Effects of Tillage and Fertilization on Soil Aggregate Stability and Agricultural Sustainability in a Wheat–Rice Rotation System

Appropriate tillage and fertilization patterns play a crucial role in enhancing agricultural sustainability. Nevertheless, limited information is available regarding soil aggregate stability, soil nutrient content and the sustainability of wheat–rice rotation systems (W-Rs) under deep tillage (DT) when adopting organic fertilizer substitution (OFS) and biochar-based fertilizer substitution (BFS). A two-year split-plot experiment was conducted in the W-R on the Yangtze River Plain of China to address this issue, with the main plots receiving tillage patterns (shallow rotary tillage (RT) and DT) and subplots receiving fertilization patterns (chemical fertilizer (CF), OFS, BFS, and organic biochar fertilization (OBF)). Compared with the RT, the DT reduced the plow pan thickness by 24.4%, but increased topsoil depth, geometric mean diameter (GMD), and the sustainability evaluation index (SEI) of the W-R by 15.2%, 6.9%, and 10.1%, respectively. Compared with the CF, both BFS and OBF significantly increased the proportion of aggregates > 0.25 mm, the values of mean weight diameter, GMD and pH, the contents of soil organic carbon, available phosphorus, available potassium, cation exchange capacity, exchangeable Ca2+ and exchangeable Mg2+, the annual average grain yields, and the SEI with the trend of OBF > BFS > OFS > CF. Among all treatments, the DT + OBF had the highest SEI value, higher by 35.5% than that under RT + CF. Therefore, the organic biochar fertilization coupled with deep tillage ameliorated soil structure, elevated soil nutrient status, and improved the sustainability of the W-R. This finding supplies strong evidence to optimize field management strategies for the wheat–rice rotation system, favoring sustainable agricultural production on the Yangtze River Plain of China.