Effect of shading on nitrogen accumulation and translocation of winter wheat with different spike types using ¹⁵N tracer technique

Shading post flowering caused by cloudy weather and the surrounding protective trees often occurs in the HuangHuaiHai Plain of China. In the present study, two winter wheat cultivars with different spike types, a largespike cultivar of Shannong8355 and a multiplespike cultivar of Jimai22, were used to evaluate the effects of shading at different grainfilling stages on nitrogen accumulation and translocation by using 15N tracer technique. There were four shading treatments, shading from day 1 to day 10 after the anthesis (T1), shading from day 11 to day 20 after the anthesis (T2), shading from day 21 to day 30 after the anthesis (T3) and no shading (T0). The results indicate that the shading at different grainfilling stages decreases the uptake and translocation of N of the two cultivars which are in the order: T0T3T2T1 The amounts of nitrogen derived from soil range from 68.0% - 71.39% and the percentages of nitrogen derived from the basal fertilizer in the vegetative organs are lower than those derived from the topdressing fertilizer. The shading at different grainfilling stages increases the absorption amount and proportion of soil N in the vegetative organs, and inhibits translocation of those to the grain. The grain yield, N uptake from fertilizer, fertilizer N use efficiency and partial factor productivity from fertilizer N at different grainfilling stages are also in order: T0T3T2T1 In conclusion, the shading at different filling stages decreases the uptake and translocation of N and grain yield, and the uptake and translocation are highest under the shading at the early filling stage and the lowest at the later filling stage. Under the same shading condition, the grain yield and N use efficiency of Jimai22 are higher than those of Shannong 8355.