Critical Study of the NH_4F-Extraction Method for Estimating the Amount of Available Phosphorus in Soils

Abstract

Fluoride solution have been used by some workers in U.S.A. for the determination of available phosphate in soils. We studied the item, whether the fluoride leaching method is appliable for the estimation of available phosphate in Japanese soils or not. The results are summarized in the followings : 1. In allitic soils, such as volcanogenous soils, considerable amount of P combined with Al_2O_3 was released by forming complex compounds, not by the anion exchange. 2. In volcanic ash-organic soils (Ando soils), large parts of the phosphorus that seemed to be in non-exchangeable form was leached with N/2 NH_4F solution (pH 5.62). And 50 to 80 per cent of dissolved phosphorus was in organic form. And therefore, in these soils, the fluoride method is not suitable for available phosphate estimation. 3. While, in siallitic soils, the amount of phosphorus released with the formation of complex was very small.