Studies on methods of available phosphate determination : (I) Comparative examination of Truog, Bray No.2 and HSPA methods (Department of Agricultural Chemistry)

沖縄県の土壌に対して各可給態リン酸測定法の比較の1過程として, Truog法, Bray No.2法及びHSPA法を比較検討した。Truog法とHSPA法及びBray No.2法の間に有意差がみられ, Truogリン酸はHSPAリン酸及びBray No.2リン酸より低い値を示した。HSPA法とBray No.2法の間には有意差がみられなかった。Truog法(浸出液0.002N硫酸)とHSPA法(浸出液0.02N硫酸)は, 赤黄色土壌において高い相関関係(r=0.978)がみられ, 回帰式はY=2.40X+2.20であった。Truog法とBray No.2法は, 相関関係がみられるものの, 回帰直線からはずれる土壌がみられた。また, Bray No.2法とHSPA法は相関が認められるものの, 二つのグループに分けられた。灰色台地土及び泥灰岩において, HSPAリン酸及びBray No.2リン酸はTruogリン酸より非常に高い値を示した。Truog, Bray No.2 and HSPA (Hawaiian Suger Planters' Association) methods were compared in determining available phosphate in selected soils of Okinawa. Available phosphate determined by the Truog method was found significantly lower than that determined by the Bray No.2 and HSPA methods. There was no significant difference between the levels of available phosphate with the later two methods. There was a close correlation (r=0.978) between the levels of available phosphate with the Truog and HSPA methods, and the regression equation was expressed as Y=2.40X+2.20 on red and yellow soils. There was a correlation (r=0.778) between the levels of available phosphate with the Truog and Bray No.2 methods, but some soils showed deviation from the correlation curve to some extent. There was a correlation (r=0.540) between the levels of available phosphate with the Bray No. 2 and HSPA methods, and there appeared 2 groups in the tested soils from the difference in the correlation curve. The Bray No.2 and HSPA methods indicated much higher levels of available phosphate than the Truog method when applied to Jahgaru (soils derived from marl) and Marl