導電率情報を利用した灌漑水の全窒素濃度の推定
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概要
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The information of electric conductivity (EC) was investigated as an indicator for estimating total nitrogen concentration (T-N) in irrigation water. Water quality indicators, such as T-N, EC, and concentration of metallic elements and anions, were measured at rice terraces in Hoshino village, Yame-gun, Fukuoka prefecture, Japan. The rice terraces were located in 3 different water systems. The result showed a positive correlation between EC and T-N. Thus, linear regression equations were calculated to estimate T-N by using EC as an independent variable. Coefficients of the slope and the intercept in the regression equations were different among water systems. The slope of a regression equation, which represented the rate in change of T-N against EC, was the largest in Hirouchi area, followed by Rokuri and Fujiyama areas. Next, the effect of ion concentration in irrigation water was investigated to identify the reason that the regression equations had different coefficients among water systems. T-N had a strong positive correlation with SO_4^<2->, Ca and Mg. It was examined that the correlation with SO_4^<2-> was caused by ammonium sulfate, which was used for fertilizer. The correlation with Ca and Mg was explained by elution of Ca^<2+> and Mg^<2+> from soil at the locations of high NO_3-N concentration. N0_3-N accounted for large portion in T-N in this study. Also, it was examined that trees around a water system would be a possible factor that affected soil components (ion amount). From the above consideration, it was indicated that T-N could be estimated by a linear regression equation for each water system based on the EC information.灌漑水中のT-Nを推定する方法として導電率 (EC)情報の利用を検討した.福岡県八女郡星野村の異なる3つの水系に位置する広内,鹿里,藤山地区の棚田を対象に水質調査したところ,ECとT-Nには正の相関が認められた.EC値に基づいてT-Nを推定する回帰式を求めた結果,回帰式の傾き,切片は水系ごとに異なり,傾き,すなわちEC値に対するT-N の変化割合は,広内,鹿里,藤山の順に大きかった.回帰式の係数が水系ごとに異なる要因として,水中のイオンの影響を考察した.T-Nに対する陰イオンおよび金属元素の濃度変化をみると,SO_4^<2->,Caおよび Mgで正の相関がみられた.SO_4^<2->との相関は,肥料として使われた硫酸アンモニウムの影響と考えられた. Ca,Mgとの相関については,本研究において,T-N のうちNO_3-Nが占める割合が大きかったことから, NO_3-N濃度が高い地点で土壌からCa^<2+>,Mg^<2+>が溶出したためと考えられる.また,水系周辺の樹木が土壌成分(イオン量)に影響を与えている可能性も考察 された.以上の結果から,水系ごとにEC値とT-Nの関係について線形回帰式を求めることにより,T-Nを推定し得ることが示唆された.
- 2008-10-29