Characterization of Chemical Phosphorus Forms in Volcanic Soils Using ³¹P-NMR Spectroscopy

Abstract

Abstract Phosphorus (P) is rapidly immobilized in Chilean volcanic soils and its availability to plant is greatly reduced. Chemical forms of P accumulated in soils would eventually determine its availability of plants and its potential to cause pollution in water bodies down stream. To characterize different chemical P species, we carried out chemical fractionation and 31P-Nuclear Magnetic Resonance (NMR) spectroscopy analyses for 10 volcanic ash-derived soils in central southern Chile. Phosphorus in the alkaline extracts of soils at 0–15 cm and 15–30 cm depth was characterized by 31P-NMR. The 31P-NMR results indicate that inorganic-P and monoester-P are the most important P forms in all soils. The diester-P and pyrophosphate were also found in some soils. The patterns of P distribution in the 0–15 and 15–30 cm were essentially the same; the signal intensities were usually stronger in the upper samples. The amounts of organic- and inorganic-P determined by 31P-NMR method correlate with those by the chemical fractionation procedure. Furthermore, the organic P of soils, calculated from NMR signals, correlates with the organic matter content of the soils (r = 0.82, p < 0.01). Those results suggest that the observed 31P-NMR signals represent the P forms in soils. Keywords: Chilean volcanic soilsOrganic phosphorusInorganic phosphorusChemical P forms Acknowledgments This study was supported by DICYT-USACH and the University of California, Riverside. M. Briceño acknowledges the financial supports provided by CONICYT to her graduate program.