The forms of inorganic phosphorus extracted from soils by N sulphuric acid

Abstract

Values for the amount of inorganic phosphorus extracted by N H₂SO₄ (P_a) from a range of New Zealand soils were compared with certain forms of inorganic phosphorus, determined by a fractionation procedure.

P_a exceeded acid-extractable Ca-P for all samples. The P_a fraction was composed of acid-extractable Ca-P plus a part of secondary inorganic phosphorus. For weakly weathered soils, P_a exceeded the sum of acid-extractable Ca-P and non-occluded P, whereas in strongly weathered soils, in which acid-extractable Ca-P was absent, non-occluded P exceeded P_a.

The decline in Ps with increasing degree of soil development was attributed to loss by leaching, conversion into organic phosphorus, and conversion into occluded forms of inorganic phosphorus.