15N tracer method was adopted to study the effects of different nitrogen forms (NH4+-N,NO3--N and NH4NO3) on the N loss of rice plant under the solution culture,and the factors affecting the N loss were analyzed.Firstly,rice seedlings were cultured in nutrient solution and fed with 15N (abundance 10%) for two weeks,and then transferred to the nutrient solution culture with different nitrogen forms for 10 d.The results showed that the rice with application NH4+-N had the highest biomass and the largest amount of N loss with the N loss rate of 17.06% compared with other nitrogen forms.The rice supplied the complex nitrogen source (NH4NO3) had no significant differences in biomass compared with that of NH4+-N,but the N loss rate decreased significantly with only 9.96%.The results indicated that the application of NH4NO3 decreased N loss of rice plant,and improved the nitrogen utilization efficiency without affecting the rice growth.In addition, NH4+ content,GOT activity and pH values of rice leaves applied with NH4+-N were higher than other nitrogen forms,indicating that ammonia volatilization resulted from the increase of NH4+ content of plant may be the main cause of the N loss of the plant.