Micro-sprinkler irrigation with optimal nitrogen application enhances winter wheat yield by regulating flag leaf physiology and root growth in the Huaibei Plain

A two-year field experiment was conducted to explore the effects of conventional flood irrigation (CI), and micro-sprinkler irrigation (SI) under three topdressing nitrogen levels (N1, 45 kg·ha−1; N2, 90 kg·ha−1; N3, 135 kg·ha−1) on flag leaf physiology, root growth, and grain yield (GY) of winter wheat in the Huaibei Plain (HP). Results showed that higher N significantly decreased the soil moisture content, but SI had higher moisture than CI at the same N level. N2 and N3 significantly increased leaf area index (LAI) compared with N1, and the LAI in SI was higher than in CI. Chlorophyll content in N2 and N3 was significantly higher than in N1 during the grain filling stage, and SI further enhanced the content under the same N level—likely because higher N increased flag leaf antioxidant enzyme activity, while SI outperformed CI. At the anthesis stage, N2 had the highest root length density below 30 cm soil depth, with SI exceeding CI at the same N level. Therefore, N2 and N3 significantly increased dry matter accumulation at maturity (DMM), and the contribution rate of post-anthesis dry matter accumulation to GY (CR). SI further enhanced DMM and CR vs CI at the same N level. Compared to N1, N2 and N3 increased GY by 23.52% and 23.13%, respectively. SI significantly enhanced GY, ranging from 6.10% to 16.99% than CI. Overall, micro-sprinkler irrigation with optimal nitrogen application at jointing and booting stages effectively promoted root growth, enhanced leaf stress resistance, and delayed leaf senescence during grain filling, resulting in improved wheat yield in the HP.