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Karnataka J. Agric. Sci.,20(3), (531-534): 2007

Coal Fly Ash as Modifier of Physico-Chemical and Biological Properties of Soil

N. A. YELEDHALLI, S. S. PRAKASH, S. B. GURUMURTHY AND M.V. RAVI

Department of Soil Science and Agricultural Chemistry

College of Agriculture, Raichur - 584 101, Karnataka, India

(Received : October, 2006)

Abstract :A field experiment was conduced to study the effect of levels of fly ash (0, 25, 50, 75 and 100 tones/ha) on physico-

chemical, biochemical and biological properties of alfisols, the yield parameters of sunflower, soil bacterial count and activity of

soil enzymes; dehydrogenase, urease and alkaline phosphatase. Two levels of fertilizers were applied; No NPK and Recommended

dose of NPK fertilizers. Physio-chemical and microbiological analysis was conducted after the harvest of sunflower. A study of

graded level of coal fly ash amended alfisols revealed an increase in the content of N, P, K, Ca, Mg, S, Fe, Mn, Zn and Cu and

disturbed the microbiological balance and soil enzyme activity.

Keywords: Coal fly ash, ameliorant, enzyme actirity

Introduction

Fly ash is produced in thermal electrical power plant.

According to the data provided by Govt. of India 110 million

tones of this kind of waste is produced in India during 2005 - 06.

Nearly 50 - 60 % of the fly ash is being stored at plant dump sites

and other sites intended for this purpose. 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-chemicalproperties of soil. Apart from necessary nutrients, ashes contain

elevated concentration of heavy metals which may disturb the

biological properties.

Fly ash may either have a positive and negative effect

on plant growth and yielding if not used in optimum doses. The

effect is determined primarily by chemical composition and the

ash dose applied. In a study by Kalara et al .,2003, application

of 5 to 12 tones ha-1 yr-1 has modified the soil physico-chemical

properties viz., reduced the bulk density, increase the water

holding capacity, improvement in the exchangeable calcium and

magnesium status of the soil which enhanced the wheat yield.

On the other hand, Khan and Khan, 1996 in their studies intothe effect of increasing the concentration of ash in the soil (from

10 to 100 % of the volume) on the growth of tomatoes observed

a positive effect of ash on plants. The greater application of fly

ash doses decreased the yield of crop due to pozzolonic effect

of fly ash in soil which induced the poor aeration and compaction.

Based on the previous results the effect of soil

fertilization with fly ash has been quite explored. Although the

effect of this on the soil microbes is not well covered in the

literature. The microbes are the important elements of the soil

environment as they participate in the degradation of the organic

matter and makes the nutrients available to other soil organisms.

This favors the formation of soil aggregates and immobilizes

the heavy metals and stimulate the activity of soil enzymes viz.,

dehydrogenase, urease and phosphatases etc., (Pati and Sahu,

2004). A great amount of elements ( C, K, Ca, Mg, Cu, Zn and

Mn) get into the soil as a result of ash used at different doses

and may probably change the chemical as well as physico-

chemical soil properties which intern may determine the biological

properties irrespective of the crop. Therefore the study was

aimed at the determining the effect of graded levels of fly ash on

physico-chemical properties and enzyme activity of soil.

Material and Methods

A field experiment was carried out at College ofAgriculture farm Raichur, Karnataka state in three replications

with RBD during the year 2001-02. The plough layer 0 15 cm of

the soil and fly ash was characterized for various parameters

and data are presented in Table 1. The red soil of the experiment

soil belongs to Rampur series (typic hapluastulf) The texture of

the soil was sandy clay loam, neutral in reaction (pH 7.09) and

low in soluble salt (EC: 0.3dSm-1) with 1.53 Mg-3 bulk density.

The coal ash was obtained from Raichur Super Thermal Power

Station, Shaktinagar, Raichur. The experiment included the

following factors (a) Dose of coal fly ash (t ha-1) (0, 25, 50, 75

and 100) with or without recommended dose of NPK fertilizer.

The test crop was sunflower (Helianthus annus L.) cv. KBSH-1.The recommended dose of fertilizer for irrigated sunflower was

62.5:75:62.5 N:P2O

5:K

2O kg ha-1.

At harvest, the yield of sunflower crop was determined

and representative soil samples were collected for further

analysis. The samples were stored in polythene bags at 4OC

until the laboratory analysis was conducted (7 days). The

microbial analysis of the soil included a determination of the

total bacterial count using the plate method in three replication

(Rangaswamy, 1966). The biochemical activity of soil enzymes;

dehydrogenase with TTC substrate (Page et al., 1982), Catalase

(Johnson and Temple, 1964), alkaline phosphate with method

developed by Alefet al 1998. The contents of particular elementsin soil and ash samples were analyzed by following standard

methods.


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Karnataka Journal of Agricultural Sciences : 20(3) , 2007

Results and Discussion

Physio-chemical properties of coal fly ash depends on

their origin and the composition of coal used for combustion.

Raichur Thermal Station fly ashes are usually alkaline and contain

high concentration of Ca, Mg, Na and heavy metals like Si, Fe,Mn, Cu and Zn. The application of graded levels of fly ashes

resulted in an increase in available nutrient (N, P, K, Ca, Mg, S,

Fe, Mn, Zn and Cu) in the soil (Table 4), which modified the

physico-chemical soil properties and affected its biological

activity significantly.

Regardless of with or without application of

recommended dose of NPK fertilizers, increasing levels of coal

fly ash resulted in significant increase in pH, the total contents

of alkaline exchange cations, cation exchange capacity and the

per cent base saturation (Table 3). This was mainly attributed to

the inherent properties of fly ash itself as evidenced from the

characteristics properties (Table 1). The results are similar to

those reported by Meller (1999). There were marginal changes

in exchangeable calcium and magnesium, CEC and per cent base

saturation due to application of fly ash with or without

recommended dose of NPK fertilizers. However, there was

significant improvement in the macro and micronutrient status

of the soil due to application of fly ash along with the

recommended dose of fertilizers at harvest of the sunflower crop

due to enhanced nutrient supply. The sunflower responded to

soil application with graded level of fly ash and manifested by

reduced the seed yield, both in the soil without recommended

dose of NPK fertilizers at higher levels of fly ash application.

However, the average seed yield of sunflower was higher in soil

fertilized with recommended dose of NPK fertilizer (Table 2).

The seed yield of sunflower varied significantly due to

application of fly ash with or without recommended NPK

fertilizers. The seed yield in control was 521 kg ha-1 which

increase significantly to 855 kg ha-1 but was lower (978 kg ha-1)

than that obtain due to application of recommended dose of

NPK. Similar response of fly ash application in sunflower was

observed by Kene et al., 1991 and Matte and Kene, 1995.

The count and activity of soil bacteria depend on a

number of factors. The climate, type and physico-chemical

properties of the soil, the composition of species and toxic

substances including heavy metals. In this study, the coal fly

ash modified the soil bacteria count and its effect depends on

the level of fly ash application, the microbes under study

(Table 5). The total microbial population (bacteria, fungi and

actinomycetes) differ significantly. The data suggested that

application of fly ash did not affect the microbial populationadversely even though there was an increase in the soil pH, but

this effect was negated by improvement in physical conditions

and due to supply of some essential trace elements for growth

of microorganisms (Lal et al., 1966) reported that the cumulative

CO2

evolution increased only up to 8 per cent fly ash level.

However, application of fly ash along with recommended dose

of NPK fertilizers increased the population of bacteria

significantly over control in all the treatments without NPK

fertilizers such an increase might be attributed to complementary

effect of fly ash and NPK fertilizer. Lal et al., (1996) and Rajkumar

(2000) observed similar increase in the bacterial population due

to combined application of fly ash and NPK and fly ash increased

the microbial count significantly. Pati and Sahu (1990) also

observed intensive respiration of fly ash amended soil, which

reflected an increased activity of soil bacteria. Vallini et al., (1999)

reported an increase in the bacterial and actinomycetes count

due to application of fly ash amendment resulted in an increase

in soil dehydrogenase activity in soil (Table 6). Not only the

Table 2. Effect of different levels of fly ash application on sunflower

yield parameters

Levels of Test weight Seed yield Stover yield Oil content

fly ash (t ha-1) (1000 seeds g-1) (kgha-1) (t ha-1) (%)

Without Recommended dose of NPKControl 36.06 521 1.70 33.34

25 34.42 1194 2.41 31.42

50 38.53 1120 2.38 35.71

75 37.36 1021 2.35 36.31

100 38.35 855 2.19 35.05

With Recommended dose of NPK

Control 43.11 923 2.25 34.52

25 38.51 1053 2.68 31.85

50 40.01 1182 2.44 34.43

75 36.72 1078 2.42 33.58

100 37.27 978 2.35 35.74

S.Em+ 1.54 30.0 0.06 0.60

CD (0.05) NS 88.1 0.18 1.76

Table 1. Physical and chemical properties of soil of experimental site

and fly ash

Parameters Red soil Fly ash

Texture Silty clay loam Silty loam

Bulk Density (Mg-3) 1.53 0.98

Maximum water holding capacity (%) 38.10 61.50

pH (1:2.5) 7.09 8.38

EC (dSm-1) 0.30 0.75

Organic carbon (%) 0.63 0.12

Total elemental concentration (mg kg-1)

Phosphorus 426.00 198.00Potassium 15580.00 560.00

Sulphur 210.00 272.50

Zinc 28.00 107.00

Iron 18861.24 16531.00

Manganese 467.00 299.00

Copper 19.78 25.25

Available nutrients (mg kg-1)

Phosphorus 11.26 21.65

Potassium 103.30 95.00

Sulphur 26.56 168.20

Zinc 1.19 1.56

Iron 22.12 8.72

Manganese 14.24 15.25

Copper 2.72 2.12


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Coal Fly Ash as Modifier . . . . . . ..

bacteria count but also biochemical soil properties are extremely

sensitive to the factors which disturb the biological balance of

soil. The activity of soil enzymes, among other factors, affect

the soil fertility /alkaline phosphates activity was least affectedby ash. Application of NPK fertilization positively affected the

activity of alkaline phosphates activity in soils (Table 6) but the

enzyme activity decrease with increase in level of fly ash

application. Similar results were observed in respect of

population indicating strong relationship between

dehydrogenase activity and microbial population as

dehydrogenase activity represents gross soil biological activity

(Wong and Lai, 1996). The decrease in the activity of

dehydrogenase and catalase with higher rate of fly ash

application might be due to increase in soil pH and dilution

effect on the organic substances (Lai et al., 1999). The urease

activity in the control was 17.90 N-NH4 g-1

which increasedsignificantly to 29.90 N-NH

4g-1 due to application of fly ash at

the rate of 25 ton ha-1. Further, there was decline in the urease

activity due to higher doses of fly ash application with NPK.

This was mainly attributed to pozzolonic effect of fly ash which

reduced the air capacity of the soil. The urease activity

significantly increased over their respective combination without

the application of recommended dose of NPK fertilizers. Of all

the factors under study, the dose of coal fly ash and growing of

crop had the most beneficial effect on increasing the nutrient

status, soil bacterial count and the soil enzyme activity. On the

other hand, the weakest effect was extended by the treatments

not receiving NPK fertilizers. Application of graded levels of

coal fly ash with or without recommended dose of NPK fertilizers

increased the soil content of organic carbon, N, K, Ca, Mg, P,

Zn, Fe, Mn and Cu. Also increased the count of total bacteria,

actinomycetes, but decreased the number of fungi. The activity

of dehydrogenase, and urease increased. Fertilizing the soil with

NPK enhanced the count of bacteria, actinomycetes and the

activity of alkaline phosphatase.

Table 3: Some physico-chemical properties of alfisols after the harvest of sunflower

Levels of fly ash pH EC OC Ex. Ca Ex. Mg CEC BS (%)

(t ha-1) (1:2.5 ratio) (dSm-1) (%) C mol (p+)kg-1

Without Recommended dose of NPK

Control 6.85 0.27 0.46 15.60 1.50 43.60 87.4025 6.95 0.32 0.66 16.80 1.88 58.00 97.70

50 7.24 0.45 0.62 17.36 2.03 63.11 98.40

75 7.12 0.58 0.61 17.88 2.43 71.56 98.90

100 7.38 0.72 0.51 18.86 2.90 86.80 98.60


Control 6.70 0.31 0.53 16.30 1.96 42.10 84.20

25 6.92 0.40 0.75 16.88 2.13 56.30 95.40

50 6.87 0.63 0.73 17.28 2.86 68.70 97.20

75 6.88 0.69 0.65 19.88 3.38 76.50 98.30

100 7.06 0.73 0.56 19.90 3.91 81.30 99.10

S.Em+ 0.09 0.009 0.05 0.35 0.17 0.74 1.04

CD (0.05) 0.27 0.027 0.14 0.50 0.50 2.20 3.09

Table 4. Available nutrients in soil after the harvest of the sunflower as influenced by the different levels of fly ash.

Levels of N P2O

5K

2O SO

4-S Fe Mn Zn Cu

fly ash (t ha-1) kgha-1 mgkg-1


Control 164.76 25.33 293.37 8.30 17.52 14.20 0.87 2.31

25 243.33 34.52 372.13 15.92 33.19 14.85 1.12 2.64

50 229.80 32.70 359.00 12.40 28.31 15.89 1.70 3.39

75 215.13 29.92 336.27 12.51 19.44 16.26 3.16 4.10

100 207.16 22.11 295.53 10.87 17.77 18.74 4.12 4.60


Control 225.08 32.77 223.80 11.51 18.79 15.94 1.50 2.56

25 318.06 38.67 407.77 14.40 37.04 16.60 1.89 2.39

50 292.83 35.70 376.73 14.00 31.81 18.08 3.14 3.22

75 278.49 31.15 365.73 11.75 20.43 22.22 3.81 3.28

100 240.91 24.38 334.87 11.25 21.40 23.58 3.90 4.26

S.Em+ 5.63 0.61 6.26 0.29 0.83 0.51 0.14 0.14

CD (0.05) 16.53 1.78 18.35 0.84 2.42 1.48 0.40 0.45


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Karnataka Journal of Agricultural Sciences : 20(3) , 2007

References

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Table 5. Count of microorganisms in kg of dry weight soil

Levels of fly ash Bacteria Fungi Actnomycetes

(t ha-1) (108) (107) (108)


Control 3.67 3.76 1.8525 6.11 1.09 3.21

50 5.62 1.51 2.53

75 6.94 1.28 2.10

100 7.01 1.16 1.86


Control 4.08 5.55 1.36

25 5.33 2.96 1.78

50 5.94 2.19 1.81

75 6.64 2.03 2.53

100 6.89 1.86 2.68

S.Em+ 0.20 0.11 0.08

CD (0.05) 0.59 0.31 0.25

Table 6. Enzyme activities in soil after the harvest of the sunflower as

influenced by the different levels of fly ash.

Levels of fly ash Dehydrogenase Urease Alkaline phosh atase

(t ha-1) (milli mhols PFF h-1) (N-NH4

g-1) (milli mhols

PNP h-1)


Control 0.38 17.90 0.86

25 0.16 29.90 1.05

50 0.05 15.70 0.94

75 0.05 12.40 0.86

100 0.04 10.30 0.90


Control 0.40 21.30 0.76

25 0.07 14.60 1.11

50 0.04 11.10 0.74

75 0.02 11.50 0.75

100 0.02 10.80 0.76

S.Em+ 0.02 0.12 0.05

CD (0.05) 0.06 0.36 0.14

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