Can Reduced Nitrogen Application of Slow/Controlled-Release Urea Enhance Maize Yield Stability and Mitigate Nitrate/Ammonium Nitrogen Leaching in Soil in North China?

Reducing nitrogen (N) fertilizer input while sustaining maize yield and alleviating nitrogen leaching is a significant challenge due to economic and practical feasibility, as well as the environmental friendliness of this process. However, it remains unclear whether reducing nitrogen by using a blend of slow/controlled-release nitrogen fertilizer (SCRNF) with urea at an equal nitrogen rate can achieve the desired yield and mitigate nitrogen leaching. A field experiment consisting of four treatments (240 kg·N·hm−2, 100% urea, CK; 240 kg·N·hm−2, 50% N from urea and 50% N from SCRNF, N100%; 192 kg·N·hm−2, 50% N from urea and 50% N from SCRNF under 20% N reduction, NR20%; 144 kg·N·hm−2, 50% N from urea and 50% N from SCRNF under 40% N reduction, NR40%) was conducted in Shanxi from 2019 to 2021. In this study, we explored the effects of a mixture of SCRNF and urea on grain yield, yield components, main agronomic traits, nitrogen partial factor productivity, and content of nitrate/ammonium nitrogen in soil in maize under decreasing amounts of nitrogen fertilization. The results showed that the mixture of SCRNF and urea can improve spring maize yield under reduced nitrogen input, with its yield and yield component factors generally performing better than those of the control. The yield of the NR20% treatment was highest in 2020 and 2021, increasing by 8.8% and 11.7% over CK, respectively; the NR20% and NR40% treatments had no significant impact on the main agronomic traits of spring maize, such as plant height, leaf area, shoot biomass, and SPAD value of the ear leaf, compared with CK; the NR20% and NR40% treatments significantly (p < 0.05) enhanced nitrogen partial factor productivity but reduced nitrate and ammonium nitrogen in 0~200 cm soil over the three years compared with CK. Therefore, reducing nitrogen input by 20% with 50% N from urea and 50% N from biodegradable film-coated urea was an appropriate nitrogen fertilizer management measure for mitigating environmental risks without compromising maize yield in North China.