Nature and distribution of soil phosphorus as revealed by a sequential extraction method followed by 31P nuclear magnetic resonance analysis

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Abstract
SUMMARY: Soil samples from long‐term plots annually fertilized with superphosphate since 1952 and also unfertilized (control) plots of an irrigated and intensively grazed pasture in Canterbury, New Zealand, were subjected to a sequential extraction procedure followed by 31P nuclear magnetic resonance (NMR) analysis of the soil phosphorus (P) forms present.Overall, 80% of the total organic P (as determined by ignition) was removed from the soil by the sequential extraction procedure. Most of the organic P (90%) detected by NMR was in the monoester fraction. Small quantities of diester and pyrophosphate were also found. Choline phosphate constituted a significant proportion (18–25%) of the monoester P in the acetylacetone and 0.5 M NaOH extracts. Long‐term superphosphate additions resulted in almost all of the P accumulated in the monoester P fraction (up to 99%).