Soil Carbon Mineralization and Aggregate Distribution in Various Tillage Practices of Rice–Wheat Cropping System: A Field and Laboratory Study

Different tillage and residue management practices can strongly impact soil structure stability and soil organic carbon (SOC) sequestration. However, the detailed information about the aggregate stability, SOC protection, and mineralization within aggregates are still lacking. Using aggregate fractionation with laboratory incubation, we investigated aggregate-associated SOC, soil structural stability, and SOC mineralization in rice–wheat rotation under different tillage treatments: CT0 (puddled rice, conventional wheat − residue); CTR (puddled rice, conventional wheat + residue); NT0 (direct rice seeding, zero-tilled wheat − residue); and NTR (direct rice seeding, zero-tilled wheat + residue). NTR significantly enhanced the large macro-aggregate fraction (> 2 mm) at the 0–45 cm soil layer and macro-aggregate-associated SOC at the 0–15 cm soil layer. However, CTR enhanced the macro-aggregate-associated SOC at the 15–30 cm layer. Notably, the mean weight diameter ( 8