Effects of Delayed Nitrogen Topdressing on Grain Yield and Photosynthetic Characteristics of Flag Leaves of Wheat

Four wheat cultivars were used to study the effects of delayed nitrogen topdressing on population structure, grain yield and photosynthetic characteristics of flag leaves under high-yielding conditions. The results showed that the nitrogen topdressing delayed from overwintering-turning green stage (N1) to turning green-jointing stage(N2) and jointing-booting stage(N3) decreased ineffective tiller in spring, retarded the decline of green leaf area and chlorophyll content in late life span, promoted photosynthetic ability of flag leaves and significantly increased the grain yield. N3 treatment was suitable for most wheat cultivars except the genotypes with higher single spike productivity and less ears in unit area.