Low-disturbance farming regenerates healthy deep soil toward sustainable agriculture - Evidence from long-term no-tillage with stover mulching in Mollisols

Currently, global agricultural development is in a critical period, as it contends with a growing population, degraded farmland, and serious environmental issues. Although low-disturbance practices are recommended to improve soil health, it is unclear whether such practices benefit critical deep soil functioning. Here, we compared the soil bacterial communities and physicochemical parameters across 3-m deep soil profiles in a Mollisol of Northeast China at the end of the dormant season after 10 years of farming under conventional tillage without stover mulching (CT), no-tillage without stover mulching (NTNS), and no-tillage with stover mulching (NTSM). We found that low-disturbance practices (NTNS and NTSM), compared with CT, evidently promoted soil bacterial species richness and diversity and enriched potential metabolic diversity. When compared to the bacterial communities in CT, the vertical dissimilarity of bacterial communities in NTNS decreased, while that in NTSM increased, indicating that no-tillage alone homogenized the composition of the bacterial community through soil depth profiles, but straw mulching enhanced the uniqueness of community composition at each layer. In comparison to CT, no-tillage with stover mulching significantly increased the soil water content and root-associated organic carbon (SEOC), and decreased soil pH. Mineral nitrogen declined with depth to 60 cm and then increased to its maximum at 250-300 cm under CT and at 120-150 cm under NTNS and NTSM. More mineral nitrogen at 0-150 cm under low-disturbance practices would provide more available nitrogen for crops in the coming growing season, while the accumulated nitrogen at 150-300 cm under CT may leach into the groundwater. Taken together, our results show that low-disturbance practices can regenerate whole-soil bacterial diversity and potential function, and promote water retention and nitrogen holding capacity within the root zone, thus reducing the dose of nitrogen fertilizer and mitigating nitrogen contamination to deep groundwater, ultimately contributing to agricultural sustainability in Mollisol regions.