Characterization of phosphorus in sub-alpine forest and adjacent grassland soils by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy

We used chemical extraction methods and 31P-nuclear magnetic resonance (NMR) to investigate the effects of vegetation on the amount and structural composition of phosphorous (P) in the sub-alpine soils of central Taiwan. Chemical extraction methods were used to measure inorganic P (Pi) and organic P (Po) in main soil horizons. The soil P composition was assessed by 31P-NMR spectroscopy on alkaline EDTA-NaOH extracts. According to the results of chemical extractions, the forest soil had a higher amount of Pi than the grassland soil, which might be a result of the mineralization of Po. 31P-NMR spectra showed inorganic orthophosphate (up to 67%) and orthophosphate monoesters (up to 75%) as the major forms of P extracted in forest and grassland soils, respectively. Smaller proportions of orthophosphate diesters and trace amounts of phosphonates and pyrophosphate were found. With possible hydrolysis of P compounds during chemical extraction and slight systemic error in the processes of extraction with NMR, the results from NMR analysis are, in general, consistent with those of chemical extraction.