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This study was performed to explore the impact of earthworm densities with addition of biofertilizer for optimizing microbial activity during vermicomposting. Equal numbers of nitrogen fixing bacteria (NFB) and phosphate solubilising bacteria (PSB) were inoculated in the vermicomposting system which was incubated separately with 0, 10, 20, 30, 40 and 50 nos. of epigeic earthworm Eisenia foetida per kg of substrate. The study revealed the nos. of inoculated microorganisms viz. NFB and PSB in the substrates to increase with increase in earthworm population up to a certain range. The values reached almost stagnation when the stocking density of earthworms was increased beyond 30 nos. kg-1. Between the two kinds of inoculated microflora, however, the trend of stagnation became more prominent for NFB than PSB. The CFU of NFB and PSB in earthworm guts also showed a similar trend. This increased CFU of the microflora was reflected in the MBC values of the substrates where incubation with 30-50 earthworms per kg substrate showed highest ranges of MBC values. Similar was the trend for microbial respiration also. CEC, easily oxidizable organic carbon and total organic carbon values were used as indices of composting in the present study. All these values showed that the rate of vermicomposting showed a stagnating trend when the earthworm density was increased beyond 30 nos. kg-1.
Mal et al. (Wed,) studied this question.