Mitigation of soil salinity by addition of different rice straw biochar doses in salt-affected acid soil

Abstract The current study was carried out to evaluate the effect of rice straw biochar amendment and to identify the appropriate dose of biochar application to reduce soil acidity, salinity, toxicity, and sodicity in salt-affected acid soils. The rice straw biochar at 4 different rates of 0%, (control) 1%, 3%, and 5% (w/w) was mixed with 6 salt-affected acid soils: S1 (non-saline), S2 and S3 (low saline), and S4, S5, and S6 (moderate saline). The mixture was continuously shaken in distilled water for 7 days. The biochar application significantly increased soil pH and saturated electrical conductivity (ECe) with an increasing biochar application rate compared with the control. Significant decreases in sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) values below the critical level of sodicity were observed above the biochar application rate of 1%. Soluble chloride (Cl – ) and soluble and exchangeable sodium (Na + ) were significantly reduced above the biochar application rate of 1%. The biochar application (≥ 1%) led to a significant increase in soluble and exchangeable potassium (K + ) and declines in soluble and exchangeable calcium (Ca 2+ ) and magnesium (Mg 2+ ). This study concluded that the biochar application rate of 1% was suitable for reducing soil acidity to a safe level for rice plants. The rice straw biochar application improved soil toxicity and sodicity by reducing soluble Cl – and soluble and exchangeable Na + , decreasing SAR and ESP. The biochar application also increased available K + , essential for rice plant growth and development in salt-affected soils.