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

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