Abstract

The phosphorus distribution in soil (<2 mm) and in clay size separates (<2 mu m) of two uncultivated volcanic soils from southern Chile (one Ultisol and one Andisol) was studied by phosphorus-31 nuclear magnetic resonance spectroscopy (31P-NMR). The total P content ranges of the Ultisol samples were 733-1108 mg kg-1 (soil) and 746-896 mg kg-1 (clay), lower than 2163-2216 mg kg-1 (soil) and 2683-3362 mg kg-1 (clay) obtained for Andisol samples. In both fractions the 31P-NMR spectra of a single alkaline extraction, using 0.25 M NaOH and Chelex 100, showed the presence of inorganic orthophosphate, monoester-P, diester-P and pyrophosphate. Phospholipids-teichoic acids P were observed, but only in the clay size separates of the Andisol. Important differences in spectra of soils and clay size separates were observed only in samples with high organic matter content. The clay size separates enriched with organic matter have more and better defined signals of organic P forms. This allows the identification of P forms that might not be detected by 31P-NMR in the whole soil extracts