Improving winter wheat N utilization efficiency and soil fertility through replacement of chemical N by 20% organic manure

Objectives The effects of different proportion of organic N in the total N input on winter wheat yield and soil fertility were explored. The purpose of this study is to provide technical support for selecting suitable replacement proportion of organic fertilizer, improving N use efficiency and high-quality wheat yield for winter wheat in the north of Henan Province.

Methods A field experiment was conducted in 2018 and 2019 using a new wheat variety Bainong 207 as experimental material. Treatments of no N fertilizer (T1), conventional N fertilizer input (T2) and three proportion of organic N (20%, 30% and 40%, recorded as T3, T4 and T5) were set up in the experiment. The wheat yield, yield components, N accumulation and allocation ratio in different organs, N use efficiency and soil fertility were investigated at harvest.

Results Compared with T2 treatment in 2018 and 2019, the replacement ratio of 20% (T3) achieved stable increased yield of winter wheat. Under the T3 treatment in 2019, the yield was increased significantly by 16.59%, while T4 and T5 treatments decreased the yield increment. Compared to T2, the total N accumulation of plants under the T3 treatment was significantly increased by 25.71% in 2019; the N accumulation of grains was significantly increased by 14.45% and 22.20% in 2018 and 2019, respectively; under the T3 treatment, the N partial factor productivity, N recovery efficiency, N agronomic efficiency were significantly higher than those under the T2 treatment. Application of organic manure for two consecutive years had little effect on soil total N content. However, the contents of available P, NH₄⁺-N and NO₃^–-N in the soil were significantly increased under the T3 treatment in 2018 and 2019. According to the correlation analysis, wheat yield was significantly and positively correlated with total N accumulation in plant, grain N accumulation and spike number per area. The spike number per area was positively and correlated with the contents of NH₄⁺-N and NO₃^–-N in soil.

Conclusions At the base of total N input of 300 kg/hm², replacing a certain proportion of N with organic fertilizers for two consecutive years is capable of increasing soil fertility and winter wheat yield. Under the current soil fertility condition, replacement of chemical N by 20% organic fertilizer could significantly increase the grain N accumulation, improve wheat N use efficiency and yield, and ensure the goal of stable and high yield of winter wheat in northern Henan.