The effect of reducing conditions on the solubility of phosphorus in a diverse range of European agricultural soils

The effects of reducing conditions on solubility of phosphorus (P) can directly influence water quality. The release of P is enhanced although the P is not directly involved in reduction processes. We here compare the responses to flooding of 12 overfertilized agricultural soils in widely varying pedological and management regimes, belonging to seven World Reference Base groups. The redox potential initially ranged from 305 to 515 mV and decreased to ?157 to ?195 mV within 32 days. The onset of reducing conditions led to an increase in the concentration of soluble P. The maximum rate of solubilization occurred within 1–3 weeks under reducing conditions, and the steady‐state concentrations of P never exceeded 200 μmol dm^?3. Four stages in the development of the reduction process are identified, and a simple empirical model describes the change in concentrations of soluble P. The potential of P release under reduction is positively correlated with the soil saturation with P. Flooding over a few weeks triggered the release of large amounts of P. Constant pe + pH is related to constant concentration of molybdate‐reactive P, suggesting that soluble P is effectively buffered so that P will be immobilized. In general the solubilization of P under reducing conditions is likely to be aggravated by the increased soil P status that has resulted from overfertilization of agricultural land with P. These findings bear on the establishment and long‐term effectiveness of riparian buffer zones where phosphorus is likely to accumulate by the interception of drainage.