20-98, 35 days after fertilization.
7.6
4.0
4.0
7.6
7.6
4.0
4.0
7.6
4.0
7.6
7.6
4.0
7.6
4.0
4.0
7.6
7.6
4.0
4.0
7.6
4.0
7.6
7.6
300
300
0
0
0
0
300
300
300
0
300
0
300
300
0
0
0
0
300
300
300
0
300
1
2
3
4
5
6
7
8
9
10
11
12
1
2
3
4
5
6
7
8
9
10
11
F
F
F
F
F
F
F
F
F
F
F
F
R
R
R
R
R
R
R
R
R
R
R
4912
2757
1071
410
787
751
632
535
5657
603
576
403
124050
341676
8180
1529
3581
10020
12906
2816
26874
2125
871
338
290
350
274
276
335
344
283
336
342
320
310
334
279
335
261
264
319
329
271
321
326
305
70.7
41.8
60.3
48.5
52.1
58.8
54.2
19.3
54.5
48.0
23.2
61.6
85.0
72.4
93.5
81.5
79.9
90.6
89.6
50.5
89.5
84.1
58.5
0.60
0.52
0.57
0.61
0.60
0.56
0.54
0.32
0.56
0.50
0.32
0.63
0.70
0.71
0.75
0.82
0.80
0.76
0.74
0.54
0.75
0.71
0.56
7.2E-06
4.1E-06
1.2E-06
1.6E-07
7.9E-07
7.0E-07
5.1E-07
3.8E-07
8.6E-06
4.7E-07
4.4E-07
1.5E-07
1.9E-04
5.5E-04
1.2E-05
2.0E-06
5.3E-06
1.5E-05
1.9E-05
4.2E-06
4.1E-05
2.8E-06
9.1E-07
3.0E-07
9.5E-08
4.3E-08
4.4E-09
2.3E-08
2.4E-08
1.6E-08
4.0E-09
2.7E-07
1.3E-08
5.7E-09
5.2E-09
9.7E-06
2.3E-05
6.8E-07
9.2E-08
2.4E-07
8.2E-07
1.0E-06
1.2E-07
2.2E-06
1.4E-07
3.0E-08
4.0
0
12
R
1529
297
91.3
0.81
1.9E-06
1.0E-07 2.0E-06
9.65
115
Table A-9.
Denitrification rate and related data. Sweet corn 1998.
Target
water
tension
ItPa
N20 in N20
core
N20 Denitrif
weight of water
jar
disolved total
rate
PLOT concentr. dry core content WFPS headspac in water f/denitr N20-N
#
ppbgmL
g/ha/d
g
g
g
N20
jar
N
kg/ha
Sampling date: 04-09-97, 24 hr after fertilization
30.0
30.0
48.0
48.0
30.0
48.0
30.0
48.0
48.0
30.0
30.0
48.0
270
0
270
0
0
270
270
0
270
0
270
0
1
2
3
4
5
6
7
8
9
10
11
12
442
386
2685
405
479
7628
547
385
1308
573
347
2626
296
413
226
381
358
392
318
382
376
333
367
349
35.9
16.5
40.9
68.3
65.9
72.1
59.1
70.3
78.7
60.2
57.6
59.6
0.37
0.13
0.53
0.53
0.54
0.54
0.54
0.54
0.60
0.53
0.47
0.50
7.9E-07
6.9E-07
4.9E-06
6.9E-07
8.1E-07
1.3E-05
9.4E-07
6.4E-07
2.2E-06
1.0E-06
5.9E-07
4.5E-06
6.5E-09
2.7E-09
3.7E-08
9.7E-09
1.4E-08
2.3E-07
1.4E-08
1.1E-08
4.4E-08
1.1E-08
8.6E-09
6.1E-08
8.0E-07
6.9E-07
4.9E-06
7.0E-07
8.2E-07
1.3E-05
9.5E-07
6.6E-07
2.2E-06
1.0E-06
6.0E-07
4.6E-06
7.76
5.07
73.14
5.87
5.73
87.41
7.82
4.58
15.17
11.14
4.34
38.20
45.9
62.6
61.4
56.8
68.5
57.8
66.1
66.9
60.8
43.5
54.3
55.5
0.43
0.56
0.59
0.52
0.59
0.51
0.55
0.56
0.51
0.40
0.44
0.51
8.2E-07
1.1E-05
4.8E-06
5.8E-07
1.5E-06
1.2E-06
7.9E-06
6.1E-07
5.9E-07
6.3E-07
1.4E-06
5.7E-07
2.2E-08
4.0E-07
1.7E-07
2.0E-08
6.3E-08
4.1E-08
3.2E-07
2.5E-08
2.2E-08
1.6E-08
4.7E-08
1.9E-08
8.4E-07
1.1E-05
5.0E-06
6.0E-07
1.6E-06
1.2E-06
8.3E-06
6.3E-07
6.1E-07
6.5E-07
1.5E-06
5.9E-07
3.27
41.60
19.84
2.26
5.61
4.48
28.60
2.18
2.14
2.49
4.91
2.23
57.7
61.8
66.3
46.6
67.6
58.1
51.8
53.2
52.2
64.7
65.7
39.7
0.50
0.60
0.57
0.42
0.57
0.51
0.45
0.45
0.46
0.53
0.53
0.37
6.1E-07
1.3E-05
9.2E-06
6.9E-07
2.5E-06
9.4E-07
1.3E-06
1.0E-06
6.4E-07
2.3E-05
5.3E-06
2.0E-06
2.1E-08
4.8E-07
3.7E-07
1.9E-08
1.0E-07
3.3E-08
3.9E-08
3.3E-08
2.0E-08
9.0E-07
2.1E-07
4.6E-08
6.3E-07
1.4E-05
9.6E-06
7.1E-07
2.6E-06
9.8E-07
1.3E-06
1.1E-06
6.5E-07
2.4E-05
5.6E-06
2.1E-06
2.27
55.03
33.86
2.62
8.94
3.58
4.70
3.83
2.40
79.36
18.60
7.92
Sampling date: 04-16-97, 7 days after fertilization.
30.0
30.0
48.0
48.0
30.0
48.0
30.0
48.0
48.0
30.0
30.0
48.0
270
0
270
0
0
270
270
0
270
0
270
0
1
2
3
4
5
6
7
8
9
10
11
12
510
6930
3048
371
993
768
5198
400
383
395
926
363
367
384
359
381
403
395
413
415
409
373
429
379
Sampling date: 04-24-97, 24 hr after fertilization.
30.0
30.0
48.0
48.0
30.0
48.0
30.0
48.0
48.0
30.0
30.0
48.0
270
0
270
0
0
270
270
0
270
0
270
0
1
2
3
4
5
6
7
8
9
10
11
12
391
8449
5981
434
1612
605
811
672
404
14958
3515
1259
396
359
403
386
410
390
398
404
390
426
427
374
116
Table A-9. Continued
core
jar weight of water
concentr. dry core content
mL
ppb
g
N20 in
N20
Target
water
tension
N
PLOT
kPa
kg/ha
#
jar
N20
disolved
N20
Denitrif
total
rate
WFPS headspac in water f/denitr N20-N
g
g
g
g/ha/d
Sampling date: 04-25-97, 48 hr after fertilization.
59.5
262
411
1
270
30.0
74.7
2
1007
410
0
30.0
63.7
1131
414
270
3
48.0
52.1
274
400
4
0
48.0
420
83.7
5
410
0
30.0
56.1
6
1378
368
270
48.0
5152
393
73.9
270
7
30.0
398
63.8
287
8
0
48.0
294
406
63.2
9
270
48.0
54.7
772
415
10
0
30.0
408
65.3
11
741
30.0
270
380
48.6
739
0
12
48.0
0.50
0.63
0.53
0.45
0.69
0.53
0.65
0.55
0.54
0.46
0.55
0.44
4.0E-07
1.5E-06
1.7E-06
4.3E-07
6.1E-07
2.2E-06
7.9E-06
4.4E-07
4.5E-07
1.2E-06
1.1E-06
1.2E-06
1.4E-08
7.0E-08
6.7E-08
1.3E-08
3.2E-08
7.2E-08
3.5E-07
1.7E-08
1.7E-08
3.9E-08
4.5E-08
3.3E-08
4.2E-07
1.6E-06
1.8E-06
4.4E-07
6.4E-07
2.3E-06
8.2E-06
4.6E-07
4.7E-07
1.2E-06
1.2E-06
1.2E-06
1.45
5.55
6.22
1.58
2.18
8.73
29.94
1.65
1.65
4.26
4.14
4.54
Sampling date: 05-18-97, 24 hr before fertilization.
49.9
761
385
1
270
30.0
55.5
1411
399
54.0
709
408
2
0
30.0
288
55.4
17931
285
295
22.5
3
270
48.0
28.4
464
334
47.4
259
340
4
0
48.0
45.4
344
351
372
52.1
5
405
30.0
0
280
43.8
496
326
27.1
6
285
270
48.0
354
34.4
277
338
52.3
7
884
270
30.0
60.8
5813
395
44.4
328
364
8
48.0
0
341
70.1
507
36.0
365
9
309
48.0
270
36.8
371
331
42.3
467
375
0
10
30.0
368
38.3
288
326
33.7
11
305
270
30.0
26.2
285
322
338
29.4
279
48.0
0
12
24.1
315
285
0.45
0.48
0.46
0.66
0.26
0.29
0.48
0.45
0.48
0.54
0.29
0.34
0.53
0.53
0.42
0.71
0.34
0.34
0.39
0.36
0.36
0.28
0.30
0.26
1.3E-06
2.5E-06
1.2E-06
3.4E-05
4.6E-07
8.0E-07
3.9E-07
5.5E-07
6.5E-07
8.6E-07
4.5E-07
4.3E-07
1.6E-06
1.0E-05
5.2E-07
8.3E-07
4.9E-07
5.3E-07
7.7E-07
4.5E-07
4.9E-07
4.6E-07
4.4E-07
4.6E-07
3.8E-08
8.1E-08
3.8E-08
1.1E-06
5.7E-09
1.3E-08
1.1E-08
1.4E-08
2.0E-08
2.1E-08
6.8E-09
8.4E-09
4.7E-08
3.8E-07
1.3E-08
3.4E-08
1.0E-08
1.1E-08
1.9E-08
9.8E-09
9.2E-09
6.6E-09
7.2E-09
6.1E-09
1.3E-06
2.5E-06
1.2E-06
3.5E-05
4.7E-07
8.1E-07
4.0E-07
5.6E-07
6.7E-07
8.8E-07
4.6E-07
4.4E-07
1.6E-06
1.1E-05
5.3E-07
8.7E-07
5.0E-07
5.4E-07
7.9E-07
4.5E-07
5.0E-07
4.6E-07
4.5E-07
4.6E-07
4.98
9.09
4.30
174.20
2.26
3.46
1.69
2.29
2.58
4.51
2.02
1.77
6.78
38.86
2.08
3.63
1.94
2.07
3.02
1.77
2.19
2.05
1.89
2.10
117
Table A-9. Continued
N20
jar
Target
water
tension
N
kPa
kg/ha
N20 in N20
jar
disolved
core
weight of water
N20
total
Denitrif.
rate
PLOT concentr. dry core content WFPS headspac in water f/denitr N20-N
#
ppb
g
Sampling date: 05-20-97, 24 hr after fertilization.
185
1
2485
270
30.0
320
177
333
185
2
0
30.0
210
307
329
136
3
270
48.0
175
303
793
173
4
0
48.0
191
456
207
5
1085
0
30.0
183
1103
136
284
6
270
48.0
277
196
191
299
7
270
30.0
228
915
186
848
8
0
48.0
177
320
170
9
235
270
48.0
163
635
219
1680
10
0
30.0
182
421
132
292
11
30.0
270
129
257
115
337
12
0
48.0
104
223
mL
g
g
g
g/ha/d
24.8
13.7
16.4
21.4
10.9
14.6
18.1
19.0
31.6
23.5
8.7
13.1
18.9
26.1
22.1
12.5
12.8
21.6
28.5
17.2
8.9
8.6
10.7
6.1
0.46
0.27
0.31
0.35
0.28
0.29
0.36
0.34
0.53
0.44
0.22
0.23
0.34
0.40
0.41
0.24
0.26
0.46
0.45
0.33
0.23
0.23
0.32
0.20
4.8E-06
5.5E-07
5.8E-07
5.1E-07
5.9E-07
5.2E-07
1.5E-06
8.2E-07
2.0E-06
2.1E-06
4.9E-07
4.6E-07
5.0E-07
1.7E-06
1.6E-06
5.6E-07
3.8E-07
1.2E-06
3.2E-06
7.5E-07
5.1E-07
4.4E-07
6.1E-07
3.7E-07
6.5E-08
4.0E-09
5.0E-09
5.9E-09
3.3E-09
4.0E-09
1.4E-08
8.3E-09
3.5E-08
2.7E-08
2.2E-09
3.2E-09
5.0E-09
2.4E-08
1.9E-08
3.6E-09
2.5E-09
1.4E-08
5.0E-08
6.9E-09
2.3E-09
1.9E-09
3.3E-09
1.1E-09
4.9E-06
5.6E-07
5.8E-07
5.2E-07
5.9E-07
5.2E-07
1.5E-06
8.3E-07
2.1E-06
2.1E-06
5.0E-07
4.7E-07
5.1E-07
1.7E-06
1.6E-06
5.6E-07
3.8E-07
1.2E-06
3.2E-06
7.6E-07
5.1E-07
4.4E-07
6.1E-07
3.7E-07
37.92
4.51
4.52
3.53
6.23
4.27
12.61
6.21
14.24
16.70
5.22
3.40
3.78
10.84
12.44
4.55
3.24
10.50
21.17
5.95
5.56
4.87
7.61
5.13
Sampling date: 05-29-97, 24 hr before fertilization.
342
36.2
587
270
1
30.0
43.8
377
281
52.0
360
277
0
2
30.0
326
46.4
1475
25.0
317
3
315
270
48.0
24.3
347
1784
43.3
323
251
4
48.0
0
30.7
307
261
31.9
351
352
5
30.0
0
35.3
382
265
20.5
275
387
6
48.0
270
22.6
280
259
33.8
348
1003
7
30.0
270
19.3
264
251
46.8
373
872
8
48.0
0
0.37
0.40
0.50
0.49
0.27
0.24
0.46
0.35
0.31
0.32
0.26
0.28
0.34
0.25
0.43
1.2E-06
5.9E-07
5.8E-07
2.8E-06
6.8E-07
3.4E-06
5.5E-07
5.8E-07
7.3E-07
5.7E-07
8.4E-07
5.9E-07
1.9E-06
5.8E-07
1.6E-06
2.4E-08
1.5E-08
1.8E-08
7.3E-08
9.4E-09
4.6E-08
1.3E-08
9.9E-09
1.3E-08
1.2E-08
9.3E-09
7.2E-09
3 3E-08
6.0E-09
4.4E-08
1.2E-06
6.0E-07
6.0E-07
2.8E-06
6.9E-07
3.4E-06
5.6E-07
5.9E-07
7.5E-07
5.8E-07
8.5E-07
6.0E-07
2.0E-06
5.9E-07
1.7E-06
4.95
2.29
2.38
12.44
3.12
14.10
2.49
2.75
3.05
2.16
4.40
3.05
8.03
3.17
6.44
118
Continued
Table A-9.
N20
jar
Target
water
tension
N
kPa
kg/ha
core
N20 in N20
disolved
jar
weight of water
N20
total
Denitrif.
rate
PLOT concentr. dry core content WFPS headspac in water f/denitr N20-N
PPb
g
mL
683
613
337
301
365
348
2893
295
325
314
287
313
371
311
322
383
294
342
37.9
28.5
42.8
32.3
33.9
28.0
60.0
24.2
34.2
Sampling date: 05-31-97, 24 hr after fertilization.
260
380
47.8
1
270
30.0
274
31.8
293
300
31.1
2
18145
0
30.0
277
42.7
763
284
33.4
303
270
3
48.0
349
26.7
293
368
37.1
4
293
0
48.0
25.8
292
230
347
30.9
5
221
0
30.0
28.4
261
370
28.5
267
368
270
6
48.0
28.5
248
358
408
58.0
345
7
30.0
270
38.8
277
376
359
46.5
8
403
0
48.0
370
55.4
203
302
94.1
272
270
9
48.0
326
30.9
800
350
35.4
296
10
30.0
0
49.1
276
371
41.8
391
11
387
30.0
270
28.6
5595
368
294
51.1
309
12
48.0
0
28.2
275
356
#
48.0
270
9
30.0
0
10
30.0
270
11
48.0
0
12
g
g
g
g/ha/d
0.42
0.34
0.47
0.30
0.38
0.30
0.54
0.28
0.35
1.4E-06
1.2E-06
7.1E-07
6.4E-07
7.7E-07
7.4E-07
5.1E-06
6.5E-07
6.9E-07
2.9E-08
1.9E-08
1.7E-08
1.2E-08
1.5E-08
1.1E-08
1.8E-07
8.6E-09
1.3E-08
1.4E-06
1.3E-06
7.3E-07
6.5E-07
7.9E-07
7.5E-07
5.3E-06
6.6E-07
7.0E-07
6.27
6.32
3.32
2.50
3.61
3.34
19.73
3.22
2.93
0.43
0.40
0.36
0.53
0.41
0.26
0.35
0.39
0.31
0.27
0.27
0.28
0.49
0.36
0.45
0.52
1.08
0.33
0.35
0.46
0.37
0.27
0.60
0.27
5.5E-07
6.5E-07
3.4E-05
1.5E-06
6.6E-07
6.3E-07
6.2E-07
6.6E-07
5.0E-07
5.7E-07
5.8E-07
5.5E-07
6.8E-07
5.9E-07
8.1E-07
4.5E-07
5.6E-07
1.6E-06
6.3E-07
5.8E-07
7.7E-07
1.0E-05
6.6E-07
6.0E-07
1.5E-08
1.1E-08
5.8E-07
3.6E-08
1.2E-08
9.4E-09
1.3E-08
9.1E-09
8.7E-09
9.1E-09
9.3E-09
8.8E-09
2.4E-08
1.3E-08
2.2E-08
1.4E-08
3.1E-08
2.7E-08
1.3E-08
1.7E-08
1.9E-08
1.7E-07
1.9E-08
9.5E-09
5.6E-07
6.6E-07
3.5E-05
1.5E-06
6.8E-07
6.4E-07
6.3E-07
6.7E-07
5.1E-07
5.8E-07
5.9E-07
5.5E-07
7.0E-07
6.0E-07
8.3E-07
4.6E-07
5.9E-07
1.6E-06
6.4E-07
6.0E-07
7.9E-07
1.0E-05
6.8E-07
6.1E-07
2.12
3.44
164.41
7.98
3.41
2.63
2.45
4.19
2.09
2.22
2.28
2.21
2.47
2.28
3.32
1.78
2.79
7.00
2.63
2.30
2.90
40.45
3.29
2.43
119
Continued
Table A-9.
Target
water
tension
kPa
N20 in N20
core
N20 Denitrif.
jar
weight of water
disolved total
rate
NPLOT concentr. dry core content WFPS headspac in water f/denitr N20-N
N20
jar
kg/ha
#
ppb
inL
g
g
g
g
g/ha/d
Sampling date: 06-02-97, 3 days after fertilization.
30.0
30.0
48.0
48.0
30.0
48.0
30.0
48.0
48.0
30.0
30.0
48.0
1
2
3
4
5
6
7
8
9
10
11
12
270
0
270
0
0
270
270
0
270
0
270
0
33625
37505
12681
848
13092
17495
113169
3007
45514
8073
295969
10362
339
412
360
356
381
320
293
362
372
388
365
372
46.7
85.9
37.1
42.7
79.0
30.0
51.0
48.6
64.7
43.6
55.9
60.5
0.48
0.72
0.36
0.41
0.72
0.32
0.60
0.46
0.60
0.39
0.53
0.56
5.5E-05
5.6E-05
2.1E-05
1.4E-06
2.0E-05
2.9E-05
1.9E-04
4.8E-06
7.1E-05
1.3E-05
4.7E-04
1.6E-05
1.5E-06
3.0E-06
4.4E-07
3.4E-08
9.6E-07
4.9E-07
5.4E-06
1.4E-07
2.7E-06
3.3E-07
1.5E-05
5.8E-07
5.6E-05
5.9E-05
2.1E-05
1.4E-06
2.1E-05
3.0E-05
1.9E-04
4.9E-06
7.4E-05
1.3E-05
4.8E-04
1.7E-05
235.87
204.40
83.49
5.64
78.56
132.41
933.49
19.53
283.84
48.47
1895.59
64.64
49.6
59.6
51.9
56.2
56.9
59.4
62.4
65.9
63.9
63.8
68.8
54.9
68.4
65.1
61.7
57.9
51.4
48.8
53.7
39.6
60.9
49.0
45.4
60.8
0.59
0.55
0.45
0.49
0.62
0.60
0.55
0.56
0.60
0.55
0.61
0.59
0.64
0.63
0.56
0.55
0.51
0.58
0.53
0.55
0.54
0.52
0.55
0.55
6.1E-05
3.7E-05
3.9E-06
5.6E-05
1.5E-04
1.9E-04
7.1E-06
2.6E-05
1.0E-04
6.1E-05
1.8E-04
7.0E-06
1.2E-04
2.3E-04
3.1E-05
1.3E-05
1.1E-05
3.7E-05
7.9E-05
3.6E-06
8.2E-05
2.6E-06
5.8E-06
1.4E-05
1.7E-06
1.3E-06
1.2E-07
1.9E-06
4.9E-06
6.6E-06
2.7E-07
1.0E-06
3.8E-06
2.3E-06
7.4E-06
2.2E-07
4.8E-06
8.8E-06
1.1E-06
4.5E-07
3.2E-07
1.0E-06
2.4E-06
7.7E-08
3.0E-06
7.2E-08
1.5E-07
5.2E-07
6.3E-05
3.8E-05
4.0E-06
5.8E-05
1.5E-04
2.0E-04
7.4E-06
2.7E-05
1.1E-04
6.3E-05
1.9E-04
7.3E-06
1.2E-04
2.4E-04
3.2E-05
1.4E-05
1.1E-05
3.8E-05
8.1E-05
3.7E-06
8.4E-05
2.6E-06
5.9E-06
1.5E-05
312.69
147.00
14.38
207.74
697.95
827.16
26.86
96.53
412.13
226.31
686.23
32.39
476.03
950.50
122.27
54.09
45.65
185.75
332.37
20.77
310.81
11.65
29.71
56.14
Sampling date: 06-26-97, 24 hr after fertilization.
30.0
270
1
30.0
0
2
48.0
270
3
48.0
0
4
30.0
0
5
48.0
270
6
30.0
270
7
48.0
0
8
48.0
270
9
30.0
0
10
30.0
270
11
48.0
0
12
33399
21165
2203
32523
83091
108003
4104
15325
58408
35552
104528
3871
68763
130717
17984
7483
6032
20165
44221
1843
47144
1373
3064
8293
288
372
401
400
316
342
394
403
366
399
388
321
371
356
379
361
349
293
348
251
388
324
284
381
120
Cumulative N lost by denitrification. Cauliflower 1996-97.
Table A-10.
Days
after
planting
N
SWT
kPa
Days
average
per
denit.
N
N
period
rate
lost
g/ha
lost
eha
kg/ha
5.2
4.0
5.2
4.0
5.2
4.0
5.2
4.0
5.2
4.0
g/ha/d
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
24
43
64
33
90
26
116
24.5
139
11.5
0.70
0.20
0.59
0.45
0.41
0.59
0.25
0.64
0.86
12.30
2.19
0.56
0.96
0.36
18.54
0.99
0.36
0.23
0.52
0.51
Cumulative
30.2
8.8
25.2
19.1
13.5
19.4
8.2
21.1
22.4
319.8
57.0
14.6
23.5
8.9
454.1
24.3
4.2
2.7
6.0
5.9
Note: For a given sampling date, days per period is the number of
days between the two adyacent sampling dates divided by two.
30.2
8.8
25.2
19.1
43.7
28.2
33.4
40.3
66.1
348.0
90.4
54.8
89.6
356.9
544.6
79.2
93.7
359.6
550.5
85.1
121
Table A-11.
Cumulative N lost by denitrification. Cauliflower 1997-98.
Days
after
planting
SWT
N
kPa
kg/ha
7.6
4.0
7.6
4.0
7.6
4.0
7.6
4.0
7.6
4.0
7.6
4.0
7.6
4.0
7.6
4.0
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
0
300
Days
average
per
denit
N
period
rate
g/ha/d
lost
21
26
32
11
44
13
58
15
74
10
78
22
117
28
135
26
4.63
1.31
2.37
2.82
1.55
0.72
1.75
2.47
1.64
3.09
2.27
2.92
0.89
1.05
1.48
0.78
4.98
3.64
1.90
4.81
2.29
4.15
4.08
16.16
2.02
8.96
2.05
5.03
2.37
11.97
2.97
20.16
Cumulative
g/ha
120.3
34.1
61.7
73.2
17.1
7.9
19.3
27.2
21.3
40.1
29.5
38.0
13.3
15.7
22.3
11.7
49.8
36.4
19.0
48.1
50.3
91.3
89.8
355.6
56.5
250.9
57.4
140.8
61.5
311.1
77.3
524.1
Note: For a given sampling date, days per period is the number of
days between the two adyacent sampling dates divided by two.
N
lost
giha
120.3
34.1
61.7
73.2
137.3
42.0
81.0
100.4
158.7
82.2
110.4
138.4
172.0
97.9
132.7
150.1
221.8
134.3
151.8
198.2
272.1
225.5
241.5
553.8
328.6
476.4
299.0
694.7
390.1
787.5
376.2
1218.8
122
Table A-I2.
SWT
kPa
48.0
30.0
48.0
30.0
48.0
30.0
48.0
30.0
48.0
30.0
48.0
30.0
Cumulative N lost by denitrification. Sweet corn 1997.
Days
after
planting
N
kg/ha
0
270
0
270
0
270
0
270
0
270
0
270
0
270
0
270
0
270
0
270
0
270
0
270
Cumulative
average
Days
per
period
17
20
24
7
32
17
58
20
71
13
85
7
denit.
N
N
rate
g/ha/d
lost
g/ha
lost
Wha
16.22
58.57
7.31
6.64
2.22
8.82
16.56
12.26
4.79
13.28
47.78
8.53
8.09
5.48
11.02
11.25
29.94
166.58
110.48
1021.65
49.96
310.05
164.03
640.42
324.4
1171.5
146.3
132.8
15.6
61.7
116.0
85.8
81.4
225.7
812.2
144.9
161.8
109.5
220.4
225.0
389.2
2165.6
1436.2
13281.5
349.7
2170.3
1148.2
4483.0
324.4
1171.5
146.3
132.8
340.0
1233.2
262.2
218.6
421.4
1459.0
1074.4
363.6
583.2
1568.5
1294.8
588.5
972.3
3734.1
2731.0
13870.0
1322.1
5904.4
3879.2
18352.9
Note: For a given sampling date, days per period is the number of
days between the two adyacent sampling dates divided by two.
123
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