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Field Infiltration of a Salt-Loaded Soil: Evidence of a Permeability Hysteresis

Central Oregon Agricultural Research Center, P.O. Box 246, Redmond, OR 97756

T. J. Donovan

USDA-ARS, U.S. Salinity Laboratory, 4500 Glenwood Drive, Riverside CA 92501

* Corresponding author.

ABSTRACT

Low water-infiltration rates may be detrimental to crop growth by reducing the water available to the plant, limiting salt leaching, and inducing ponding that may result in poor aeration during irrigation. Permeability has been shown to be a function of both the total salinity and the exchangeable sodium percentage (ESP) of the soil. Our objective was to measure the changes in water infiltration that occurred following extended salt loading on a Holtville silty clay (clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent) with permeability problems. An earlier 4-yr salt-tolerance experiment provided large plots (6 by 6 m) with six levels of salinity-sodicity and three replicates. Plots were surrounded by fiberglass barriers and were adequately drained. Colorado River water, with an electrical conductivity (EC) of 0.9 dS m^–1, was used to reclaim the plots in a series of small 80-mm irrigations. Measurements of the salinity and the exchangeable cations of saturated soil extracts were taken before, midway through, and following reclamation. Infiltration rates were measured after 4 h of ponding and were found to differ significantly both during and after salt removal by leaching. The infiltration rates showed a hysteretic effect (delayed reaction) of saline and sodic treatments on soil water permeability. We attributed the effect to the slowly reversible flocculation and deflocculation of clay particles. Final soil ESP data from different treatments indicated that a traditional ESP threshold value may be of limited worth unless past salt history of the soil is considered. Models of hydraulic conductivity should account for this permeability hysteresis. Strategies of reusing saline drainage water may benefit from the hysteretic permeability by allowing high infiltration rates to persist.

Contribution of the USDA-ARS U.S. Salinity Laboratory.

Received for publication May 14, 1990.