The Effect of Soil-Mineral Weathering on the Sodium Hazard of Irrigation Waters
1968
Rhoades, J. D. | Krueger, D. B. | Reed, M. J.
The extent to which the release of solutes from soil-mineral weathering processes changes the composition of applied irrigation waters has been evaluated for six arid-land soils. Soil samples were packed in plexiglas permeameters and pretreated to remove readily soluble organic matter, to minimize subsequent microbial activity, and to equilibrate the soil exchange-complexes with the irrigation waters. Soil solutions were displaced from the nearly saturated columns and analyzed at biweekly intervals until a steady composition was attained. The effluent solutions were 3 to 5 meq/liter higher in total salt content than the applied waters. The gains were accounted for primarily by Ca + Mg and HCO₃ ions. The net effect of these changes in solution compositions was a 30 to 90% reduction in the SAR values of the applied solutions. The SAR reductions were greatest for the waters of lower salt concentrations, but were significant even for waters containing as much as 15 to 20 meq of salt per liter. This phenomenon reduces the Na hazard expected with certain irrigation waters, and should be considered in water-quality evaluation.
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