Blending of Slow-Release N Fertilizer and Urea Improve Rainfed Maize Yield and Nitrogen Use Efficiency While Reducing Apparent N Losses

Effective nitrogen (N) management practices are essential for achieving efficient and sustainable agricultural production. The purpose of this study was to improve N use efficiency (NUE) and minimize N loss by optimizing the rate and type of N fertilizer application while maintaining a high yield of maize. A two-year field experiment with U (urea), S (slow-release N fertilizer), and SU (blending of S and U) under four N application levels (N1: 90 kg ha−1, N2: 120 kg ha−1, N3: 180 kg ha−1, N4: 240 kg ha−1) was conducted to investigate their effects on ammonia (NH3) volatilization, residual soil nitrate N (NO3−-N), yield, NUE, apparent N losses of rainfed maize. NH3 volatilization in SU and S were 38.46% and 16.57% lower than that in U, respectively. SU and S were found to reduce the apparent N losses by 42.98% and 62.23%. SU decreased NO3−-N leaching in deep soils and increased NO3−-N content in topsoil. Compared with U and S, SU significantly increased yield, plant N accumulation, and NUE. SUN4 achieved the maximum maize yield and plant N accumulation, averaging 7968.36 kg ha−1 and 166.45 kg ha−1. In addition, the high yield and NUE were obtained when the mixing ratio of S and U was 53–58% and the N application rate was 150–220 kg ha−1. The findings highlight that SU effectively reduces N losses while ensuring high yield, which could be used as one of the optimal N fertilization strategies for rainfed maize in Northwest China.