Controlled-Release Urea Coordinates Maize Physiology with Soil Nitrogen Retention: Balancing High Yield and Environmental Sustainability

Controlled-release urea (CRU) can improve nitrogen (N) use efficiency and yield, but comprehensive evaluations of its agronomic, physiological, and environmental impacts remain limited. Through a two-year field experiment comparing three CRU types with conventional urea at five N rates (0-280 kg N ha−1), we demonstrate that CRU at 180 kg N ha−1 maintained high maize yields (13.9 Mg ha−1) while improving N use efficiency, with thermosetting polymer-coated samples (TCU) showing superior performance. There was a significant increase in the net photosynthetic rate by 7.9–32.7% and intercellular CO2 concentration by 20.6–40.0% under CRU treatments during the silking and milking stages. The CRU treatments also sustained optimal levels of hormones, N metabolism enzymes, and sucrase and urease activities. Compared to common urea, life cycle assessment indicates that CRU has achieved a 47.5% reduction in reactive N losses and an 18.7% decrease in greenhouse gas emissions. Economically, CRU outperformed common urea, with TCU providing the highest net benefit through yield stability and labor savings. These findings establish TCU at 180 kg N ha−1 as an optimal strategy of maize production in the North China Plain, balancing productivity, profitability, and environmental protection.