Partial substitution of exogenously applied phosphatic fertilizers by phosphate solubilizing bacteria in maize under calcareous soil

Phosphorus (P) availability is the major constrain in obtaining optimum crop yield in calcareous soils due to its precipitation as dicalcium and octacalcium phosphate by reacting with Ca.sup.+2 and Mg.sup.+2 . Therefore, we explored the role of phosphate solubilizing bacteria (without and with PSB @ 2 kg ha.sup.-1 ) in optimizing maize yield and P availability from soluble and insoluble P sources applied @ of 100 kg P.sub.2 O.sub.5 into calcareous soil. PSB inoculation significantly improved maize plant height (5.6%), 1,000 grain weight (11%), dry matter (7.5%), stover (10.8%) and grain yield (6.8%), plant P concentration (10.1%) and uptake (18.6%), extractable P (3.1%), agronomic (48%) and uptake (53%) P use efficiency over uninoculated plots. Phosphorus application significantly improved maize yield, soil health and agronomic P use efficiency (4.84 times over control); however, its impact was more pronounced when applied as 50% P each from farmyard manure (FYM) and single super phosphate (SSP). On the basis of overall performance, the sources were ranked as 50% FYM + 50% SSP >50% rock phosphate (RP) + 50% SSP > 100% SSP > 75% FYM + 25% SSP > 75% RP +25% SSP > 100% FYM > 100 RP > control. Interactively, a significant and maximum increased over absolute control in most of the soil and plant tested characteristics were observed when 100 kg P.sub.2 O.sub.5 ha.sup.-1 was supplemented 50% each as FYM and SSP along with PSB inoculation which was followed by 50% P each as FYM and SSP demonstrating that PSB were effective in enhancing RP solubilization under calcareous soil. Maximum value cost ratio of 3.1 was observed for 50% P each as FYM and SSP + PSB which was similar to 100% P as FYM + PSB and 75% FYM+ 25% SSP + PSB. Therefore, in calcareous soil P shall be amended 50% each as organic and mineral sources with PSB for its efficient utilization and obtaining optimum yield of maize.