Abstract: From the period before over-wintering to the period of stem alongation of the next spring, soil N-min in the 0 -90cm depth of the winter wheat fields changed as follows: Soil N-min reached the peak value, and 3/4 in the 0-60cm depth when winter wheat broke dormancy. Therefore the most suitable time for sampling soil should be the dormancy-breaking period, and the sampling depth should be 0 - 60cm for the recommendation of nitrogen fertilizer application for. winter wheat in spring. With this sampling method, the correlation between the soil N-min and the economic optimum amount of topdressing N was r= - 0.8401**(n= 11). However, the correlation between the economic optimum amount of topdressing N and the soil available N determined with the modified Conway method was r= -0.8935**. The latter was better and simpler than the N-min method. It is more suitable to the conditions in China. At the yield level, of 5250-6000kg / ha, the equation comprising the optimum amount of topdressing N and the soil available N determined by the modified Conway method was Nf = 239.4- 0.7766 (soil N) (unit: N kg/ha) .

Key words: Modified Conway method, Soil available nitrogen, Topdressing for winter wheat in spring