Abstract: A study of the effect of excessive nitrogen application during different growing stages on the growth and stress resistance of winter wheat was conducted from 1984 to 1985. The results are as follow:1. Excessive application of N fertilizer during the early growing stage of winter wheat is the main cause for large field population, long basal interno-des, low heading percentage, small size of ears and grains, low 1000-grain weight and retardation of growth.Therefore, the early growing stage is "the critical period of fertilization" (or "the sensitive period of N excess" ,which may cause late-ripening and lodging.2.Both non-application of N or proper application of basal N during the early-growing stage, and heavy application of N during the middle and late growing stages do not cause late ripening and lodging.They can increase the efficiency of photosynthesis,stress resistance and heading percentage, and raise grain weight and dry matter production to 90% of the total seed production. Therefore, the jointing period either can be called "the maximum efficiency period of N" or "the sensitive period of N defficiency" , which is the safe and economical period of fertilization.

Key words: Winter wheat, Growing stages, Nitrogenous fertilizer, Adversity resistance