Enrichment and Biopelletization of Phosphate Solubilizing Diazotrophic Bacterial Isolates Using Earthworm as a Tool

Aims: The beneficial role of earthworm Eudrilus eugeniae in enhancing the populations of two phosphate solubilizing diazotrophic isolates viz., Bacillus sp. (DT) and Azotobacter chroococcum (DT), isolated from the rhizosphere of finger millet [Eleusine coracana (L) Gaertn] was studied.

Place and Duration of Study: The experiments were conducted at the campus of M/s. Chaitra Biofertilizers and Chemicals (P) Ltd, Mysore, between January – June 2018.

Methodology: To the glass jars containing three week old partially decomposed green leafy material and cow dung, 0.5 gram of lignite based phosphate solubilizing diazotrophic isolates were added. To this eight medium sized earthworms were allowed and moisture is maintained at 50-60%. The population of isolates in the gut of earthworm and vermicasts were estimated on 2nd, 20th, 40th and 60th day by dilution plate method using Pikovskaya’s and Jensen’s agar medium

Results: The population of Bacillus sp. (DT) and A. chroococcum (DT) increased by 22.14, 42.14 and 97.62 percent in the fore gut, mid gut and hind gut regions respectively while A. chroococcum (DT) by 24.05, 41.19 and 110.95 percent as compared to their initial population in the feeding material. Both the isolates increased enormously in the vermicasts up to 40th day and thereafter declined as recorded in 60 days old vermicasts. Bacillus sp. (DT) increased by 196.91 and 247.16 percent in 20 and 40 day old vermicasts and decreased by 54.72 percent on 60th day while A. chroococcum (DT) recorded an increase of 217.34 and 270.77 percent and thereafter declined by 41.18 percent in 60 days old casts.

Conclusion: The earthworm can be used as a tool for secondary level multiplication and biopelletization of the isolates to produce enriched vermicompost for use in finger millet cultivation. It also indicated that the vermicasts should be applied soon after it is harvested.