SOLUTE DISPERSION IN SANDY SOIL AS AFFECTED BY WETNESS, INFILTRATION, AND EVAPORATION REGIMES

Abstract

We investigated the effect of initial soil water content (θi) and single (continuous) or split application of a fixed amount of water on the displacement and distribution of a surface-applied chloride slug in loamy sand and sandy loam soils under two potential evaporation rates, viz., 10 and 15 mm day−1] approximated by free water surfaces. During infiltration, we added salt-free water at 1.0 cm h−1]. For the split application, water applied at 1-week intervals and the total period of evaporation were kept equal to those for the single application. Irrespective of evaporation rate, the chloride (Cl) peak occurred at a shallower depth when θi was increased from 0.008 to 0.05 cm3] cm−3] in loamy sand. In sandy loam, an increase in θi from 0.05 to 0.10 cm3] cm−3] did not affect the occurrence of the Cl-peak, but the solute dispersion was larger with higher θi. For equal water application and θi, the depth of the solute peak decreased with increasing E0 to 15 mm day−1]; this effect was more pronounced in loamy sand soil. For otherwise comparable conditions, an appreciable amount of salt was transported back to the soil surface during evaporation when (1) a small amount of water was added, (2) displacing water was applied in two rather than in one installment, and (3) the columns were subjected to higher E0. In all cases, the solute was displaced deeper with a single than with a split application of water.