Nitrogen is very important for soybean growth.It is controversy whether additional nitrogen fertilizer needed or not in soybean production as soybean rhizobium can fix nitrogen. This experiment was carried out by using twelve soybean cultivars from different regions in 2006 and 2007.And the cultivars were divided into three groups:current Ohio cultivar, current Liaoning cultivar and old Liaoning cultivar.Urea fertilizer(0,100,200 kg/hm~2) was topdressed at soybean seedling stage.The physiology and bi...