FANG Yanfei, FU Xiaowen, XU Wenxiu, LIU Wen, HUANG Hongmei, ZHANG Na, DU Xiaojing, ZHANG Yongjie
In order to explore the effects of different ombinations of nitrogen application on the soil nitrogen and yield of the winter wheat-summer soybean rotation system in 2017-2018, field experiments were carried out in the Yining County Agricultural Science and Technology Demonstration Garden, using the winter wheat-summer soybean rotation. Four nitrogen application levels were set in the previous wheat season: 0 (N0), 104 (N1), 173 (N2), 242 kg·hm-2 (N3) and 3 nitrogen application levels were set in the subsequent soybean season: 0 (S0), 69 (S1), 138 kg·hm-2 (S2), to study the effects of different nitrogen application combinations on the soil nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4+-N) and inorganic nitrogen residue in the 0~100 cm soil layer and yield of the farmland after crops harvest. The results showed that soil NO3-N and NH4+-N contents of winter wheat at different nitrogen levels reached the maximum in the 20~40 cm soil layer, and the soil NO3-N and NH4+-N contents of N3 reached the highest, reaching 14.65 mg·kg-1 and 4.26 mg·kg-1, respectively, the soil NO3-N content were 92.86%, 44.69%, and 17.03%, respectively, higher than that of N0, N1, and N2, and the soil NH4+-N increased by 69.95%, 26.10% and 8.46% in turn. The higher the nitrogen application rate in winter wheat, the greater amount of residual inorganic nitrogen in the soil, among them, N3 was the highest in the wheat season, which was 200.62 kg·hm-2. In addition, nitrogen application in the previous wheat season could also affect the content of soil NO3-N, NH4+-N and residual inorganic nitrogen in the following soybean; the soil NO3-N and NH4+-N content of summer soybeans were also highest in the 20~40 cm soil layer, and the soil NO3-N, NH4+-N content and inorganic nitrogen residues of N3S2 were largest, the average value was 18.61 mg·kg-1, 5.10 mg·kg-1 and 258.36 kg·hm-2, respectively. The winter wheat yield was the highest with 7 828.64 kg·hm-2 under the nitrogen application of 173 kg·hm-2 (N2), and the average yield was 35.45%, 16.77%, and 6.26% higher than that of N0, N1, and N3, respectively; On this basis, when 69 kg·hm-2 nitrogen was applied to summer soybeans (S1), the yield of summer soybeans was the highest, with an average of 2 988.93 kg·hm-2, and the annual total yield also reached the highest, at 10 817.5 kg·hm-2. In summary, 173 kg·hm-2 nitrogen application in the wheat season and 69 kg·hm-2 nitrogen application in the bean season not only benefit to increase the annual yield of wheat and beans, but also reduce the residual nitrogen in the soil, which can provide a certain reference standard for two crops a year system with high efficient nitrogen application.