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Nitrogen balance in the regional scale which was calculated the difference between nitrogen input and output was estimated to assess the impact of rice cultivation on water environment. Nitrogen balances in Gyeonggi province, where nitrogen concentration in irrigation water was high and in Chungnam province, where nitrogen absorbtion by rice was high, were -5.4 and -8.3 kg ha-1 yr-1, respectively. Nitrogen balances of paddy field in Gangwon province, where nitrogen output was small and irrigation water was clean, and in Gyeongnam province, where organic matter content of soil was high and rice yield was low, were 4.9 and 14.0 kg ha-1 yr-1, respectively. Average nitrogen balance and total nitrogen absorption of paddy field in Korea were estimated to -0.3 kg ha-1 yr-1 and -3,315 Mg yr-1, respectively. When the nitrogen concentration in irrigation water was increased by 1 mg L-1, nitrogen balance of rice paddy changed by -2.91 kg ha-1 yr-1. Also, when nitrogen fertilizer applied was decreased from 110 to 90 kg ha-1 and the same harvest was maintained, the nitrogen absorption by rice paddy from irrigation water was estimated to increase by 10,600 Mg per year in Korea. However, in cases, the harvest was reduced to either 90% or 85%, nitrogen balances were changed from -11.7 to -2.3 and 2.4 kg ha-1, respectively. These results suggest that the reduction of nitrogen fertilizer use may not always lead to a negative nitrogen balance and sustainable agriculture can achieve by not cutting down the use of fertilizer only but by reduction of fertilizer application concurrently by maintenance of harvest and by utilization of environmental characteristics such as nutrient contents in irrigation water and soils.