Rice straw incorporation mobilizes inorganic soil phosphorus by reorienting hysteresis effect under varying hydrothermal regimes in a humid tropical Inceptisol

Abstract

To mobilize inorganic soil phosphorus (P), soils from humid tropical agro-ecosystems were treated with P solubilizing microbes (PSMs) and graded doses of rice straw (RS) under varying hydrothermal scenarios (temperature and soil moisture suctions), likely, S1 (25 °C and 0.033 MPa), S2 (35 °C and 0.033 MPa), S3 (25 °C and 0.1 MPa), and S4 (35 °C and 0.1 MPa). Six treatments were obtained, T0 (no PSMs and no RS), T1 (RS at 3570 mg kg−1 or 8 Mg RS ha−1 + PSMs), T2 (RS at 4465 mg kg−1 or 10 Mg RS ha−1 + PSMs), T3 (RS at 5355 mg kg−1 or 12 Mg RS ha−1 + PSMs), T4 (RS at 6250 mg kg−1 or 14 Mg RS ha−1 + PSMs), and T5 (RS at 0 mg kg−1 + PSMs). Temperature sensitivity of organic P mineralization was the highest for T5, whereas, inorganic P solubilization was the highest for T4 at 0.033 MPa and for T5 at 0.1 MPa. Inorganic P solubilization rate under S1, S2 and S4 were ∼167%, 288% and 54% greater than S3, respectively. Under S2, T4 could solubilize ∼11, 21 and 9.2 ppm of NH4F-P, NaOH-P and H2SO4-P, respectively. At 0.033 MPa suctions, T3 significantly reduced hysteresis by ∼10% at 25 0C and 12% at 35 0C, respectively, over control. Path analysis indicated silicon concentrations and changes in soil pH were the most significant factors to influence soil environment to mobilize soil P. Reduction in hysteresis effect was mostly achieved by altering microbial factors. T3 could solubilize ∼2.96% and 3.26% of inorganic P under S1 and S2 enhancing P availability by 3.35, and 4 times over control, respectively. Overall, annual RS (12 Mg ha−1)+PSMs application under varying moisture availability could sustain P availability in humid tropical Inceptisols of India.