Evaluation of Nitrogen Removal in Paddy Fields at a Watershed Level

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  • 流域レベルでの水田の窒素除去量評価に関する研究
  • リュウイキ レベル デ ノ スイデン ノ チッソ ジョキョリョウ ヒョウカ ニ カンスル ケンキュウ

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A high nitrate nitrogen concentration in leaching water from a tea field is observed in Japan. A small river called the Tanno River is located in a watershed where a tea field is caltivated. There are paddy fields along the Tanno River and denitrification occurs there during irrigation period. The authors and the Ministry of Agriculture and Fishery measured the discharge and water qualities at four poins on the Tanno River and measured denitrification rate at three paddy fields. The authors simulated the discharge and N concentration for the four points using the water quality tank mode (WQSTM), which takes into account the denitrification of paddy fields and N accumulation in soils. The authors also simulated the water qualities for the four points and evaluated the quantity of N removed from the on the basis of the obtained results. An aerial ratio of the paddy field to the tea field is 19.6% in the watershed, and the rate of nitrogen removal reached 41% during the irrigation period. The annual average rate of N removal was 14%. Moreover, the authors demonstrated that a future change in N concentration can be predicted by this WQSTM.


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