Inorganic phosphorus fractions in south island soils and their solubility in commonly used extracting solutions

Abstract

Abstract Inorganic phosphorus in three groups of South Island soils has been fractionated into aluminium‐, iron‐, and calcium‐bound forms. Results show that Taitapu gley soils and Waimakariri recent soils in general contain the major part of their phosphorus in calcium‐bound form; zonal soils contain a much lower proportion of this form. Highly significant relationships were found between the soil pH and the proportion of calcium‐bound phosphorus for the Taitapu soils and for the zonal soils. This relationship approached significance for the Waimakariri soils. “Available” phosphorus was determined by five different methods. Correlation and multiple regression analyses indicated that the Truog extractant removed mainly calcium‐bound phosphorus; the Bray No. 2 and Egner‐Riehm extractants both aluminium‐ and calcium‐bound phosphorus; the Bray No. 1 and Olsen extractants mainly aluminiumbound phosphorus. No extractant removed significant amounts of iron‐bound phosphorus.