Balancing soil nitrogen supply and environmental risks in sub-humid maize systems: The role of hydrothermal-redox-enzymatic interactions under contrasting mulching patterns

Global climate change exacerbates hydrothermal stress in sub-humid rain-fed agriculture. While mulched drip irrigation is widely adopted, the ways in which mulching strategies modulate the ridge soil microenvironment to influence nitrogen (N) transformation remain insufficiently characterized. A two-year field experiment using in situ incubation was conducted to compared no mulching (NM), ridge mulching (RM), and full ridge-furrow mulching (FM) to evaluate soil hydrothermal dynamics, enzyme activities, and N transformation. Results showed that, compared with NM, both RM and FM significantly increased soil temperature (T s ), relative extractable water (REW), and redox potential (Eh). Mulching significantly reduced urease activity in the 0-20 cm layer without affe-cting L-asparaginase activity, suggesting a selective regulation of exogenous N transformation processes. Compared with NM, FM increased net soil N mineralization by 23.6%-28.5% and RM by 3.6%-16.2%. Analysis of correlations suggested that T s was positively associated with N transformation and enzymatic activity; conversely, elevated REW appeared to suppress nitrification, mineralization, and specific enzymatic rates. While mulching practices enhanced organic N mineralization and may help reduce ammonia losses, increased nitrate leaching risks and potential for faster depletion of soil organic matter were also observed. Consequently, prioritizing RM combined with precision water and N management may offer a pathway to enhance climate resilience and ecological sustainability in sub-humid regions.