Effect of Soluble Species Released from Soil Sources on the Composition of Soil and Drainage Solutions

Abstract

AbstractTwo soils differing in the amounts of calcium and magnesium released during dissolution of soil minerals, cation exchange capacity (CEC), lime content, and water‐holding capacity were irrigated under the same conditions with four synthetic waters. Two of the waters contained only chloride, and the other two contained both chloride and bicarbonate anions. Sodium adsorption ratios of the two chloride and two bicarbonate waters were either 10 or 20. Following every 10 wetting and drying cycles the two soils were leached with about 10% excess water. Five such leachates were collected and analyzed. Soil analysis was performed after 20 and 40 irrigation cycles. A significant difference was found between the chemical composition of the drainage and soil solutions of the two soils. To evaluate this diversity, the law of mass conservation was used to calculate the amount of calcium and magnesium released by dissolution in the absence and presence of carbonate precipitation. Two assumptions were used in these calculations: (i) during irrigation with the chloride waters no precipitation of carbonates occurred, and (ii) during irrigation with the bicarbonate waters no dissolution took place. These assumptions proved valid only for the soil that released small amounts of salt by dissolution. The two soils released almost equal amounts of calcium and magnesium from exchange sites, although there was a significant difference in CEC. It was concluded that the primary source that induced the differences in chemical composition of the drainage and soil solutions was the amount of calcium and magnesium released by mineral dissolution.