Effects of Straw Return and Nitrogen Fertilization on Grain Yield and Leaf Senescence of Maize in Northeast China

Northeast China (NC) has significantly contributed to grain production in China. However, in recent years, NC has also faced the challenges of gradual soil degradation and excessive straw burning. Our study explored the impact of the maize (Zea mays L.) straw deep-plowing into the topsoil layer, combined with nitrogen (N) fertilization, on the yield and leaf senescence of spring maize in NC. This study was conducted from October 2019 to October 2021 and comprised six treatments: no straw returning (S0N0), half straw returning (7.5 t ha–1, S0.5N0), and full straw returning (15 t ha–1, S1N0) without N fertilizer; no straw returning (S0N200), half straw returning (S0.5N200), and full straw returning (S1N200) with 200 kg N ha–1. The result indicated that (1) the grain yield and yield components were not affected by straw returning in 2020–2021. However, the 1000-kernel weight was reduced by 6.5% and 9.0% in S0.5 and S1 in 2021 compared to S0. The grain yield, kernel number per ear, and 1000-kernel weight in N200 increased by 28.7%, 9.0%, and 9.9% compared to N0, respectively. (2) N fertilization raised the leaf area above the ear, leaf area index, leaf N uptake, and the leaf green value (SPAD) by 9.8%, 6.7%, 40.1%, and 12.3%, respectively. (3) The leaf senescence equation (R2 = 0.61–0.99) indicated that the mean rate of decrease in the SPAD of leaves was higher in S0.5 and S1 than in S0 by 21.0% and 31.0%, respectively. Overall, straw returning in NC combined N fertilization could stabilize grain yield in the short term, however, leaves in the maize canopy were susceptible to N deficiency by straw returning. Thus, strategic straw management based on choosing an appropriate application of N fertilization and integrated agronomic practices may be a promising approach to raise the radiation utilization efficiency and delay leaves senescence in the canopy, thus sustaining the benefits of straw management.