Multiple cropping on soils treated with a mixture of sewage

Multiple cropping on soils treated with a mixture of sewage
CHAPTER 2
Prepared according to the guidelines of the Journal of Environmental Quality
Multiple cropping on soils treated with a mixture of sewage
sludge, lime and fly ash (SLASH)
W.F. Truter 1 and N.F.G. Rethman
ABSTRACT
Due to limited prime agricultural land, South Africa is heavily reliant on the use of acidic
and nutrient deficient soils to meet the needs for increased food production. The growing
South African population has an increased need for food security. Rapid urbanization is
producing vast amounts of sewage sludge and electricity generation facilities are
producing millions of tons of fly ash. Both waste products need a safe disposal method,
beneficial to the user.
Environmental legislation has, however, placed restrictions on the application of
sewage sludge to agricultural land. The prime concern being the accumulation of heavy
metals and risk of disease.
This pot study describes the beneficial effects of SLASH (60% Sewage sludge, 30%
class F fly ash and 10% CaO) incorporation into soils. SLASH incorporation at rates
between 5% - 10% of the soil volume, provided prolonged growth enhancement and yield
increases over several cropping cycles. Other parameters such as root development ,
inflorescence production and stem development were also improved by the residual effect
of SLASH.
W .F. Truter and N.F.G. Rethman, Department of Plant Production and Soil Science, University of
1
Pretoria, Pretoria South Africa . Corresponding author: [email protected]
107
INTRODUCTION
South Africa is characterized by a rapidly growing population
and a poor
agricultural resource base (Rethman et al., 1999b). Increased food production is
therefore, urgently required to improve both national and household food security
(Truter and Rethman, 2000). Sustainable increases in food production are difficult
on a limited resource base. Acidic soils in South Africa are quite common,
especially in high rainfall areas. It is essential to utilize these areas effectively, to
ensure sl.lstainability. In many rural development
able to obtain or use lime to
farmers are not always
their acidic or nutrient depleted soils, because
they lack appropriate transport infrastructure and equipment, and it can become
very expensive. Many factors, as previously mentioned, emphasize the need for
amelioration and the possible use of alternative liming materials, which are more
economically viable and easily accessible.
Previous work by Reynolds et
(1999), to determine the feasibility of
converting waste disposal problems in South Africa into a soil beneficiation
strategy. have proven viable. The co-utilization of fly ash and sewage sludge with
added lime delivered a product termed SLASH (that contains 60 % class F fly
ash, 30 % sewage sludge and 10% unslaked lime on a dry matter basis), which
has beneficial soil amelioration effects.
In the past several problems with waste disposal have been experienced
globally. One of these problems is that sewage sludge, which is often used in
agriculture, often contains heavy metals and pathogens. As a result, its use is
restricted for agricultural land application. Secondly, fly ash production in
countries, which rely on coal for energy, such as South Africa, presents a major
problem to those responsible for the consequences and implications of disposing
of such a "waste" product (Truter et al., 2001).
As with fly ash, only a fraction of total nutrients (especially Nand P) supplied
by organic wastes are available to crops in a season, since they must be
mineralized from organic to inorganic forms. Despite these limitations, sewage
108
sludge and animal manures may be the most cost effective supplement for co­
utilization with fly ash in crop fertilization. Mixtures of fly ash with organic wastes
already have a proven track record (Pitchel and Hayes, 1990; Belau, 1991;
Schwab et
,1991; Sims et a/., 1993; Vincin; et
1994; Sajwan et a/., 1995;
Wong, 1995; Schumann and Sumner, 2000), but the preparation of mixtures has
usually proceeded by trial and error.
Reynolds et a/., (1999), Rethman et a/., (1999a) and Rethman et a/., (1999b)
have reported on the manufacture and use of a soil ameliorant for a variety of
crops- including com, beans, potatoes, spinach and a flower crop such as asters.
These reports highlighted the use of SLASH to eliminate the potential problems
with disease organisms or heavy metal pollutants, while improving soil pH. Ca.
Mg and P. The growth and productivity of such test crops was improved markedly
under conditions of low fertility (Rethman and Truter, 2001).
This study concentrated on the multiple cropping of soils that had been treated
with SLASH. The objective of this study was to determine the long-term residual
effect of this waste product mixture on crop production.
MATERIALS AND METHODS
A pot trial was conducted on the Hatfield Experimental Farm, Pretoria, South
Africa (25°45'S 28°16'E), 1327m above sea level. A uniform sandy loam soil was
ameliorated with SLASH [a mixture of sewage sludge, fly ash and reactive lime
(CaO)] (Reynolds
1999). This mixture of SLASH and soil was placed in 10
litre pots after previous cropping cycles reported by Rethman
al., (1999b).
The work conducted by Rethman et aJ. (1999b) on this soil, reported that this
ameliorant had been applied in December 1998, and planted to vegetable and
flower crops. These crops represented the first two cropping cycles of the study.
The design used in this study, was a randomized plot design with four
treatments (T1 - Control (0% SLASH), T2 - 5 %
T3 - 10% SLASH and
T4 - 30% SLASH) replicated five times under natural temperature conditions.
The treatments were calculated as a percentage of the soil volume.
kilograms of substrate were weighed out and used as the value from which the
109
treatments were calculated and then placed into the 10 litre pots. The soils were
irrigated regularly, supplementing rainfed conditions, to eliminate moisture as a
limiting factor. No additional lime or fertilizer was applied to the treated soils
throughout this study.
This study entailed the cropping of four different crop species, including
ornamental sunflower, buffelgrass, sorghum
and 6th cropping cycles.
3rd Cropping Cycle
Once the 2nd cropping cycle by Rethman et a/., (1999b) was completed, the
soil from those pots was used in this study. An ornamental sunflower (Helianthus
sp. cv. ORIT) was used in the 3rd cropping cycle. Five seeds where planted and
once seeds had germinated, two weeks later, the weaker plants were removed.
The three most vigorous plants were left, to ensure a representative number of
plants in all the pots. During the growth period and at maturity, the length of
sunflowers was measured.
soon as the plants had reached maturity, an
inflorescence count was conducted. These observations were to establish
whether SLASH,
different levels, contributed to longer stem development or
higher flower production. Dry matter production was also measured.
The sunflower study was followed by a perennial grass species, buffelgrass
(Cenchrus ciliaris). This grass was selected because it is reasonably susceptible
to acid soils. It is a palatable grass commonly used for animal forage in dry areas.
(Tainton
a/., 1976). As a result of harsh growing conditions, only two harvests
were taken. The only parameter measured, was dry matter (OM) production.
110
Cropping Cycle
At the beginning of the following summer growing season, the treated soil, still
with no additional SLASH application or any other
was planted to an
annual forage crop, Sorgum sp. cv. Hypergraze. Plants were grown from seed.
Ten seeds were planted and once seedlings were well established the weaker
plants were removed. This was to ensure five strong and healthy plants in all the
pots. The DM production was measured in this growing season.
Three harvests were taken, to establish whether plant growth was still
benefiting from the SLASH treatments, and at what level
performance
was obtained. The pots were harvested as soon as the best treatment reached
flowering stage. This observation was approximately 36 months after the initial
application of SLASH.
soon as the production cycle for sorghum was
terminated, these plants were lifted in June 2001, to assess the influence of
SLASH on root development
6th Cropping Cycle
the summer growing season, winter rye (Secale cerea/a cv. SSR
was planted. Ten rye seeds were initially planted and once they had germinated,
the weaker plants were removed, leaving five vigorous plants so that all the pots
had the same number of plants. Two harvests were taken. All the pots were
harvested when the best treatment reached flowering stage. This, the final DM
production observation for the pot study was approximately 42 months after the
initial application of SLASH.
Statistical analyses
Data on the sunflower inflorescence count and stem length measurements
were not statistically analyzed. All dry matter production data and root study data
was statistically analyzed using PROC GLM (1996/1997 and 199711998).
Statistical analysis was performed using
(SAS Institute, 1996) software.
LSD's were taken at Ps 0.05.
111
treatment. This verifies how different crop species respond to the SLASH
treatments.
Table 2: The mean dry matter production (g/pot) and , ...'w,......., of buffelgrass
ciliaris) on soils amended with different levels of SLASH.
T1-Control
Mass
Mass
Production
(g/pot)
(g/pot)
(g/pot)
(± 0.77)
3.25* (± 0.92)
0.63)
4.07"b (± 0.60)
4.62"b (± 0.51)
5.48\ (± 0.86)
7.71 6 (± 1.06)
c
10.10 (± 0.75)
1.33'\, (± 0.31)
T2-5% SLASH
T3 -10% SLASH
T4
30% SLASH
8
8
10.17
c
2.22)
1.92
"
10.14ac
2.15)
20.31
D
(± 2.55)
Row means with common alphabetical superscripts do not differ significantly (P> 0.05) (Bonferroni
"'abc Column means with common alphabetical subcripts do not differ Significantly
*A Column means with common alphabetical
",<>,'f'rj",tc:
do not differ Significantly
0.05) (Bonferroni
0.05) (Tukey's
The response of buffelgrass to the 30 percent SLASH treatment can possibly
be ascribed to the residual effect of SLASH, where N is becoming more available
over time.
When comparing the results obtained from this fourth cropping cycle to the
third cropping cycle, it seems that there is a tendency that the 5% and 10%
treatments are gradually becoming depleted, although still maintaining a better
yield than the control. This assumption cannot necessarily be accepted, because
it is important to consider the possibility of various individual crop/plant
responses.
Although a root study was not conducted, a marked visual response was
noted, with SLASH dramatically improving root development. FigA illustrates how
buffelgrass root development was influenced by the various SLASH treatments
relative to the control. This dramatic improvement in root development holds
important implications for the erosion control capacity of the species (because of
the binding or re-inforcing properties of such root systems) as well as improving
the plant's ability to survive harsh environmental conditions.
115
The production of the control, for the entire growing season, was however, at
least 40% less than the lowest SLASH treatment.
The results presented in Table 4, indicates a decline in production between the
first harvest and the 2 nd harvest. The decline can be ascribed to the fact that this
crop is a winter crop and the 2nd harvest represents the growth of the crop during
the transition phase from winter to spring. With reference to the total dry matter
(DM) production of rye (Table 4), it is notable that there were no significant
differences between the SLASH treatments.
Nevertheless, the SLASH treatments outperformed the control; giving up to 65%
better yield.
It is evident from this final cropping cycle of this study that the SLASH treated
soils were beginning to show signs of depletion 36 months after the initial SLASH
application.
Table 4: The mean dry matter production (g/pot) and (±MSE) of rye (Seca/e cereala cv. SSR
729) on soils treated with various levels of SLASH. Treatments
na
Harvest Dry
Total OM
Mass
Mass
Production
12110/01
21/11/2001
(g/pot)
(g/pot)
1sf Harvest Dry
T1 - Control
3.00 8 (±O.49)
T2-5% SLASH
3.33
T3 - 10% SLASH
4.08
T4 - 30% SLASH
8
2
b
1.37
8
4.37 (±O.S5)
6.10 (±1 .17)
(±O.71)
2.77\ (±1 .24)
a
(±O.87)
2.62
b
4.24 • (±O.90)
2.36
b
8
8
A
(±O.28)
•
8
(g/pot)
8
8
b
(±O.98)
6.70 (±1.42)
b
(±O.78)
6.60 (±1 .0S)
8
*ab Row means with common alphabetical superscripts do not differ significantly (P> 0.05) (Bonferroni Test)
*ab Column means with common alphabetical subcripts do not differ significantly (P> 0.05) (Bonferroni Test)
*ABC Column means with common alphabetical supercripts do not differ significantly(P> 0.05) (Tukey's Test)
118
CONCLUSION Disposal of waste products such as sewage sludge and 'fiy ash is of major
concern in South Africa and many other countries. Combinations of these and
other waste products to develop a beneficial product, has been extensively
investigated worldwide. Very little work has, however, been done on the use of
such ameliorants in long-term plant production systems to evaluate their residual
effects.
It is very clear that in the SLASH programme, it is of cardinal importance to
examine a wide range of
or even cultivars, under different levels of
intensification (different fertility levels, different water levels, different populations)
and on different substrates, to be able to extrapolate conclusions.
From the results obtained in this study, it may be concluded that SLASH does
improve the growth rate of various crop species. Furthermore, it has a long-term
residual effect, even after cropping the soils intensively over a 36th month period.
It is evident from the results that, on average, the 5% - 10% SLASH levels
delivered the best yields. Another important aspect of the study which became
clear, was that
improved the root development of both sorghum and
buffelgrass, stimulated a higher production of inflorescence's of the ornamental
sunflower, and caused accelerated stem elongation of the sunflower. This
enhancement of both below and aboveground biomass can be ascribed to two
reasons. Firstly, favorable soil conditions were created by SLASH. Secondly,
there was a slow release of essential macro- and micronutrients from the sewage
sludge and the fly ash.
When mixing two waste products, an amendment is created which can be
more beneficial than either component alone. The reason for using an organic
waste such as sewage sludge, is to supplement the bulking agent fly ash with
macronutrients, which it lacks.
advantage of combining two different waste
products, is that different amending qualities of the individual components are
brought together.
doing this, two major problems that are common in highly
productive agricultural soils, such as acidity and nutrient deficiency, can
resolved. The other benefit is that a safe disposal method for large quantities of
119
and can be used in areas in close proximity to the raw
waste products is
materials.
REFERENCES
Belau, L 1991. Laboratory investigations into the microbial decomposition and
nitrogen supply of mixtures of poultry excrement and power plant ash in soils.
Zentralblatt fur Mikrobiologie. 146:117-1
Pichtel, JR., and J.M. Hayes. 1990. Influence of fly ash on soil microbial activity
and populations. J. Environ. Qual. 19:593-597.
Rethman, N.F.G., K.A Reynolds, and RA Kruger. 1999a. Crop responses to
SLASH (mixture of
sludge, lime and fly ash) as influenced by soil
texture, acidity and fertility. Proc. 1999 Internat. Ash Utiliz. Sympos.
Lexington, Kentucky, U.S.A pp. 387-397.
Rethman, N.
, K.A. Reynolds, RA Kruger, E.J. Ramagadza, and E.S. du
1999b.
for flower and vegetable production in the informal sector
in South Africa. Proc. Internat. Ash Utiliz.
Sympos. Lexington, Kentucky,
U.S.A p83-86.
Rethman, N.F.G., and W.F. Truter. 2001 Plant responses on soils ameliorated
with waste products. 18 th National Meeting of ASSMR Albuquerque, New
Mexico. U.S.A pp. 425
Reynolds, K.A. , RA. Kruger, and N.
evaluation of an artificial
Rethman.1999.
manufacture and
prepared from fly ash and sewage sludge. Proc.
1999 IntematL Ash Utiliz. Sympos. Lexington Kentucky, U.S.A pp. 378- 385.
Sajwan, K.S., W.H. Ornes, and
Youngblood. 1
The effect of fly
ash/sewage sludge mixtures and application rates on biomass production. J.
Environ. Sci. Health 30:1327-1337.
SAS Institute Inc. 1996. The SAS system for Windows. SAS Institute Inc. SAS
Campus drive, Cary, North Carolina, USA
Schumann AW" and M.
Sumner. 2000. Chemical evaluation of nutrient supply
from fly ash-biosolids mixtures. Soil Science Society of America Journal Iss 1
64:419-426
120
Schwab, AP., M.B. Tomecek, and
D. Ohlenbusch. 1991. Plant availability of
lead, cadmium, and boron in amended coal ash. Water
Soil Pollut.
58:297-306.
Sims, J.T.,
Vasilas, and M. Gbodrati. 1993.
of coal fly
and co­
composted sewage sludge on emergence and early growth of cover crops.
Comm. Soil Sci. Plant Anal. 24:503-512.
Tainton, N.M.,
I. Bransby, and
de V. Booysen. 1976. Common veld and
pasture grasses of Natal. Shuter and Shooter, Pietermaritzburg. 18-1
Truter, W.F., and N.F.G. Rethman. 2000. Crop productivity in fly ash/sewage
sludge amended soils. Proc. Joint. Conf. Pretoria, South Africa.
Truter, W.F., N.F.G. Rethman, K.A Reynolds, and R.A Kruger. 2001. The use of
a soil ameliorant based on 11y ash and sewage sludge.
2001 Internat.
Ash Utiliz. Sympos. Lexington. Kentucky. U.S.A.
Vincini, M.,
Cairini, and
Silva. 1994. Use of alkaline fly ash as an
amendment for swine manure.
Wong, J.W.C. 1
Technol.
production of artificial soil mix from fly ash and sewage
sludge. Environ. Technol. 16:741-751.
121
CHAPTER 3 Prepared according to the guidelines of the European Journal of Agronomy
The influence of a mixture of sewage sludge, fly ash and lime
(SLASH) on biomass production of two grasses and two
legumes
W.F. Truter a * and N.F.G Rethman
a Department
a
of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South
Afric,a
Abstract
South Africa is characterized by a large and rapidly growing population. Sustainable increases
in forage production are difficult on the limited resource base. The effective use of acidic soils is
also critical in many areas. Air pollution from burning fossil fuels is the major cause of acid rain
and together with incorrect management practices results in the physical (e,g, soil erosion,
compaction), chemical (e,g, soil acidification , salinization) and biological (e,g, declining biological
activity) degradation of soils.
The rapidly increasing cost of nitrogen fertilizers and protein rich forage provided by
leguminous forages, makes the use of legumes in agricultural production systems and mine
rehabilitation essential. Although South Africa has very limited prime agricultural land, we are
reliant on the use of acidic and nutrient deficient soils to meet the needs for highly productive
systems.
In the past, sewage sludge application to agricultural soils was a common practice to improve
infertile soils. Environmental legislation has, however, placed restrictions on such applications.
The prime concern being heavy metal accumulation and risk of disease, Previous research has,
however, indicated that sewage sludge, when treated with a mixture of class F fly ash and lime, is
characterized by the immobilization of heavy metals and pasteurization of disease organisms,
Corresponding author.: Tel. +27-420-3224 Fax. +27-420-4120
Email address: [email protected]
122
This product (SLASH) has been shown to have significant amelioration ......""",.-h",,,, when applied to
acidic and nutrient ae~)letE~a
in enhanced crop productivity.
This work describes the beneficial effects of SLASH incorporation into
in comparison
to an untreated control. It was found that SLASH incorporation rates of 5 - 10% of the soil volume,
provided prolonged growth enhancement of Kentucky
(Poa pratensis), Tall Fescue
White Sweet clover (Meli/otus alba) and Crown vetch (Coronilla varia).
(Festuca
SLASH definitely had beneficial effects on both legume and grass biomass production.
Keywords: Acidic soils; Amelioration;
ash; Legumes; Sewage Sludge; SLASH;
1. Introduction
In South Africa approximately 28 million tons of ash is produced annually as a
result
energy generation to
million people and growing.
the energy reqUirements of a population of 45
largely untapped resource, together with the fact
that, power utilities, are generally situated in areas with a high agricultural
potential, which are being acidified because of the effect of "acid rain" and
agronomic practices, makes it's use a viable proposition. Only a small percentage
of this untapped resource of fly ash is currently used in the cement, plastics,
rubber and paint industry (Reynolds et ai, 2002).
Sewage sludge on the other hand is classified as a toxic waste and it is
produced at a rate of 800 tons/day dry mass in South Africa (Reynolds, 1996).
These problems emphasize the need for co-utilization of wastes and the
identification of possible strategies for the safe disposal and use of such waste
products. Nutrient poor and acidic soils in South Africa are becoming more
prevalent and many farmers require alternatives to the high priced conventional
methods of soil amelioration currently in use (Truter et aI., 2001).
The use of fly ash (FA) as a soil amendment
hindered by a lack of
macronutrients in the ash and concerns about trace element availability or
toxicity. Mixing FA with an organic waste can increase macronutrients while
reducing odor and improving material handling properties, but the trace element
solubility requires further investigation. (Jackson
aI., 1999)
123
The extreme variability measured in waste materials in terms of total nutrient
concentrations, extractable nutrients and the relative nutrient balances is quite
common in other studies, and reinforces the urgent need to characterize waste
materials before mixing and use in crop fertilization. The potential pitfalls of
indiscriminate waste application to soil include (I) potential phytotoxicity from
micronutrient excess (especially B); (ii) shortages of essential macro nutrients
such as N, P, and K due to low supply; (iii) nutrient deficiencies caused by
unfavorable fly ash pH, slow nutrient release, and fixation of other nutrients such
as P already present in the soil solution; and (iv) induced nutrient deficiencies
from the supply of elements in incorrect proportions. Most of these problems can
be overcome by exploiting the complementary nature of fly ash, sewage sludge,
and poultry manure, and additional nutritional benefits (especially N-P-K
balancing) should be possible by mixing these waste materials together
(Schumann and Sumner, 2000).
A soil ameliorant based on fly ash that is supplemented with a small amount of
unslaked lime and mixed with sewage sludge delivers a resultant odour free,
pasteurized, soil-like product, which has growth enhancing properties, trace
minerals from fly ash and organics from the
(Reynolds
sludge is termed SLASH.
aI., 1999)
Reynolds et aI., (1999), Rethman
aI., (1999a) and Rethman et al., (1999b)
have reported on the manufacture and use of a soil ameliorant for a variety of
crops- including corn, beans, potatoes, spinach and a flower crop such as
~~r,Qr~
These reports highlighted the use of SLASH to eliminate the potential
problems with disease organisms or heavy metal pollutants, while improving soil
pH, Ca, Mg and P. The growth and productivity of such test crops was improved
markedly under conditions of low fertility (Rethman and Truter, 2001).
Furthermore, a study conducted by Truter (2002) on the multiple cropping of
treated with SLASH to evaluate the long term residual effect of this waste product
mixture has shown
that substantial yield
increases and
improved
root
development occurred in the soils treated with SLASH.
SLASH has also had marked beneficial effects on productivity and root
development of forages for as long as two years after initial treatment {Rethman
124
and Truter, 2001 ; Truter et aI. , 2001) . While this study emphasized the potential
of such soil amelioration for improved forage productivity and root development. It
also resulted in considerable interest in the potential use of such waste products
to re-vegetate and restore productivity of disturbed soils (Rethman et aI., 2000;
Truter et aI., 2001).
A conclusion drawn from a study of the growth responses of both grasses and
legumes to SLASH, within the limited range of species that were evaluated,
indicated that grasses (which are dependent on Nand P) respond favorably to
the N in SLASH, up to the highest levels of application . This N also has the
advantage of having good persistence by virtue of its "slow release" properties
and/or the favorable C: N ratio created when SLASH is used. In contrast the
legume response (which is usually less dependent on applied N) is more closely
correlated with pH and P status of the growing medium and optimum levels were
much lower than with grasses. Finally it was emphasized that SLASH did not
contain a full range of plant nutrients. Even at the high rates used in trials (50 ­
600 tons ha- 1) regular monitoring of the soil and crops should be employed as the
basis for determining the need for supplementary fertilization. If low levels (100's
kg ha- 1) are recommended, because of the high cost of transport, it is unlikely that
the product will have any meaningful effect on pH, mineral status or organic
matter content of the soil (Rethman and Truter, 2001).
The objective of this study was to further evaluate the use of SLASH in soils
planted to two perennial legumes and two perennial grasses in terms of long term
residual effects.
2. Material and methods
A pot trial was conducted at the Hatfield Experimental Farm, Pretoria, South
Africa (25°45'S 28°16'E), 1327m above sea level. A uniform sandy loam soil was
ameliorated with SLASH (a mixture of sewage sludge, fly ash and reactive lime
(CaO)) .
125
Rethman et al (1999b) reported that SLASH had been applied to the sandy loam
soil in December 1998, and planted to vegetable and flower crops thereafter.
These crops represented the first two cropping cycles of the study. Subsequently,
a study was conducted, where the ameliorated soil used for the first two cropping
cycles, was removed and placed into 10 litre pots. These soils where then planted
to ornamental sunflower (Helianthus sp. cv. ORIT), buffelgrass (Cenchrus ciliaris),
sorghum (Sorghum sp. cv. Hypergraze) and rye (Secale cerea/a cv. SSR 729) as
successive 3rd , 4 th , 5th and 6th cropping cycles (Truter, 2002).
Some of the soil that was used for the first two cropping cycles which was
eventually removed, (Rethman et a/., 1999b) was also planted to sweet clover
(Melilotus alba), crown vetch (Coronilla varia) and Kentucky bluegrass (Poa
pratensis) in spring/summer of the 1999/2000 growing season, simultaneously to
the previously mentioned cropping cycles. Five seeds were planted and once the
seedling stage had been reached; the number of seedlings was reduced to two.
This study was conducted to eventually evaluate total biomass production for a
growing season and to compare production between alternate growing seasons.
The objective of the study was to determine if there was any decrease in
production over time.
Once the 3rd and
4th
cropping cycles were completed, and the plants were
removed before the tall fescue was planted, a further observation was made, and
that was a root study. This was to evaluate what the influence of SLASH was on
root development of bluegrass and sweet clover. At the start of 2000/2001
season, tall fescue was established in the pots that had been planted to Kentucky
Bluegrass and Sweet clover. During this
4th
cropping cycle and the ongoing 3rd
cropping cycle of crown vetch, forage yield was the only measurement to be
taken, to establish what the long term residual effect of SLASH could be relative
to the other treatments. The tall fescue and crown vetch were harvested
whenever the best treatment reached the flowering stage. Eight harvests were
recorded for the tall fescue over the period October 2000 to January 2002, with
ten harvests for the crown vetch over the period December 1999 to January
2002.
126
The design used in this study, was a randomized plot design. The four
treatments that were replicated five times under natural temperature conditions
were: T1 - Control (0% SLASH), T2 - 5 % SLASH, T3 - 10% SLASH and T4 ­
30 % SLASH. The treatments were calculated as a percentage of the soil volume.
Ten kilograms of treated soil was weighed out and used as the value from which
the treatments were calculated and then placed into the 10 litre pots. Soils were
irrigated to eliminate water from being the limiting growth factor. No additional
fertilizer was applied to the treated soils throughout the entire study.
2. 1 Statistical analyses
Data for the Kentucky bluegrass density rating and sweet clover seedling count
was not statistically analysed. All dry matter production data and root study data
was statistically analyzed using PROC GLM (1996/1997 and 199711998) and
PROC ANOVA (1997/1998). Statistical analysis was performed using SAS (SAS
Institute, 1996) software. LSD's were taken at P ~ 0.05.
3. Results and discussion
3. 1 White sweet clover (Melilotus alba)
Seedling survival, forage production and root development of white sweet
clover (Melilotus alba) as influenced by the level of SLASH application, eight
months prior to planting of sweet clover and after two preceding cropping cycles
with flowers and vegetables, are shown in Table 1, Fig. 1 & 3. Seedling survival
was improved by the addition of SLASH to the soils. The higher the SLASH
application the better and quicker the seeds germinated and established
themselves.
127
retarded seedling establishment was most significant, recovered more gradually
and yield was only improved in the subsequent harvests. The conditions created
by the high SLASH ameliorated soil were not optimum for Kentucky bluegrass
although the 30 percent SLASH treatment did deliver the best yields overall.
Table 2
Tlhe mean dry matter (OM) production (g/pot) and (±MSE) of Kentucky bluegrass (Poa
pratensis) as influenced by SLASH.
no
st
2 Harvest
Treatme
1 Harvest
nt'S
-T1Control
3Fd Harvest
4th Harvest Dry
Total OM
Production
Dry Mass
Dry Mass
Dry mass
mass
0211211999
07/01/2000
10/03/2000
17/0412000
(g/pot)
(g/pot)
(g/pot)
(g/pot)
(g/pot)
0.10Ss(±0.02)
0.42 a(±0.23)
0.88aa(±0.43)
1.08Sa(±0.45)
2.47A (±1.02)
2.44\(±2.21 )
2.82ab(±2. 05)
a
2.92 b(±1.61)
2.56ab(±O.71)
10.74 (±6.19)
a
1.13 ab(±0.67)
ab
2. 39 b(±0.89)
b
3.34 b(±0.80)
2.98 bbc(±0.82)
9.84 (±2.46)
a
0.68 ab(±0.47)
b
3.72 b(±0.70)
6.60\(±0.88)
4.26 c(±0.54)
8
n-5%
SLASH
8
T~I - 10%
SLASH
8
T4-30%
SLASH
d
8
15.26 (±2.46)
*abcd Row means with common alphabetical superscripts do not differ significantly (P> 0.05) (Bonferroni Test)
*abcd Column means with common alphabetical subcripts do not differ Significantly (P> 0.05) (Bonferroni Test)
*ABC Column means with common alphabetical supercripts do not differ significantly(P> 0.05) (Tukey's Test)
An even more marked response was noted, with respect to root development.
Increases of up to two thousand one hundred percent were obtained relative to
the control. This dramatic improvement in root development holds important
implications for the erosion control capacity of the species (because of the
binding or re-inforcing properties of such root systems) as well as improving the
plant's ability to survive stress situations.
132
Table 3: The mean dry matter production (g/pot)) of tall fescue (Festuca arundinaceae) in
response to various SLASH treatments.
st
ra
4tH
Treatments
2nd
1
3
T1 - Control
th
SIR
7m
SiR
5
Total
Dry
Harvest
Harvest
Harvest
Harvest
Harvest
Harvest
Harvest
Harvest
Matter
Dry
Dry
Dry
Dry
Dry
Dry
Dry
Dry
Production
Mass
Mass
mass
mass
mass
mass
mass
mass
(g/pot)
(g/pot)
(g/pot)
(g/pot)
(g/pot)
(g/pot)
(g/pot)
(g/pot)
2.98
a
a
1.84
a
a
1.72
a
a
2.32
a
a
2.80
3.68
d
b
3.83
a
5.03° a
a
1.84Ca
a.
(g/pot)
A
a
20.33
ef
a
15.039 a
29.64
8
e
15.80 b
35.14
8
14.43
T2 - 5%
5.61\
SLASH
3.05\
2.61
bc
a
e
b
a
5.4r
a
b
6.62
ab
7. 97
ad
ab
2. 64
T3 -10%
6.33
SLASH
a
b
b
3.46
e
4.98
b
3.26°Cb
4.61
bd
b
5.13
d
e
6.18b
b
2.90
f
a
T4 - 30%
8.69
SLASH
a
b
e
4.70
bc
e
6.57
cde
b
f
c
3. 38 a
g
17.44
e
45.85 c
"abcdefg Row means with common alphabetical superscripts do not differ significantly (P> 0.05) (Bonferroni Test)
"abc Column means with common alphabetical subcripts do not differ significantly (P> 0.05) (80nferroni Test)
"ABC Column means with common alphabetical supercripts do not differ significantly (P> 0.05) (Tukey's Test)
#
No MSE for large data set.
The total OM production (Table 3) for tall fescue over the entire experimental period indicates that all SLASH treatments gave much higher yields than the control. These results emphasize that SLASH definitely has a long-term residual effect. 3.4 Crown Vetch (Coronilla varia cv. Penngift)
Crown Vetch showed a marked response to the SLASH treatments. From Tables 4 and 5 it can be seen that the various treatments performed substantially better than the control in both summer and winter growing seasons. The markedly better response of this legume, compared with tall fescue, may be attributed to the fact that like lucerne it is very sensitive to pH, Ca and P levels, all of which were markedly improved by SLASH. 134
Table 4
The mean dry matter production (g/pot) of crown Vetch (Coronilla varia), in two
consecutive winter growing seasons as influenced by SLASH.
T2 - 5%SLASH
T3 - 10% SLASH
T4 • 30% SLASH
Harvest
Harvest
Total DM
Harvest
Harvest
Total DM Dry Mass
Dry Mass
Production
Dry mass
Dry mass
Production. 0
21.76"b
11.50
19.67"0
b
24.08
"
9.25 o
b
8
b
10.27 o
*ab Row means with common alphabetical superscripts do not differ significantly (P> 0.05) (Bonferroni Test) *abc Column means with common alphabetical subcripts do not differ significantly (P> 0.05) (Bonferroni Test) *AB Column means with common alphabetical
# No
MSE for
do not differ significantly (P> 0.05) data set Table 5 The mean dry matter production (g/pot) of Crown vetch (Coronilla varia), in two consecutive summer growing seasons, as influenced by SLASH. Summer Growing Season 2000/2001
Treatments
Summer Growing Season 2001/2002
4ffi
f11
5
SM
Total Dry
gM
10M
Total Dry
Harvest
Harvest
Harvest
Harvest
Matter
Harvest
Harvest
Matter
Dry
Dry
Dry
Dry
Production
Dry
Production
mass
mass
mass
mass
(g1pot)
(g/pot)
(g/pot)
(g/pot)
8.01""
3,6
mass
mass
(g/pot)
(g/pot)
(g/pot)
(g/pot)
5.87""
26.35A
23.1
12.48
11
35.63A
24.12\
79.56 B
45.54\
24.98\
70.15B
nControl
a
5.96
8
8
T2 - 5%
19.18\
SLASH
"
"
T3 -10%
SLASH
9.03"ab
13.73"b
19.16"0
b
22.87 b
63.80 B
46.26"b
21.67\
68.29 B
12.29""
18. 52Eib
24.81\
27.66"b
83.28B
43.01\
21.21\
64.226
T4 -30%
SLASH
wab Row means with common alphabetical superscripts do not differ Significantly (P> 0.05) (Bonferroni Test)
*ab Column means with common alphabetical subcripts do not differ Significantly
0.05) (Bonferroni Test)
'"AB Column means with common alphabetical supercripts do not differ significantly (P> 0.05) (Tukey's Test)
#
No MSE for large data set.
136
Conclusion
It is currently of cardinal importance to start considering the efficient utilization of
waste products. The pre-eminent environmental issue of waste disposal problems
is becoming more serious by the day. Alternative uses of waste products, such as
fly ash and sewage sludge, have definite agricultural potential.
product mixtures like SLASH, N-Viro soil and other mixtures,
oa~;ea
waste
on
same
principles of production, are excellent additives and amendments for acidic and
nutrient poor soils.
it
very clear from the SLASH programme, that it is of cardinal importance to
examine a wide range of species, or even cultivars, under different levels of
intensification (different fertility levels, different water levels, different populations)
and on different substrates, to
able to extrapolate conclusions.
Crop production responses of all the different plant species throughout the trial
period, gave consistently good
Once again the 5% and 10% SLASH
treatments proved to be superior, resulting in prolonged growth enhancement.
The two grasses used in this study gave Significantly better results on SLASH
treatments than on the control. This can be attributed to the essential macro­
nutrients, which are "slowly released" by the organiCS from the sewage sludge. In
addition to the macro nutrient supply, the equilibrium of nutrient supply was
maintained by the micronutrients, which were supplied by the fly ash in
combination.
The two legumes used in this study, had virtually the same response to
SLASH. It is important to establish a legume with Rhizobia to ensure a symbiosis,
which will benefit the growth of
piant. From this work it can be concluded that
fly ash on it's own, as found by Gutenmann
aI., (1981), and in combination with
an organic waste encourages microbial populations. Root development was also
enhanced by of SLASH, with well-developed root structures resulting. This is very
important to ensure good yields and to stabilize soils.
From the results obtained during this study, it can be concluded that SLASH
long-term residual effects. The
of nutrient """',::I"'''' is not predictable, but
137
it can be stated that such a mixture is characterized by
"slow release" of
nutrients.
The rationale behind such waste mixtures is that the mixture itself is a superior
soil amendment to either component alone. The use of an organic waste
addresses the deficiency of macronutrients in fly ash, while fly ash can act as a
bulking agent for the organic wastes, substantially reducing odor, and offsetting
soil acidity problems that may arise through continued land application of organic
wastes.
References
Adriano, D.C., Page, AL., Elseewi, AA, Chang, AC., Straughan, I. 1980.
Utilization and disposal of fly ash and other coal residues in terrestrial
ecosystems: A review. J Environ. Qual. 9,333-344
Gutenmann, W.H., Elfving, D.C., Valentino, C.I., Lisk, D.J. 1981. Trace element
absorption on soil amended with soft-coal fly ash. Biocycle, 21,42-44.
Jackson, B.P., Miller, W.P., Schumann, AW., Sumner, M.E. 1999. Trace element
solubility from land application of fly ash/organic waste mixtures. J. Environ.
Qual. Iss. 2 28,639-647
Rethman, N.F.G., Reynolds, K.A, Kruger, RA 1999a. Crop responses to
SLASH (mixture of sewage sludge, lime and fly ssh) as influenced by soil
texture, acidity and fertility. Proc. 1999 Internat!. Ash Utiliz. Sympos.
Lexington, Kentucky, U.S.A pp. 387-397.
Rethman, N.F.G. , Reynolds, K.A, Kruger, RA, Ramagadza, E.J., du Toit, E.S.
1999b. SLASH for flower and vegetable production in the informal sector in
South Africa. Proc. Internat. Ash Utiliz. .
Sympos. LeXington, Kentucky,
U.S.A p83-86.
Rethman, N.F.G., du Toit, E., Ramagadza, E., Truter, W.F., Reynolds, K.A,
Kruger, RA 2000. Soil Amelioration Using Waste Products. Proc. Remade
Lands Recl. Conf. Perth, Western Ausralia. pp. 127-128.
138
Rethman, N
Truter, W.F. 2001. Plant responses on soils ameliorated with
waste products. 18th
National Meeting of ASSMR Albuquerque, New
Mexico. U.S.A. pp. 425
Reynolds, K.A. 1996. Ash Utilization - Evaluation of Ash Soil. Eskom Research
Report. TRRlS96/158. Eskom Technology Services.
Reynolds, K.A. , Kruger, RA., Rethman, N.F.G. 1999. The manufacture and
evaluation of an artificial soil prepared from fly ash and sewage sludge. Proc.
1999 Internatl. Ash Utiliz. Sympos. Lexington Kentucky,
pp.
385.
Reynolds, K.A., Kruger, RA., Rethman, N.F.G., Truter, W.F. 2002. The
production of an artificial soil from sewage sludge and fly ash and the
subsequent evaluation of growth enhancement, heavy metal translocation
and leaching potential. Proc. WISA Cont. Durban, South Africa (In Press)
SAS Institute Inc. 1996. The
system for Windows. SAS Institute Inc. SAS
Campus drive, Cary, North Carolina, USA.
Schumann A.W., Sumner, M
2000. Chemical evaluation of nutrient supply from
fly ash-biosolids mixtures. Soil Sci. Soc. Am. J.
Truter, W.F., Rethman, N
1 64,419-426
, Reynolds, K.A., Kruger, RA. 2001. The Use of a
Soil Ameliorant based on fly ash and Sewage Sludge. Proc. 2001 Internat.
Ash Utiliz. Sympos. Lexington, Kentucky, U.S.A.
Truter, W.F. 2002. Multiple cropping of soils
with a mixture of sewage
sludge, lime and fly ash (SLASH). MSc(Thesis) Use of waste products to
enhance plant productivity on acidic and infertile substrates. University of
Pretoria. Chapter 2 pp. 106-121.
139
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