Effect of Combined Application of Slow-Release and Conventional Urea on Yield and Nitrogen Use Efficiency of Rice and Wheat under Full Straw Return

The effects of one-time basal application of different mixtures of slow-release urea (SRU) and conventional urea (CU) on yield and nitrogen use efficiency (NUE) of rice and wheat were investigated to determine the appropriate ratios of SRU to CU for one-time basal fertilization in a rice–wheat rotation farmland under full residue incorporation. A field plot experiment was used in this study. Six treatments were established as follows: CK (no nitrogen fertilizer applied), T0 (100% CU, 50% applied as basal fertilizer and 50% applied as jointing fertilizer), T3 (one-time basal application of SRU and CU mixture with 30% SRU), T5 (one-time basal application of SRU and CU mixture with 50% SRU), T7 (one-time basal application of SRU and CU mixture with 70% SRU), and T10 (one-time basal application of 100% SRU). The results showed that the combined application of SRU and CU increased the yields of rice and wheat. Treatment T7 resulted in the highest rice yield, and T3 resulted in the highest wheat yield, which were 25.6% and 29.4% higher, than those of treatment T0, respectively. Compared with treatment T0 (application of CU alone), the combined application of SRU and CU resulted in 27.4–96.5% and 22.8–57.1% higher NUE in rice and wheat, respectively.