Effects of stover mulching combined with N application on N use efficiency and yield of summer maize in Hetao Irrigated District

To explore the dynamic response of nitrogen transport of summer maize and distribution of soil nitrate nitrogen to different straw mulching methods and nitrogen application, the orthogonal field experiments were carried out in Hetao Irrigation District in 2017 and 2018. Two different straw mulching methods were set up including the straw surface covering treatment B and the straw deep burial treatment S. Four different nitrogen application rates were designed including no nitrogen application rate(N0), low nitrogen application rate treatment (N1), medium nitrogen application rate treatment (N2) and high nitrogen application rate treatment (N3). The traditional farming mode was used as contrast (CK) treatment. The results showed that in the soil layer between 0 and 100 cm, the accumulation of soil nitrate nitrogen increased with the increase of N application rate in each treatment. The B treatments significantly increased nitrate nitrogen content in 0-20 cm soil layer, and the straw deep burial treatments significantly increased nitrate nitrogen content in 20-40 cm soil layer (P<0.05). With the increase of the soil depth, the accumulation of soil nitrate nitrogen increased first and then decreased by treatments S, while the accumulation of soil nitrate nitrogen decreased first and then increased by the straw surface covering treatments. No significant difference in soil nitrate nitrogen accumulation and loss was found between the straw surface covering treatments and CK treatment, but the straw deep burial treatments significantly reduced nitrate nitrogen accumulation and loss. In the soil layer of 0-100 cm, compared with summer maize jointing stage, the cumulative loss of nitrate nitrogen of SN2 treatment at the mature stage of summer maize was 39.6% lower on average than that in CK, which reduced the NO3--N migration to deep soil and reduced the risk of groundwater pollution. Significant difference in nitrogen accumulation was found among different organs of summer maize. The interaction effects of straw mulching and N application rate on nitrogen absorption and utilization, transport and distribution and summer maize yield were significant (P<0.05) or extremely significant (P<0.01), respectively. The straw mulching increased the nitrogen utilization efficiency, and the contribution rate of nitrogen transfer of summer maize to grain yield. And straw deep burial effect was better than the other treatments. Compared with the straw surface covering treatment and CK, the straw deep burial treatment significantly improved the N absorption and utilization and summer maize yield. The SN2 treatment showed the best effect. No significant difference in N absorption and utilization and summer maize yield was found between the straw surface covering treatments and CK. Compared with CK, the SN2 treatment improved the N utilization efficiency by 28.5%, the contribution rate of nitrogen transfer in summer maize to grain yield increased by 32.1%, and increased the yield by 9.3% on average during the two years. Based on the comprehensive analysis, the effect of straw deep burial treatments combined with medium nitrogen application rate was best, which can achieve the goal of increasing summer maize yield and reduce the risk of NO3--N leaching in Hetao Irrigated District. The research provides a technical support for straw resource utilization, alleviating agricultural non-point source pollution, optimizing tillage and fertilization patterns in Hetao Irrigated District.