Effects of nitrogen reduction rates on grain yield and nitrogen utilization in a wheat-maize rotation system in yellow cinnamon soil

Excessive nitrogen (N) fertilizer application severely degrades soil and contaminates the atmosphere and water. A 2-year field experiment was conducted to investigate the effects of different N fertilizer strategies on wheat-summer corn rotation systems in yellow-brown soil areas. The experiment consisted of seven treatments: no N fertilization (CK), conventional fertilization (FP), optimized fertilization (CF), reduced N rates of 10% (90% FP), 20% (80% FP), 30% (70% FP), and a combination of controlled release with conventional urea at 7:3 ratio (CRU). The results indicate that under the condition of 80% FP, both CF and CRU treatments can increase the yield of wheat and corn for two consecutive years. Compared with FP treatment, the wheat yield of CF and CRU treatments increased by 3.62-2.57% and maize yield by 3.53-1.85% with N fertilizer recovery rate (NRE) of crops by 46.2-37.8%. The agronomic N use efficiency (aNUE) under CF treatment increased by 35.4-37.7%, followed by CRU, which increased by 30.5-33.9%. Moreover, compared with FP treatment, both CF and CRU treatment increased the content of organic matter (OM), total N (TN), and hydrolyzed N (HN) in the topsoil layer, and 70% FP treatment significantly reduced the HN content. Both CF and CRU treatments significantly increased the NO3 concentrations in the 0-20 cm soil depth during the wheat and maize season at maturity stages and decreased the residual inorganic N below the plow layer (40-60 cm). During the corn season, the CF and CRU treatments significantly reduced the NO3 concentration in the 40-60 cm soil layer from seedling to jointing. Considering various factors, CRU treatment under 80% FP conditions would be the best fertilization measure for wheat -corn rotation in yellow -brown soil areas.