Stability and mineralization of organic phosphorus incorporated into model humic polymers

Abstract

The stability of the phosphate ester linkage in phosphoserine (PS) and phosphoethanolamine (PE) was evaluated after incorporation of these compounds into model humic polymers. Humic polymers prepared by oxidation of a mixture of substituted phenols in the presence of either PS or PE resulted in model humic materials containing from 0.25 to 0.94% P, values within the range found for organic P in natural soil humic materials. The organic P contained in model humic polymers was resistant to hydrolysis with 1 n HC1 and 1 n NaOH and resistance of the P ester to hydrolysis with 6 n HCl was increased through incorporation into model humic polymers. Organic P in model humic polymers was also stabilized towards hydrolysis with acid and alkaline phosphomonoesterases. Less than 11% of the organic P in polymers containing PS and PE was hydrolyzed by acid or alkaline phosphatase. The incorporation of PE into a model humic polymer markedly reduced the amount of P mineralized during incubation in soil when compared to P mineralized in soils treated with PE. For all environmental conditions imposed during soil incubations (i.e. pH, aeration, temperature), only 20% of the P in model humic polymer containing PE was released during a 16-week period. In contrast, > 60% of the P in either PS and PE added individually to soils or PS and PE intimately mixed with preformed model humic polymer and then added to soils was released during the initial 7 days of soil incubation. The results suggest that a portion of the unidentified organic P in soils may arise from the incorporation of organic compounds containing both amine and phosphate ester functional groups into humic materials and that the organic P thus formed is resistant to both chemical and enzymatic hydrolysis.