Comparison of immiscibly displaced soil solutions and saturated paste extracts from saline soils

Abstract

Soil solutions from four salt-affected soils in Alberta were extracted by immiscible displacement from field moist soils and saturated pastes after air-drying to examine the implications of using saturated paste extracts as a proxy of soil solutions. Solutions ranged in pH from 7.8 to 10.6 and in electrical conductivity (EC) from 6 to 45 dS m−1. Sodium dominated the cation suite, with Mg and K concentrations varying by several orders of magnitude between sites. Calcium was the major cation in lowest abundance at all sites. Sulfate was the predominant anion. Phosphorus concentrations ranged from 1 to 247 ppm. Considerable variation was seen between the properties of saturated paste extracts and immiscibly displaced solutions, with the saturated paste extracts having lower conductivities and Na, Mg, K and anion concentrations. The differences in composition between the two extraction methods resulted in differences in ion speciation, SAR and ESP values and mineral stabilities. Saturation indices for evaporite minerals were poor predictors of minerals formed in evaporated soil solutions. It was also found that even in chemically similar solutions, different minerals precipitated, and therefore the prediction of evaporite mineral formation from extracted soil solutions is not recommended. Key words: Salinity, saturated paste extracts, soil solutions, evaporites, mineral stability