Phosphorus release capacity of soluble P fertilizers and insoluble rock phosphate in response to phosphate solubilizing bacteria and poultry manure and their effect on plant growth promotion and P utilization efficiency of chilli (<i>Capsicum annuum</i> L.)

Abstract

Abstract. The ability of soil microorganisms and organic manures to convert insoluble phosphorus (P) to an accessible form offers a biological rescue system for improving P solubilization and utilization in soil-plant systems. Our objective was to examine the P supplying capacity of soluble P fertilizers (SPF) i.e. single super phosphate (SSP) and di-ammonium phosphate (DAP) and insoluble rock phosphate (RP) after adding phosphate solubilizing bacteria (PSB) and poultry manure (PM) and their subsequent effect on the growth, yield and P-utilization efficiency (PUE) of chill (Capsicum annuum L.). An incubation study was carried-out on a sandy loam neutral soil with twelve treatments including T0: control; T1: RP; T2: SSP; T3: DAP; T4: PM; T5: 1/2 RP + 1/2 SSP; T6: 1/2 RP + 1/2 DAP; T7: 1/2 RP + 1/2 PM; T8: RP + PSB; T9: 1/2 RP + 1/2 SSP + PSB; T10: 1/2 RP + 1/2 DAP + PSB; T11: 1/2 RP + 1/2 PM + PSB. Phosphorus release capacity of added amendments was measured by analyzing extractable P from the amended soil incubated under controlled condition at 25 °C for 0, 5, 15, 25, 35, 60 days period. To complement the incubation study, a greenhouse experiment was conducted in pots with chilli (Capsicum annuum L.) used as a test crop. Growth, yield, P-uptake and PUE of the chilli was determined during the study. Results indicated that P release capacity of soil amended with RP varied between 6.0 and 11.5 mg kg-1 while the soluble P fertilizers i.e. SSP and DAP displayed a maximum of 73 and 68 mg P kg-1 at the start of the experiment (day 0). However, the P released tendency from SSP and DAP declined during incubation and at the end 82 and 79% of P initially present had been lost from the mineral pool. Integrated use of PSB and PM with RP in 1/2 RP + 1/2 PM + PSB treatment stimulated P mineralization by releasing a maximum of 25 mg P kg-1 that was maintained at high levels without any loss. Application of PSB tended to decrease pH showing an acidifying effect on soil. In the greenhouse experiment, RP alone or RP + PSB was not able to generate any significant impact on plant while DAP displayed the superiority over the remaining treatments. Combined use of RP, PM and PSB in 1/2 RP + 1/2 PM + PSB resulted in the growth, yield and P-uptake of chilli comparative/equivalent to that recorded under DAP. The PUE of applied P varied between 4–29% and higher in the treatments supplemented with PSB compared to those without PSB. These results suggest that use of PSB and PM with insoluble RP or with soluble P fertilizers could be a promising management strategy and viable technology to utilize both low-grade RP and SPF or PM efficiently for crop production and nutrient improvement in our cropping systems.