Chemical Effects of Saline Irrigation Water on a San Joaquin Valley Soil: I. Column Studies
- Catherine Thellier,
- Garrison Sposito * and
- Kenneth M. Holtzclaw
A glasshouse soil column experiment was performed to characterize salinity and sodicity developed from waters of differing composition applied to a representative soil from the San Joaquin Valley of California. The soil column experiment was designed to simulate physicochemical conditions in a field experiment conducted in the western San Joaquin Valley, where an Entisol above a shallow, saline aquifer was irrigated with waters of varying quality. Columns 0.46 m long containing the Entisol were leached with “California Aqueduct water” (EC = 0.72 dS m−1, SAR = 4 molc 1/2m−3/2) or with saline “well water” (EC = 8 ds m−1, SAR = 13 molc 1/2m−3/2) for periods up to 1 yr. When a simulated “aquifer” was 0.43 m below the soil surface, leaching with aqueduct water produced a positive downward gradient of soluble salt concentrations and exchangeable Na, whereas leaching with well water produced a dramatic increase of sodicity at the soil surface and a zone of soluble bivalent cation accumulation about 0.2 m below. These effects reflected the combined influence of the applied water quality and evaporative capillary rise from the saline “aquifer.” After the simulated “aquifer” was withdrawn, soil saturation extracts indicated equilibration with the applied waters after 0.5 to 1 yr, the rate being greater under leaching with aqueduct water. The saturation extract and drainage effluent for the soil receiving aqueduct water became more dilute, producing calcite dissolution and increasing exchangeable Ca, with a consequent decline in sodicity. The soil receiving well water showed an increase in exchangeable Na at the expense of exchangeable Ca, with little or no change in exchangeable K and Mg. At the completion of the experiment, the soil irrigated with well water had become more saline and sodic but, since EC was sufficiently high as compared to SAR, no major permeability problems with the soil were expected. Therefore, from the results of this study, the reuse of saline drainage water would appear to be suitable for agricultural purposes provided that salt-tolerant crops were grown.
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