Reclaiming Sodic Soils Using Gypsiferous Amendments.

Gypsum (CaSO₄^.2H₂O) is a naturally occurring mineral, as well as an industrial byproduct that is useful in altering the chemical properties of the soil exchange complex and soil solution. It is effective in replacing sodium with calcium on the soil exchange complex, increasing soil solution electrical conductivity and reducing soil pH. Replacing monovalent sodium with divalent calcium reduces clay mineral swelling and dispersion; increasing calcium in the soil solution further depresses clay mineral swelling. Increased divalent cations reduces the thickness of the layers of cations that balance the negative charge on the clay, allowing clay particles to flocculate. Reduced swelling and dispersion reduces soil crusting, increases infiltration, and reduces runoff and soil erosion. This talk briefly reviews the elegant physical chemistry that explains the effectiveness of gypsum applied to sodic soils.