Russo, D.

Leaching a gypsiferous‐sodic soil under different soil conditions and water qualities was investigated using the transport model of E. Bresler (1973) combined with the salinity model of C. W. Robbins et al. (1980b). Incorporating field‐measured values of the soil hydraulic properties and the dispersivity coefficient, profiles of the soil solution concentration of Cl, SO4, Ca and Na, and soil solution electrical conductivity (EC) obtained under intermittent leaching were simulated for a set of representative cases typical to gypsiferous‐sodic soils. For a given soil depth and amount of applied water the simulated soil solution concentration of chloride was affected only by the initial soil salinity and the salinity of the applied water. Simulated soil solution concentrations of calcium, sodium, and sulfate were also affected by the initial soil exchangeable sodium percentage (ESP), initial gypsum content, and the cation exchange capacity (CEC) of the soil. Sensitivity analysis of the model results suggest that soil CEC, initial soil salinity and ESP, and gypsum content have a significant impact on the soil salinity profiles during leaching. Possible applications of the combined model results for salinity control were demonstrated. Expressing the soil system response in terms of the soil solution EC, rather than the specific ion concentrations, the combinations of water quantity and quality (salinity) which yield a given soil solution EC at a given soil depth for different initial conditions and soil CEC were calculated. For a given salinity of the applied water, the amount of water required to maintain a given EC at a given soil depth increased as the initial soil salinity, soil ESP, gypsum content, and CEC rose. The calculated isosoil salinity lines can be used for economic evaluation of the least cost combination of the applied water quantity and quality which will ensure that a critical salinity at a given soil depth is not exceeded. Copyright 1986 by the American Geophysical Union.