Abstract:In this paper, 15N differential method was adopted to study the influences of nitrogen fertilizer levels on N loss from rice plant tissue, and the factors of affecting the N loss were analyzed. The N loss from rice tissue was studied by supplying different N rates (N 0, 40, 80 and 160 mg/L) for 10 d under solution culture. Before the treatments, the N was fed with 15N (abundance 10%), and then the 15N was substituted by normal N during the 10 d treatments. The results show that there are not significant changes in biomass for the 10 d treatments with application of different N rates, which indicates that the absorbed N at the previous stage is available to maintain the growth of rice plant for a period of time. N contents of leaves and root are increased with the increase of N levels, while the 15N abundances of leaves and root are decreased noticeably with the increase of N levels, and the 15N abundance of leaves is noticeably higher than that of root. Obviously, N absorption by plants is increased in the high N treatment, and the absorbed 15N at early stage is diluted, which indicates N is transferring from root to leaves. N deficiency (N 0 mg/L) and over N supply (N 160 mg/L) both increase N loss from plant noticeably, and appropriate N supply (N 80 mg/L) increases N utilization noticeably. The growth stages of rice affect N loss rates remarkably. Under the condition of N 80 mg/L, N loss from plant is increased from 11.6% to 22.3% with the increase of rice growth period. Meanwhile, NH+4-N contents, and GOT activities are increased with the increase of N amount, and pH values of rice leaves are also increased. These results indicate that N use efficiency N is decreased due to the N loss from rice tissue, and ammonia volatilization may be one of the reasons for the N loss.