Nitrate budget in the shallow unconfined groundwater of double cropped paddy area considering chemical fertilizer input

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  • SHIMADA Jun
    Graduate school of Science and Technology, Kumamoto University
  • ITO Saki
    Graduate school of Science and Technology, Kumamoto University
  • ARAKAWA Yusuke
    NARO Kyushu Okinawa Agricultural Research Center
  • TADA Kazuhiro
    Geosphere Environmental Technology Co. Ltd.
  • MORI Koji
    Geosphere Environmental Technology Co. Ltd.
  • NAKANO Kei
    Graduate school of Science and Technology, Kumamoto University
  • KAGABU Makoto
    Graduate school of Science and Technology, Kumamoto University
  • MATSUNAGA Midori
    Graduate school of Science and Technology, Kumamoto University

Bibliographic Information

Other Title
  • 二毛作水田地帯における施肥起源の窒素負荷による浅層不圧地下水中の窒素収支の検討
  • 二毛作水田地帯における施肥起源の窒素負荷による浅層不圧地下水中の窒素収支の検討 : 地下水観測結果を踏まえた地下水シミュレーションに基づいた考察
  • ニモウサク スイデン チタイ ニ オケル セヒ キゲン ノ チッソ フカ ニ ヨル センソウ フアツチ カスイチュウ ノ チッソ シュウシ ノ ケントウ : チカスイ カンソク ケッカ オ フマエタ チカスイ シミュレーション ニ モトズイタ コウサツ
  • ─地下水観測結果を踏まえた地下水シミュレーションに基づいた考察─
  • - Results of 3 D groundwater flow simulation with observed water chemistry data -

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Three years of field observations conducted of the groundwater level, nitrate concentration, and isotope ratios (δ15NNO3 • δ18ONO3) of groundwater in the Sata River alluvial fan, Asakura, Fukuoka revealed that groundwater levels fluctuated seasonally and that nitrate concentration fluctuation is affected both by paddy irrigation and timing of fertilization activities. To evaluate nitrogen behavior and its budget in the groundwater aquifer system, a three-dimensional groundwater flow coupled with convection-dispersion model was developed, incorporating detailed nitrogen load information including the fertilizing rate, timing, and effects of nitrogen uptake rate by planted crops at the ground surface for each agricultural land use. Results suggest that nitrate concentration in the studied groundwater shows clear seasonal fluctuation annually with the lower nitrate concentration around 3 mg/L. Because the nitrogen budget under the present condition shows a quasi-steady state with nitrate concentrations that cannot decrease below 3 mg/L, this concentration limit has been created by the long-term cumulative effect of the nitrogen load. The nitrogen discharge rate through the discharge flow of the groundwater from the surface of the studied alluvial fan to the lowland area outside of the study area was estimated using this model as 106 kg/ha/y.

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