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

Abstract

Phosphorus fractions from three highly calcareous soils (average, 24.9 ± 4.8%CO32-) from sampling sites with a Mediterranean 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 NH 4F, 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 which NaOH-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., ΔP = TP - (NH 4F-P + NaOH-P) is defined by the status of Mn- and Fe-humic complexes or by the concentration of hydroxyl-ions.