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Title: 見かけの塩吸収によるアロフェン質黒ボク土下層土の硝酸イオン吸着と移動遅延
Other Titles: Adsorption and retarded transport of nitrate in Andisol subsoils caused by the apparent salt sorption
Authors: 田村, 和杏 Browse this author
中原, 治 Browse this author
田中, 正一 Browse this author
加藤, 英孝 Browse this author
長谷川, 周一 Browse this author
Keywords: 硝酸態窒素
Issue Date: 5-Apr-2011
Publisher: 一般社団法人 日本土壌肥料学会
Journal Title: 日本土壌肥料学雑誌
Journal Title(alt): Japanese Journal of Soil Science and Plant Nutrition
Volume: 82
Issue: 2
Start Page: 114
End Page: 122
Abstract: 北海道を中心に採取した9種の黒ボク土下層土を用いて,NO3-吸着およびそれに伴う他のイオンの吸着・脱着収支を測定した.溶液中NO3-濃度0~14mmol L-1(0~196mgNO3-NL-1)の範囲では,供試したすべての土壌において,NO3-着は,等量の陽イオン吸着量増加を伴う「見かけの塩吸収」,すなわち,陽イオン吸着によるH+生成 2SiOH + Ca2+ = (SiO-)2・Ca2+ + 2H+ で生じた新しい陰イオン吸着基 2A1OH + 2H+ = 2A1OH2+ へのイオン吸着(Wada,1984) として起きていた.予め土壌に吸着していたSO4 2-とのイオン交換はNO3-吸着に一切関与していなかった.NO3-吸着量は平衡溶液のNO3-濃度とほぼ正比例の関係を示し,分配係数が一定の線形吸着で記述できた.得られた分配係数の値から,黒ボク土下層土ではNO3- の2.5~7割程度が固相に吸着して存在していると推定された.次いで,これらの土壌を用いたカラム試験によってNO3-流出濃度曲線を求めた.NO3-吸着実験で得られた分配係数の高い土壌ほど,水移動に対するNO3-流出の遅延の程度が大きくなった. NO3-流出濃度曲線に移流分散式の解析解を適用して求めた遅延係数は,分配係数をもとに推定した遅延係数とほぼ一致した.得られた遅延係数の値から,黒ボク土下層土では,水が1m移動する時にNO3-は0.8mから0.3m程度しか移動しないと見積もられた.以上の結果から,選択流が生じなければ,NO3-吸着の分配係数を用いることで,黒ボク土下層土のNO3-移動の吸着による遅延を予測できると結論された.
Adsorption and retarded transport of nitrate (NO_3^-) was studied using 9 Andisol subsoils in Japan. In all the soils investigated, NO_3^- adsorption in the NO_3^- concentration of 0-14mM was caused almost exclusively by the apparent salt sorption, the simultaneous adsorption of equivalent amounts of cations and anions, and was not accompanied by the desorption of indigenous sulfate through anion exchange. The NO_3^- adsorption was approximated by a linear adsorption isotherm with the distribution coefficient, K_d, ranging from 0.3 to 1.6L kg^<-1>, which suggests that 25 to 70% of NO_3^- in the subsoils were in the adsorbed phase. Nitrate transport in repacked soil columns showed increasing delay of NO_3^- breakthrough with the increase in K_d. Retardation factor, R, obtained by fitting the convection-dispersion model to the experimental NO_3^- breakthrough curves ranged from 1.3 to 3.2, and was in close agreement with that estimated from K_d for each soil. These results suggest that, in the absence of preferential flow, NO_3^- travel distance is 0.3 to 0.8 times that of water flow, and can be predicted using K_d obtained from batch adsorption experiments.
Type: article
Appears in Collections:農学院・農学研究院 (Graduate School of Agriculture / Faculty of Agriculture) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 中原 治

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