Effects of blending ratios of slow-release nitrogen fertilizer and urea on yield and nitrogen uptake of winter wheat

Objectives To explore the optimal blending ratio that is beneficial to increase the yield of winter wheat in Guanzhong Plain, Shaanxi, to provide a scientific basis for fertilizer management in efficient winter wheat production.

Methods Field experiments were conducted to study the effects of slow-release nitrogen fertilizer and urea blending on the growth, yield, nitrogen uptake and utilization and soil nitrate nitrogen residue of three different winter wheat varieties under different nitrogen fertilizer types and blending ratios. There were four nitrogen fertilizer application treatments (U: urea, S: slow release nitrogen fertilizer, SU₁∶a mixture of slow release nitrogen fertilizer and urea with N ratio of 8∶2 and SU₂∶a mixture of slow release nitrogen fertilizer and urea with N ratio of 6∶4) in this experiment, and three winter wheat cultivars popularly planted by farmers in Guanzhong Plain, Xiaoyan 22 (XY22), Xinong 979 (XN979) and Zhengmai 379 (ZM379). Plant height, leaf area index, dry mater accumulation, yield, nitrogen uptake and utilization and soil nitrate nitrogen residue of winter wheat were measured. 180 kg/hm² of nitrogen was applied in this research, and no nitrogen plot was designed as the control (CK).

Results Slow-release nitrogen fertilizer and urea blending could significantly promote plant growth and increase crop yield, nitrogen uptake and utilization efficiency of winter wheat. The plant height, leaf area index, yield and nitrogen accumulation at maturity stage of different winter wheat cultivars under SU₂ treatment reached the maximum values, the cumulative amount of nitrate nitrogen in the 0–100 cm soil layer under SU₂ treatment reached the minimum value simultaneously. Commpared to U and S treatment, the yields were 31.81%–31.99% and 9.66%–25.38% higher; and the N translocation rates were 21.31%–51.12% and 2.60%–20.78% higher under SU₂ treatment, respectively. In addition, slow-release nitrogen fertilizer and urea blending markedly increased nitrogen uptake and use efficiency of three winter wheat cultivars, significantly promoted the transport of nitrogen from the vegetative organs to grains after flowering. Under SU treatment, the contribution rates of nitrogen transport to grain of XY22, XN979 and ZM379 were 49.71%, 48.32% and 49.39%, respectively. The nitrogen agronomic use efficiency and partial factor productivity from applied N of XY22, XN979 and ZM379 under SU₂ treatment reached their largest values, 17.54 kg/kg and 41.95 kg/kg, 17.94 kg/kg and 41.53 kg/kg, 11.32 kg/kg and 38.56 kg/kg, respectively. The cumulative amount of nitrate nitrogen in the 0–100 cm soil layer of XY22 under SU₂ treatment reached the minimum value of 112.67 kg/hm² among the three varieties after harvest, which was 13.48% lower than that under U treatment, with a significant difference. Slow-release nitrogen fertilizer and urea blending distinctly increased the content of nitrate nitrogen in surface soil at maturity stage, reduced nitrate leaching to deep soil, and improved nitrogen use efficiency.

Conclusion These results demonstrate that a mixture of slow release nitrogen fertilizer and urea with N ratio of 6∶4 is the optimal blending ratio when 180 kg/hm² of nitrogen is applied..