Manual 21435905

Manual 21435905
CHAPTER 4 Prepared according to the guidelines of Agriculture, Ecosystems & Environment
Comparative study on the influence of SLASH and its individual
components on the production of maize (Zea mays) and heavy
metal accumulation.
W.F. Truter a * and N.F.G Rethman
a
a
Department of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South
Africa
Abstract
Utilizing a poor agricultural resource base to produce a staple commodity such as maize for a
growing population, poses some significant challenges. A large percentage of South Africa's
cropping soils are acidic and costs of fertilizers and lime for both subsistence and commercial
farmers are becoming extremely difficult to meet. The need exists for alternative soil amendments
and other forms of fertilizers to enhance plant productivity.
In many countries technologies have been developed to use waste materials with agricultural
benefits, and combine them to get a product, which serves as a soil ameliorant. In South Africa ,
the ameliorant produced is termed SLASH. SLASH is a mixture of sewage sludge, lime and class
F fly ash. Sewage sludge's agricultural application is restricted because of its pathogenicity and
possible heavy metal content whereas fly ash's restriction lies in its lack of macro nutrients such
as N, P and K. However, sewage sludge is a good source of macronutrients and organic matter,
and fly ash has liming qualities. Together a superior product is created.
SLASH has proven to be a beneficial soil ameliorant and enhances plant growth substantially.
Applications of between 7.5%-10% of the soil volume delivered the best results for maize
Corresponding author.: Tel. +27-420-3224
Fax. +27-420-4120
Email address: [email protected]
140
production. Although heavy metal translocation and B phytotoxicity were a major concern,
show that
amounts of Ni, Cd and the micronutrient B were translocated, and
that these were well below safety limits. Heavy metals are, therefore, not as mobile in SLASH as
in sewage sludge.
phytotoxicity, SLASH, soil
Keywords: Acid
<:Im,:>I,n'<:I
1. Introduction
In South Africa increased food production is urgently required to improve both
national and household food security. (Truter and Rethman, 2000). This is quite
difficult especially on a poor agricultural resource base and with a population that
is growing at an exponential rate. (Rethman et at, 1999b). Acid soils make up a
large percentage of South Africa's arable land.
sustainable
soils are required to ensure
in the nations staple commodity, maize.
Soil acidification is, therefore, a serious socio-economic concem. Very few
countries can afford the decline in food production, which often accompanies the
changes, which are taking place in our soils. Nutrient management practices
the viability of agricultural ecosystems. Soil acidity affects plant
development by its influence on the availability of certain elements required for
growth (Tisdale and Nelson, 1975). Maize (Zea mays
is the third most
important cereal grown in the world. In South and Central America, maize is
grown mostly on acidic soils. On these soils, yields are limited by deficient levels
of available P, Ca and Mg, and toxic
of AI and Mn (Baligar et aI., 1997).
Practices, which focus on reducing inputs, especially fertilizer inputs provide an
important link between the needs of commercial farmers and those involved in
subsistence agriculture. With commercial systems, the aim is to reduce inputs for
economic/environmental reasons. Subsistence farmers have similar aims, but, in
this
it is because they have restricted access to inputs.
Many countries including South Africa are experienCing waste material
disposal problems. Two waste materials of major concern, are fly ash and
sewage sludge. A growing population and increasing urbanization creates the
need for more electricity, resulting in more fly ash being produced. In addition to
141
this is the higher production of sewage
due to the increasing population. It
is, therefore, desirable that one problem should be a solution for another.
Reynolds et aI., (1999) determined the feasibility of converting waste disposal
problems in South Africa into a soil beneficiation strategy. The alkaline
stabilization of
sludge with fly ash and 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 ameliorant effects.
This study entails the comparison fly ash, sewage sludge and lime with SLASH in
maize production.
1.1 Fly ash
The potential limitation of fly ash's agronomic use includes its low levels of N,
and excessive levels of B (Aitken et aI., 1984). Selenium and boron, which can be
the rate-limiting elements for maximum permissible loading rates of fly ash for soil
amendments, did not, however, accumulate in plants in quantities that would be
of concern for plant health or animal and human consumption (Cline et aI., 2000).
Boron in fly ash is also readily available to plants. In fact numerous investigators
(Holliday et aI., 1958; Cope, 1962; Hodgson and Townsend, 1973; Townsend and
e t , 1978; Ciravolo and Adriano, 1979; Adriano et aI.,
Gillham, 1975;
1980) considered B to be a major limiting factor for successful cropland utilization
of ashes, especially when such ash is not fully weathered. Crops also exhibit
varying degrees of tolerance to B in soils (Bingham, 1973; Adriano et ai., 1980).
Fly ash application may also decrease plant uptake of elements such as Cd,
Cu, Cr,
Petruzzelli
Mn, and Zn (Schnappinger et aI., 1975; Adriano et aI., 1
et
aI.,
1986;
Schumann
and
Sumner,
2000).
Phosphorus
concentrations in plant foliage were often reduced by fly ash applications (Elseewi
et aI., 1980; Moliner and Street, 1982; Schumann and Sumner, 2000). Corn (Zea
mays L) plant emergence, grain yield, percent moisture, and harvest index were
not significantly influenced by fly ash applications either.
142
1.2 Biosolids
Local authorities, both overseas and in South Africa, are continually searching
for environmentally acceptable as well as beneficial and economical means of
disposal of sewage sludge. Biosolids that have not undergone pathogen
destruction cannot be land applied. Land application of sludge is not common in
many countries since very little research has been carried out under local
conditions. While extensive overseas studies can provide some guidance to the
potential for sludge utilization, ultimately sludge management practices should be
developed on local soils under local conditions. Existing regulations set limits for
the content of heavy metals in sewage sludge as well as the maximum annual
and cumulative loadings to land. These loadings are primarily based on health
risk
(pathogenic micro-organisms) and soil contamination aspects
(heavy metals) (Barry
aI., 1995).
Dowdy et aI., (1983) found that the Ni and Zn content of corn (Zea mays L.)
silage increased linearly with biosolid application rate (Sloan
aI., 1997). In a
study conducted in Australia on estimating sludge application
to land, they
concluded that elements Cd, Ni and Cu were all retained to a greater extent in the
surface horizon, most likely due to their affinity for organic matter (Barry
aI.,
1995).
Liming acidic soils that have received biosolids application reduces plant
uptake of Cd,
and to lesser extent Cu and Pb (Braillier et aI., 1996; Logan and
Chaney, 1983; Mahler et
1987; Basta and Sloan, 1999). Alkaline biosolids,
produced when biosolids is treated with alkaline materials to kill pathogens, have
a relatively high CaC03 and may serve as a liming material (Little et aI., 1991;
Basta and Sloan, 1999). Because alkaline biosolids are effective liming materials,
application of alkaline biosolids resulted in less plant uptake of Cd (Brown and
Brush, 1992;
and Sloan, 1999) and Cu, Ni, and Zn (Mulchi et
, 1987;
Basta and Sloan, 1999). Cadmium and Zn are usually the most bio-available
heavy metals of sludge origin (Alloway 1995; Berti and Jacobs, 1996; Sloan et aI.,
1997; McGrath
aI., 2000).
Cadmium is of major concern in terms of the
transfer into the food chain (Sanders et aL, 1987; Lubben
aI., 1991 ;Chandri et
143
aI., 1993; McGrath et aI., 1995; McGrath et at, 2000), but plant species differed
markedly in the transfer efficiency of
and Cd from soil to plants (McGrath et
aI., 2000),
1.3 Alkaline- biosolids
Application of alkaline biosolids to acidic soil to achieve final soil pH > 5 will
minimize risk from soil solution Cd and
and plant uptake of heavy metals
(Basta and Sloan, 1999). Metal movement is
<;.;a.:><;.;y
to increase with
soil pH. It is possible that the same mechanism that facilitates Ca
movement may permit the movement of trace metals through the soil profile
(Brown et aI., 1997).
A leaching potential test of the ameliorant SLASH was conducted by Reynolds
al., (2000) and shown to
within the
(Toxicity Characteristics Leaching
Procedure) guidelines. The TCLP leaching of the SLASH product showed that the
heavy metals of
sewage sludge are immobilized within the fly ash component
and do not leach out in either of the simulated conditions. Although the two
methods gave similar results, it was noted that Mn, Mo, Ni, and Zn leached more
in the TCLP leachate than in the acid rain leachate, while Cu leached less. This
may
as a result of the differing pHs of the leachates (Reynolds et ai, 2002).
Fly ash alone is a poor source of the macronutrients such as Nand P (Carlson
and Adriano, 1993; Jackson et aL, 1999). Nitrogen is volatilized during the
process of coal combustion, while most fly ash P is relatively unavailable
(Bradshaw and Chadwick, 1980; Jackson
at, 1999). Sewage sludge on the
other hand can be a valuable source of plant nutrients such as N, P, and S, and
the organic matter contained in the sludge also can help improve soil conditions
(McGrath, 2000) and enhance plant growth. The high Nand P content of sewage
sludge complements the higher levels of
micronutrients in the fly ash
and will thus reduce the need for inorganic fertilizers. Therefore, fly ash mixed
with other organic waste will be an attractive and economical option that should
be considered (Wong and Wong, 1990).
144
2. Material and Methods
A study of maize (Zea mays) in a raised bed trial was undertaken and was
based on the work which Rethman et aI., (1999a,b) conducted. Rethman et aI.,
(1999a,b) and (Truter, 2002c) concluded that the best plant growth responses
had been achieved on the 5 and 10% SLASH treated soils. Essentially it was
because of those results that this study on SLASH was initiated.
A randomized layout of constructed raised beds (net plot: 1m x 0.30m =
0.3m 2) as illustrated in (Fig.1) 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 sewage sludge, fly ash and reactive lime (CaO) in
combination (SLASH) at four different levels and individually. The treatments
were: T1 (Control - 0% SLASH), T2 - [2.5% SLASH (8kg)], T3 - [5.0% SLASH
(16kg)], T4 - [7 .5% SLASH (24kg)], T5 - [10% SLASH (32kg)], T6 - Sewage
Sludge (4.32kg), T7 - Fly ash (10.24 kg) and T8 - Lime (1.44kg) and were
.
replicated five times.
Initially these raised beds were planted to cabbages, carrots, stocks, sweet
peas and statice. These vegetable and flower crops represented the 1st cropping
cycle of the raised bed trial (Ramagadza, 2002). The 2nd cropping cycle was
maize (Zea mays). Ten seeds were planted, and the seeds that did not germinate
were blanked in. After the 2nd cropping cycle of maize (Zea mays) the soils were
planted to Triticale (Triticale hexaploide), sorghum (Sorghum sp.) and rye (Secale
sp.) as successive 3rd , 4th , and 5th cropping cycles (Truter, 2002c).
The objective of the study was to compare the SLASH at different levels to the
separate components of SLASH. These raised beds were used to evaluate the
relative effects of SLASH, sewage sludge, lime and fly ash in soil on the dry
matter production of maize (Zea mays) at different stages of the growth cycle.
Three plants were harvested when the best treatment reached a height of 20 cm
(1 st harvest); 40 cm (2 nd harvest) and the other 4 plants were harvested when
they were fully grown. (3 rd harvest). This observation was to determine at what
stage the various treatments started to have an effect on plant growth .
145
Ramagadza (2002) reported that the plants of the 1st cropping cycle were
showing signs of K deficiency. Due to this, K had been applied to the treatments
at the beginning of the 2nd cropping cycle of maize to eliminate K deficiency as a
limiting growth factor. The treated soils received regular watering, to eliminate
moisture as an additional limiting growth factor.
1 Statistical analyses
All dry matter-, grain production data and elemental analyses 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.
were taken at
0.05.
Results and Discussion
Previous studies reported on the growth
of various crop species to
SLASH and the ingredients on which it is based (Rethman
1999a,b;
Rethman 2000a,b; Rethman and Truter, 2001 Truter and Rethman 2000; Truter,
2002a,b, c). The findings of those studies have been confirmed in this study.
From all the work conducted on SLASH the conclusion has been drawn that
levels of SLASH at
0% of the soil volume enhanced plant growth remarkably.
Table 1 clearly indicates that even at an early stage of the maize growth cycle
SLASH had an effect on growth rate. Sewage sludge had the most substantial
influence on the growth of the maize plants.
results emphasize the
importance of organic matter, which is evidently supplied by sewage sludge.
Despite the good results obtained from the sewage sludge (T6) treatment, it can
not be recommended because of the variability of the sludge sources which can
possibly contain a wide range of heavy metals and can often be pathogenic.
Similar results had been observed for the harvest taken at 40 cm with sewage
sludge maintaining an exceptionally higher yield than the
of
treatments.
SLASH treatments were performing Slightly better than the control, fly ash and
lime treatments, but not significantly. Nevertheless, treatment effects could be
seen throughout the cropping cycle.
147
Table 1
Dry matter production (g/plant) of maize (Zea mays) at different stages on soils treated
with SLASH (T2-T5), sewage sludge (T6), fly ash (T7) and lime (T8).
T1- Control
b
14. 94b
b
16.18
T2- 2.5% SLASH
1.36
T3- 5% SLASH
1.42
T4-7.5% SLASH
1.62b
T5- 10% SLASH
T6- Sewage sludge
T7- Fly ash
b
486. 94 b
b
526. 96
14.74
14.06
11
52.94
b
13.00
Bb
b
8
15.34
1.26
445.10bC
b
629.92
320.28
11
cd
T8- Lime
" abc Column means with common alphabetical superscripts do not differ significantly (P> 0.05)
(Tukey's Studentized Range Test)
Individual plants harvested at maturity illustrate how SLASH treatments had
benefited plant growth by as much as 100% on average. The sludge treatment
yielded 140% more on average than the control (Table 1). Although it seems that
when combining sewage sludge with fly ash, the effect of sewage sludge on plant
growth is reduced. It has been shown that even though this comment
true, the
compromise is reached evidently in the conclusion drawn from the work done by
Truter, (2002a,b, c), that SLASH has a longer residual effect than sewage sludge.
SLASH therefore, prolongs significantly higher yields than the sewage sludge
treatment relative to the control. Sewage sludge eventually becomes depleted,
while SLASH maintains it's "slow release" of nutrients over a longer period of time
(Truter, .....,...'......,/
As for grain production, similar trends, as for the plant material, are noted in
2. SLASH treatments gave up to 225% better yields than the control while the
sludge treatment gave 385% better yields. Once more, the 7.5% (T4) and 10%
(TS) SLASH treatments delivered the best results for the SLASH treatments for
both dry matter yields and grain yields.
148
The risk of heavy metal translocation from sludge will depend on the source of
sludge. In contrast, SLASH ensures the immobilization of heavy metals and a
safer product to handle and apply in
of possible disease organisms.
With respect to the micronutrient B and heavy metals analyses of
11'>:;;1',/1'>";:
(Table 2) the results obtained were compared to the limits set by law (Kabata­
Pendias and Pendias, 1984). In Table 2 the
Cd and Ni analyses indicate that
all treatments had insignificant levels and that they were well below these limits
(Kabata- Pendias and Pendlas, 1984).
However, the SLASH treatments tended to have a higher B concentration, and
this can possibly be ascribed
the contribution of B, which is usually found in fly
ash.
Table 2
The mean elemental concentration and (±MSE) in maize leaves (mg kgT5), sewage
T1-Control
T4- 7.5% SLASH
(mg kg-i)
(mg kg-i)
2.90£1 (±0.45)
2.59 (±1.06)
(±0.54)
(±13.03)
1
a
5.64 (±4.07)
TS- 10% SLASH
3.93
T6-
3.30
T7- Fly ash
TS- Lime
grown on SLASH (T2-
fly ash (17) and lime (T8) treated soils
T2- 2.5% SLASH
T3- 5% SLASH
1
)
8
.30)
a
8
a
3.18 (±1
(mg kg-i)
8
27.96 (±0.45)
8
23.93 (±0.45)
(±1.76)
45.71£1 (±0.45)
5.64£1 (±3.75)
34.41 a (±O.45)
6.19£1 (±S.22)
3S.66 (±0.45)
a
(±2.40) (±1.1S)
8
24.30 (±O.4S) 26.40£1 (±O.45)
*a Column means with common alphabetical superscripts do not differ significantly (P> 0.05) (Tukey's
Studentized
The concern about heavy metals (Ni and Cd) translocation was not supported
by the results obtained for the leaf analysis, although the concern about
translocation to the most important plant component, grain, prevailed. Although
Rethman et aI., (1999a) found no significant translocation of heavy metals to the
151
grain at 1% SLASH applications, grain produced on soils treated with higher
SLASH applications was of concern.
Table 3 provides the results obtained for heavy metal content of selected
treatments. The analysis of grain indicated that there was heavy metals present in
all the treatments including the control. The B concentration differed from what
was found in the leaf material, this demonstrates that B is not concentrated more
in the grain than in the leaf material, and is still well below the limits set by law. To
support the fact that the heavy metal content of sewage sludge varies, depending
on the source, the sludge's Ni and Cd content was similar to that of the SLASH
treatments and the control. However, Ni was more concentrated in the grain than
in the leaves of the plant. It was, nevertheless, still well below the safety limits.
Table 3
The mean elemental concentration and (±MSE) in maize grain (mg kg·
1
)
grown on SLASH (T2-
T5), sewage sludge (T6), fly ash (T7) and lime (T8) treated soils
B
Cd
Ni
(mg kg"')
(mg kg"')
(mg kg"')
Treatments
8
B
B
T1 - Control
26.28 (±3.42)
9.89 (±0.32)
T3 - 5% SLASH
9.36 (±0.53)
102.79 (±4.43)
9.81a (±0.38)
T6 - Sewage sludge
27.278 (±5.76)
8
29.26 (±5.24)
8
25.61 (±5.64)
8.81c (±0.29)
104.45 (±2.17)
c
99.13 (±3.59)
Safety limit
80
15.7
400
T5 -10% SLASH
b
106.99 (±3.33)
b
b
*abc Column means with common alphabetical superscripts do not differ Significantly (P> 0.05) (Bonferroni Test)
4. Conclusion
Maize can be produced on acidic or nutrient depleted soils, by using an
alternative method rather than the conventional liming and inorganic fertilization
of soils. At the same time the environmental problem of waste disposal can be
alleviated.
With the exception of sewage sludge, SLASH offered greater benefits than any
individual ingredients. Plant growth responded exceptionally well to sewage
sludge. It cannot, however, be recommended due to the pathogenicity of the
sludge ,and the possible heavy metal content, depending on the source of sewage
152
sludge, and the fact that heavy metals are not immobilized in the sludge, as they
are in the SLASH. This ameliorant SLASH has promising liming qualities and is a
good source of nutrients, which improves soil condition making it more suitable
for plant growth.
Although SLASH is seen as a good source of nutrients required for plant
growth, it does not necessarily contain a full range of nutrients. The batch of
SLASH that was used in this study was devoid of K, for example, and the need
to supplement it with an inorganic fertilizer or possibly another organic
will
material, which has high concentrations of K, such as animal manures.
Since waste material composition, nutrient balance and nutrient bioavailability
is extremely variable, it is important to characterize
waste materials before
mixing them and using them to the benefits of plant growth. Various problems can
experienced with the application of such wastes, such as possible
phytotoxicity from trace element excesses or possible a fixation of other nutrients
such as
Most of these problems can be overcome by combining two or more
waste materials together, thereby utilizing the combined complementary qualities
of each waste for crop production.
The rationale behind such mixed wastes is that the mixture itself is a superior
soil amendment to either component alone.
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 reduces odor, and can offset
soil acidity problems that may
through continued land application of organic
wastes.
It is concluded that the
0% SLASH application rates ultimately deliver the
best results compared to the other SLASH treatments. Regarding the uptake of
potentially toxic elements, no significant uptake was noted or even translocated to
the grain under regulated experimental conditions. The two potential problem
heavy metals, Ni and Cd, and the micronutrient
which can be toxic at very high
levels, were within the current safety specifications, but these may be open for
review.
economic reasons, in South
use of SLASH at high levels is
limited due to high transport costs, and the ameliorant's use will
restricted to
153
sites in relative close proximity to the waste raw materials used in it's
manufacture. Nevertheless, the ameliorant SLASH has definite agricultural
potential!'
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Petruzzelli,
,Lubrano,
L., Cervelli
seedlings grown on fly
Ramagadza,
,1986. Heavy metal uptake by wheat
amended soils. Water Air Soil Pollut. 32,389-395.
. Utilization of
"SLASH" for flower and vegetable
production in the informal sector in South Africa. Mlnst.Agrar (Thesis).
University of Pretoria.
Rethman, N.F.G., Reynolds, K.A, Kruger, RA, 1999a. Crop responses to
SLASH (Mixture of sewage sludge, lime and fly ash) as influenced by soil
texture, acidity and fertility.
1999 Internat. Ash Utiliz. Sympos.
Lexington, Kentucky, U.S.A pp.
Rethman, N.F.G., Reynolds. K.A, Kruger,
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, USA.
pp.83-86
Rethman, N
du Toit,
Ramagadza,
,Truter, W.F., 2000a. The use of fly
ash and biosolids to ameliorate soils, revegetate disturbed areas and improve
plant productivity. Proc. 25th Cont. Canadian Land Recl. Assoc. Edmonton,
Canada.
Rethman, N.F.G., du Toit,
Ramagadza,
,Truter, W.F., Reynolds, K.A,
Kruger, RA, 2000b. Soil amelioration using waste products. Proc. Remade
Lands Recl. Cont. Perth, Western Ausralia. pp. 127-128.
Rethman, N.F.G., Truter, W.F., 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, Kruger, RA, Rethman,
1999. The manufacture and
evaluation of an artificial soil prepared from fly ash and
sludge. Proc.
1999 Internat. Ash Utiliz. Sympos. Lexington Kentucky. U.S.A. pp. 378- 385.
Reynolds, K.A, Kruger, RA., 2000. SLASH Field Trials, Eskom Research Report.
RES/RR/00/13251. Eskom Technology Services International.
Reynolds, K.A, Kruger, RA., Rethman.
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 Conf. Durban, South Africa {In
157
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Campus drive, Cary, North Carolina, USA.
Sanders, J.R, McGrath,
P., Adams, T.C.M., 1987. Zinc, copper and nickel
concentrations in
extracts and crops grown on four soils
with
metal-loaded sewage sludges. Environ. Pollut. 44,193-210.
Schnappinger, M.G., Jr, Martens, D.C., Planks,
, 1975.
availability as
influenced by application of fly ash to soil. Environ. Sci.
9,258-261.
Schumann A.W., Sumner, M.E., 2000. Chemical evaluation of nutrient supply
from fly ash-biosolids mixtures. Soil Science
of America Jou mal Iss 1
64,41
Sloan, J.J., Dowdy,
H., Dolan, Linden, DR., 1997. Long-Term Effects of
Biosolids applications on heavy metal bioavailability in agricultural soils. J.
Environ. Qual. 26,966-974
L., Nelson, W.L., 1
Tisdale,
Soil fertility and fertilizers. Macmillan, New
York.
Townsend, W.N., Gillham, E.W.F., 1
Pulverized fuel ash as a medium for
plant growth. In: M.J. Chadwick and G.T. Goodman (Editors),
Resource Degradation
, Rothmans, N.
Truer,
amended soils.
Ecology of
Renewal. Blackwell, Oxford, pp. 287-304.
2000. Crop productivity in fly ash/sewage sludge
Joint. Cont. Pretoria, South Africa.
Truter, W.F., Rethman, N.F.G. , Reynolds, K.A., Kruger, RA., 2001.
use of a
soil ameliorant based on fly ash and se\JV2CIA sludge. Proc. 2001 Internat. Ash
Sympos. Lexington, Kentucky, U
Truter, W.F., 2002a. Multiple cropping of soils
sludge,
and fly ash (SLASH). MSc
with a mixture of sewage
Use of
products to
enhance plant productivity on acidic and infertile substrates. University of
Pretoria. Chapter 2.pp 107-121.
W.F., 2002
The influence of a mixture of sewage sludge, fly
and
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(Agric) Thesis. Use of waste products to enhance plant productivity on acidic
and infertile substrates. University of Pretoria. Chapter
pp 122-139
158
Truter, W.F., 2002c. Forage production from cereal and grain crops on fly ash­
biosolid amended soils. MSc (Agric) Thesis.
of waste products to
enhance plant productivity on acidic and infertile substrates. University of
Pretoria. Chapter 5 pp160-173.
Truter, W.F., 2002d. The influence of a fly ash-biosolid mixture on chemical soil
properties. MSc (Thesis) Use
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crops in fly ash-amended soils. Agric., Ecosys. and Environ. 26,23-25
159
CHAPTER 5
Prepared according to the guidelines of the Journal of Plant Science Forage production from cereal and grain crops on fly ash­ biosolid amended soils W.F.Trute,.a· and N.F.G. Rethman a • Oepartment of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South
Africa
Abstract
The non-agricultural activities of man compete with agriculture for land. The demands
on land made by increasing urban, industrial, mining, recreation and other developments,
and the attendant infrastructure - largely the result of a fast growing population - leave an
ever-shrinking area for producing food and fibre. Utilization of natural resources is of
importance for the survival of people as long as it is not at the expense of environmental
degradation i.e. it must be sustainable.
Many waste materials, which are the end products of processes that ensure life on
earth, have to be used beneficially. The combination of waste materials such as sewage
sludge and fly ash is not unknown to the scientific world as a beneficial technology to
stabilize sewage sludge by adding an alkaline material. The use of such a mixture of waste
products for agricultural purposes, still, however, needs to be refined.
Previous research, both internationally and in South Africa, has developed effective
waste product mixtures, which can be used for agricultural purposes. SLASH (60% class F
fly ash, 30% sewage sludge and 10% reactive lime (CaO)) is such a waste product mixture,
which can be used as a soil ameliorant to address the problems of soil acidity and
infertility.
The utilization of SLASH as such in crop production has already been researched but
what is relevant in this study is how the SLASH compares to its individual components in
terms of forage production and long-term residual effects. It was evident from this study
that the effect of 5-10% SLASH treatments still persisted and gave up to 30% better yields
Corresponding author.: Tel. +27-420-3224 Fax. +27-420-4120
Email address: [email protected]
160
36 months after the initial application of treatments. Sewage sludge on the other hand.
although giving the best
production for almost the entire study. can not be
recommended because of its pathogenicity and possible heavy metal translocation.
Furthermore, the sewage sludge treatment showed signs of becoming depleted by the end
of the study, indicating that it did not compare favourably with the "slow release"
capability (slow release of essential nutrients required for plant growth) of SLASH.
Keywords: Acid and infertile soils, fly ash, sewage sludge, SLASH, soil ameliorant, waste
materials.
1. Introduction
South Africa is characterized by a poor resource base [1
Socio-economic
problems in this resource poor sub-continent have been compounded by a large
population, a rapid population growth rate of 2.5% per annum, growing
urbanization and a high
of unemployment. There is, therefore, a desperate
need for strategies, which will improve both national and household food security.
at the same time create more job opportunities. In a country where natural
resources have already been seriously impacted by agricultural, industrial
mining industries, and where the disposal of waste products is often a problem,
the possibility of using waste products to improve the natural resources
(especially soil) deserves more intensive investigation.
Previous work conducted to determine the feasibility of converting waste
disposal problems in South Africa into a soil beneficiation strategy has been
positive [3]. Two problems experienced in the
sludge
were, firstly, that
contains heavy metals and pathogens. As a result
restricted for agricultural land application. Secondly, fly
use is
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 "waste" products [4],
co-utilization of fly ash and sewage sludge with added lime delivered a
product termed SLASH (containing
% class F fly ash, 30 % sewage sludge
and 10% unslaked lime on a dry matter basis), which has beneficial soil
161
ameliorant effects [3].
use of fly ash (FA) as a soil amendment is hindered by
a lack of macronutrients in
Mixing
and concerns about trace element availability.
with an organic waste can increase macronutrients while reducing odor
and improving material handling, but the
element solubility requires
investigation.
As with fly ash, only a fraction of total nutrients (especially Nand P) supplied
by organic wastes are available to crops in a particular season, since they must
be mineralized from organic to inorganic forms.
sewage sludge and animal manures may be
these limitations,
most cost effective supplement
for co-utilization with fly ash in crop fertilization. Mixtures of fly
with organic
wastes already have a proven track record [5,6,7,8,9,10,11,12,13], but the
preparation of mixtures has usually proceeded by trial and error.
Prediction of plant nutrient supply from fly
and bio-solids (sewage sludge
and poultry manure) may enhance their agricultural use as a crop fertilizer. The
resin method was useful for major nutrient (N, P, K,
Mg, S) extraction from fly
and organic materials, particularly where mineralizable fractions of Nand P
under aerobic conditions are required {13]. Extraction of fly ash using a dilute­
buffered nutrient solution was more successful because micronutrient recovery
was improved; macronutrients were correlated to the resin method.
nutrient supply from extremely variable fly ashes was: Cu =
B, Mo >
overall
>S>
>Mn > N > Mg > P > K (high micronutrient, low macro nutrient supply).
bio-solids, the macronutrients ranked: P> N, Ca > S> Mg > K (sewage sludges),
and N > Ca, K > P > Mg > S (poultry manures). In mixtures of fly ash with 26%
sewage sludge the order was: Ca > S > N > Mg > P > K, while in mixtures of fly
and 1
poultry manure, the nutrients ranked:
> K, N, S > Mg > P.
Optimal plant nutrition (especially N-P-K balancing) should be possible by mixing
these three
materials [13].
initial cropping cycle of this programme was to determine how sewage
sludge, fly ash and lime both in combination (SLASH)
individually, would
affect the growth of various flower and vegetable crops [14]. Subsequently,
another study, prior to the one being reported on, had also been undertaken
which represented the
cropping cycle of the programme [1
It focused on the
162
production of
mays) on the soils, which were used in this study.
objective of that study was to determine if two specific heavy metals (Ni, Cd) and
micronutrient B would
translocated to the leaves and grain of maize.
Translocation would possibly
place from soils treated with SLASH and it was
compared to the individual components of which SLASH is made
In addition
this, dry matter (OM) and grain production were also recorded. This investigation
followed on that work.
objective of this study was to further evaluate the long-term residual
effect, which different levels of SLASH might have (in terms of forage production),
in comparison to the individual components of SLASH. It is hypothesized that
while the individual components
have their own beneficial characteristics,
these do not compare with the complementary effect of the mixture in sustaining
optimal plant growth. The soils treated with different amendments were utilized
intenSively
the
cropping cycle of maize, with consecutive crops such as
Triticale (Triticale sp.), sorghum (Sorghum sp.) and rye (Secale sp.) as
successive 3rd , 4th and 5th cropping cycles over a period 24 months.
2. Material and Methods
When using SLASH for flower and crop production, the best performance was
achieved with the 5% and 10% SLASH levels [16,1
It was because of this
conclusion that this raised bed study was undertaken to compare SLASH
treatments to the individual components of SLASH. Constructed
plot: 1.2m x 0.50m ::: 0.6m
Experimental
2
)
(net
as illustrated in (Fig.1) were used at the Hatfield
, Pretoria, South Africa (25°45'S 28°1
1327m above sea
level.
163
growing grain crop. These crops are generally used for animal
crops were sown
These
a rate of 150kg/ha in three evenly spaced rows of 12.5cm for
each treatment in the
beds (Fig 1). Forage production was
regular harvests within each growing season.
by
Once the best treatment had
reached flowering stage, the harvest was taken.
harvests were recorded
for Triticale hexaploid and Sorghum sp. and two harvests
Secale cerea/a .AII
treatments received regular watering to eliminate moisture as a limiting growth
factor. No additional fertilizer had been applied to the soil during the period of this
study, since the cropping with maize.
1 Statistical analyses
All dry matter production and root study data was statistically
using
PROC GLM (1996/1997 and 199711998). Statistical analysis was performed
using SAS software [20].
were taken
0.05.
3. Results and Discussion
response of Triticale (Triticale hexaploide), a hybrid between wheat
(Triticum) and Rye (Seca/e) , in the third cropping cycle on these
(a) different levels of
and (b)
beds to
different components which make up
SLASH, was assessed in the winter and spring of 2000. The relative mass (g) of
uniform sample taken from each treatment for consecutive harvests is shown
in Table 1.
Despite this being the
cropping cycle on
beds,
response
pattem of the Triticale (in terms of forage production) was still essentially the
same as that of maize in the second cropping cycle [1
The growth response of
Triticale to the SLASH and sewage sludge treatments was markedly beUer than
the control, fly
and lime treatments. Nevertheless, fly
and lime treatments
had a marginal beneficial effect on plant yield above the control, (12 and 11%
respectively). SLASH, in contrast, improved plant yields by 240%. However,
sludge on its own improved plant yields by 368% over the control.
165
Table 1
Influence of sewage
lime and fly ash individually and in combination
(SLASH) on the mean dry matter production
(Triticale hexaploid) - 350
T2- 2.5% SLASH
after the treatment
T5- 10% SLASH
T6- Sewage sludge
T7­
ash
and
by
Mass
Mass
Mass
Relative mass (g)
Relative mass (g)
Relative mass (g)
25.06 f1 b (±7.70)
22.28 as (±3.1 0)
(±3.85)
27.70s a (±5.12)
T3- 5% SLASH
T4- 7.5% SLASH
plot) and the ±MSE of the cereal crop
f1
32.54 b (±4.81)
B
45.76 b (±16.27)
44.92f1b (±9.84)
17}
4.57)
31.08"a (±3.58)
" (±5.84)
a
35.00 a
a
46.46
b
a
(±7.11)
(±5.48)
a
53.10 B (±8.03)
b
(±8.33)
31.00B"
*abc Column means with common alphabetical subscripts do not differ significantly (P> 0.05) (Boflferroni Test)
Due to sludge's limitations it is not, however, safe and practical to use. It
should
noted, that the higher the SLASH application, 0-10%, the higher the
growth response was in terms of yield. This substantiates the results obtained
from other studies [16,17J, that the best results were obtained from the 5-10%
SLASH levels. It is evident from Table 1 that the third harvest gave a much higher
yield that the other two harvests. This can
ascribed to the longer interval
between harvests because seasons were changing and Triticale was becoming
reproductive. The total dry matter production (all three harvests) of aU
harvests Triticale (Triticale hexaploid) for the growing season is illustrated in
2).
It is shown that the total dry matter production of Triticale (Triticale hexaploide)
as illustrated in the histogram (Fig 2) for the entire growing season, was most
definitely the highest on the sewage sludge treatment (T6). Sewage sludge
improved the yield of Triticale by 268%. Due to the limitations on the use of
sewage sludge, as previously mentioned, the next best treatment to sewage
166
Table 2
Influence of sewage sludge, lime and fly ash individually and in combination (SLASH) on the
mean dry matter production (g/net plot) and (±MSE) of sorghum (Sorghum sp.cv. Hypergraze)
- 470days after the treatment application and preceded by three cropping cycles
Treatments
st
1 Harvest Dry
2
nd
Harvest Dry
Mass
T2- 2.5% SLASH
Tl-5%SLASH
T4- 7.5% SLASH
TS- 10% SLASH
TS- Sewage sludge
T7­
ash
TS- Lime
Mass
8
87.24 a (±14.36)
90.42
8
b
(±16.61)
102.48\ (±15.11)
71.24
73.0B
47.46
8
(±i6.B6)
8
7.30)
a
8
8
65.44
8
ab
69.78
82.34
(±1S.49)
81
(±10.38)
8
8
60.20 a
(±7.35)
65.72
abc
(±8.8S)
78.1
(±19.24)
abc
a
45.64
mass
ab
8
91
130.40\
8
lrd Harvest Dry
8
a
82.26
8
8
(±9.12)
a
(±9.74)
8
11
5.73)
(±11.74)
(±3B.68)
(±S.43)
(±7.B7)
5.02)
11
(±6.37)
a
(±5.34)
8
46.74
"abc Column means with common alphabetical subscripts do not differ significantly (P> 0.05) (Bonferroni Test)
Fig. 3 clearly shows that, on average, the 10% SLASH treatment
forage production. The
the best
treatment gave approximately 120% beUer yield than
the control, 80% better yield than the sewage sludge treatment (T6) and 60%
better yield than the fly ash treatment (T7). Reasons for this sudden change in
production on the sewage sludge treatment may be ascribed to the depletion of
the organic and nutrient source.
In other studies it is noted that after 36 months of multiple cropping, the
soils treated with sewage sludge had markedly high phosphate levels [19]. These
nutrient inbalances could impact negatively on plant growth, which may explain
the reduction in plant growth response to the sewage sludge treatment. On the
other hand SLASH treatments maintained a relatively good performance.
168
4. Conclusion
The addition of SLASH to infertile or acidic soils as a soil ameliorant holds
definite agricultural potential. 7.5%-10% SLASH delivers the best results
compared to the rest of the
good source
treatments. Although
nutrients required for plant growth, it
of nutrients. Depending on the source of
example, adequate K,
creating
is seen as a
not contain a full range
sludge
it may lack, for
need for supplementary fertilization.
Quality control of waste products used in such mixtures, is therefore, essential to
be able to calculate the required levels for speCific soils and crops.
Focusing on the performance of the individual waste products (sewage sludge
and fly ash), it is clear from the results that sewage sludge (T6) gave the best
overall yields. Although sewage sludge is a good source of organic material with
high amounts of essential macronutrients, it must be taken into consideration that
the use of sludge is limited because of its potential disease risk and possible
heavy metal pollution. The fly ash treatment (T7) did not give significantly higher
yields than the control. This supports the importance
organic material for
optimum plant growth. Fly ash is a good source of micronutrients, which may
beneficial to certain plant growth processes, but on
contribute to the enhancement of plant growth.
own it does not necessarily
ash characteristically has a
larger influence on the soil properties and hence indirectly enhances plant growth,
by ensuring a good medium for plant growth, especially in acidic soils.
Sustainable crop productivity depends on the use of non-acidic soils and
ameliorated acid soils. From this study the conclusion can be drawn that
U L /....
~I
has marked beneficial effects on plant productivity. This is ascribed to the
ameliorating effects, which this product has on soil pH and
nutrient status.
These effects, unlike many inorganic fertilization programmes, have long-term
residual effects.
171
5. References
[1] D.M. Scotney, J.E. Volschenk, P.S. van Heerden, The potential and
utilization of the natural agricultural resources of South Africa. Dept. Agric.
Devpt. Pretoria, South Africa. (1990) 11 p.
[2] N.F.G. Rethman, E. du Toit, E.J. Ramagadza, W.F. Truter, The use of fly
ash and biosolids to ameliorate soils, revegetate disturbed areas and
improve plant productivity. (2000a) Proc. 25th Conf. Canadian Land Recio
Assoc. Edmonton, Canada.
[3] K.A Reynolds, R.A Kruger, N.F.G. Rethman, The manufacture and
evaluation of an artificial soil prepared from fly ash and sewage sludge.
(1999). Proc. Internat. Ash Utiliz. Sympos. Lexington Kentucky, U.S.A pp.
378- 385.
[4] W.F. Truter, N.F.G. Rethman, K.A Reynolds, R.A Kruger, The use of a soil
ameliorant based on fly ash and sewage sludge. Proc. 2001 Internat. Ash
Uti liz. Sympos. Lexington, Kentucky, U.S.A (2001)
[5] B.P. Jackson, W.P. Miller AW. Schumann, M.E Sumner, Trace element
solubility from land application of fly ash/organic waste mixtures . J. Environ.
Qual. Iss. 2 28 (1999) 639-647
[6] J.R. Pichtel, J.M. Hayes, Influence of fly ash on soil microbial activity and
populations. J. Environ. Qual. 19 (1990) 593-597.
[7] L. Belau, Laboratory investigations into the microbial decomposition and
nitrogen supply of mixtures of poultry excrement and power plant ash in
soils. Zentralblattfur Mikrobiologie.146 (1991) 117-123.
[8] AP. Schwab, M.B. Tomecek, P.O. Ohlenbusch, Plant availability of lead,
cadmium, and boron in amended coal ash. Water Air Soil Pollut. 57-58
(1991) 297-306.
[9] J.T. Sims, B.L. Vasilas, M. Gbodrati.
Effect of coal fly ash and co­
composted sewage sludge on emergence and early growth of cover crops.
Comm. Soil Sci. Plant Anal. 24 (1993) 503-512 .
[10] M. Vincini, F. Cairini, S. Silva, Use of alkaline fly ash as an amendment for
swine manure. Biores. Techno!. 49 (1994) 213-222.
172
[11] K.S. Sajwan, W.
Youngblood, The
Omes,
of fly ash/sewage
sludge mixtures and application rates on biomass production. J. Environ.
Health
(1995) 1
337.
[12] J.W.C. Wong, The production of artificial soil mix from fly ash and sewage
sludge. Environ. Technol. 16 (1995) 741
[13] AW. Schumann, M.E. Sumner. Chemical evaluation of nutrient supply from
fly ash-biosolids mixtures. Soil
Am. J.
1 64 (2000) 419-426
[14] E.J. Ramagadza, Utilization of "SLASH" for flower and vegetable production
in the informal sec:tor in South Africa. Mlnst.Agrar (Thesis). University of
(2002)
[15] W.F. Truter. Comparative study on the influence of SLASH and its individual
components on the production of Zea mays and heavy metal accumulation.
of waste products to enhance plant productivity on acidic
MSc (Thesis)
and infertile substrates. University of
Chapter 4 (2002) pp.140-1
[16] N.F.G. Rethman, K.A Reynolds, R.A Kruger, Crop responses to SLASH
(Mixture of Sewage Sludge,
and Fly Ash) as Influenced by Soil
Texture, Acidity and Fertility. Proc. 1999 Internal. Ash Utiliz. Sympos.
Lexington, Kentucky,
(1999) pp. 387-397.
[17] N.F.G. Rethman, K.A Reynolds, R.A Kruger, E.J. Ramagadza,
, du
for flower and vegetable production in the informal sector in
Toit,
South Africa. Proc. Internal. Ash Utiliz. (1999)
[18] W.F. Truter,
influence of a fly ash-biosolid mixture on chemical soil
properties. MSc (Thesis) Use of waste products to enhance plant
productivity on
and infertile substrates. University of Pretoria. Chapter
6 (2002) pp. 174-1
[19] Institute Inc., The SAS system for Windows. SAS Institute Inc. SAS
Campus drive, Cary, North Carolina, USA (1
173
CHAPTER 6 Prepared according to the guidelines of Journal of Waste Management
The influence of a fly ash-biosolid mixture on soil chemical
properties
W.F. Truter a
a Department
and N.F.G Rethman
a
of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South
Africa
Abstract
Agricultural and industrial activities have greatly accelerated the pace of soil acidification. Soil
acidification and nutrient depletion is, therefore, a serious socio-economic concern. Very few
countries can afford the decline in food production, which often accompany the changes, which
are taking place in our soils. Nutrient management practices affect the viability of agricultural
ecosystems. External sources of plant nutrients will, therefore, continue to be an essential part of
agriculture as we strive to replace the nutrients lost in successive crop harvests.
Many countries experience waste product disposal problems. Many of these waste materials
are excellent sources of plant nutrients and also have potential soil ameliorating qualities, which
can be utilized for crop production if rendered innocuous. One of the more recent methods of
sewage sludge treatments, which are being more widely used, is the alkaline stabilization of
biosolids. This process involves the mixing of partially dewatered sewage sludge with an alkaline
material such as fly ash or a blend of materials. This advanced technology, which has also been
used in South Africa, has provided a product termed SLASH. Not only has SLASH become a
possible solution to various problems experienced in South Africa such as ash and sewage sludge
disposal, but is also an alternative measure for ameliorating our acid and nutrient depleted soils.
Where fertility was limiting, SLASH had a beneficial effect. 5-10% SLASH levels improved the
soil pH and have thereby made essential plant growth elements more readily available over a
longer period. SLASH does have beneficial soil ameliorating qualities, and can be used as an
Corresponding author. : Tel. +27-420-3224 Fax. +27-420-4120
Email address: [email protected]
174
alternative amendment. SLASH's effectiveness has been recorded over at least 36 months,
maintaining an improved pH of one pH unit on average relative to the
even during
intensive cropping of soils. Long-term residual effects of sewage sludge are also prolonged by
combining it with fly ash. SLASH and similar products definitely have agricultural potential.
Keywords: Alkaline stabilization,
nutrient dep,letlcm
soil acidification
1. Introduction
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 [1].
Previous work has indicated that the application of limestone and CCS's (coal
combustion by-products)
P availability efficiency (the amount of plant
yield produced per unit of extractable P and P utilization (amount of plant yield
produced per unit of P in the plant) [2,3,4,5]. Either limestone or CCS application
increased the availability of soil P to plants. probably due to a better developed
root system resulting from the alleviation of AI toxicity and increased availability of
[6, 9). It can, therefore, be said that the application of CCS's and limestone to
acidic soils results in healthier plants with a better developed root system due to
higher soil pH and increased Ca and Mg supply. The better developed root
systems result in an enhanced P availability and P utilization efficiency and thus
improved plant-soil relationship of P in acid soils [5].
Coal combustion by products (CCS's) have
widely
as cost effective
amendments for acid soils. It holds true that ashes have several advantages, and
their application is often recommended [6]. Although information is needed on the
proper combination of CCS's with chemical fertilizers or other organic and
inorganic amendments to improve the productivity of acid soils. [7]
1.1 Fly
In South Africa approximately 28 million tons
the energy generation industry to
ash is produced annually, by
the energy reqUirements of a population of
175
45 million people and growing. This largely untapped resource, together with
power utilities, is generally situated in areas with high agricultural potential, which
are being acidified because of
effect of "acid rain" and agronomic practices.
Only a small percentage of this untapped resource of fly ash is currently used in
the
plastics, rubber and paint industries [8].
The alkaline nature of fly ash
led to an examination of its use as a liming
grade CaC03 on acidic agricultural soils and coal mine
to replace
spoils [9,10,11]. Furthermore, the enriched macro- and micronutrients which fly
ash contains, may enhance plant growth in nutrient-deficient soils [12,13,11].
fly ash is relatively rich in trace elements, it has also been
successfully used to alleviate micronutrient deficiencies [14,15]. Fly ash
amendments have been used to correct deficiencies of B [9,16,17], Mg [1
Mo [17,19,20,], S [17,18,20,21], and
[9,17,22,].
Fly ash alone, as previously mentioned, is usually a poor source of the
macronutrients such as Nand P [15]. Nitrogen
coal combustion, while most fly
volatilized during the process of
P is relatively unavailable [1
Notwithstanding these facts, land application of fly ash is still viewed as an
attractive alternative means of disposal [1
Coal fly ash
physical
chemical characteristics that make it useful as a
soil amendment. One of the more important of these being the potential to
permanently improve
Changes in the infiltration
soil water relations of sandy, drought-prone soils.
and water holding capacity of a sandy soil after
application of high rates (up to 950
ha- 1) of a Class F fly ash were examined.
Fly ash amendment not only increased water-holding capacity but also increased
plant available water. [24].
1.2 Biosolids
Sewage sludge is classified as a toxic waste and
produced at a
of 800
tons/day dry mass in South Africa [25]. This problem, in addition to the large
volumes of fly ash produced, emphasizes the need for co-utilization of wastes
176
and thereby identifies possible strategies for the safe disposal (use) of such
waste products.
Regarding amendment of infertile soils, many studies have demonstrated the
ability of sewage sludge to restore degraded lands [26]. Sewage sludge can be a
valuable source of plant nutrients such as N, P, and S, and
organic matter
contained in the sludge can also help improve soil physical conditions thereby
reducing runoff and increasing infiltration, which in turn results in increased
biomass growth and quality. Of the major environmental problems associated
with the land use of sewage sludge is the addition of potentially toxic heavy
metals in soils and possible pathogenicity. Repeated applications of
contaminated sewage sludge can result in an accumulation
metal­
such toxic metals
in the soil. Once accumulated, heavy metals are highly persistent in the topsoil,
and can cause potential problems such as phytotoxicity, injury to soil
microorganisms and elevated transfer to food chain [27J especially under acidic
conditions.
Local authorities, both overseas and in South Africa, are continually searching
for environmentally acceptable, as well as beneficial and economical, means of
disposal of sewage sludge [28]. Land application of biosolids is still not
completely accepted in the scientific community as a beneficial disposal option,
with concern persisting over the fate and phyto-availability of biosolids-applied
trace metals over time [29,30].
1.3 Biosolid-fly ash mixtures
The addition of organic wastes such as sewage sludge, chicken manure or
compost will increase the organic carbon content in soil receiving ash
amendment. This will initiate soil microbial activities for the cycling of nutrients
[31, 32J. The high Nand P contents in these wastes may also reduce the need
for inorganic fertilizer. Fly ash mixed with other organic waste will be an attractive
and economical option that should be considered [32].
If the pathogen reduction process in sewage sludge treatment involves the
addition of hydrated lime and/or an alkaline substance, resulting in a pH of 12, a
177
built in source of alkalinity is realized [33], and can be regarded as a possible
amendment for acidic and infertile
The extreme variability measured in fly ash and organic wastes in terms
total
nutrient concentrations, extractable nutrients, and relative nutrient balance is
common in many studies, reinforcing the urgent need to characterize waste
materials before mixing and use in crop fertilization.
potential pitfalls of
indiscriminate waste application to soil include (I) potential phytotoxicity from
micronutrient excesses (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
(especially N-P-K
balancing) should be possible by mixing these three waste materials together
[17].
Previous work by Reynolds et al [34] to determine the feasibility of converting
waste disposal problems in South Africa into a soil beneficiation strategy has
proven viable. The co-utilization of fly ash and sewage sludge with added lime
delivered a product termed SLASH (that contains 60 % fly ash, 30 % sewage
sludge and 10% unslaked lime on a dry matter basis), which has beneficial soil
ameliorant effects.
Reynolds et a/., [341, Rethman et aI., [35,36] have reported on the use of
SLASH for a variety of
flower crop such as
including corn, beans, potatoes, spinach and a
These reports highlighted
eliminate the potential problems with
use of SLASH to
organisms or heavy metal
pollutants, while improving soil pH, Ca, Mg and P. The growth and productivity of
such
crops was improved markedly under conditions of low fertility
type, rate of SLASH application and plant species were identified as being
important in this regard. It was concluded that wherever fertility was limiting,
SLASH had a beneficial effect [1,35]. At
pot
low application
it was found that no heavy metals had
used in these
translocated. Subsequent
178
trials with higher application rates (up
30
of soil volume) were conducted and
it was concluded that rates at 30 % were too high, compared to the
0 %
treatments [1,38, 39].
The rationale behind such mixed wastes, are that the mixtures are superior soil
amendments to either fly
addresses
or sewage sludge. The use of an organic waste
deficiency of macronutrients in fly ash, while fly ash can act as a
bulking agent for
organic wastes, substantially reduces odor, and can offset
soil acidity problems that may
through continued land application of organic
wastes. [40,15] .
.........,,,....... on the conclusions made by Rethman et
36, 39,] and Truter, [1]
this study concentrated on the effects SLASH had on soils at levels that did not
exceeded 10%. The SLASH treatments were compared to sewage sludge, fly
and lime in this study.
2. Experimental procedures
A randomized trial was conducted in constructed
O.SOm ::: 0.6m
2
)
(net plot: 1
x
on the Hatfield Experimental Farm, Pretoria, South Africa
o
(2S 4S'S 28°16'E), 1327m above sea level, to determine whether a mixture of
waste materials could improve infertile acidic soils, thereby creating better soil
conditions for crop production.
A uniform sandy loam soil was ameliorated with sewage sludge, fly ash and
reactive lime (CaD), in combination (SLASH) at four different levels and
separately. These treated soils were placed into these constructed raised
treatments [T1 (Control - 0% SLASH), T2 - [2.5% SLASH (8kg)],
- [5.0%
SLASH (16kg)], T4 - [7.5% SLASH (24kg)], TS - [10% SLASH (32kg)], T6 Sewage Sludge (4.32kg),
- Fly ash (10.24 kg) and
- Lime (1.44kg)] were
replicated five times.
These raised beds were used to evaluate the
effects of SLASH,
sewage sludge, lime and fly ash in soil on the dry matter production of various
crops and soil chemical properties. Initially
raised beds were planted to
179
cabbages, carrots, stocks, sweet peas and statice. These vegetable and flower
crops represented the 1st cropping cycle of the raised bed trial [42]. Maize (Zea
mays) [38], Triticale (Triticale hexaploide), sorghum (Sorghum sp.) and rye
(Secale cerea/a) represented the 2nd , 3rd, 4th and 5th cropping cycles [43]. The
treatments were applied to the soil in the raised beds at the start of the trial and
were monitored over a period of 36 months.
initial analyses for this work was
after the 1st cropping cycle done by Ramagadza [42].
The study. also aimed to evaluate the
effect treatments on crop
production and the soils condition. The soils were sampled and analyzed once
each cropping cycle had been completed. The chemical properties that were
analyzed by the Soil Science Department, University of Pretoria, were the pH
(H 20) and the content of macronutrients (Bray 1 P), K, Ca and Mg. The %C was
also occasionally determined.
The soils received regular watering to eliminate moisture as a limiting growth
factor. Due to the variability of the raw materials used in these waste material
mixtures, a relatively low concentration of a macronutrient was expected. Plants
in the 1st cropping cycle showed symptoms of K deficiency and to determine if this
was true for the batch of
used for that study, K was applied to
2nd
cropping cycle (maize) only. This was necessary to eliminate K from being a
possible growth-limiting factor for the 2nd cropping cycle. Thereafter, no additional
inorganic fertilizer or additional applications of
or other components were
applied.
When using SLASH for flower and crop production, the best performances
were achieved with the 5% and 10% SLASH levels (35,36,43]. It was because of
this conclusion that this raised bed study was undertaken to compare
treatments to the individual components of SLASH to notice the benefits of
combining the waste materials.
Forage production for the various test crops was assessed by regular harvests
within each growing season. These soils had been intensively cropped to get
maximum production.
180
which is relatively low in P, it can reduce the availability of P in
sludge
and make it slowly available over time (Fig. 6).
These effects can be attributed to an increase in soil pH by
formation of insoluble complexes [53, 54].
SLASH treatments, can be related
ash and the
lower soil P levels seen on the
the conclusion made by Schumann and
Sumner, [54] that the soil P deficiencies were exacerbated by fly ash applications,
due to precipitation of P and cation imbalances caused from excess Ca
compounds.
The P level obtained in the analysis at 360 days is not valid. This may
ascribed to a non-representative sample, which did not contain significant sewage
sludge, which influenced the mean value for that period. This observation
emphasizes the difficulty of handling, applying and incorporating a waste material
such as sewage sludge. SLASH and similar waste product mixtures, based on
same principles, deliver a more granular soil like texture facilitating it's even
incorporation into the soils.
3.3 Calcium (Ca)
Calcium is absorbed by plants in relatively large amounts and
regarded as a macro nutrient.
function of
in the plant is the formation of
Ca pectates in the middel lamella of the cell wall and
membranes
therefore,
stabilization of
Thus, damage of the root could result from a disturbance
of cell wall formation in the root meristem or through disturbance of the integrity
and function of membrane, especially the plasmalemma.
The chemical barrier to root development existing in the sub-soils of acid
is a subject of increasing interest. In order to better understand the factors
involved in the amelioration of subsoil acidity,
phosphogypsum and calcium carbonate on
phases of subsoil samples and on
mays L.) were evaluated
effects of calcium sulphate,
properties of solid and liquid
growth and nutrient uptake by maize
Calcium carbonate reduced activity of A1 3+ IIJ'V'"Q"H:O'V
of the increase in pH. The subsoil samples presented severe restrictions for
maize root growth and all
treatments were equally effective in increasing
root development, which could be attributed to the supply of calcium and a
186
360 days
the KCL application, the K levels had returned to the original level
after being depleted by the two crops that utilized this K.
as seen from 540
remaining K levels
onwards, are not sufficient for optimum crop production
and quality plant material. The need, therefore, exists
supplemental inorganic
fertilization, or the addition of an organic material, which is relatively high in K as
are animal manures.
3.5 Magnesium (Mg)
Magnesium forms the core of the complex chlorophyll molecule, which is
important in the photosynthetic process. Shortages can occur in
low CEC
or sandy soils. Mg is also present in seeds and is involved in the
translocation of P. Once an adequate amount of exchangeable Mg2+ is present, it
has been shown that the ratio of Ca/Mg can
anywhere in the range of 1:1 to
49:1 without affecting crop yields [60].
Sewage sludge can supply Mg and other essential nutrients, but it depends
greatly on the source from where
sewage sludge comes from. Fly
produced from South African coals, can be relatively low in Mg.
Nevertheless, 180 days after the application of treatments the Mg levels
weren't Significantly different to each other. In the following months, it is obvious
from Fig. 9 that the lime, the lowest SLASH treatment, sewage sludge, fly
and control's Mg
dropped. While the other SLASH treatments maintained
relatively constant Mg levels for at least
days longer than the other
treatments.
These results re'nect
variation in the
of
various
interactions between
elements themselves, but
can also be ascribed to the different nutrient requirements
crop species. Overall, the
0% SLASH treatments gave the
results, which can thus emphasize the benefits of combining two waste
products that have unique characteristics in
of improving specific soil
conditions or enhancing plant growth processes.
189
levels were not considerable. Therefore, the optimum level of SLASH can
5-10% of the soil volume depending on the specific soil condition.
range
Sewage sludge is an excellent source of N and
of
can result
Unfortunately; P fixation
excessively high levels
P supplied by sewage
By mixing sewage sludge with fly ash (SLASH) the P
were lowered
to more acceptable levels, and made available over time.
Potassium is a very essential nutrient for plant growth. Very low levels of K are
found in both sewage sludge and fly
It is, therefore, critical that K is
supplemented by adding K in an inorganic form, or possibly combining with an
additional organic material, which is high in K, such as animal manures.
improvement
physical
properties were observed but not measured.
This requires further investigation to substantiate the hypotheSiS that SLASH
does improve physical
properties.
Combining waste materials produces mixtures, which are superior soil
amendments than
individual components.
these mixtures can resolve the deficiency
use of organic wastes used in
macronutrients in the fly ash, as can
fly ash address the deficiency of micronutrients in the organic wastes. In
addition to this, the fly ash acts as a bulking agent for organic wastes, reducing
odour, and can offsetting soil acidity problems as well.
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197
CHAPTER 7
General conclusions and recommendations
The land application of by-products from municipal, industrial or agricultural
sources is certainly not a new phenomena. In many cases, a coal combustion by­
product (CCB) or an organic waste may not be ideal by itself for land application
as a soil amendment.
The coal combustion by-product fly ash, has shown potential as a soil
amendment and is a source of trace elements beneficial to plants. However,
agricultural utilization of fly ash has been restricted because it is a poor source of
macronutrients such as Nand P, which is evident from the results obtained in the
raised bed trials. Another assumption that can be made, but needs to be
researched properly, is that P can become more available, because of the Si
present in the fly ash, which can physically compete with the P on the clay
minerals, thus making P more available for uptake by plants. The alkaline nature
of fly ash, however, has made some significant contributions to the neutralization
of acid soils. It can also be hypothesized that fly ash is more mobile in the soil
than lime, which is not. This is important in neutralizing subsoil acidity, and this
can possibly be ascribed to the presence of Ca silicates in the fly ash, but this
requires further investigation. Another conclusion drawn from these studies, is
that initially the fly ash application rates were calculated on a neutralizing value of
20% of agricultural lime, but from these studies, it can be concluded that fly ash
has a higher neutralizing capacity than 20%. This, however, needs to be
researched in more detail. Significantly high B levels in fly ash, which can be
detrimental to crop production, were of no concern in these studies, and this may
be due to the source, quality and age of the fly ash used in this programme.
The application of sewage sludge, more recently known as biosolids, is not
very common in many countries because very little research has been carried out
under local conditions, because of the high variability of biosolid compositions. It
is clear from the high yields obtained in this study that sewage sludge is a good
198
source of organic material with high amounts of
macronutrients
(especially Nand P). Unfortunately, P fixation can
because of these
high levels of P present in sewage sludge.
Sewage sludge
the ability to improve physical soil properties.
Improvements in water holding capacity were noted during the cultivation of the
treated with
Despite the statistically different yields obtained
with the sewage sludge,
legislation
""u:..
use of this by-product '-''''''.............''' of associated problems,
pathogenic micro-organisms, which can become a
,J"'.....
restrictions on the
as the high levels of
the possible
contamination aspects, as a result of excessive heavy metal contents, the
associated odour problems and the acidifying effect it
on agricultural soils. In
addition to sewage sludge's limitations, practical restrictions such as transport,
handling and application
makes sewage
a difficult by-product
to use for agricultural
It was, therefore, very important to develop tec:nnOIOlalEIS that can be used to
produce soil ameliorants from these waste products with
can be beneficially used to address problems
properties that
with conventional
sludge and fly ash disposal practices, while simultaneously creating a beneficial
use
waste products to the benefit of interested parties.
Co-utilization is simply the production of new products by combining two or
more by-products.
of two or more
value added product. South Africa has successfully
materials results in a
other countries in
developing a technology to convert waste
beneficiation strategy. By combining sewage sludge, fly
into a soil
and CaO, a
ameliorant SLASH is produced locally. SLASH is a superior soil amendment,
which combines the amending qualities of two
materials, which can
overcome soil acidity and infertility problems by exploiting the complementary
of fly ash and
sludge.
SLASH programme has been concentrated on the agricultural use of
To extrapolate conclusions, biomass
species, long term residual effects, heavy metal
of a wide range of
and
199
chemical properties were examined. During these studies, suprising results were
"nl~onJon
which emphasizes the need to investigate further possible
v"~Anv
Concerning the rate of SLASH application, it is clear from the
in these
that the optimal level of SLASH is between
sandy loam
volume. One may require different application
and type of soil that is being dealt with and
on the acidity
long term
obtained
10% of the
ncr,cTI
from the
of SLASH. The reason one would apply lower more
frequent
time.
hor,otl't~
would
LlG"~'lG"I"" ex(~ee,amla
may
to have a slow response over a longer period of
10% will still deliver substantial
in
of inhibiting germination of seeds or
in
of
but
growth
growth stages. The visual observations
germination indicate that the 30% SLASH treatment for
of
an
inhibiting and
on seed germination and subsequently
establishment.
once seedlings had established themselves, exponential
growth
These were, however, not necessarily better than
treatments. It is, therefore, concluded that the
the 5-10%
between
0%
level and the 30% SLASH level in
did not justify the higher level of SLASH .
........ ,""'''''''' of all the different species in
Crop production
were
conSistently good.
prolonged growth enhancement over a minimum
period of 36 months
the SLASH and other treatments showed signs
depletion. Ne'verme,less. the
contributed significantly to the immediate growth
yields.
and produced high yields from the germination
enhancement
SLASH
treatment still maintained the better
improved
and high yielding
production of leguminous plants. For a healthy
to establish itself, a legume needs to develop healthy
nodules (usually by inoculating with Rhizobia) on it's roots to be able to fix N. This
aspect is important in
inputs of inorganic nitrogen in any crop production
system, which is reliant on nitrogen for production. Legumes produced on
treated soils had
Th is may be ascribed to
yield improvements and consistently high production.
reasons, firstly, the organic contribution from
200
SLASH with the essential macronutrients and microorganisms suppJied by the
sewage sludge component
the supply of micronutrients from the fly
component of SLASH. Secondly, the amendment of soil pH creating a beUer
thirdly the development and presence of a vast
medium for root development
amount of nodules, which were observed visually. This was an interesting
researched more intensively to obtain clarity on
observation, but would need to
this aspect, although the literature has indicated that fly
encourages or
stimulates microbial populations.
studies conducted in the
From
programme, many answers have
been provided. Nevertheless, gaps in our knowledge
obtained
to many other questions.
applications of SLASH
whether
response to, and
from crop to crop and often
and the results
effect of, high
especially on
test crop was planted with fine seed, vegetative material or
seedlings.
findings
find application in strategies using SLASH other
than purely agricultura!.
These ameliorating
unlike many inorganic fertilization programmes,
have long residual effects, which is clear from the studies conducted. The
length of
effects is approximately
condition of the soil involved and the
crops etc.). This finding,
months depending on the type and
nTOnC:H'I'\/
of cropping (irrigation, multiple
important implications for
and frequency
application of SLASH. In this context the following questions should also
addressed: Should heavy applications of SLASH be applied infrequently or lighter
applications each year
crops? Although, the lifespan of SLASH
been 36 months with one heavy application (30% of soil volume), compared to
lighter applications (5-10% of the soil volume), no significant differences in
were noted. Should applications be incorporated or may top dressings also
used? Consistently good results have been obtained when the SLASH
applications were incorporated, so that the treatments were able to react with the
medium. The use of
as a top-dressing, however, remains to
investigated.
creates favourable conditions for improved root development, which is
essential to ensure
aboveground plant growth.
can provide a
201
good balance of essential nutrients, which are slowly released. Although SLASH
is a good source of a wide
of nutrients, it often
low levels of K, because
sludge and fly ash are often K deficient. This aspect emphasizes the
need to supplement SLASH with a potassium source. This limitation has
the need for further
incorporating other
material,
to
as animal
manures, which are a good source of K.
SLASH also
definite potential to improve soil physical properties, but
research must be conducted to
able to substantiate the visual observations
made during this study.
An important consideration, which should be kept in mind, is that eliminating
water as a limiting growth factor plays an important role in the rate at which soil
chemical reactions
place. Mine rehabilitation studies, using the ameliorant
SLASH to improve degraded mine
(soils impacted by acid mine drainage
and acidic cover soil used in the rehabilitation process) after open
operations can
mrnrng
important for future application. Results from dry-land crop
production studies and mine rehabilitation studies using SLASH as an
amendment, to improve poor agricultural soils and degraded mine soils (soils
impacted by acid mine drainage and acidic cover soil used in the rehabilitation
process), should
for large
provide valuable information in terms of recommendations
application.
Sewage sludge, which comes from a source which contains high levels of
heavy metals,
the concern of translocation to plant material. If sewage
sludge with a high heavy metal content is used in the manufacturing
SLASH, authorities
During the process of
of
concern about possible heavy metal contamination.
manufacture, heavy
have been immobilized,
and this programme has substantiated this. No significant translocation
two
hazardous heavy metals (Ni and Cd) or the micronutrient B was measured in
maize plant material. The levels measured were within current
speCifications but these may be open for review. Uptake by different crop species
is
important factor to consider. It is recommended that heavy metal and
other toxic element analyses be continued on other crop species.
202
Despite the good results obtained with SLASH, guidelines for the effective use of
SLASH need to
as a
compiled, for specific situations or conditions. Nevertheless,
of the high amounts of SLASH required for ameliorating soils in an
extremely poor condition, such a product should only be used in close proximity
to
source of individual waste products.
Many by-products
low intrinsic value, but co-utilization strategies are
aimed at producing value added products. Any activity performed on a by­
product, e.g. loading on trucks, transporting
adds an additional cost.
economics of utilizing these by products are further complicated by the fact that
for many industrial, agricultural or muniCipal wastes, the money spent on dealing
with
generated is relatively low. However, the fact remains that this
money is used to dispose of, or manage the waste, not necessarily
waste. Co-utilization products can change the natural resource base, provide
value-added products, create new industries and associated employment, and
in handling
wastes produced by sectors of the population, and being
both economically and sociably viable. Thus, production of waste product
mixtures can be one of the many tools for achieving sustainability.
Future research needs to include: the evaluation of by-products mixtures
ensuring an optimal nutrient balance for large scale land application; development
of accurate, calibrated analyses of organic and nutrient content; environmental
impact of land spreading; economic value of by-products and improved storage
and handling of by-products to reduce nutrient loss. Most importantly, logistical
difficulties, such as transportation and application
and social acceptance
issues (which require education of the public, government officials, and the
agricultural community) need to be addressed. If the agronomic community can
realize the full benefits of co-utilization
high quality by-products, these may
viewed as the great resources they can be, rather than the difficult disposal
problems they are.
203
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