Chemical nature of organic phosphorus in cultivated and uncultivated soils under different environmental conditions

SUMMARY A sequential alkali extraction procedure followed by ultrafiltration and quantitative 31P nuclear magnetic resonance (NMR) spectroscopy was used to examine organic phosphorus in a Brown Chernozem, and an adjacent Gleysol developed under native prairie vegetation, and a Grey Luvisol formed under aspen forest in Saskatchewan, Canada. Differences in the nature of organic P in the native soils were related to moisture status and vegetation. In the grassland soils, a greater proportion of orthophosphate diester P was found in the bottom-slope Gleysol. This difference was partly attributed to less favourable conditions for mineralization in the bottom slope soil compared with the mid-slope Brown Chernozem. Teichoic acid P occurred only in the native Grey Luvisol (NMR δ p.p.m. 0.36-0.95) under boreal forest and not under native grassland. At all three sites, soils under long-term cultivation were also examined and while orthophosphate monoester P (83.4-94.6% total Po), orthophosphate diester P (3.9–8.7% total Po) and teichoic acid P (12.7% total Po in forested Grey Luvisol) were detected in native soils, only orthophosphate monoester P was found in the corresponding soils that had been cultivated for 70–80 years. These findings suggest that orthophosphate diester P and teichoic acid P are more readily mineralized in the soil environment than orthophosphate monoester P forms.