Synergistic effects of rice straw and its biochar on availability of phosphorus fertiliser in acidic soils

Abstract

Contexts Increasing the availability of phosphorus fertiliser is needed for better crop production in acidic soils. Aims To observe how rice straw and its biochar affect phosphorus fertiliser recovery in an Ultisol and an Oxisol as a measure for the availability of phosphorus in acidic soils. Methods A 60-day incubation study was conducted using treatments comprising of straw (1.5%, w/w) and biochar produced at 400°C (1.5%, w/w), a mixture of each at the same rate, and a control with two phosphorus rates of 0 and 100 mg kg−1. Key results The application of both the straw and the biochar alone and in combination raised the soil pH by 0.12, 0.20, 0.32, 0.17, 0.31 and 0.38 units, and cation exchange capacity by 2.06, 3.02, 2.72, 2.56, 6.28, and 8.40% compared to control for both the Ultisol and the Oxisol, respectively. Similarly, dissolved organic matter also increased by 74.19, 55.28, 84.63, 24.39 and 136.44%, respectively compared to control for the corresponding treatments and soils except the straw amended Ultisol. With an increase in the soil pH, the rate of phosphorus recovery increased by 11.73, 12.99, 23.89, 2.72, 5.23 and 6.28% compared to control for the corresponding treatments and soils, respectively. Phosphate adsorption by the soils became hindered by increased cation exchange capacity and dissolved organic matter but decreased exchangeable trivalent aluminium cations, which led to a greater phosphorus recovery in both the amended soils. Conclusions The combined application of rice straw and biochar would be the appropriate choice for increasing the applied phosphorus fertiliser availability in acid soils.