Articles | Volume 12, issue 15
Research article
05 Aug 2015
Research article |  | 05 Aug 2015

Mineralization of soluble P fertilizers and insoluble rock phosphate in response to phosphate-solubilizing bacteria and poultry manure and their effect on the growth and P utilization efficiency of chilli (Capsicum annuum L.)

M. K. Abbasi, N. Musa, and M. Manzoor

Abstract. The ability of soil microorganisms and organic manure to convert insoluble phosphorus (P) to an accessible form offers a biological rescue system for improving P utilization efficiency in soil–plant systems. Our objective was to examine the P mineralization potential of two soluble P fertilizers (SPF), i.e., single superphosphate (SSP) and diammonium phosphate (DAP), and of insoluble rock phosphate (RP) with and without phosphate-solubilizing bacteria (PSB) and poultry manure (PM) and their subsequent effect on the growth, yield and P utilization efficiency (PUE) of chilli (Capsicum annuum L.). An incubation study was carried out on a loam (slightly alkaline) soil with 12 treatments: 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; and T11 – 1/2 RP+1/2 PM+PSB. Phosphorus mineralization was measured by analyzing extractable P from the amended soil incubated under controlled conditions at 25 °C for periods of 0, 5, 15, 25, 35 and 60 days. A complementary greenhouse experiment was conducted in pots with chilli (Capsicum annuum L.) as a test crop. Growth, yield, P uptake and PUE of the chilli was determined during the study. Results indicated that P mineralization in soil amended with RP was 6.0–11.5 mg kg−1, while both soluble P fertilizers resulted in 68–73 mg P kg−1 at day 0, which decreased by 79–82 % at the end of incubation. The integrated use of PSB and PM with RP in T11 stimulated P mineralization by releasing a maximum of 25 mg P kg−1 that was maintained at high levels without any loss. Use of PSB decreased soil pH. In the greenhouse experiment, RP alone or RP+PSB did not have a significant impact on plant growth. However, the combined use of RP, PM and PSB in T11 resulted in similar growth, yield and P uptake of chilli as DAP. The PUE of applied P varied from 4 to 29 % and was higher in the treatments that included PSB. We conclude that the use of PSB and PM with insoluble RP or with soluble P fertilizers could be a promising approach to enhance P availability from both low-grade RP and SPF for crop production in intensive cropping systems.

Short summary
P release capacity of soil amended with RP varied between 6.0–11.5 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 release 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 ½RP+½PM+PSB treatment stimulated P mineralization by releasing a maximum of 25mg P kg-1.
Final-revised paper