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Correlations of Phosphorus Availability by Chemical Tests With Inorganic Phosphorus Fractions¹

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 NH₄Cl-soluble P, NH₄F-soluble P, and negatively correlated with clay content. In a multiple correlation analysis, water-soluble P was correlated only with NH₄Cl-soluble P. The P extracted by the Bray reagent was positively correlated with NH₄Cl-soluble and NH₄F-soluble P and negatively correlated with clay content. In a multiple regression analysis, an expression of the NH₄Cl-soluble plus NH₄F-soluble P as ppm. P in the clay fraction was the only significant factor. The P extracted by NaHCO₃ was positively correlated with NH₄Cl-soluble, NH₄F-soluble, and NaOH-soluble P. In a multiple regression analysis, the NaHCO₃-P was related to NH₄Cl-soluble, NH₄F-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 NaHCO₃ 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.

¹ Paper No. 1480 University of California Citrus Research Center and Agricultural Experiment Station, Riverside.

² Associate Chemist and Associate Biometrician, respectively.

Received for publication February 20, 1963. Accepted for publication May 6, 1963.