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Gypsum Dissolution and Sodic Soil Reclamation as Affected by Water Flow Velocity¹

ABSTRACT

The dissolution rate of gypsum fragments in aqueous solutions was studied for Ca-soil-gypsum mixtures at two gypsum contents and four soil water velocities. Equations were derived to estimate the dissolution rate coefficient of gypsum fragments at different soil water velocities for a given surface area of gypsum. The soil water velocity controls both the time in which an elemental volume of water is moving in the soil-gypsum layer and the dissolution rate coefficient. Increasing the soil water velocity increased the dissolution rate coefficient but decreased the contact time between an elemental volume of water and a unit of surface area of the gypsum fragments; the net effect is that increasing the water velocity decreases the gypsum dissolution rate. The effect of contact time on gypsum dissolution rate is much greater at the higher soil water velocity range than at the lower range. The soil water velocity also has a significant effect on sodic soil reclamation. The slower the soil water velocity, the higher the efficiency of replacing Na⁺ by Ca²⁺. The probable reasons for these findings are discussed.

¹ Journal article no. 894. Agric. Exp. Stn., New Mexico State Univ., Las Cruces, NM 88003.

² Visiting Soil Scientist and Associate Professor of Agronomy, respectively. The permanent address of R. Keren is Institute of Soils and Water, ARO, The Volcani Center, Bet Dagan, Israel.

Received for publication October 1, 1981. Accepted for publication February 15, 1982.