Using a lysimeter self-designed

the dynamic variation of nitrogen leaching and its amount loss in paddy field were studied under 5 different nitrogen treatments with controlled water irrigation systems in 2003. The result showed that NH_4~ -N and NO_3~--N concentration of the leakage water remained at a very low level during the whole growing period of rice

which were lower than 1mg/L. The main leaching form in the leakage water was dominated by NO_3~--N. Nitrogen loss from leaching increased gradually with fertilizer applications increase. After the application of fertilizer for each time

the concentration of NO_3~--N in different treatments increased rapidly during a short period and then decreased gradually. The concentration dynamic patterns of NH_4~ -N had the similar trends and regularity as NO_3~--N

but it showed the peak concentration value of NH_4~ -N exceeded that Of NO_3~--N .There were significant correlation between nitrogen fertilizer applied and the accumulative amount of NH_4~ -N

NO_3~--N and TN of the leakage water in the lysimeter of different plots and the coefficient is 0.933~*

0.984~(**)

0.982~(**) respectively. Based on the point of economy and environment consideration

it is suggested that 75~150 kg/hm~2 with N application in paddy field with sticky and higher soil fertility could be reasonable for better yield and reducing the N leaching. The period within a week after the N application was critical time to control N leaching from paddy field

especially for the first N application in paddy field.