Mechanistic Responses of Summer Maize Growth and Farmland N2O Emissions to Real-Time Water–Fertilizer Synergistic Regulation in the North China Plain

With the advancement of agricultural modernization, issues related to resource conservation, intensive utilization, and green, low-carbon development have become increasingly prominent. To enhance water and fertilizer use efficiency in Henan Province and promote green, low-carbon, and sustainable agricultural development, field experiments were conducted during 2023–2024. The experiment employed a randomized complete block design with three replications. Each plot measured 30 m2 (5 m × 6 m), totaling 36 plots. An IoT-based real-time coordinated water-fertilizer regulation technology, driven by continuous WSH-TDR310S sensor monitoring of soil moisture and nitrogen status with automated threshold-based control logic, was implemented. By transforming the traditional static scheduling approach into a dynamic feedback mechanism driven by real-time sensor data, the synchronization between resource supply and crop demand was achieved. This study aimed to elucidate the response characteristics of summer maize growth dynamics and farmland N2O emissions under the proposed regulation strategy. The experiment included three levels of water deficit (mild, moderate, and severe) and three fertilization levels (low, medium, and high), resulting in a total of nine real-time water–fertilizer coordinated regulation treatments, along with three local border irrigation control treatments. The results showed that under real-time water–fertilizer regulation, plant height, stem diameter, and leaf area index of summer maize exhibited unimodal variation patterns, with the medium irrigation–medium fertilization (B2) treatment performing optimally. Compared with the border-irrigation medium-fertilization control (D2), plant height and stem diameter under the B2 treatment increased significantly. Cumulative farmland N2O emissions increased with higher irrigation and fertilization levels, with the border-irrigation high-fertilization treatment producing the highest emissions. Yield formation was mainly governed by structural growth traits, with plant height showing the strongest predictive ability, followed by stem diameter, whereas leaf area index showed weaker explanatory power. Summer maize yield exhibited a unimodal response to both irrigation and nitrogen input levels. Compared with the D2 treatment, the B2 treatment increased grain yield by 41.33%, while achieving water-saving and fertilizer-saving rates of 38.10% and 35.75%, respectively, thereby achieving an optimal balance between high yield and efficient water–fertilizer utilization. These findings provide theoretical support for summer maize production in the North China Plain and contribute to the promotion of green and sustainable agricultural development.