Potential of Microbial Solubilization of Rock Phosphate for Use in Sustainable Agriculture: Does Biochar Application Enhance Microbial Solubilization?

The present study was carried out to investigate the strategies for microbial solubilization of Eppawala rock phosphate in Sri Lanka as an alternative to chemical acidulation by using biochar and microbial inoculants. A pot experiment was carried out in the plant house at Faculty of Applied Sciences, Rajarata University of Sri Lanka, Mihintale, Sri Lanka. The treatments were different combinations of field soil, biochar, mycorrhizae and Pseudomonas fluorescens with rock phosphate (RP). The experimental treatments were arranged in a completely randomized block design (CRBD) with eight replicates and the treatment means were compared by the Tukey’s test (p<0.05). The soil available phosphorus (P) and leaf P were estimated after 120 days of growing maize in pots. Total bacterial and fungal counts of the soil and mycorrhizal colonization were also estimated. Results showed that the highest available soil phosphorus was observed in biochar, mycorrhizae and P. fluorescens addition with 3% RP and highest leaf phosphorus was observed in biochar and mycorrhizae with 3% RP. The addition of biochar to the soil containing RP caused a significant increase (p<0.05) of solubilized P in soil. These results suggested that biochar can be used to enhance microbial RP solubilization and mycorrhizae inoculants to increase P uptake. Significantly high bacterial count and fungal count were observed in biochar, P. fluorescens and RP added and mycorrhizae, P. fluorescens and RP treatments respectively. Greater efficiency of P solubilizing bacteria has shown with the addition of biochar and through co-inoculation with mycorrhizae. Findings of this research increase the prospects of using biochar and P solubilizing microorganisms (PSM) including P. fluorescens and mycorrhizae for RP solubilization.