Effect of reaction-rate on leaching of phosphate through sandy soils of Western-Australia

Abstract

The effect of reaction rate on the mobility of phosphate in soils was measured from breakthrough curves in the leachate from small columns of soil, following step increases in the input concentration of phosphate. Average mobilities of phosphate in columns of soil, following a step increase in the input concentration, decrease with decreasing rate of flow and with increasing distance travelled and appear to be linearly correlated on a log-log scale with both flow rate and distance travelled. An empirical equation, describing these relationships, fits data from leaching experiments at flow rates between 30 and 600 cm/day in columns of soil ~10-30 cm in length. Two coefficients are required and are obtained by curve fitting breakthrough curves, calculated with a numerical computer simulation model, to experimental breakthrough curves. The fitted equation enables extrapolation to flow rates and distances travelled that are more relevant to a field situation.