Amelioration of Saline-Alkali Soil with Rice Straw Biochar: Impacts on Aggregate Composition, Organic Carbon, and Microbial Biomass

Abstract

Against the backdrop of increasingly severe global food security challenges and constraints on arable land, the remediation and efficient utilization of saline-alkali land has become a critical issue. While biochar shows significant potential for the remediation of saline-alkali soil, the mechanisms involved at the aggregate scale remain unclear. This study investigated the effects of application levels (0%, 1%, 2% and 5%) of rice straw biochar on the physicochemical properties, aggregate organic carbon, and mineralization in saline-alkali soil. The results indicated that biochar application significantly decreased soil pH and the concentrations of Na⁺ and Mg²⁺ ions, while increasing the levels of K⁺ ions and exchangeable Ca²⁺ ions. These changes effectively improved the soil's ionic environment and fertility, thereby promoting the growth of rapeseed seedlings. Biochar also enhanced microbial biomass carbon and activity, facilitating organic carbon transformation and stabilization. Furthermore, an appropriate amount of biochar significantly increased the proportion of 0.075 to 0.2 mm and 3 to 2 mm aggregates, thereby promoting the aggregation of microaggregates into macroaggregates. These findings clarify how biochar enhances the stability of aggregate organic carbon by improving soil structure, regulating ion composition, and modulating microbial activity. This provides a theoretical basis for the remediation of saline-alkali soil.