Effect of Winter Cropping Forage on Soil Aggregate Distribution and Stability

Soil structure is crucial for maintaining soil health and can be improved through winter cropping. This study evaluated the effects of winter cropping Italian ryegrass (WI), rye (WR), oat (WO), and winter fallow (CK) on soil aggregate structure and explored the role of soil-cementing materials and arbuscular mycorrhizal fungi (AMF) communities in regulating soil aggregate distribution and stability. Compared to CK, the WI and WR treatments increased the proportion of water-stable large macroaggregates (>2 mm diameter) by 45.7% and 41.5%, respectively. Both WI and WR treatments enhanced the mean weight diameter and geometric mean diameter of soil aggregates, while soil porosity increased by 15.7% and 21.7%, respectively. The contents of amorphous iron oxide, humic acid, and fulvic acid were significantly higher in the WI and WR treatments. The WR treatment improved the Shannon index of AMF communities by 14.6%, and the relative abundances of Claroideoglomus increased by 55.3%, 51.3%, and 43.5% in the WI, WR, and WO treatments, compared to CK, respectively. Dominant AMF genera had a substantial impact on soil aggregate distribution. The partial least squares path model indicated that distinct AMF communities contributed to variations in soil aggregate distribution following winter cropping forages. Both Italian ryegrass and rye showed the greatest potential for enhancing soil structure and are recommended for winter cropping in Southern China. These findings suggest that winter cropping forages can improve soil aggregate structure primarily by enhancing AMF communities, providing a promising strategy for improving soil health.