Simultaneous Transport of Surface‐Applied Salts and Water Through Unsaturated Soils as Affected by Infiltration, Redistribution, and Evaporation

A study, conducted in soil columns and involving three texturally different initially moist and dry soils, verifies certain concepts regarding simultaneous transport of surface‐applied salts and water under transient unsaturated flow conditions. Calcium chloride, spread on the soil surface, was leached with water under transient and steady infiltration conditions. Salt and water profiles were determined immediately following infiltration and after matching total infiltration, redistribution, and evaporation times. Chloride was leached more efficiently and to relatively deeper depths with lower than with higher rates of water application only in sandy and sandy loam soils. Appreciable chloride accumulation occurred during evaporation in surface layers of these soils in columns initially leached with continuous ponding of water. Irrespective of water application rates, nearly no upward movement of salts occurred in clay soil due to evaporation. In all cases, the displacement of salts by invading salt‐free water did not show piston‐like behavior as reported by some workers. In contrast to some earlier reports, the advance of the salt front was dependent on the initial soil water content. Upward movement of salts toward surface layers due to evaporation was greater in initially moist sandy loam and initially dry sandy soils.