Numerical analysis of the nonsteady transport of interacting solutes through unsaturated soil: 2. Layered systems

Transient one-dimensional vertical transport of interacting solutes through a saturated-unsaturated stratified soil profile during infiltration was studied using a modified version of the transport model described in part 1 [Russo, this issue], taking into account the depth variations of the coupling interacting soil input parameters. The solute transport was analyzed for two sequences of soil layering: a fine-textured soil overlying coarser textured soils and a coarse-textured soil overlying finer textured soils. Each sequence was analyzed for two different initial conditions and a given surface boundary condition pertinent to a common irrigation practice using nonsaline water. Results of the analyses suggested that the effect of soil-matrix-soil-solution interactions on the transport of water and solutes may be significant and generally depends on the sequence of the soil layering and on the shape of the initial soil solutions's sodium adsorption ratio (SAR) profile. For a given initial soil solution's SAR profile the effect of soil-solution-soil-matrix interactions on the transport process is greater when a fine-textured soil is overlying coarser textured soils. For a given sequence of layering the movement of the interacting solutes may be retarded or accelerated relative to a reference inert state, depending on the shape of the initial soil solution's SAR profile relative to the sequence of the layering. The possible effects of soil-solution-soil-matrix interacting on the spatial variability of solutes on a field scale are discussed briefly.