Correlation between ion solubilty and electric conductivity in ditermination of the coefficient of plant nutrient adsorption of soil

[Author abstract]The experiments were carried out to investigate the relationship between ion solubity and electric conductivity of the equilibrated suspension of soil and ca. 2.5% neutral diammonium phosphate solution. Since it was found that a high correlation exists between the amount of P_2O_5 or N (mg/lOOg soil) sdsorbed and electric conductivity, the adsorption coefficients of phosphate and nitrogen were estimated for 37 soil sampls. Measurements were estimated for solubility of Na^+, K^+, Mg^ and Ca^ ions for 37 samples. The results are summarized as follows: 1) Ionic strength, calculated from the activities of dissolved major ions in the bulk solution, correlates with the electric conductivity of the bulk solution with a high correlation coefficient (γ=0.890). 2) The difference involved in the estimation of the adsorption coefficient from the electric conductivity data was 28.8% for phosphate and 15.3% for nitrogen. 3 )The differences are mainly attributed to the precence of unbalanced phosphate ion species in the treated soil samples. The large difference for phosphate compared with that of nitrogen suggests that the method is not suitable for phosphate. No signifficant difference was observed for cations, Na^+, K^+, Mg^ and CA^, provided their concentrations are low. 4) Not only the major ions in the bulk solution, but also many other ions were dissolved through soil reaction. Especially, higher solubility of Na^+, K^+, Mg^ ion in the bulk solution than that in the water extracted treatment of the same soil was recognized. 5) The solubility of Ca^ in the bulk solution was less than that in water extraction of the same soil. However the variation of Ca^ solubility was the lowest among the analysed cations in the bulk solution.[著者抄録]土壌によるリン酸およびアンモニウムの吸着を常法(2.5%リン酸二アンモニウム溶液を中性に補正した液を使用)に準じて行ない、吸着平衡液の成分溶存性を電気伝導度の性質と関連づけた。さらに処理液の電気伝導度から吸着成分量の予測可能性が現われたので、37種類の土壌について予測値の検討を行なった。また本平衡液中の主要イオン以外の溶存塩基について調べた。それらの結果を以下のように要約することができる。1. 成分吸着平衡後の外溶液中の主要イオンH_2PO_4^-、HPO_4^、NH_4^+の各活量より算出したイオン強度はそれらの外液の電気伝導度と有意な相関があった。2. 処理外液の電気伝導度より推定した養分吸収係数の差異は実測値に対してリン酸では平均28.8%、窒素では平均15.3%であった。リン酸の値が大きいのは実測値の不安定性にも原因した。3. 推定した養分吸収係数の差異はリン酸イオンの荷電のバランスの不一致性の問題が大きく影響し、外液中に溶存する主要イオン以外の共存イオンは影響が小さい。特にイオン強度中でのHPO_4^活量の占める割合が大きい場合は差異が大きいと予想された。4. 常法による処理外液中には土壌塩基が共存しているが、水浸出の場合より高いNa^+、K^+、Mg^イオンの溶存性が大部分の土壌処理区で認められた。5. 処理外液中のCa^イオンの溶存性は逆に水浸出の溶存性が高く、しかも溶存量のバラツキが測定塩基中でもっとも少なかった