Solute Movement in a Field Soil1

Solute and water movement was studied under steady-state flow conditions in a field soil consisting of 70 cm of clay to silty clay over a medium sand. A steady-state water flow condition was maintained by applying irrigation water at a constant flux of 2 cm per day. During the steady-state condition some of the water leached into the plot was labelled with chloride and tritium. The positions of the chloride and tritium as functions of soil depth and time were measured by extracting samples of the soil solution with soil suction probes. Extremes in solute displacement occurred at equal and different depths within the plot. An analysis of these measurements indicated that observations of the pore-water velocity and the apparent diffusion coefficient were log normally distributed. Twenty-four soil suction probes, used to identify the rate at which a solute was displaced in the soil, will yield an estimate of the mean pore-water velocity of this soil within a range of approximately ±25% of its true value providing the effects of potential solute-soil interactions are taken into account.