Green manure improves humification and aggregate stability in paddy soils

Soil organic matter (SOM) is essential for soil health and carbon (C) sequestration, offering benefits in mitigating global warming. Anaerobic conditions in rice paddies alter carbon dynamics by slowing decomposition rates, with the stability of carbon depending on its form, whether labile or recalcitrant. This study aimed to evaluate whether incorporating green manure could enhance soil C quality and stability compared to conventional practice. Green manure (GM) was supplied using a winter cover crop mixture of barley and hairy vetch, while the conventional practice involved the application of only NPK fertilizer. Although GM treatment led to elevated CO₂ and CH₄ emissions compared to NPK, it significantly improved soil physical properties, as indicated by a 21.9% increase in mean weight diameter (MWD). The incorporation of organic matter through GM in rice paddies significantly improved soil physical properties, enhancing aggregation formation and stability by 21.9 % as measured by mean weight diameter (MWD) compared to conventional NPK fertilizer. In addition, GM increased the concentration of C in the aggregate and raised the high-temperature reactive C level under 0.25 mm aggregate size. Notably, both the quantity and C content of humic acids were higher in GM-treated soils, contributing to greater carbon accrual and improved soil organic matter stability. These findings show that adopting GM-based organic matter strategies can enhance soil structure, bolster carbon stability, and improve soil quality in paddy fields, ultimately supporting sustainable agriculture. • Green manure application increased water-stable aggregate stability by 21.9 % compared to NPK. • Humic acid content in the largest aggregates rose by up to 471 % under green manure, indicating enhanced carbon stabilization. • Incorporating green manure maintained higher hot water-extracted carbon (HWEC) in aggregates smaller than 0.25 mm.