Bioresource Technology 76(2): 173-175 (Jan 2001)
Enriching vermicompost by nitrogen fixing and phosphate solubilizing bacteria
Vivek Kumar and K. P. Singh


The effect of inoculation of vermicompost with nitrogen-fixing Azotobacter chroococcum strains, Azospirillum lipoferum and the phosphate solubilizing Pseudomonas striata on N and P contents of the vermicompost was assessed. Inoculation of N2 fixing bacteria into vermicompost increased contents of N and P. Enriching vermicompost with rock phosphate improved significantly the available P when inoculated with P. striata. During the incubation period, the inoculated bacterial strains proliferated rapidly, fixed N and solubilized added and native phosphate.

3. Results and discussion

The results presented in Table 1 show that there was a significant increase in the inoculated bacterial populations in vermicompost by the second week. Maximum numbers were found between 45–60 days. After the 60th day there was a decline in count of microbes.

Data of Table 2 show an increase in N and available P contents during the incubation period. Initially at day 0 vermicompost contained only 1.40 (g/100g) of N which was increased to 2.72 (g/100 g) at the 60th day after inoculation with A. chrooccocum (Mac27). Similarly, with inoculation of other strains of Azotobacter, N content increased up to 2.53 and 2.50 (g/100 g). Azospirillum lipoferum also increased N content up to 2.18 (g/100g) but this bacterium was less effcient than Azotobacter strains.

The inoculated phosphate-solubilizing bacterium P. striata, caused a significant effect on the available P content in vermicompost when inoculated alone or with 1% MRP, but available P content was greater with MRP and P. striata combination (1.97) at 60th day. Without addition of MRP the available P content was 1.51 (g/100 g). At 75th day N and P contents were more or less similar to those of the 60th day.

Addition of rock phosphate inoculated with P. striata led to more availability of P, most likely due to the production of organic acids by the bacteria which solubilized the rock phosphate (Premono et al., 1996). The P content in other treatments was higher at 45th and 60th day than at day 0, which was due to release of P present in the agricultural wastes.

It is evident from this experiment that Azotobacter, Azospirillum and Pseudomonas inoculation helped to increase the N and P contents of vermicompost, and rock phosphate was solubilized during composting.

Bacteria and Soil Fertility