ChangBin Liu^{1, 2}, ZiMeng Tian^{1, 2}, ZeWei Qi^{1, 2}, JingJing Han³, XingHua Zhao¹, JianFu Xue^{1, 2,}

Three-harvest in two years is a traditional farming system in the Jinzhong Basin of Shanxi Province of the eastern Loess Plateau in China. Recently, an innovative farming system of winter wheat-fresh maize with two-harvest per year, making full use of temperature and light resources, is proposed. However, there is little known of the optimal nitrogen application rate for the innovative farming system to increase crop yield and improve ecological environment. In current study, six nitrogen application rates were carried out, consisting of winter wheat/fresh maize season 0/0 kg·ha^-1 (N₀, Control), 75/75 kg·ha^-1 (N₇₅), 150/150 kg·ha^-1 (N₁₅₀), 225/225 kg·ha^-1 (N₂₂₅), 300/300 kg·ha^-1 (N₃₀₀) and 375/375 kg·ha^-1 (N₃₇₅). The grain yield, dry matter and nitrogen accumulation and remobilization were analyzed to determine the optimal nitrogen application rate in the winter wheat-fresh maize cropping system in the Jinzhong Basin. The results showed that in the winter wheat and fresh maize season, compared with the N₀, N₇₅ and N₃₇₅ treatments, total dry matter accumulation at winter wheat maturity and fresh maize harvesting increased significantly by 82.9%-94.5% and 26.1%-197.1%, respectively, and dry matter remobilization in leaves and stem+sheath (+tassel) increased significantly under the N₁₅₀ treatment. Total nitrogen accumulations under the N₁₅₀, N₂₂₅ and N₃₀₀ treatments increased significantly by 58.2%-162.9% and 55.7%-301.7% compared with those under the N₀ and N₇₅ treatments, respectively. Nitrogen remobilization in the kernel and stem+sheath (+tassel) under the N₁₅₀ treatment increased significantly compared with the N₀ and N₇₅ treatments. In addition, nitrogen partial factor productivity of winter wheat and fresh maize under the N₇₅ and N₁₅₀ treatments increased significantly by 36.7%-534.1% and 45.2%-390.4% compared with the other nitrogen treatments, respectively, and nitrogen uptake efficiency also increased significantly by 79.1%-321.4% and 58.3%-239.5%, respectively. The yield of winter wheat and fresh maize under the N₂₂₅ treatment was the highest, which significantly increased by 54.1% and 71.6% compared with that under the N₀ treatment, respectively. In summary, nitrogen application rates of 150-225/150-225 kg·ha^-1can be potential recommended use amounts with higher crop yield and nitrogen use efficiency in winter wheat-fresh maize cropping system in the Jinzhong Basin.

nitrogen application rate, fresh maize, winter wheat, dry matter accumulation, nitrogen use efficiency