4. Implications

• Calcareous irrigated arable soils of the western US contain only small amounts of organic P, but some of these compounds are soluble and occur in forms that are readily degraded by common soil phosphatase enzymes.

• Soil organic P may, therefore, make an important contribution to plant nutrition in soils that are low in soluble orthophosphate.

• Concentrations of organic P in these soils appear to be controlled by a balance between the potential for stabilization in the soil and the suitability of the environment for biological activity.

• Despite the highly calcareous nature of the soils, calcium carbonate was apparently of minor importance in controlling organic P accumulation.

• Results from NMR spectroscopy suggest that soil organic P in alkaline extracts may be over-estimated by conventional colorimetric procedures.
  

Acknowledgement: NMR analysis was performed at the Stanford Magnetic Resonance Laboratory with support funding from the Stanford University School of Medicine.

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