Hydro-physical Properties and Solute Movement in Black Alkali Soils

Abstract

The black alkali soils, occurring in the Indian states of Maharashtra, Madhya Pradesh, Gujarat, and adjoining areas, can be classified as fine montmorillonitic hyperthermic – family of Typic Haplusterts – alkali phase (clay >35 %, silt >30 %, sand <15 %, CaCO₃ <3 %, pHs ≥8.6, ESP >15, and CEC >35 c mol (+) kg⁻¹). The clay fraction is dominantly montmorillonite (>78 %) and the soils exhibit swell-shrink properties. A review of studies carried out during the last four decades on the nature and properties of these soils reveals the broad characteristics: the soluble salts (mainly chlorides and sulfates of sodium) are confined primarily to the upper soil layers; the exchange complex is dominantly saturated with sodium throughout the soil profile; the soils generally contain calcium carbonate to the extent of 5–15 % in the surface layers with an increasing trend; clay pan exists in the subsurface horizons; soluble and exchangeable calcium is often low, and the pHs seldom go beyond 9.5; the fine clay remains in dispersible condition (even up to 45 %) at higher ESP values; the dispersion ratio goes as high as up to 85 %; and the critical ESP lies in between 8 and 10 at which the physical properties start deteriorating, and low water transmission properties are chief causes of unproductive nature of these soils. These soils exhibit very special characters regarding salt movement, oxygen movement in profile, higher anion exclusions, and very restrictive water movement and require special care during its management.