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 at he 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 0.1 M NaOH) depended on the constituents of the oxide hydroxide-clay association, the humic substances and Eh-related factors. In those soils in which NaOH-P is defined by the oxide-hydroxide-clay association, the participation of Fe as a bridge-forming metal is proposed. The main part of total P, i.e., Delta P = TP - (NH4F-P + NaOH-P) is defined by the status of Mn- and Fe-humic complexes or by the concentration of hydroxyl-ions.

Iz tri visoko-krečnjačka zemljišta (prosečni sadržaj CO 3 2- 24.9 ± 4.8%, pH 8.0 - 8.2), sa lokacija sa sredozemnom klimom, izolovane su frakcije fosfora sekvencijalnom ekstrakcijom. U cilju obezbeđivanja pouzdanije osnove za definisanje dobijenih frakcijafosfora (P-frakcija), primenjena je analiza principalne komponente (PC-analiza). Među 14 hemijskih karakteristika zemljišta, izdvojene su one koje definišu sadržaj pojedinih P-frakcija i prirodu njihove asocijacije sa sastojcima zemljišta. Frakcija NH 4-P (izolovana sa 0,5M NH 4F, pH = 8,2) definisana je sadržajem glavnih metala oksidne-hidroksidne-glinene asocijacije (Al, Fe, Mn) ili Eh-statusom izraženim sadržajem Mn. Akumulacija NaOH-P (ekstrahovanog sa 0,1 M NaOH) zavisila je od sastojaka oksidne-hidroksidne-glinene asocijacije, od huminskih supstanci i od faktora koji stoje u vezi sa Eh. U onim zemljištima u kojima je NaOH-P definisana sastojcima oksidne-hidroksidne-glinene asocijacije, pretpostavljeno je vezivanje fosfora preko Fe-mostova. Glavna količina fosfora ∆P = TP - (NH 4F-P + NaOH-P), u pojedinim zemljištima definisana je ili statusom Mn- i Fe-huminskih kompleksa, ili pH-vrednošću.