Journal of Environmental Quality 31:2116-2119 (2002)
© 2002 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
SHORT COMMUNICATIONS
Increasing Bioavailability of Phosphorus from Fly Ash through Vermicomposting
S. S. Bhattacharya and
G. N. Chattopadhyay*
Institute of Agriculture, Visva-Bharati, Sriniketan 731236, West Bengal, India
* Corresponding author (gunindranath_c{at}hotmail.com)
Received for publication June 12, 2001.
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ABSTRACT
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Due to the environmental problems created by large-scale fly ash generation throughout the world, efforts are being made to recycle these materials. An important component of the recycling effort is using fly ash to improve low-fertility soils. Because availability of many nutrients is very low in fly ash, available ranges of such nutrients must be improved to increase the effectiveness of fly ash as a soil amendment. In the present study, we assessed the possibility of increasing P bioavailability in fly ash through vermicomposting in a yard experiment. Fly ash was mixed with organic matter in the form of cow (Bos taurus) dung at 1:3, 1:1, and 3:1 ratios and incubated with and without epigeic earthworm (Eisenia fetida) for 50 d. The concentration of phosphate-solubilizing bacteria (PSB) was found to increase many fold in the earthworm-treated series of fly ash and organic matter combinations compared with the series without earthworm. This helped to transform considerable amounts of insoluble P from fly ash into more soluble forms and thus resulted in increased bioavailability of the nutrients in the vermicomposted series. Among different combinations of fly ash and organic matter, P availability in fly ash due to vermicomposting was significantly higher in the 1:1 fly ash to cow dung treatment compared with the other treatments.
Abbreviations: CD, cow dung • FA, fly ash • PSB, phosphate-solubilizing bacteria
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INTRODUCTION
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FLY ASH IS A residue resulting from pulverized coal combustion (Nass et al., 1993). Huge amounts of fly ash originate from different coal-fired power stations throughout the world, presenting several problems, the most important ones being environmental pollution and occupation of large storage areas. Hence, the urgent needs to overcome these problems arise not only through safe disposal but also through gainful use of these materials (Chattopadhyay and Bhattacharya, 2000). In recent years, there has been growing interest in using fly ash for crop production, especially for regenerating wastelands (Adriano et al., 1980; McCarty et al., 1994; Schutter and Fuhrman, 1999). These soils are predominantly poor in fertility and need high amounts of nutrients for their restoration. However, the major constraint of providing such nutrition through fly ash lies in the low availability of many plant nutrients, despite a relatively high total concentration in fly ash. This problem is very apparent with phosphorus nutrition from fly ash. While total occurrence of P in fly ash may be as high as the concentrations observed in many organic manures (Table 1), the P availability in fly ash generally remains very low (Kumar et al., 1998). While discussing P insolubility in fly ash (FA), Adriano et al. (1980) stated that most studies indicate that FA application caused no substantial changes and in some cases even lowered plant tissue P concentrations. Therefore, to increase fly ash acceptability as a source of plant nutrients, it is necessary to increase its phosphorus bioavailability. Microbial management may be an effective means for increasing such P bioavailability. However, the major problem with microbial management of fly ash is the sensitivity of different microorganisms to fly ash, as stated by Pichtel and Hayes (1990). Under this context, vermicomposting may be a good proposition. Vermicomposting involves using epigeic earthworms to increase the microbial population in vermicasts and helps to produce high-quality compost from different organic wastes in a lesser period of time (Edwards and Lofty, 1972). In the present study, an effort has been made to encourage P bioavailability in fly ash by using organic materials as the source of energy through an adoption of vermicomposting technology for promoting microbiological activities.
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Materials and Methods
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The study was performed in yards with burnt earthen pots (4.5-L volume), which were inert in nature. Five combinations of fly ash (FA) and cow dung (CD) versus FA alone (FA), CD alone (CD), FA + CD (1:1), FA + CD (1:3), and FA + CD (3:1) were used for the study on a weight basis for each of the materials, at a total weight of 1 kg material in each pot. Each of the treatments was replicated thrice in a completely randomized design (CRD) and incubated with and without epigeic (surface-living) earthworm at 10 worms kg-1 material. Earthworms did not survive properly in the treatment with FA alone and periodic additions were made during the sampling dates as necessary. The materials under each treatment were incubated under moist conditions for 50 d at a room temperature range of 29.5 to 33.7°C, observed at 1000 h on a daily basis. Samples were drawn periodically at 10-d intervals from each of the incubated materials and were analyzed for easily available P (Olsen's extraction method with 0.5 M NaHCO3 as extractant); saloid-bound P, which remains loosely bound with soil particles (extracted with 0.5 M NH4Cl); and Al-, Fe-, and Ca-bound P (following Chang and Jackson, 1957). In each case, P was estimated colorimetrically with the molybdenum blue method as described by Jackson (1973). Because about 40 to 50% moisture levels were maintained in the samples for vermicomposting, moisture content of the samples was determined gravimetrically with the differences between moist and dried samples and necessary corrections were made to get the results on a dry-weight basis. Contributions of FA to availability of P under different treatments were determined by calculating the contribution of CD to availability of P from the CD treatment and subtracting the respective amount from the different FA + CD contributions. All the results were computed for analysis of variance. Phosphorous-solubilizing bacteria (PSB) were analyzed at the microbiological laboratory of the Central Sericulture Training and Research Institute (Berhampore, India). The samples were cultured in phosphate-containing Pikovskayas medium with the dilution plate technique. Colonies having transparent zones around microbial colonies were counted to estimate PSB.
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Results and Discussion
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Changes in available and saloid-bound forms of P in different combinations of fly ash with and without epigeic earthworms are presented in Table 2.
Phosphorus availability was lowest in FA, as discussed earlier (Kumar et al., 1998), and was highest in the CD treatment. Incorporating organic matter with FA in different combinations resulted in increased P availability. Beneficial effects of organic matter on P transformation through various pathways have been discussed by Mandal (1964). It was interesting to observe that adopting vermicomposting technology through the use of epigeic earthworms helped to increase the available P status further (Fig. 1)
. The behavior was similar with the saloid-bound form of P, which remains loosely bound with different soil constituents and may contribute to P nutrition to a certain extent (Table 2). Improvement in the amount of easily extractable P during the course of vermicomposting has been reported by Ghosh et al. (1999). While beneficial effects of organic matter in solubilizing P are well documented (Mandal, 1964), the accelerating effects of vermicomposting may be due to rich microbial populations in the earthworm intestines (Edwards and Lofty, 1972), which might have played an important role in solubilizing P from unavailable forms. To establish this hypothesis, an attempt was made to study the occurrences of PSB in the two series of treatments after 50 d of incubation (Table 3). As shown in the table, inclusion of earthworms in the waste materials resulted in many-fold increases in the concentrations of PSB over the respective series without earthworms. These microorganisms tended to increase the P solubility in the waste materials. However, such increment was marginal in the FA-only series. The bacterial population probably could not get sufficient energy from FA, which was practically devoid of organic matter. Pichtel and Hayes (1990) have also reported restricted microorganism growth in FA. However, in the present study, when FA was treated with organic material in the form of cow dung at different concentrations, the PSB populations were active and they tended to solubilize P from fly ash to a considerable extent.
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Fig. 1. Phosphorus availability in different combinations of fly ash (FA) and cow dung (CD) treated with (E) and without (E0) earthworms after 40 and 50 d of incubation (values indicate mean ± standard error, n = 3).
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Occurrences of three inorganically bound P forms in different combinations of FA and CD have been presented in Table 4. The total P amount fixed in three major inorganic forms tended to decline in the vermicomposted series. This was attributed largely to increased effect of PSB on solubilizing different inorganic P forms in this series. Increased P availability under vermicomposted series could be attributed to a lowering in the concentration of different inorganic forms.
The contribution of FA to increased availability of P under different treatments was calculated by taking into account the available phosphorus status under the treatments after 50 d of incubation. The contribution was lowest under the treatment with FA alone and increased with use of organic materials in different combinations. As observed from analysis of variance, all the vermicomposted treatments with FA + CD resulted in significantly higher amounts of P extractable from FA into an available form (Table 5). Among these treatments, 1:1 FA + CD appeared to be the most efficient (Table 6). This was probably due to the occurrence of the highest concentrations of PSB in this treatment due to sufficient availability of organic materials. Presence of a good amount of FA in this treatment might have also allowed the PSB to extract higher amounts of P from FA into a solubilized form. For the saloid-bound P form, however, the contributions were not significant.
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Table 5. Analysis of variance (completely randomized design, CRD) for fly ash (FA) contribution to P solubility after 50 d of vermicomposting.
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Although the other two treatments with FA + CD registered considerable contribution of FA to P availability, the values were much less compared with the 1:1 FA + CD treatment. It was also observed that under both the 3:1 and 1:3 situations, PSB occurred in much lesser concentrations. In the 3:1 FA + CD treatment, the lower extraction of P from FA may be from the higher amount of FA in this treatment, so that the microorganisms could not get their energy in sufficient amounts. On the other hand, in the 1:3 treatment, the bacterial population probably received most of its sustenance from higher amounts of organic materials supplied in the treatment and hence did not extract much P from FA.
This study demonstrates the efficiency of vermicomposting in increasing P availability in FA for better use in agriculture. Adopting the technology described here will not only provide greater availability of valuable P from FA, but will also promise more effective use of this waste material for agricultural benefits by taking the advantage of increased microbial activities provided by earthworms. Out of different ratios of FA and CD, the 1:1 ratio appeared to be the most effective for solubilizing P from FA.
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ACKNOWLEDGMENTS
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The authors thank the Pollution Control Board, Government of West Bengal, India, for sponsoring the study. They are also indebted to Sri P. Sudhakar, Senior Research Officer, Central Sericulture Training and Research Institute, Berhampore, India, for his help in microbial analyses of the samples.
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REFERENCES
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- Adriano, D.C., A.L. Page, A.A. Elseewi, A.C. Chang, and I. Straughan. 1980. Utilization and disposal of fly ash and other coal residues in terrestrial ecosystems—A review. J. Environ. Qual. 9:333–334.[Abstract/Free Full Text]
- Chang, S.C., and M.L. Jackson. 1957. Fractionation of soil phosphorus. Soil Sci. 12:286–293.
- Chattopadhyay, G.N., and S.S. Bhattacharya. 2000. Possibility of increasing available nutrient status of fly ash through vermicomposting. Sec. IX. p. 14–16. In Proc. 2nd Int. Conf. on Fly Ash Disposal and Utilisation, New Delhi. Vol. 2. Central Board of Irrigation and Power, Government of India, New Delhi.
- Edwards, C.A., and J.R. Lofty. 1972. Biology of earthworms. Chapman and Hall, London.
- Ghosh, M., G.N. Chattopadhyay, and K. Baral. 1999. Transformation of phosphorus during vermicomposting. Bioresour. Technol. 69:149–154.
- Jackson, M.L. 1973. Soil chemical analysis. Prentice Hall, New Delhi.
- Kumar, A., A.K. Sarkar, R.P. Singh, and V.N. Sharma. 1998. Characterization of fly ash from steel plants of eastern India. J. Indian Soc. Soil Sci. 46:459–461.
- Mandal, L.N. 1964. Effect of time, starch and lime on the transformation of inorganic phosphorus in a water-logged rice soil. Soil Sci. 97:127–132.
- McCarty, G.W.R., R.J. Siddarmappa, E.E. Wright, and G. Gao. 1994. Evaluation of coal combustion byproducts as soil liming materials: Their influence on soil pH and enzyme activities. Biol. Fertil. Soils 17:147–172.
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ABSTRACT
INTRODUCTION
