Abstract

The present study is incorporated with agrowaste management and biofertilizer production in tropical India. For this, an exotic earthworm species Eisenia fetida and a local species Perionyx sansibaricus were used to decompose cumin straw and cow dung and evaluated vermicomposting efficacy. Physicochemical parameters of the vermibed such as pH, electrical conductivity, water holding capacity, organic carbon, C/N ratio, total nitrogen, phosphorus and potassium were evaluated in the vermicompost. The values of all the above physicochemical parameters of E. fetida worked bedding material varied significantly (P<0.001) with respect to initial day values. Likewise, these parameters in the bedding substrate fed by Perionyx sansibaricus also varied significantly (P<0.001) as compared to 0 day values. The organic waste conversion efficiency of E. fetida was better than P. sansibaricus for cumin plus cow dung bedding. Though E. fetida is better agrowaste converter but both the earthworm species may be used for organic waste management in desert region. It may provide the support in the form of biofertilizer to enhance the organic farming in region of the Thar Desert.

1. Introduction

Use of chemical fertilizer is adversely affecting the Human health, agroecosystem, sustainability of soil and below-ground biological diversity. This problem could be overcome by adopting organic farming, which demands development of a suitable technology for proper recycling of organic wastes. There is tremendous increase in agrowastes with the increase in agricultural production. These agrowastes pollute the surrounding environment leading to diseases in animals and human. The wastes also act as a reservoir of fungal diseases of next crop. So there is a warranted need to convert the agricultural wastes into assets i.e. vermicompost. Use of vermicompost rejuvenates the exhausted soil fertility, enriches the available nutrients to sustain soil quality and enhances water holding capacity and biological resources ^{1, 2, 3}. Application of earthworm resources in conversion of agricultural, urban and industrial wastes into vermicompost is much liked method of recycling organic substrates worldwide ^{4, 5, 6}.

Available nutrients in vermicompost are much higher than traditional garden compost ⁷. Vermicompost is also helpful in reducing the population of soil pathogenic microorganisms ⁸ and inducing nitrogen fixation ^{9, 10}. Several workers have documented the use of organic waste in vermicomposting such as sewage sludge ^{11, 12}, pig manure ^{13, 14}, combined sewage sludge and municipal refuse ¹⁵, cotton industry waste ¹⁶, industrial and vegetable waste ¹⁷, animal and vegetable waste ^{18, 19, 20, 21, 22}, leaf litter ²³, wheat straw plus paddy straw plus cow dung ²⁴ and mustard straw plus cow dung ³. Use of various earthworm species in vermicomposting is popularized still much study is need to evaluate composting potentials of E. fetida and P. sansibaricus for different agricultural wastes. Cumin is a very important cash crop and enormous waste is generated after each harvesting in western Rajasthan, India. But no information is available on composting of cumin waste by earthworm. At this juncture, a suitable technology should be developed to convert cumin waste into biofertilizer.

Under the above background, experiments were conducted to decompose cumin straw with cow dung by employing Eisenia fetida and Perionyx sansibaricus earthworm species.

2. Material and Methods

Cumin is a spice crop grown on a large scale particularly in western parts of Rajasthan in India. Its straw was collected from agricultural farm of village-Chheela, tehsil-Lohawat of Jodhpur district (27º 01’41” N 72º28’50” E). Generally, cumin straw is dumped in huge quantity after each harvesting in Rabi season. Partially decomposed straw was collected from one season old (dumped open sky) harvested pool. Air dried cow dung was taken from a cow owner of Adeshwar Nagar of Jodhpur city. The materials were filled in bags and brought to the vermiculture laboratory. The earthworm species Eisenia fetida was collected from a farmer’s vermiculture centre of village Chheela with a small amount of culture material i.e. cow manure, in perforated bags. Whereas, Perionyx sansibaricus was used from previously prepared stock culture originally collected from Jodhpur city. These two species of earthworm were cultured separately in cow dung vermibed as stock culture also for future use.

The collected cumin straw and cow dung were left for one week at room temperature. Dried cow dung was powdered on hard surface, whereas mustard straw was grinded in mixer-grinder after thorough chopping. The powdery materials were sieved by 1mm (palatable size for earthworm) pore sized net separately and stocked in plastic bags for use in vermicommposting.

Three sets in triplicate of vermibeds (500g each) were prepared using powdered cumin straw and cow dung in equal ratio in plastic containers (30 cm x 25 cm) and moistened to stabilize within 48 hours. In the experimental set, 25 mature worms of each species (E. fetida and P. sansibaricus) were inoculated separately. One set of control bedding material (without earthworm) was run simultaneously. The plastic containers for culture were perforated at 2-3 places to assist leaching of excess water. However, leached water was collected in other containers and reused for watering the vermibeds so as to prevent the washout of nutrients. The vermiculture experiment was conducted for 60 days. During composting period, 60-70% moisture was maintained by spraying water on the bedding regularly. The temperature of vermibed was 30±3°C and wet jute cloth was used to maintain the temperature of vermibeds.

During decomposition, changes in pH, electrical conductivity, water holding capacity, organic carbon, total nitrogen, carbon/nitrogen ratio, available phosphorus and potassium were estimated after an interval of 15 days of worm working viz., 0, 15, 30, 45 and 60 day. For this purpose, 10g dry weight basis samples were collected from each experimental as well as control vermibed in plastic pouches. The pH and electrical conductivity of bedding materials were measured with the help of a digital pH meter. An examination of Degtjareff method was used for determination of organic carbon ²⁵. Total nitrogen was measured by Kjeldahl method ²⁶ employing Kel plus system (Kes-20 and Distyl-EM). Available phosphorus was estimated as described by Anderson and Ingram ²⁷ and exchangeable potassium was determined by the method of Simard ²⁸. The temperature of vermibeds was recorded with the help of thermometer (MEXTECH multi-thermometer). Moisture of bedding substrates was estimated by oven drying method.

The collected data was subjected to statistical analysis. A one way analysis of variance (ANOVA) was performed to test the level of significance. The level of significance was set at 0.05.

3. Results and Discussion

Cumin straw plus cow dung bedding material showed significant changes (P<0.001) in physicochemical properties of earthworm worked vermibed with respect to decomposition duration. Whereas control bedding material indicated insignificant changes (P>0.05). However, water holding capacity increased significantly (P<0.05) by 1.44 fold. Likewise, organic carbon and C/N ratio declined significantly (P<0.05) by 32.17% and 43.20% respectively as compared to initial level.

Introduction of E. fetida in the bedding material showed significant (P<0.001) increase in electrical conductivity, water holding capacity, total nitrogen, phosphorus and potassium by 1.59, 2.25, 2.26, 1.83 and 2.07 fold respectively. While pH, organic carbon and C/N ratio decreased significantly (P<0.001) by 12.19%, 64.34% and 81.13% respectively from 0 to 60 days.

Like E. fetida, physicochemical properties of the bedding material differed significantly (P<0.001) after 60 days feeding of P. sansibaricus. The bedding material exhibited increase in electrical conductivity, water holding capacity, total nitrogen, phosphorus and potassium by 1.39, 2.21, 1.91, 1.59 and 1.84 fold respectively. However, values of pH, organic carbon and C/N ratio decreased by 11.25%, 57.27% and 80.13% respectively within 60 days of the earthworm activities (Figure 1).

Decomposition of cumin straw plus cow dung in absence and presence of earthworm showed significant changes. The pH of control group bedding declined by 4.01%. However, pH in E. fetida induced compost decreased by 12.19% and in P. sansibaricus inoculated bedding by 11.25% during 60 days of composting period. Maximum pH value declined in E. fetida compost followed by P. sansibaricus and control group. The reduction in pH value may be due to formation of acids and release of CO₂ during decomposition and earthworm respiration respectively. In the control group decline in pH was because of microbial activity. Decreased trend of pH in the vermicompost and compost substrates is in agreement to the reports of previous workers ^{3, 5, 19, 29, 30} who showed lower pH. The present findings are contradictory to the work of some researchers who described a gradual increase in pH from substrate to compost to vermicompost ^{31, 32}. Electrical conductivity increased by 1.08 fold in control group, while it increased by 1.59 and 1.39 fold in E. fetida and P. sansibaricus compost respectively. The EC value of vermicompost differed significantly in comparison to control. However, E. fetida showed greater increase in electrical conductivity of compost bedding. Increasing trend of electrical conductivity during composting and vermicomposting was probably due to release of minerals such as potassium, phosphorus and calcium in the available form. Our results are supported by the observations of earlier workers ^{3, 33, 34, 35, 36}. It has been also documented that increase in EC may be probably due to the degradation of organic matter releasing minerals such as exchangeable Ca, Mg, K and P in the available form, that is, in the form of cations in the vermicompost and compost ³⁷. Likewise, the present investigations are also vindicated ²³. He studied the earthworm numbers and biomass and their impact on Physicochemical characteristics of vermicompost. He observed that the leaf litter waste decomposition by E. eugeniae and D. modesta on day 40 produced vermicompost that had an increased level of nutrients like total nitrogen, available Perionyx sansibaricus and available potassium and decreased level of pH, organic carbon and C/N ratio. However, the present findings are not in conformity to the report ³⁸ who demonstrated reduction in EC during vermicomposting.

Water holding capacity improved by 1.44 fold in control group. Whereas, in the E. fetida and P. sansibaricus bedding materials, it increased by 2.25 and 2.21 fold respectively. The water holding capacity was enhanced due to fragmentation of substrate by earthworm digestive system and mineralization during composting. The present finding was supported by the work ⁸ who found that vermicompost is a peat like material with excellent structure, aeration, drainage and water holding capacity. Similarly, the documentation of other workers show increased water holding capacity after vermicomposting ³⁹. In contrast, organic carbon of the compost and vermicompost decreased from their initial level of substrate in control as well as experimental group. Figure 1 showed that organic carbon of earthworm containing bedding material was consumed significantly (P<0.001) faster than control group. In this respect, E. fetida was better as compared to P. sansibaricus.

Total nitrogen, available phosphorus and potassium increased by 1.19, 1.10 and 1.05 fold respectively as compared to their 0 day values in control substrate. Whereas, vermicompost prepared by E. fetida and P. sansibaricus showed increase in its values by 2.26, 1.83 and 2.07 fold and 1.91, 1.59 and 1.84 fold respectively as compared to starting values. Our findings revealed that organic waste processed by earthworms had considerably higher level of major nutrients. Higher level of nitrogen, phosphorus, potassium, calcium and magnesium in vermicompost has also been reported ^{24, 34, 40}. The increase in nitrogen, phosphorus and potassium and decrease in the organic carbon and C/N ratio in the earthworm compost are in concurrence with the documentation of previous investigator ⁴¹.

4. Conclusions

Cumin straw plus cow dung bedding materials were used to prepare vermicompost by two earthworm species viz., Eisenia fetida and Perionyx sansibaricus. Physicochemical properties of vermibeds were analyzed periodically. Water holding capacity, electrical conductivity, total nitrogen, phosphorus and potassium increased as a function of vermicomposting period. However, pH, organic carbon and C/N ratio decreased gradually during the experiments. Cumin straw can be a very useful organic material for vermicomposting. Both the E. fetida and P. sansibaricus species of earthworms were found suitable for preparation of vermicompost of cumin straw in rural area. This strategy may be adopted for popularization of this ecofriendly vermitechnology for benefit of human beings and environment.

Acknowledgements

KRP wishes to thank the University Grants Commission (UGC), Government of India, New Delhi, for providing financial support in the form of Teacher Research Fellow (TRF), and to the Commissionerate of College Education, Government of Rajasthan, for providing leave to carry out the research work.

References