Abstract: In recent years, excessive nutrient loss in subsurface drainage from agricultural land is identified as a major source of non-point source pollution, and has been attended globally. This study was conducted to determine the effect of nutrient leaching from paddy field in rice-planting season under different fertilizer application levels on water quality by using Lysimeter experiment. The results showed that the concentration of NH₄⁺-N in surface water raised quickly after fertilization, reached the highest in 2 or 3 days with the maximum value of 26.2 mg·L^-1,and then,dropped quickly within 7 or 10 days. The concentration of NH₄⁺-N in leachate was very low, only accounted for 0.008%～0.074% of total fertilizer applied. The nitrate content in the solution and lossed from leaching increased gradually with fertilizer application rate, with a range from 0 to 7.14 mg·L^-1. The nitrate concentration in leachate over the soil profile was characterized by a gradual increase from the top to bottom. Nitrogen was leached away mainly in the form of NO₃^--N in rice-planting season, and the net NO₃^--N loss was 3.2～8.3kg·hm^-2,accounted for 1.40%～2.78%.Under the experiment level, nitrogen leaching may lead to a potential pollution of underground water. The concentration of phosphorus in surface water reached the highest in one day after fertilization, after then dropped. The concentration of phosphorus in lower depth was very low, almost not affected by the amount of fertilizer applied. Application of pig manure could increase the transfer of phosphorus.

Key words: Nutrient leaching, Paddy field, Taihu Lake area