Modeling of Water, Heat, and Nitrogen Dynamics in Summer Maize under Broad Furrow Irrigation and the Mechanism of Enzyme Activity Response

This study explores the impact of water and nitrogen management on the dynamics of water, heat, and nitrogen in farmland soil. It also explores the correlations soil factors, enzyme activity, and crop yield. To achieve this, field experiments and HYDRUS model simulations were conducted in the broad furrow irrigation system of the Yinhuang Irrigation Area. The experiment involved three irrigation levels (60%, 70%, and 80% of field water holding capacity, labeled as W1, W2, and W3, respectively) and three nitrogen application rates (120, 220, and 320 kg·ha−1, labeled as N1, N2, and N3). Results indicated that the HYDRUS model, optimized using field trial data, accurately represented soil dynamics. Soil profile water and nitrogen exhibited greater variation in the root zone (0–40 cm) than in the deeper layers (40–100 cm). Water–nitrogen coupling predominantly influenced water and nitrogen content changes in the soil, with minimal effect on soil temperature. Soil enzyme activities at the trumpet, silking, and maturity stages were significantly affected by water–nitrogen coupling, displaying an initial increase and subsequent decrease over the reproductive period. The highest summer maize yield, reaching 10,928.52 kg·ha−1 under the W2N2 treatment, was 46.64% higher than that under the W1N1 treatment. The redundancy analysis revealed a significant positive correlation between soil nitrate nitrogen content and soil enzyme activity (p < 0.05). Furthermore, there was a significant positive correlation between soil enzyme activity and both maize yields (p < 0.01). This underscores that appropriate water and nitrogen management can effectively enhance yield while improving the soil environment. These findings offer valuable insights for achieving high yields of summer maize in the Yellow River Basin.