Optimizing the blending ratio of urea with slow-release N fertilizer improves maize yield and N use efficiency while reducing N losses.

INTRODUCTION: Blending urea (U) with slow-release N fertilizer (R) can improve the synchrony between N supply and crop demand, while mitigating N losses to the environment. However, cultivar-specific responses to varied U/R blending ratios under rainfed conditions remain poorly characterized. METHODS: In this study, two dominant maize cultivars (ZD958 and QL14) widely planted in Northwest China were selected as experimental materials. Five fertilization treatments (U, R, and three U/R blending ratios: UR1, UR2, UR3) each at two N rates (N1: 180 kg·ha-1; N2: 240 kg·ha-1) were tested. RESULTS: The results showed that UR treatments generally achieved higher grain yield and N use efficiency (NUE), while reducing cumulative NH3 volatilization and soil NO3 --N residue compared with U and R. For both ZD958 and QL14, the maximum grain yield and NUE were achieved under the UR2N1 (U/R = 3/7, 180 kg·ha-1). Compared with other treatments, UR2N1 increased NUE by 3.51-19.07% (ZD958) and 4.01-20.41% (QL14), while reducing NH3 volatilization soil NO3 --N residue. Notably, under UR2N1, QL14 showed 9.70% higher NUE than ZD958, along with 8.78% lower soil NO3 --N residue and 14.12% lower NH3 volatilization. CONCLUSION: Under rainfed conditions, the UR2N1+QL14 combination effectively balances the trade-off between grain yield and environmental impact, and is therefore recommended as an optimal fertilization-cultivar strategy for rainfed maize production in Northwest China.