Introduction

Fly ash is the portion of the combustion residue that enters the flue gas stream in power generating facilities and consists of many small, glass-like particles ranging in size from0.01 to 100 µm(1). Fly ash which contains silica, aluminum, oxides of iron, calcium, magnesium, arsenic, chromium, lead, zinc, nickel and other toxic metals is a by product of coal-fired power plants.

Most fly ash materials are disposed in landfills or slurry ponds. Land filling of fly ash may serve as a major source of environmental pollution through erosion and leaching of heavy metals (2). To prevent fly ash from being air borne, the dumping ground needs to be kept well at time. However in India where 150 million tones fly ash is produced annually, there is an urgent need to develop methods for use of fly ash, on a small scale as well as on large scale. Each new application has to be evaluated from the environmental point of view(3).Another use of fly ash is in agriculture since the hydroxide and carbonate salts give fly ash one of its principle beneficial chemical characteristics, the ability to neutralize acidity in soils(4). Fly ash amendment has been reported to modify soil pH, improve soil texture, and provide essential plant nutrients for increasing crop production(5).

Cashew nut (Anacardium occidentale L.) is a multifaceted industrial and commercial crop cultivated in tropical and sub-tropical region. World production of cashew nut is around 9 lakhs tonnes per year and the highest production (42%) has been recorded in India. Leaf litter is a potential and unexploited source of nutrients inputs in agriculture. The natural decomposition of cashew leaves requires long period. Hence the accumulation of cashew leaves causes environmental pollution, forest fire, nutrient loss etc. The dry leaves of cashew trees served as a good manure if properly decomposed(6).

Lampito mauritii was chosen as an indicator species in India because of its wide spread occurrence in aerable and pasture lands and its consequent vulnerability to surface applied pesticides, making it an ideal candidate for assessment of agro ecosystem contamination(7).

The reproductive potential of earthworm was influenced by the quality and availability of food (8,9). Vermicomposting is an eco friendly and inexpensive

technology in which the earthworms are used as bioreactors to convert the organic materials into valuable compost. Bhattacharya and Chattopadhyay (10) found the survival of earthworms in three different ratios (1:1, 1:3 and 3:1) of cow dung and fly ash. Ananthakrisnasamy(11)also reported the survival of earthworms in three different ratios (1:1, 2:1 and 3:1) of cow dung and fly ash mixture. The fly ash was vermicomposted with cow dung and solubility of micronutrients was analysed (12).To the authors knowledge no studies have been made on the toxic role of fly ash on the growth and reproduction of indigenous anaecic earthworm. The main objective of the present study was (i) To find out the appropriate proportion of fly ash –leaf litter-cow dung for sustainable and efficient vermicomposting. (ii) To know the toxic role of fly ash on the growth and reproduction of earthworms in different fly ash mixtures.

Materials and methods

The FA was collected from a thermal power station I, Neyveli Lignite Cooperation, Neyveli. The fallen leaves (CLl) of cashew trees were collected from cashew fields around Neyveli, Tamil Nadu, India. The CD was collected from the dairy farm, Faculty of agriculture, Annamalai University.

The FA was thoroughly mixed with CLl and CD (w/w). All these mixtures were maintained at 60% moisture content. Six replicates were maintained in all the treatments. Treatment substrates were prepared in the following proportions on weight basis such as; T₁-FA+CLl+CD (2:4:4), T₂-FA+CLl+CD (3:3.5:3.5), T₃-FA+CLl+CD (4:3:3), T₄-FA+CLl+CD (5:2.5:2.5) and T₅-FA+CLl+CD(6:2:2) CD alone was used as control(C). In each treatment one kg of mixture was added with 200 gram of clay loam soil (CLS) to prepare the substrate and it was precomposted for 30 days.

After 30 days 15.0 gram of adult clitellate L.mauritii were collected from the stock culture and introduced in control and treatment substrates. Once in 15 days upto 90 days weight of the worms (gram), number of cocoons and number of hatchlings were observed and recorded. The statistical significance of the data was tested by two way ANOVA.

Results

The growth and reproduction of L.mauritii were observed in different level of fly ash mixture. Table 1-3 show the values obtained for different parameters of growth and reproduction of L.mauritii.

Biomass (gram) of earthworms in general increased in control and in all fly ash mixtures significantly(p<0.05), but the rate of biomass production decreased after 60^th day (i.e 75^th and 90^th day). The overall rate of biomass production was maximum in T₂ (27.6±1.51 gram) and the least growth was observed in T₅ (16.5±1.37 gram) on 60^th day.

The variation in the cocoon production is depicted in Table.2.The inoculated adult clitellate worms started to produce cocoon and they were observed on 15^th day in C, T₁, T₂ and T₃ but in T₄ observed on 30^th day and in T₅ on 45^th day. Among all the treatments the total number of cocoon was higher in T₂ (108.9±1.76) than the other treatments; it was followed by T₁, C, T₃, T₄ and T₅ respectively. From the table significant (p<0.05) differences were found in the cocoon production

Figure 1

Table 1. Role of flyash (with cashew leaf litter and cowdung) on the biomass (gram) of

Figure 2

Table 2. Role of flyash (with cashew leaf litter + cowdung) on the coccon production (number) of

Figure 3

Table 3. Role of flyash (with cashew leaf litter + cowdung) on the hatchling production (number) of

The numbers of hatchlings by the L.mauritii in various combinations are presented in Table.3.The hatchlings were observed in all treatments except T₅ from 30^th day onwards. In T₅ the hatchlings were observed only on 60^th day. More number of hatchling were observed in T₂ (Total number143.9±1.52) and the least number of hatchlings were observed in T₅ (Total number 20.6±1.55). The Hatchlings in other treatments are in the following order T₁(133.6±0.94)> C(109.9±1.67)> T₃(89.3±1.32)>

T₄ (41.8±1.48)> T₅ (13.1±1.55).

Discussion

The enhanced growth and reproduction of L. mauritii were observed in control and in treatments, but the rate of biomass production decreased after 60^th day because the availability of feed is decreased in the total experimental period of 90 days. As described by Neuhauser et al (13)When E. foetida received food below a maintenance level, it lost weight which depended upon the quantity and nature of its ingestible substrates.

The rate of biomass and reproduction of L. mauritii were maximum in T₂ mixture.

The growth and reproduction of earthworms are highly influenced by the quality and availability of feed, various physiochemical parameters etc (14,15). Growth and reproduction in earthworms require OC, N and P (16) which is obtained from litter, grit and microbes (17, 18). The first step in the vermiculture is selection of suitable feed materials for earthworms. These can be nitrogen rich materials like cow dung, pig manure, poultry manure, etc or other organic material should be like leguminous agro waste(19).

Manivannan et al (20) reported higher growth of earthworm Eudrilus eugeniae, Perionyx excavatus, Eisenia fetida and Lampito mauritii in press mud, trash, bagasse(PTB) mixture. They added the enhanced growth and reproduction must be due to rich cellulose content, rich microbial population and higher nutritive value. Studies of Ananthakrishnasamy et al.(21) revealed that cow dung- bagasse mixture 2:8 ratio was the better feed mixture to increase the biomass of L. mauritii. They reported that particular mixture probably provided earthworm with sufficient amount of easily metabolizable organic matter and non-assimilated carbohydrates that favors growth and reproduction. The Perionyx sansibaricus grew faster and had higher fecundity when feeding on nitrogen rich diets such as vegetable waste and leaf litter (22) and E. fetida in leguminous leaf litter (9).

According to Sarojini et a l(23) E. fetida was able to grow more in bedding material alone, which contains more nutrients than the other mixtures of bedding material and fly ash in various proportions. At the same time the mixture which contains less quantity of FA seems to be the better combination than the others which contains more quantity of FA. This could be probably due to contribution of more nutrients to the medium by the addition of more quantity of bedding materials.

In our observation, the maximum worm biomass and reproduction was observed in T₂-FA+CLl+CD (3:3.5:3.5). It may be due to higher N content/ higher microbial content/ higher palatability for the growth of earthworms. Similarly, Gupta et al (3) reported higher zoo mass in 20% FA+CD and higher number of juveniles and more vermicast recovery in 40% FA+CD mixture and it was due to less toxicity exerted by less quantity of fly ash in these combinations than 60% and 80% FA+CD mixtures. They added that the use of E. fetida to mitigate toxicity of metals seems to be feasible technology and upto 60% FA+CD mixture can be sustainable and efficient vermicomposting without showing any toxicity to earthworms.

Acknowledgement