Phosphorus in the fulvate fraction of soil organic matter

The concentration of phosphorus in preparations of fulvic acids separated from soils according to a modified IHSS method varies from 0.03 to 0.23%; it is considerably lower than the concentration of phosphorus in preparations of humic acids (0.15-1.54%). A predominant part (> 90%) of phosphorus-containing compounds in the fulvates is not sorbed on the polymethylmethacrylic resin Supelite DAX-8 used for the isolation of fulvic acids. These compounds are highly hydrophilic, and their sorption on the polystyrene-divinylbenzene resin XAD-4 used for the isolation of nonspecific organic compounds with a lower molecular weight and higher hydrophily does not exceed 20%. The results of the study attest to the quantitative indefiniteness of the notion of "phosphorus of fulvic acids" and cause doubt upon a hypothesis about an important role of fulvic acids in the migration of phosphorus compounds in soils and landscapes.