Research on the variation of nitrogen in the rice-soil-water system under 5 different nitrogen amount treatments and their effects on environment was conducted in Yuhang experimental station of Zhejiang in 2003. The results indicated that the N content in the rice

paddy soil

surface water and leakage water were greatly influenced by different N application amounts. The N use efficiency was low

70%-80% of fertilizer nitrogen applied were transited into environment. The loss of fertilizer is very high when N applied in rice transplanting time and with high N proportion. The accumulation of soil N content in the paddy is not clear during the first three rice growth stages

but the final effect of the fertilizer on soil N in the last stage is obvious. There is no benefit to soil N if use of nitrogen fertilizer is under 150 kg/hm^2. The proportion of chemical nitrogen contributed to soil N increase account for 30 %-40 % of total chemical N entering the environment amount. The concentration of nitrogen in the surface water reached its maximum value at the first day after N fertilizer applied. The concentration of nitrogen in the surface water was greatly reduced to a CK level after one week

so a week after N fertilizer application is a critical period to avoid the N loss. The chemical N loss is very low through leakage water

but it will pollute water environment after a long time of rice cultivation when the N fertilizer amount exceeds 225 kg/hm^2.