Dongliang QI ^* Si Chen Wenjun Yue Yonggang Duan

• School of Water Conservancy and Environmental Engineering, Zhejiang University of Water Resource and Electric Power, Hangzhou, China

Water-saving irrigation and the mixed application of controlled-release nitrogen fertilizer (CRNF) and common urea (CU, with relatively higher nitrogen release rate) have shown promise in improving rice yield with high resource use efficiency.However, the physiological mechanism underlying this effect remains largely unknown. This study involved a field experiment on rice in Central China, in 2020 and 2021. Two irrigation regimes were employed: alternate wetting and drying irrigation (AWD) and conventional flood irrigation (CI), with three nitrogen (N) compounding modes: 100% CU (N1), 60% CRNF + 40% CU (N2), and 100% CRNF (N3), with an equal N rate of 240 kg ha -1 . The results indicated a significant interactive effect of watering regimes and N compounding modes on net photosynthetic rate (Pn), leaf area index (LAI), SPAD value, activities of superoxide dismutase (SOD), peroxidases (POD), catalase (CAT), glutamine synthetase (GS), glutamine 2-oxoglutarate amidotransferase (GOGAT), and nitrate reductase (NR), as well as on the contents of malondialdehyde (MDA) and soluble protein in rice leaves.Compared with N1, N2 and N3 increased the Pn, LAI, SPAD value, activities of SOD, POD, CAT, NR, GS, and GOGAT, and soluble protein content, but decreased MDA content in the post-growth (heading and maturity) stages by 8.7%-31.2% under the two irrigation regimes. Compared to CI, AWD had higher Pn, LAI, SPAD value, activities of SOD, POD, CAT, NR, GS, and GOGAT, and soluble protein content (increased by 12.1%-38.0%), and lower MDA content (reduced by 13.1%-27.6%) irrespective of N compounding modes. This suggested that AWD combined with N2 and N3 could delay the leaf senescence of rice, thus achieving a larger grain yield. Moreover, AWD significantly decreased water costs (irrigation amount) and labor costs (irrigation frequency), thus increasing total income. N2 decreased fertilizer costs with a higher or comparable total income compared with N3.Therefore, the AWDN2 treatment achieved the highest net income (13907.1 CNY ha -1 in 2020 and 14085.7 CNY ha -1 in 2021). AWD interacted with 60% CRNF + 40% (N2) to delay leaf senescence by improving photosynthesis, antioxidant defense system, osmoregulation, and N assimilation, contributing to high grain yield and net income in rice.