The Influence of Wetting Rate and Electrolyte Concentration on the Matrix Failure Patterns of a Degraded Red Earth

Abstract

The hydrologic response of a degraded red earth's topsoil to varying wetting rates (w) followed by falling electrolyte concentration (c) was investigated. Rapid wetting and the resulting structural failure increased total porosity and water retention across the 0 to 1500 kPa matric potential range. Substantial macroscopic swelling of rapidly wetted soil was attributed to air compressed into the largest available voids. Consequent soil matrix failure resulted in macroscopic swelling and increased sorption of water. Hydraulic conductivity appeared to be a non-linear function of wetting rate over the range w = 0-30 mm min-1. Similarly, for a given wetting rate, hydraulic conductivity increased with c, over the range 0.2-12 mmolc dm-3, according to the function log[1/Kr 1] = a + blogc where Kr = K(c,w)/K(12,w). The slope b decreased as w increased indicating an increased sensitivity to low electrolyte concentrations at high wetting rates.


Transactions of the Zimbabwe Scientific Association Vol. 74 2000: 25-32