Optimized split nitrogen fertilizer increase photosynthesis, grain yield, nitrogen use efficiency and water use efficiency under water-saving irrigation.

This study aims to investigate optimization of the basal-top-dressing nitrogen ratio for improving winter wheat grain yield, nitrogen use efficiency, water use efficiency and physiological parameters under supplemental irrigation. A water-saving irrigation (SI) regime was established and sufficient irrigation (UI) was used as a control condition. The split-nitrogen regimes used were based on a identical total nitrogen application rate of 240 kg ha but were split in four different proportions between sowing and the jointing stage; i.e. 10:0 (N1), 7:3 (N2), 5:5 (N3) and 3:7 (N4). Compared with the N1, N2 and N4 treatments, N3 treatment increased grain yield, nitrogen and water use efficiencies by 5.27-17.75%, 5.68-18.78% and 5.65-31.02%, respectively, in both years. The yield advantage obtained with the optimized split-nitrogen fertilizer application may be attributable to greater flag leaf photosynthetic capacity and grain-filling capacity. Furthermore, the N3 treatment maintained the highest nitrogen and water use efficiencies. Moreover, we observed that water use efficiency of SI compared with UI increased by 9.75% in 2016 and 10.79% in 2017, respectively. It can be concluded that SI along with a 5:5 basal-top-dressing nitrogen ratio should be considered as an optimal fertigation strategy for both high grain yield and efficiency in winter wheat.