Soil containing high concentrations of soluble salts and exchangeable sodium frequently produce distinct agricultural and management problems. Soluble salts in the Low Plain Aranca arise from the upward movement by capillarity from a high saline water table. Three mechanisms operate to transport solutes in soils: advection, diffusion and dispersion. Flow through the vadose zone requires study of saturated and unsaturated flow through variably saturated media. Solutes can interact strongly with soil surfaces and their transport can be appreciably slowed in a process known as retardation. Soils with high smectite content may also swell considerably more in the presence of high sodium and/or low salt concentrations. The study is based on a detailed soil survey effectuated in the hydrographical basin Aranca in order to achieve soil map and to take soil samples for the laboratory studies about solute transport and swelling-shrinking in salt-affected soils. There were studied 79 main soil profiles, from which 36 profiles are Fluvisols, 31 profiles are Vertisols, 8 profiles are Chernozems and Phaeozems, 2 profiles are Solonetz and 2 profiles are Gleysols. Because of their coarse or medium texture, in the case of Fluvisols, Chernozems, Phaeozems and Gleysols, solute transport was easily and the soluble salts are concentrated in the upper part of soil profile. A different situation is in Vertisols, which is a deep clayey soils, dominated by clay minerals such as smectites, that expand upon wetting and shrink upon drying. They form wide cracks from the soil surface when drying out. The water potential Φ in swelling systems is the sum of the gravitational potential with capillary and overburden potential. The overburden potential is related to the civil engineers' effective stress. Soil-solution-soil-matrix physicochemical interactions enhanced by dilute soil solution with relatively high sodium to calcium ratios, can affect the flow parameters considerably. The retardation caused by Na/Ca exchange increases with increasing SAR and decreasing C and h, especially in relatively fine-textured soils.

soluble salt; clay; water; soil; transport

Presentation: oral