Transport times of dissolved inorganic phosphate in soils

An empirically based equation is proposed for calculating the decrease, relative to water, of the mobility of phosphate in columns of soil, with increasing distance travelled and decreasing flow rate. The equation requires experimental determination of two parameters: the ratio of added phosphate in adsorbed and mobile phases of a soil, 1 d after an addition, and a coefficient determined by the decrease in rate of adsorption of phosphate with time. Breakthrough times of phosphate were obtained from leaching step increases in the concentration of dissolved phosphate through saturated columns of soil for a wide range of concentrations, rates of Bow, soils, and column lengths. Calculated and experimentally observed mobilities of phosphate, relative to water, appear to fit a log-linear relationship. This relationship allows prediction of mobilities of phosphate in soils at rates of Bow and for distances travelled that are representative of field conditions.