Russo, D.

The effect of physicochemical interactions between the soil solution and the soil matrix on the spatial variability of the soil‐dependent variables during transient transport of mixed Na/Ca−Cl salts through the unsaturated zone of a large field‐scale soil is analyzed. The spatial variability of the soil water and solute transport properties evaluated in part I were used as inputs to a conceptual stochastic model describing one‐dimensional vertical transport of water and soil‐interacting solutes through the unsaturated zone of a spatially variable soil, viewed as a collection of vertically homogeneous and independent soil columns. Using data of the spatial distributions of pertinent soil properties from the Bet Dagan field, the transport process was simulated for boundary and initial conditions pertinent to the application of low‐salinity and low‐alkalinity waters (rain) to the surface of a saline‐alkaline soil, considering effects of the soil solution concentration and composition on the soil water and solute transport properties. The spatial variability (in terms of field averages and coefficients of variation CV) of the profiles of the soil water content θ, the chloride concentration C, and the sodium adsorption ratio SAR of the soil solution and the soil hydraulic conductivity K at given elapsed times t were presented and compared with those evaluated from simulations of the same boundary value problem where the effect of the soil solution concentration and composition on the water and solute transport properties was disregarded. Results of the analyses suggested that because of soil solution‐soil matrix interactions the field‐average movement of both the water and the solutes may be retarded and their spatial variability may be increased relative to the case where these interactions had not been considered. In the Bet Dagan field, after t = 5 hours of continuous infiltration, the field averages of the positions of the wetting front and the chloride front were retarded by 10 and 15%, respectively; the relative variabilities of the positions of these fronts were increased by 16 and 38%, respectively; and the equivalent effective dispersivity was increased by 18%, relative to the reference inert case. Copyright 1989 by the American Geophysical Union.