Phosphorus in calcareous soils. I. —The inorganic phosphate fractions and their relation to the amount of calcium carbonate present

Abstract In a fractionation study with six calcareous soils varying widely in carbonate content, it was observed that the amount of the different inorganic phosphate fractions expressed as a percentage of the total soil phosphorus decreased in the order ‚inert’︁ phosphate, apatites, non‐apatitic calcium phosphates, aluminium‐bound phosphate, iron‐bound phosphate, ‚easily‐replaceable’︁ phosphate. The aluminium‐bound phosphate expressed as percentage of total soil phosphorus was significantly correlated (negatively) with CaCO3%. The proportion of the other forms of phosphate were not significantly correlated with soil CaCO3 content. The non‐apatitic calcium phosphate and the aluminium and iron‐bound phosphates accounted for a smaller proportion of total soil phosphorus in calcareous soils, than values given in literature for non‐calcareous soils. The ‚inert’︁ phosphate and the apatitic fractions accounted for a greater proportion of the phosphate in the calcareous than in the non‐calcareous soils.