Use of Flyash in Agriculture: A Way to Improve Soil Fertility and its Productivity
Fly Ash (FA)-a coal combustion residue of thermal power plants has been regarded as a problematic solid waste all over the world. Disposal of high amount of fly-ash from thermal power plants absorbs huge amount of water, energy and land area by ash ponds. Therefore, fly-ash management would remain a great concern of the century. However, several studies proposed that FA can be used as a soil ameliorate that may improve physical, chemical and biological properties of the degraded soils and is a source of readily available plant micro-and macro-nutrients. Practical value of FA in agriculture as an eco-friendly and economic fertilizer or soil amendments can be established after repeated field experiments for each type of soil to confirm its quality and safety. Fly-ash has great potentiality in agriculture due to its efficacy in modification of soil health and crop performance. The high concentration of elements (K, Na, Zn, Ca, Mg and Fe) in fly-ash increases the yield of many agricultural crops. But the use of fly-ash in agriculture is limited compare to other sector. An exhaustive review of numerous studies of last four decades took place in this study, which systematically covers the importance, scope and apprehension regarding utilization of fly-ash in agriculture. This study also identified some areas, like soil fertility and its response on cereal oil seed and vegetable crops. Agricultural lime application contributes to global warming as Intergovernmental Panel on Climate Change (IPCC) assumes that all the carbon in agricultural lime is finally released as CO2 to the atmosphere. It is expected that use of fly-ash instead of lime in agriculture can reduce net CO2 emission and also reduce global warming.
Fly ash is produced as a result of coal combustion in thermal power station
and discharged in ash ponds. Combustion of bituminous and sub-bituminous coal
and lignite for generation of electricity in thermal power plants produces solid
wastes such as fly ash, bottom ash, boiler slag and Flue Gas Desulphurization
(FGD) materials, which are commonly known as coal combustion by-products (CCPs)
(Vom Berg, 1998). The material is produced in the flue
gas scrubbers by reacting slurried limestone or lime with the gaseous SO2
to produce CaSO3. Now-a-days fly ash (FA) disposal into the environment
is one of the major concerns throughout the world mainly in developing countries.
Flyash production depends on the quality of the coal, which contains a relatively
high proportion of ash that leads to 10-30% Flyash formation (Singh
and Siddiqui, 2003). In India 75% of electricity is generated by coal based
thermal power plants, according to the data revealed in Table
1, provided by Government. of India 112 million tones of this kind of waste
is produced in India during 2005-06 of which 4 mt is released into the atmosphere
(Jamwal, 2003). Percentage ash utilization of the total
ash generated in different countries amounts to more than 85% in West Germany,
100% in Denmark, 85% in France, 50% in UK, 45% in China and 38% in India. Kalra
et al. (1997) have reported that FA production in India will exceed
140 million tons by 2020. Nearly 50-60% of the fly ash is being stored at plant
dump sites and other sites intended for this purpose. The disposal of such a
huge amount of FA is one of the major problems of developing countries and is
usually disposed in basins or landfills near the power plants. Fly ash is some
times used in buildings, construction of roads, embankment and cement industries.
Its alkaline character and a high concentration of mineral substances have resulted
in attempts at using it as fertilizer or amendment to enhance the physico-chemical
properties of soil. The FA contains a high concentration of toxic heavy metals
such as Cu, Zn, Cd, Pb, Ni, Cr etc. (Rautaray et al.,
2003; Lee et al., 2006; Tiwari
et al., 2008) along with low nitrogen and phosphorus content and
pH ranged from 4.5 to 12.0 depending on the S-content of parental coal. Fly
ash is disposed of either by dry or wet methods. In dry disposal, the fly ash
is dumped in landfills and fly ash basins. In the wet method, the fly ash is
washed out with water into artificial lagoons and is called pond ash. Both methods
ultimately lead to dumping the fly ash on open land, which degrades the soil
and endangers human health and the environment. Fly ash particles are small
enough to escape emission control devices and easily get suspended in the air.
Repeated exposure to fly ash can cause irritation in eyes, skin, nose, throat
and respiratory tract and result in arsenic poisoning (Carlson
and Adriano, 1993; Finkelman et al., 2000).
Therefore, disposal and utilization of fly ash needs careful assessment to prevent
conversion of arable land into landfills and accumulation of toxic metals in
soil (Petruzzelli, 1989) and use it as an ameliorant
for problem soils. Restoration and utilization of fly ash dumps for biomass
production will be an adjunct to these efforts. The current article reviews
various attributes of fly ash for its application in agriculture and deriving
PHYSICO-CHEMICAL AND MINERALOGICAL PROPERTIES OF FLYASH
Physical Properties of Fly Ash
The mineralogical, physical and chemical properties of fly ash (Adriano
et al., 1980; Carlson and Adriano, 1993)
depend on the nature of parent coal, conditions of combustion, type of emission
control devices and storage and handling methods.
Physical properties of fly ash
characteristics of Flyash C and F|
Therefore, ash produced by burning of anthracite, bituminous and lignite coal
has different compositions. In general, flyash particles are spherical and have
a size distribution with medium around 4 μm while the bottom ash has a
medium around 70 4 μm and settle close to plant site (Sadasivan
et al.,1993). Fly ash generated from various thermal power plants
in India comprise ranges of silt 8-85, clay 0-10, sand 7-90 and gravel 0-10%
(Table 2). Bulk density of fly ash varies from 1 to 1.8 g
cm-3. Water Holding Capacity (WHC) of flyash is generally 49-66%
on weight basis, while the moisture retention ranges from 6.1% at 15 bar to
13.4% at 1/3 bar. The specific gravity of fly ash ranges from 2.1 to 2.6 g cm-3.
Mean particle density for non-magnetic and magnetic particles is 2.7 and 3.4
g cm-3, respectively (Natusch and Wallace, 1974).
Flyash has unusually high surface area and light texture due to the presence
of large, porous and carbonaceous particles.
Chemical Properties of Fly Ash
Chemically, 90-99% of fly ash is comprised of Si, Al, Fe, Ca, Mg, Na and
K with Si and Al forming the major matrix (Adriano et
al., 1980). There are mainly two types of ash: Class F (low lime) and
Class C (high lime) based on silica, alumina and iron oxide content of fly ash.
Al in fly ash is mostly bound in insoluble aluminosilicate structures, which
considerably limits its biological toxicity (Page et
al., 1979). It is substantially rich in trace elements like lanthanum,
terbium, mercury, cobalt and chromium (Adriano et al.,
1980). Many trace elements including As, B, Ca, Mo, S, Se and Sr (Page
et al., 1979) in the ash are concentrated in the smaller ash particles
(Adriano et al., 1980). Table 3
revealed that the content of oxide in flyash varies from class C and class F.
The Fe-oxide contents of spheres influences their color which ranges from water-white
to yellow orange to deep red or brown to opaque. Ca was found to be the dominant
cation in ESP ash and fly ash collected from dump sites, followed by Mg, Na
and K (Matti et al., 1990). The pH of fly ash
varies from 4.5 to 12.0 depending largely on the sulphur content of the parent
coal (Plank and Martens, 1974) and the type of coal
used for combustion affects the sulphur content of fly ash (Page
et al., 1979).
||Macro and micronutrients content in flyash
The concentration of various elements in flyash decreased with increasing particle
size (Adriano et al., 1978). Eastern US coals
that include anthracite are generally high in S and produce acidic ash, While
western US coals, which includes lignites, tend to be lower in S and higher
in Ca and produce alkaline ash (Furr et al., 1977;
Page et al., 1979). Chemical constituents of
fly ash had a relatively low content of major and trace elements (Table
Mineralogical Properties of Flyash
Minerals such as quartz, mullite, hematite, magnetite, calcite and borax
were also identified in fly ash and oxidation of C and N during combustion drastically
reduces their quantity in ash (Hodgson and Holliday, 1966).
The coal produced in India is low in S but high in ash content (40%) whereas
the coal produced in US is rich in S (2%) and contains only 5-10% ash.
IMPACT OF FLYASH ON SOIL FERTILITY
Soil properties as influenced by fly-ash application have been studied by several
workers (Inam, 2007) for utilizing this industrial waste
as an agronomic amendment.
Effect of Flyash on Physical Properties of Soil
Fly-ash application to sandy soil could permanently alter soil texture,
increase microporosity and improve the water-holding capacity (Ghodrati
et al., 1995; Page et al., 1979).
Fly-ash addition at 70 t ha-1 has been reported to alter the texture
of sandy and clayey soil to loamy (Capp, 1978). Addition
of fly-ash at 200 t acre-1 improved the physical properties of soil
and shifted the USDA textural class of the refuge from sandy loam to silt loam
(Buck et al., 1990). The particle size range
of fly-ash is similar to silt and changes the bulk density of soil. Chang
et al. (1977) observed that among five soil types, Reyes silty clay
showed an increase in bulk density from 0.89 to 1.01 g cc-1 and a
marked decrease in soils having bulk density varying between 1.25 and 1.60 g
cc-1 when the corresponding rates of flyash amendment increased from
0 to 100%. Application of fly-ash at 0, 5, 10 and 15% by weight in clay soil
significantly reduced the bulk density and improved the soil structure, which
in turn improves porosity, workability, root penetration and moisture-retention
capacity of the soil (Kene et al., 1991). Prabakar
et al. (2004) concluded that addition of fly-ash up to 46% reduced
the dry density of the soil in the order of 15-20% due to the low specific gravity
and unit weight of soil. A gradual increase in fly-ash concentration in the
normal field soil (0, 10, 20 up to 100% v/v) was reported to increase the porosity
and water-holding capacity (Khan and Khan, 1996). This
improvement in water-holding capacity is beneficial for the growth of plants
especially under rainfed agriculture. Amendment with fly-ash up to 40% also
increased soil porosity from 43 to 53% and water-holding capacity from 39 to
55% (Singh et al., 1997). Fly-ash had been shown
to increase the amount of plant available water in sandy soils (Taylor
and Schumann, 1988). The Ca in fly-ash readily replaces Na at clay exchange
sites and thereby enhances flocculation of soil clay particles, keeps the soils
friable, enhances water penetration and allows roots to penetrate compact soil
layers (Jala and Goyal, 2006). Water-holding capacities
of fly-ashes from different thermal power plants in Eastern India were compared
and the effect of size fractionation on the water-holding capacity was determined
in an investigation by Sarkar and Rano (2007).
Effect of Flyash on Chemical Characteristics of Soil
Lime in flyash (FA) readily reacts with acidic components in soil and releases
nutrients such as S, B and Mo in the form and amount beneficial to crop plants.
FA improves the nutrient status of soil (Rautaray et
al., 2003). The FA has been used for correction of sulphur and boron
deficiency in acid soils (Chang et al., 1977).
Application of fly ash for increasing the pH of acidic soils (Phung
et al., 1979). Most of the fly-ash produced in India is alkaline
in nature; hence, its application to agricultural soils could increase the soil
pH and thereby neutralize acidic soils (Phung et al.,
1978). The hydroxide and carbonate salts give fly-ash one of its principal
beneficial chemical characteristics, the ability to neutralize acidity in soils
(Cetin and Pehlivan, 2007). Fly-ash has been shown to
act as a liming material to neutralize soil acidity and provide plant-available
nutrients (Taylor and Schumann, 1988). Researches have
shown that the use of fly-ash as liming agent in acid soils may improve soil
properties and increase crop yield (Matsi and Keramidas,
1999). The electrical conductivity of soil increases with fly ash application
and so does the metal content. Decolorization of effluents by fly ash has been
reported earlier by a number of workers (Robinson et al.,
2001) and a mixture of fly ash and coal in the ratio of 1:1 can be substituted
for activated carbon owing to increase in surface area available for absorption
(Gupta et al., 1990). Metals like Fe, Zn, Cu,
Mn, Ni and Cd have been shown to be available at higher concentrations in DTPA
extracts of FA (Gupta et al., 2007). The increased
accumulation of essential ions such as Zn, Mn and Cu by the paddy shoot/grain
might be due to increased activity of ionic transporters (Hall
and Williams, 2003), in turn due to higher essential ion availability in
the FA. Sarangi et al. (2001) observed that gradual
increases in soil pH, conductivity, available phosphorus, organic carbon and
organic matter with increased application rate of fly ash (Table
5). Flyash is considered to be a rich source of Si and application of FA
in Si-deficient soils has been demonstrated to improve the Si content of rice
plants as well as their growth (Lee et al., 2006).
Effect of Flyash on Biological Properties of Soil
There is a dearth of studies regarding the effects of FA amendment on soil
biological properties. Numerous short-term laboratory incubation studies found
that the addition of unweathered FA to sandy soils severely inhibited microbial
respiration, numbers, size, enzyme activity and soil nitrogen cycling processes
such as nitrification and N mineralization (Cerevelli et
al., 1986; Wong and Wong, 1986; Pichtel,
1990; Garau et al., 1991). Information regarding
the effect of fly-ash amendment on soil biological properties is very scanty
(Schutter and Fuhramann, 2001). These adverse effects
were partly due to the presence of excessive levels of soluble salts and trace
elements in unweathered fly-ash. However, the concentration of soluble salts
and other trace elements was found to decrease due to weathering of fly-ash
during natural leaching, thereby reducing the detrimental effects over time
(Sims et al., 1995). Moreover, the use of extremely
alkaline (pH 11-12) fly-ash could also be the reason for those adverse effects.
The application of lignite fly-ash reduced the growth of seven soil borne pathogenic
microorganisms, whereas the population of Rhizobium sp. and P-solubilizing
bacteria were increased under the soil amended with either farmyard manure or
fly-ash individually or in combination. Amendment of Class F, bituminous flyash
to soil at a rate of 505 Mg ha-1 did not cause any negative effect
on soil microbial communities and improved the populations of fungi, including
arbuscular mycorrhizal fungi and gram-negative bacteria as revealed from analysis
of community fatty acids (Schutter and Fuhrmann, 2001).
Machulla et al. (2004) suggested that the microbial
communities that developed in 17-20-year-old lignite ash deposits in Germany
contained specific ash-tolerant populations that different significantly from
those in surrounding soils. Kumar et al. (2008)
isolated metal tolerant plant growth promoting bacteria (NBRI K28 Enterobacter
sp.) from FA contaminated soils and found that the strain NBRI K28 and its siderophore
overproducing mutant NBRI K28 SD1 are capable of stimulating plant biomass and
enhance phytoextraction of metals (Ni, Zn and Cr) from FA by metal accumulating
plant i.e., Brassica juncea (Indian mustard). Concurrent production of
siderophores, Indole Acetic Acid (IAA) and phosphate solubilization revealed
its plant growth promotion potential. Finally, in most of the cases mutant of
NBRI K28, exerted more pronounced effect on metal accumulation and growth performance
of B. juncea plants than wild type. Actinomycetes and fungi declined
with 5% FA and all populations declined at the 10 and 20% rate. With 20% FA
bacteria, actinomycetes and fungi decreased by 57, 80 and 86%, respectively
(Pichtel, 1990). Garampalli et
al. (2005) revealed on the basis of pot-culture experiment that using
sterile, phosphorus-deficient soil to study the effect of FA at three different
concentrations viz., 10, 20 and 30 g FA kg-1 soil on the infectivity
and effectiveness of vesicular arbuscular mycorrhiza (VAM) Glomus aggregatum
in pigeonpea (Cajanus cajan L.) cv. Maruti. All the concentrations of
FA amendment in soil were found to significantly affect the intensity of VAM
colonization inside the plant roots and at higher concentration (30 g FA kg-1
soil); the formation of VAM fungal structure was suppressed completely. The
dry weight of the pigeonpea plants under the influence of FA amendment in VAM
fungus infested soils was found to be considerably less (though not significant
enough) when compared to the plants grown without FA that otherwise resulted
in significant increase in growth over the plants without G. aggregatum
inoculation. However, FA amendment without VAM inoculation was also found to
enhance the growth of plants as compared to control plants (without FA and VAM
inoculums). Hrynkiewiez et al. (2009) evaluated
the use of inoculation with a mycorrhiza-associated bacterial strain (Sphingomonas
sp. 23L) to promote mycorrhiza formation and plant growth of three willow clones
(Salix sp.) on fly ash from an overburdened dump in a pot experiment.
They conclude that inoculation with mycorrihza promoting bacterial strains might
be a suitable approach to support mycorrhiza formation with autochthonous site-adopted
ectomycorrhizal fungi in FA and thereby to improve re-vegetation of FA landfills
of Flyash on soil enzymes activity|
Ray and Adholeya (2008) presented a correlation between
organic acid exudation and metal uptake by ectomycorrhizal fungi grown on pond
ash in vitro and this finding supports the widespread role of low molecular
weight organic acid as a function of tolerance, when exposed to metals in
vitro. The enzymatic activity of soil is also an important factor for measuring
soil biological properties after FA amendment in soil. The high pH and electrical
conductivity of FA have been suggested to be important elements limitingmicrobial
activity (Elliott et al.,1982). Sarangi
et al. ( 2001) reported that invertase, amylase, dehydrogenase and
protease activity increased with increasing application of flyash up to 15 t
ha y-1, but decreased with higher levels of flyash application (Table
6). Pati and Sahu (2004) taken 7 concentrations
of FA amended soil (0, 2.5, 5, 10, 15, 25 and 50%; w/w) for the toxicity test
of earthworms (Drawida willsi) and studied the CO2 evolution
and enzyme activities (dehydrogenase, protease and amylase) in the presence
and absence of D. willsi. They found little or no inhibition of soil
respiration and enzyme activities up to 2.5% FA amendment. With further addition
of FA, all the above activities were significantly decreased. On the other hand,
significant stimulation of soil respiration and microbial activities were observed
up to 5% FA amendment when the soils contained earthworms. This may be due to
increased microbial activity induced by substrates that are produced by the
earthworms. Lal et al. (1996) reported that FA
added to soil at 16% (w/w) increases enzyme activities (urease and cellulase).
However, acid phosphatase activity was depressed and with FA application. So,
mix application of FYM and FA proved to be beneficial in augmenting proliferation
and activity of microorganisms in acid soils. Fly ash composted with wheat straw
and 2% rock phosphate (w/w) for 90 days enhanced chemical and microbiological
properties of the compost and fly ash up to 40-60% and did not exert any detrimental
effect on either C:N ratio or microbial population (Gaind
and Gaur, 2004). The available phosphorus estimation of soil receiving fly
ash at varying rates of 0-80 t ha-1 showed higher availability of
this element compared to control (no fly ash). Both 40 and 60 t ha-1
of fly ash resulted in the same status of soil available P. The improved availability
may partly have been contributed by fly ash which itself contained some available
P and partly to some native phosphate solubilizers. However, the treatments
receiving P. striata inoculation showed further enhancement in P availability
due to their ability to solubilize insoluble phosphorus. The inoculation effect
was most pronounced in F40 treatment with available P being 34.7 ppm. Both F40
and F60 treatments were statistically at par with each other but superior to
EFFECT OF FLYASH ON SOIL CARBON SEQUESTRATION POTENTIAL
A significant enhancement of C-sequestration by terrestrial ecosystems is needed
to help offset the growth in atmospheric CO2 inputs during the transition
from fossil fuels to renewable and alternative-energy sources over the next
50-100 years. While trees and the ocean are important sinks for C, soils can
make a large one-time contribution to this effort if ways can be found to return
them to pre-agricultural levels of C. Our part of the challenge is to explore
ways of enhancing net sequestration of C by soils while minimizing release of
other GHGs. Agricultural lime contributes a prime role in the global fluxes
of the greenhouse gases such as carbon dioxide, nitrous oxide and methane. According
to the Intergovernmental Panel on Climate Change (IPCC), agricultural lime application
contributes to global warming through emission of CO2 to the atmosphere,
the US EPA estimated that 9 Tg (teragram = 1012 g = 106 metric ton) CO2
was emitted from an approximate 20 Tg of applied agricultural lime in 2001 (McBride
and West, 2005). Some researchers have been worked on utilization of FA
in place of agricultural lime for minimizing global warming (West
and McBride, 2005). An experimental study revealed that 1 tonne of FA could
sequester up to 26 kg of CO2, i.e., 38.18 ton of FA per tonnes of
CO2 sequestered. This study confirmed the possibility to use this
alkaline residue for CO2 mitigation (Montes-Hernandez
et al., 2009). So, use of FA instead of lime as soil ameliorant can
reduce net CO2 emission and thereby, lessen global warming. In other
sector, using FA to replace cement can decrease cement in concrete mixture and
results in decreasing CO2 from the production of cement. This CO2
is thought to be a major contributor to the greenhouse effect and the global
warming of the planet (Ferreira et al., 2003;
Tietenberg, 2003). According to one estimate, use of 1
tonne of FA in concrete will avoid 2 tones of CO2 emitted from cement
production and reduces green-house effect and global warming (Krishnamoorthy,
2000; Naik and Tyson, 2000). So, there are some
advantages of using FA in concrete and cement production as well as in agricultural
sector: (1) use of a zero-cost raw material, (2) conservation of natural resources
mainly land (topsoil), water, coal and lime as well as one other resource as
chemical fertilizer, (3) elimination of waste and (4) minimization of global
FLY-ASH IMPROVE CROP GROWTH AND THEIR YIELD
Agricultural utilization of fly ash has been proposed because of its considerable
content of K, Ca, Mg, S and P (Kalra et al., 1997;
Singh et al., 1997). Fly ash addition generally
increases plant growth and nutrient uptake (Aitken et
al., 1984). Weinstein et al. (1989) reported
that fly ash increased crop yield of alfalfa (Medicago sativa), barley (Hordeum
vulgare), Bermuda grass (Cynodon dactylon) and white clover (Trifolium
repens). Addition of unweathered western US fly ash up to 8% (w/w) to either
calcareous or acidic soils resulted in higher yield of several agronomic crops
(Page et al., 1979) mainly due to increased availability
of S to plants. Furr et al. (1977) demonstrated
that alfalfa, sorghum (Sorghum bicolor), field corn (Zea mays),
millet (Echinochloa crusgalli), carrots (Daucas carota), onion
(Allium cepa), beans (Phaseolus vulgaris), cabbage (Brassica
oleracea), potatoes (Solanum tuberosum) and tomatoes (Lycopersicon
esculentum) could be grown on a slightly acidic soil (pH 6.0) treated with
125 mt ha-1 of unweathered fly ash. These plants exhibited higher
contents of As, B, Mg and Se. Also winter wheat (Triticum aestivum) grown
on a deep bed of fly ash produced grains containing higher Se (Stoewsand
et al., 1978). Greenhouse experiments conducted by Sikka
and Kansal (1994) showed that application of 2-4% fly ash significantly
increased N, S, Ca, Na and Fe content of rice (oryza sativa) plants.
The foliar application of fly ash also enhances growth and metabolic rates,
as well as increasing the photosynthetic pigments of crops like maize and soybean
(Mishra and Shukla, 1986). They did not find any residual
effect of fly ash application on the following wheat crop except for a slight
increase in Fe content of the soil.
||Saving of chemical fertilizers and nutrient use efficiency
under different mode of fertilization sources in rice-peanut cropping system
|*CF: Chemical fertilizers, **FA: Flyash
The post harvest soil samples from rice and wheat also did not show any change
in the nutrient content and pH. The iron content of the soil however, increased
to 18 from 12%. Khan and Khan (1996) reported that application
at 40% fly ash can increase the yield of tomato by 81% and market value (mean
fruit weight). Increased selenium accumulation in plant tissues with increased
fly ash application warrants close monitoring and use of appropriate quantity
of weathered fly ash depending upon the end use of the produced biomass (Straughan
et al., 1978). Application of 5-20% fly ash on w/w basis in the plough
layer (0-15 cm) increased both grain and straw yield of pearlmillet (Pennisetum
sp.) followed by wheat (Grewal et al., 2001).
Lau and Wong (2001) reported that weathered coal fly
ash at 5% resulted in higher seed germination rate and root length of lettuce
(Lactuca sativa). The amino acid content in soybean (Glycine max)
was found to show an increase when grown in fly ash amended soils in pot cultures
(Goyal et al., 2002). High yield of aromatic grasses
particularly palmarosa (Cymbopogon martini) and citronella (Cymbopogon
nardus), in presence of different fly ash-soil combinations, was attributed
to increased availability of major plant nutrients (Neelima
et al., 1995). Fly ash applied at 25% showed higher yield of brinjal
(Solanum melongena), tomato and cabbage. Oil seed crops such as sunflower
(Helianthus sp.) and groundnut (Arachis hypogaea) also responded
favorably to fly ash amendment. Medicinal plants such as cornmint (Mentha
arvensis) and vetiver (Vetiver zizanoides) were successfully planted
in fly ash used in conjunction with 20% farmyard manure (FYM) and mycorrhiza
(Sharma et al., 2001). The level of 40% fly ash
was found to have nematicidal effect and was suggested for the management of
root knot disease in tomato caused by Meloidogyne sp. and providing
nutrients (Khan et al., 1997). Tomato cultivars
grown on fly ash amended soils had higher tolerance to wilt fungus Fusarium
oxysporum (Khan and Singh, 2001).
REDUCES THE COST OF CULTIVATION
Saving of chemical fertilizers use of fly-ash along with chemical fertilizers
and organic materials in an integrated way can save chemical fertilizer as well
as increase the fertilizer use efficiency (FUE). According to Mittra
et al. (2003), integrated use of fly-ash, organic and inorganic fertilizers
saved N, P and K fertilizers to the range of 45.8, 33.5 and 69.6%, respectively
and gave higher FUE than chemical fertilizers alone or combined use of organic
and chemical fertilizers in a rice-groundnut cropping system (Table
FA can be used as a potential nutrient supplement for degraded soils thereby solving the solid waste disposal problem to some extent. However, the bioaccumulation of toxic heavy metals and their critical levels for human health in plant parts and soil should be investigated. An ultimate goal would be to utilize FA in degraded/marginal soils to such an extent as to achieve enhanced fertility without affecting the soil quality and minimizing the accumulation of toxic metals in plants below critical levels for human health. There are several potential beneficial and few harmful effects of FA application in soil.
(1) Improves soil texture; (2) reduces bulk density of soil; (3) improves
water holding capacity; (4) optimizes pH value; (5) increases soil buffering
capacity; (6) improves soil aeration, percolation and water retention in the
treated zone (due to dominance of silt-size particles in FA; (7) reduces crust
formation; (8) provides micro-nutrients like Fe, Zn, Cu, Mo, B etc.; (9) provides
macro-nutrients like K, P, Ca, etc.; (10) reduces the consumption of soil ameliorants
(fertilizers, lime); (11) FA can also be used as insecticidal purposes and (12)
decreases the metal mobility and availability in soil.
(1) Reduction in bioavailability of some nutrients due to high pH (generally
from 8 to 12); (2) high salinity and (3) high content of phytotoxic elements,
The authors wish to express their sincere gratitude to HOD, Soil Sci. and Agril. Chemistry, Institute of Agricultural Chemistry, Banaras Hindu University, Varanasi , India for providing necessary facilities.
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