The chemical characteristics of soil which determine phosphorus partitioning in highly calcareous soils

Phosphorus fractions from three highly calcareous soils (average, 24.9 ± 4.8 %CO32-) from sampling sites with aMediterranean climate were isolated by sequential extraction. In order to provide a more reliable basis for the definition of the obtained P-fractions, principal component analysis was applied and from the chemical characteristics of the 14 investigated soils, those characteristics which define the content and association features of the P-fractions were assessed. The soils are characterized by a relatively high pH (8.0 – 8.2) and by significantly differing contents of organic mater, acid-soluble Mg and total P. These differences affected the various association features of the P-fraction with the soil constituents. The NH4F–P fraction (isolated with 0.5 M NH4F, pH 8.2) is defined by the contents of the main metals of the oxide–hydroxide–clay associations (Al, Fe,Mn) or by the the redox potential (Eh) of Mn. The accumulation of NaOH–phosphorus (extractable with 0.1M NaOH) depended on the constituents of the oxide–hydroxide–clay association, the humic substances and Eh-related factors. In those soils in whichNaOH–Pis defined by the oxide–hydroxide–clay assoiation, the participation of Fe as a bridge-forming metal is proposed. The main part of total P, i.e., DP = TP – (NH4F–P + NaOH–P) is defined by the status of Mn– and Fe–humic complexes or by the concentration of hydroxyl-ions.