The Synergistic Effects of Rice Straw-Pyrolyzed Biochar and Compost on Acidity Mitigation and Carbon Sequestration in Acidic Soils: A Comparative Study

Straw biochar and compost can mitigate soil acidity and enhance carbon sequestration in acidic soils. However, their differential synergistic effects and underlying mechanisms remain poorly understood. To address this gap, an incubation experiment was conducted in which rice straw biochar (BC) and compost (DC) were incorporated into an Ultisol at rates of 1% and 3%. BC outperformed DC in elevating the soil pH (0.39 vs. 0.28 units), reducing the exchangeable acidity (69% vs. 62%), and decreasing the potential active aluminum pool (35.1% vs. 25.2%) due to its higher alkalinity. Additionally, BC enhanced the soil organic carbon more effectively than DC (83.7% vs. 64.0%). While 3% BC treatment reduced the readily oxidizable and dissolved organic carbon in the soil, DC increased these parameters. This contrasting effect is attributed to BC’s lower carbon reactivity, higher alkalinity, and greater C/N ratio compared to DC. Compared with the control, BC and DC also increased the soil exchangeable K + (14.0-fold vs. 12.3-fold), Ca 2+ (5.4-fold vs. 4.9-fold), and Mg 2+ (3.7-fold vs. 5.2-fold). Overall, BC demonstrated superiority in mitigating acidity and sequestering carbon, while DC showed greater potential for improving fertility in acidic soils. Elucidating the distinct benefits of biochar versus compost provides valuable insights into the sustainable amelioration of acidic soils.