Relative Movement and Soil Fixation of Soluble Organic and Inorganic Phosphorus

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Abstract
There is considerable concern about pollution of surface waters with P. Although most of the research has focused on inorganic P in surface runoff, it has recently become possible to easily follow the fate of soluble organic P forms in soils and waters. Two experiments were performed to compare the relative mobility and soil fixation affinity of orthophosphate monoesters, orthophosphate diesters, and soluble inorganic P. We used three P substrates, 4‐methylumbelliferyl phosphate (MUP), deoxyribonucleic acid (DNA), and KH2PO4 in (i) a soil column experiment and (ii) a soil P adsorption test tube experiment. Shortly after columns were prepared, approximately two pore volumes of 0.005 M CaCl2 were passed through 25 cm length columns containing 10 cm of loamy sand amended with approximately 10 mg P as MUP, DNA, or KH2PO4 above 15 cm of nonamended loamy sand. The total net quantity of 757.8 μg P 2L−1 of orthophosphate diesters in the leachate from the DNA columns exceeded the net quantity of orthophosphate monoesters in leachate from the MUP columns (4.6 μg P 2L−1) and soluble inorganic P from the KH2PO4 columns (34.0 μg P 2L−1). Adsorption of soluble organic and inorganic P in the test tube experiment yielded similar results: DNA, containing orthophosphate diesters, had a relatively low affinity for soils. In both experiments, high concentrations of other P compounds were identified in samples treated with organic P substrates, suggesting enzymatic hydrolysis by native soil phosphatase enzymes. These findings indicate that repeated application of organic forms of P could lead to significant leaching of P to ground water.
Funding Information
  • USDA CSREES
  • Agricultural Experiment Station (#VT-PS-01003)

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