AbstractThe effect of soil ESP on soil moisture retention and volume change of montmorillonitic type clay soil (vertisol) in the 10–58 ESP range showed increase in moisture retention with soil ESP in 10‐bar suction range. Soil moisture suction (h) – water content (θ)relationship of the form h = ho(θ/θs)−b, where ‘ho’is air entry suction and ‘b’ is a constant, was obtained at all ESP levels. Soil bulk density at low moisture contents increased considerably with soil ESP due to dispersion and decreased linearly with increase in soil water content because of mineral swelling.The soil water diffusivity and conductivity in the 0.15–0.35 g/g moisture content range followed an exponential increase with soil moisture content recording a sharp decrease at soil ESP 10. The effect of high exchangeable sodium, however, was mitigated, to a large extent, by the increase in electrolyte concentration of permeating water to 5 mmhos/cm or greater. Decrease in water transmission parameters ascribed to exchangeable Na+in the drier moisture regime was accounted for by dispersion of soil particles at low ESP. Whereas adsorbed Na+– induced swelling was regarded as the major factor modifying soil water relations at relatively high ESP under wet moisture regime. Soil ESP of 10 may be treated as critical for swelling clay soil from soil and water
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