Abstract:A pot experiment was conducted to study the nitrogen uptake,accumulation,distribution and utilization efficiency characteristics on Wancao 2(Sorghum Sudangrass hybrid)and Zea mexicana using 15N labeled technique. The results showed that nitrogen accumulation of these two cultivars increased gradually during the growth season.The nitrogen distribution ratio of leaves was the highest and reduced with harvest times increasing,while that of stalks increased gradually.Nitrogen uptake intensity of Wancao 2 enhanced gradually,and that of Zea mexican presented an odd peak curve.The ratio of nitrogen derived from fertilizer for Zea mexicana was about 97.6% to 100%,and it took on "Z" cure trend, but it decreased gradually for Wancao 2.Comparison between the two modes of nitrogen application showed that nitrogen of two grasses in the first harvest derived from basel nitrogen fertilier was 18.2% and 19.3% higher than that from nitrogen fertilizer applied at three times,and the nitrogen uptake intensity of regrowth grass was higher when nitrogen split applied at three times,however,there were no statistical difference of nitrogen harvest index between these two treatments(P=0.05).Wancao 2 could gain higher dry weight of each harvested grasses,nitrogen accumulation,content and use efficiency than Zea mexicana.In conclusion,in order to increase grass nitrogen use efficiency(NUE) and reap high quality forage grasses in practice,nitrogen should be applied at three times for Wancao 2 and as base fertilizer for Zea mexicana.