Application of phosphate solubilizing fungi and lime altered the soil inorganic phosphorus fractions in an Ultisol of north-eastern India

ABSTRACT The gradually dwindling reserves of rock phosphate, the primary material used in the manufacturing of phosphatic fertilizers, encourages researchers to look for ways to exploit the accumulated fixed P pool in soil. Phosphate solubilizing microorganisms (PSM) could be a viable option for addressing the problem at a lower cost. Keeping these in mind, the present study was undertaken to evaluate the changes in the distribution of P in soil as affected by P fertilization, phosphate solubilizing fungi (PSF) and liming vis-à-vis the contribution of these fractions toward P nutrition of a test crop soybean (Glycine max L.). A bulk surface soil sample (0–15 cm) was obtained from Negheriting tea estate of Golaghat district of Assam, India (Ultisol, pH = 4.23) and after processing, three levels of P [0, 50, and 100% of recommended dose of P (RDP)], two levels of lime [No lime, 1/10th of Lime Requirement (LR)] and two levels of PSF (No-PSF, PSF) were applied in a completely randomized design with three replications. Sequential P fractionation was done in the post-harvest soil. On an average, the abundance of different P fractions in the soil, expressed as % of total P, followed the order: residual P (67.5%)> Fe bound P (12.1%)> reductant soluble P (8.85%)> Al bound P (4.04%)> occluded P (3.79%)> Ca bound P (3.11%)> soluble and loosely bound P (0.46%). All the inorganic P fractions except the residual P, increased significantly with P fertilization. Either liming or PSF application significantly increased the soluble and loosely bound P fraction and decreased the Al bound and Fe bound P fractions in soil. Positive growth response of soybean was obtained due to the application of P, lime, and PSF. Liming increased the P uptake by 30.4% and dry matter yield of soybean by 18.5% over no liming. On the other hand, PSF inoculation increased the P uptake by 16.7% and dry matter yield by 7.77% over no inoculation. So, it is evident that in short term, either liming or PSF was able to solubilize the native soil P. Phosphorus×lime and lime×PSF interactions should also be exploited in future endeavors.