Phosphate solubilizing bacteria inoculated low-grade rock phosphate can supplement P fertilizer to grow wheat in sub-tropical inceptisol

Soil phosphorus (P) despite being an important element for plant growth, its high reactivity and low solubility has challenged the farming community for its efficient utilization. P fertilizers are produced from high grade rock phosphates. Reserve of this non-renewable resource is getting exhausted very rapidly. That establishes the need of using non-conventional P sources to grow crops. In this study, low grade rock phosphates (LGRP) were used as alternate P source to grow wheat in Inceptisol. Different quantities of phosphate solubilizing bacteria (PSB) inoculated LGRP were applied in incubation and pot experiments and were compared with a commercial P fertilizer. It was hypothesized that PSB inoculation would increase P solubility from LGRP and reduce P fixation in soil, thus improve supply parameter and increase P availability to the crop. Short term P dynamics at three different growth stages of wheat, enzyme activities, P-fixation and adsorption chemistry were studied. Incubation experiment established that PSB inoculated LGRP can supply significantly higher amount of P as compared to untreated LGRP. It also proved the potentiality of PSB inoculated LGRP treatment to maintain better supply of P in soil for long term. Pot experiment revealed that combined application of PSB inoculated LGRP + di-ammonium phosphate (DAP) can supplement 50% P fertilizer and maintain similar yield and P uptake as compared to DAP treatment. Applied PSB solubilized P from LGRP and soil, also prevented P fixation in soil by producing organic acids, siderophores, phosphatase enzymes. Thereby, application of PSB inoculated LGRP provided steady supply of available and saloid P for wheat throughout the growth stages and synchronised P supply with its demand. Application of PSB inoculated LGRP reduced the value of P adsorption maxima by similar to 18% and bonding energy related constant of P-fixation by similar to 11%; while value of P supply parameter enhanced by similar to 14% over no PSB application. The PSB inoculated LGRP application enhanced inherent microbial activities by 10-24%, slashed P-fixation capacity by altering P adsorption chemistry and optimised P supply parameter. Thus, application of PSB inoculated LGRP could be recommended to crops to save similar to 50% of the commercial P-fertilizer without affecting crop yields.

Automated summary

In this study, the combined application of low-grade rock phosphates (LGRP) and phosphate solubilizing bacteria (PSB) was found to significantly increase the availability of phosphorus in the soil. This approach can save commercial phosphorus fertilizers without compromising crop yields.