Pot experiments were carried out to study the effect of nitrogen application on winter wheat under different status of soilmoisture, so that the key and sensitive stage of winter wheat responses to water and nitrogen coordination were determined.The results showed that the application of N fertilizer was more effective in early stage than in later stage, and at the lowerN rates than at the higher N rates under non-irrigated conditions. N treatments had great effect on spikelet bearing numberand grain number per spike, but had no effect on 1 000-grain weight; Grain yield and yield component responses to Ntreatment were greater under irrigated conditions than under non-irrigated conditions. The joining stage was the key andsensitive stage of winter wheat responses to water and nitrogen coordination, and the grain yield, grain number per spikeand 1 000-grain weight increased, when water and N Fertilizer were applied at this stage. The mechanism is that water andfertilizer supply at joining stage can speed up the growth of above-ground crops, enhance the abilities to absorb andutilize nitrogen fertilizer, and meanwhile, delay the aging of the root and keep the root vigor for a longer period.
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