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

Values for the amount of inorganic phosphorus extracted by N H 2 SO 4 (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.