EFFECT OF EXCHANGEABLE SODIUM ON THE FIELD-DRYING PATTERN OF SOIL AT 2 EVAPORATIVE DEMANDS

The drying pattern of two soils with exchangeable sodium percentages (ESP) of 4 and 38 in the surface 0–15-cm layer was studied in the field in winter and summer seasons when the average evaporative demands were 2.5 and 12.5 mm/day respectively. ESP significantly affected the magnitude and pattern of water content changes in the profile following evaporation. The surface layers of the high ESP soil, with a low upward water flux, dried more rapidly than the surface layer of low ESP soil. The total surface-water loss under both evaporative demands was higher from the low ESP soil than from the high ESP soil because the hydraulic conductivity was greater. For both ESP soils, cumulative water loss at any time was greater under conditions of high evaporative demand than under low evaporative demand conditions. The studies indicate that the adverse effect of high ESP on plant growth is likely to be accentuated under conditions of high evaporative demand, and this would make water management more demanding. © 1979 The Williams & Wilkins Co.