Chloride displacement by water in layered soil columns

The displacement of a surface slug of chloride as affected by rates of water application (v) and redistribution time in two-layered combinations of loamy sand, sandy loam, and silt loam soils was studied in 10 cm I.D., 95 cm long plexiglass columns. The salt moved deeper with a given amount of water in coarse-over-fine than in the fine-over-coarse sequence of layering. This is attributed to the low water retention of the coarse top layer and more complete and rapid redistribution of water due to greater suction in the lower fine layer. The chloride peak, after redistribution, coincided with the wetting front in the coarse-over-fine, but lagged behind it in fine-over-coarse profiles. However, the solute front coincided with the wetting front in all cases. Immediately following infiltration, salt was displaced deeper with v = 0.1 cm h-1 than with 1.0 cm h-1 (or ponding) in all combinations. But when infiltration plus redistribution times were matched for the two rates, v = 1.0 cm h-1 (or ponding) was more efficient than v = 0.1 cm h-1 in a coarse-over-fine profile, except in loamy sand-over-silt loam. In fine-over-coarse profiles both rates displaced the solute to comparable depths. The findings have implications in reducing leaching losses of nutrients.