Correlations of Phosphorus Availability by Chemical Tests With Inorganic Phosphorus Fractions

Abstract

Abstract Linear and multiple correlations are presented between and among data for 3 soil tests for available P, 4 inorganic P fractions, clay content, and pH of acid soils. Water‐soluble P was positively correlated with NH 4 Cl‐soluble P, NH 4 F‐soluble P, and negatively correlated with clay content. In a multiple correlation analysis, water‐soluble P was correlated only with NH 4 Cl‐soluble P. The P extracted by the Bray reagent was positively correlated with NH 4 Cl‐soluble and NH 4 F‐soluble P and negatively correlated with clay content. In a multiple regression analysis, an expression of the NH 4 Cl‐soluble plus NH 4 F‐soluble P as ppm. P in the clay fraction was the only significant factor. The P extracted by NaHCO 3 was positively correlated with NH 4 Cl‐soluble, NH 4 F‐soluble, and NaOH‐soluble P. In a multiple regression analysis, the NaHCO 3 ‐P was related to NH 4 Cl‐soluble, NH 4 F‐soluble plus NaOH‐soluble P in parts per million P in the clay fraction. The effect of increasing clay content in decreasing the effectiveness of the Bray and NaHCO 3 reagents to extract P from soils was related to exhaustion of the reagent in the case of the former and to exhaustion of the reagent and secondary precipitation in the case of the latter.