Microbial enrichment of vermicompost prepared from different plant biomasses and their effect on rice (Oryza sativa L.) growth and soil fertility

Vermicomposts prepared from rice straw, Eichhornia crassipes, Ipomoea carnea, and their mixed biomass, were enriched with microbial inoculants and evaluated for their effect on growth and yield of rice, and nutrient availability andmicrobial population in soil. Irrespective of the vermicompost sources, significant increases in nitrogen (N) content and microbial population in vermicomposts were recorded after eight weeks of incubation with inoculation of Azotobacter chroococcum, Azospirillum brasilense, and Pseudomonas fluorescens, either alone or in consortia, and the highest increase was observed with A. chroococcum followed by A. brasilense. Among different vermicomposts, Ipomoea vermicompost was found superior in N content and microbial population. Vermicompost enriched with A. chroococcum resulted in the highest improvement in plant growth, grain yield, leaf chlorophyll content and nitrate reductase activity of rice, followed by enrichment with A. brasilense. Nutrient content in plant and organic C, available N, P, K, and CEC in post-harvest soil were also significantly improved by the application of enriched vermicomposts, with the best result obtained with Azotobacter-enriched vermicompost. Overall, the results suggest that the locally available plant biomasses, particularly Ipomoea carnea, a weed abundantly available in northeast India, can be easily converted into an environment-friendly nutrient source by vermicomposting, using plant-growth-promoting microorganisms such as A. chroococcum and A. brasilense.