Effect of water and nitrogen coupling on leaf senescence and yield of Zhengmai 9023wheat during the grain-filling stage

Soil moisture and nitrogen nutrients are the principal factors affecting crop production.Elucidation of their influences and coupling effects would have great significance for optimizing yield and input efficiencies.Domestic and foreign scholars have conducted extensive research on interactions between water and fertilizers but most research to date has focused on soils rather than plant effects and the conclusions are not consistent.The purposes of this study were to investigate leaf senescence and yield differences in crops grown under conditions of nitrogen and water coupling.Three nitrogen levels of no nitrogen(N1),200 kg N/ha(N2),300 kg N/ha(N3)and two irrigation regimes of irrigation control(W1),water stress conditions(W2)were trialed in the field during the grain-filling stage of Zhengmai 9023,a winter wheat cultivar.Chlorophyll content,photosynthetic rate,malondialdehyde(MDA)content and relative conductivity in flag leaves,along with soluble sugar and starch in stems and grain yield,were measured at 7and 21 days after the flowering stage.The results showed that leaf chlorophyll contents and photosynthetic rates increased with nitrogen augments.However,MDA content and relative conductivity decreased in flag leaves 7days after anthesis under the same levels of water treatment.Non-structural carbohydrate content first increased and then decreased with increases in nitrogen application.Soluble sugar and starch content in stem and sheath decreased by 10.6%and 10.1% under the condition of 300 kg N/ha(N3)compared with 200 kg N/ha(N2).Chlorophyll content,photosynthetic rate,soluble sugar and starch content reduced under water stress conditions(W2)with the same nitrogen level as the irrigation control(W1),while the opposite result was observed with MDA content and relative conductivity in flag leaves,especially in the N3 treatment.These trends applied to both 7and 21 days after anthesis.Wheat yield was higher for the N2 treatments when crops were grown under the same water conditions.Compared with N1,N2 increased yields by 72.1%and N3 by 61.4%.The N3 treatment returned 6.6%less yield than N2.With the same levels of nitrogen fertilizer,water stress improved wheat production compared to the control.These results suggest that mild water stress and appropriate nitrogen applications can produce interaction effects that promote nitrate assimilation and increase yield by improving seed-setting rates and grain weight.