Abstract: Pot experiments were carried out to study the effect of nitrogen application on winter wheat under different status of soil moisture, so that the key and sensitive stage of winter wheat responses to water and nitrogen coordination were decided. The results showed that the application of N fertilizer was more effective at early stage than at late stage, and at the lower N rates than at the higher N rates under non-irrigated conditions, N treatment had greet effect on spikelet bearing number and grain number per spike, but had no effect on 1 000-grain weight. Grain yield and yield component responses to N treatment were greater under irrigated conditions than under non-irrigated conditions. The jointing stage was the key and sensitive stage of winter wheat responses to water and nitrogen coordination. The grain yield, grain number per spike and 1000-grain weight increased when water and N fertilizer were applied at this stage. The mechanism is that the growth and development, absorption and application of nitrogen, and root activities of winter wheat increased when fertilizer and water were applied at this stage.

Key words: Winter wheat, Water and nitrogen coordination, The key and sensitive stage