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In China, the most common grain crop is maize (Zea mays). The increasing pressure to meet the food demands of its growing population has pushed Chinese maize farmers toward an excessive use of chemical fertilizers, a practice which ultimately leads to a massive waste of resources and widespread environmental pollution. As a result, increasing the yield and improving the nitrogen (N) use efficiency of maize has become a critical issue for agriculture in China. This study, which analyzes the combined data from a simulation carried out using the Decision Support System for Agrotechnology Transfer (DSSAT), a field experiment, and a household survey, explored the effectiveness of several approaches aimed at narrowing the maize yield gap and improving the N utilization efficiency in the Huang-Huai-Hai Plain (HHHP), the most important area for the production of summer maize in China. The various approaches we studied deploy different methods for the integrated management of N fertilizer input and the planting density. The study produced the following results: (1) For the simulated and actual maize yields, the root mean square error (RMSE), the normalized root mean squared errors (NRMSE) and the index of agreement (d) were 1,171 (kg ha–1), 12% and 0.84, respectively. These results show that the model is viable for the experiment included in the study; (2) The potential yield was 15.58 t ha–1, and the yields achieved by the super-high-yield cultivation pattern (SH), the optimized nutrient and density management pattern (ONM), the simulated farmer's practice cultivation pattern (FP) and actual farmer's practice (AFP) were 11.43, 11.06, 10.33, and 7.95 t ha–1, respectively. The yield gaps associated with the different yield levels were large; (3) For summer maize, the high yield and a high N partial factor productivity (NPFP) was found when applying a planting density of 9 plants m–2 and an N application amount of 246 kg ha–1. These results suggest that the maximum yield that can actually be achieved by optimizing the N application and planting density is less than 73% of the potential yield. This implies in turn that in order to further narrow the observed yield gaps, other factors, such as irrigation, sowing dates and pest control need to be considered. [ABSTRACT FROM AUTHOR]

• Controlled-release urea with irrigation affects maize biomass and N accumulation. • Optimum controlled-release urea improved photosynthetic capacity for each irrigation level. • The interaction of irrigation and controlled-release urea on maize yield was significant. Effective irrigation and nitrogen (N) management is crucial for sustainable agricultural development. Controlled-release fertilizer has been widely used to improve N use efficiency and save labor in one-off application. A specially designed soil column and field trial were conducted to investigate the effect of the interaction of irrigation management and nitrogen on yield, N uptake, and photosynthetic characteristics of summer maize. In the soil column experiment, severe water stress (W1) significantly decreased the leaf area index, relative chlorophyll content, and net photosynthesis and delayed maize growth, resulting in significant yield loss. Under mild water stress (W2), increased controlled-release urea (CRN) application counteracted the inhibition of maize growth. Under adequate water condition (W3), the yield and maize growth exhibited no significant difference between CRN 210 and 315 kg N ha–1. In the field experiment, CRN 210 and 315 kg N ha–1 also exhibited similar yield and were significantly higher than common urea 315 kg N ha–1 under conventional irrigation (CI). Under half-reduced conventional irrigation (RI), yields of CRN 315 kg N ha–1 increased by 10.5% and 7.5% compared with that of CRN 210 kg N ha–1 in 2014 and 2015. The interaction between irrigation and CRN could effectively alleviate the adverse effects of mild drought on summer maize by delaying leaf senescence, increasing chlorophyll content, and improving photosynthetic performance during the grain-filling period. These characteristics allowed more water and nutrients for maize plant and ultimately increased the yield. In areas with adequate irrigation conditions, CRN reduced to 210 kg N ha–1 could satisfy maize growth. In mild water stress and half-reduced conventional irrigation area, the CRN rate of 315 kg N ha–1 used by traditional farmers showed superior benefits. [ABSTRACT FROM AUTHOR]