Iron-related phosphorus in eroded sediments from agricultural soils of Mediterranean areas

The ratio of Feca to Fecbd was higher at low sediment charge in runoff. The mean P/Fe mole ratio in citrate ascorbate extracts (essentially dissolves poorly crystalline Fe oxides) was higher in soils (0.068±0.056) than in sediments (0.022±0.009); in citrate bicarbonate dithionite extracts (dissolves oxides not reduced by citrate ascorbate), it was the same for soils and sediments (0.01). This indicates that poorly crystalline oxides with low P contents are preferentially eroded. The concentration of P fractions associated to Fe oxides in sediments decreased at increased sediment concentration in runoff, due to a decrease in Fe (ca and cbd extractable) with increasing sediment concentration in runoff.