Effects of nitrogen application rate on the accumulation of C assimilates after flowering and water-nitrogen use efficiency of wheat under supplemental irrigation based on soil moisture.

This study aimed to explore nitrogen fertilizer management measures to synergistically improve wheat yields and water and nitrogen use efficiency under supplemental irrigation based on soil moisture in the Huang Huai winter wheat area. Wheat variety "Yannong 1212" was used as the test material. There were three nitrogen application levels, 150 kg·hm (N), 210 kg·hm (N), and 270 kg·hm (the conventional nitrogen application rate in the Huang Huai winter wheat area, N), with the relative soil water content of 0-40 cm of each treatment was supplemented to 70% at the jointing and flowering stages. We investigated the effects of nitrogen rates on photosynthetic characteristics of flag leaves after flowering, C assimilate accumulation and transport, and water and nitrogen use efficiency after flowering of wheat. The results showed that photosynthetic capacity of flag leaves in the N and N was significantly higher than that in N 14-35 days after flowering, and that there was no significant diffe-rence between N and N treatments. The C isotope tracing results showed that the translocation amount of C assimilates in vegetative organs in N was 12.1% and 7.1% higher than that in N and N, respectively. The distribution amount of C assimilates in grains at maturity was 10.1% and 5.3% higher than that of N and N, respectively. The amount of nitrogen fertilizer affected water consumption, water consumption proportion, and total water consumption in different growth stages of wheat. Water consumption during the whole growth period showed no difference between N and N treatments, but both were significantly higher than that for N. Water consumption and water consumption proportion of N were higher from the jointing to maturity stages, water use efficiency of N was 7.5% and 4.8%, and grain yield was 4.7% and 10.9% higher than that of N and N treatments, respectively. The partial productivity of nitrogen fertilizer was 34.6% higher in the N than that of N. Considering wheat grain yield and water and nitrogen use efficiency, 210 kg·hm nitrogen application was the best rate under water-saving condition of supplementary irrigation after soil moisture measurement in the study area.