Effects of Nitrogen Fertilizer Reduction Combined with Foliar Fertilizer Application on the Physiological Characteristics and Yield of High-Quality Japonica Rice

High-quality japonica rice, distinguished by its unique flavor and enriched nutritional value, has attracted significant attention across Asia. The over-application of nitrogen (N) fertilizers, however, is a growing concern, threatening both the rice quality and the environmental sustainability of its production. This situation calls for a reevaluation and modification of traditional agricultural practices. Our study investigates the effects of reduced N fertilizer use, complemented by foliar fertilizer application, on the physiological attributes and yield of high-quality japonica rice. The aim is to achieve efficient N use and enhanced crop productivity. The experiment employed ‘Sujing 1180’, a high-quality japonica rice cultivar, utilizing urea as the N source and a comprehensive macronutrient-rich water-soluble fertilizer for foliar application. Five treatments were established: conventional N application (270 kg ha − 1 , N 100 ), 10% N reduction (N 90 ), 10% N reduction with foliar application (N 90 + FF), 20% N reduction (N 80 ), and 20% N reduction with foliar application (N 80 + FF). These treatments were meticulously examined throughout various growth stages. Photosynthetic parameter analysis indicated that N 90 + FF significantly boosted the net photosynthetic rate during the heading stage. N 80 + FF maintained higher stomatal conductance at the maturity stage, suggesting that foliar fertilizer is effective in enhancing photosynthetic efficiency and stomatal conductance. In terms of N metabolism, N 90 + FF notably increased the accumulation of nitrate N during the jointing stage, surpassing other treatments. While N 90 and N 80 showed reductions in both nitrate and ammonium N levels compared to N 100 , N 90 + FF was particularly effective in elevating nitrate and ammonium N as well as free amino acid concentrations. Regarding N fertilizer efficiency, N 90 + FF surpassed N 100 across several critical parameters, specifically total N absorption, N recovery efficiency, N agronomic efficiency, and N physiological efficiency. Significantly, N 90 + FF showed marked improvements in both N agronomic efficiency and N partial factor productivity. In examining yield and its components, the N 90 + FF treatment achieved a higher yield of 9872.48 kg ha − 1 , surpassing the 9383.75 kg ha − 1 of N 100 . N 90 + FF had better results in seed-setting rate and average grain number per panicle, with its 1000-grain weight similar to that of N 100 . The N 90