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Measurements of intrinsic sorptivity (S*) by using both ethanol and water were used to indicate the extent of water-repellency in soil. Experiments with initially dry, acid-purified sand verified that in a non-repellent, nonswelling porous medium S' was indeed intrinsic to the medium, and independent of the sorbing liquid. For initially water-moist, non-repellent sand, the measured S* was different when ethanol and water were the invading fluids. But a bound can be put on this difference. It was concluded that in structurally stable soils, the ratio of S* from ethanol to that for water may be used as an index of water-repellency. In the laboratory, disturbance of repellent soil by sieving or shaking effectively removed the repellency. Subsequent incubation restored it. Field measurements of sorptivity, at a scaled negative surface potential, into an initially moist, fine, sandy loam were made. While the soil appeared to absorb water normally, the sorptivity for water was an order of magnitude lower than expected from the ethanol data. This was due, we suggest, to repellency. Some possible implications of this unexpected result are discussed.

To investigate a rapid, nondestructive way of characterizing solute transport properties, time domain reflectometry (TDR) and disk permeametry have been used in combination. Calibration measurements had previously related TDR measurements to both the volumetric water content and the pore water concentration of Cl‐. Laboratory measurements from a horizontal TDR probe were used to estimate transport parameters in a soil column by applying a one‐dimensional numerical model in an inverse sense. A vertical TDR probe was used to provide independent verification of these parameters. A repacked column of Ramiha silt loam (an Andic Dystrochrept) was used under unsaturated, transient flow conditions. The disk permeameter, set to a pressure head of −50 mm and containing a solution of 0.032 M KCl, was placed straight onto the repacked soil column, which had an initial water content of 0.32 m3 m‐3. The soil wet to 0.60 m3 m‐3. However, in the columns only an envelope of Cl‐ concentration could be obtained, due to exchange between the initially resident Ca2+ and the invading K+. This illustrates why cation exchange needs to be considered when TDR is used to infer solute dispersivity and the retardation were found to be 2.3 mm and 1.2, respectively. The retardation is shown to be due to the anion‐exchange capacity varying with the concentration of the invading soil solution.

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Two surface soils (Patua and Tokomaru) of contrasting mineralogy were incubated with several levels of either CaCO, or HCI. The effects of ionic strength on pH, on surface charge, and on the adsorption of phosphate and sulphate were measured in three concentrations of NaCI.The pH at which the net surface charge was zero (point of net zero charge-PZC) was 1.8 for the Tokomaru soil and 4.6 for the Patua soil: differences that can be related to mineralogical composition. There was an analogous point of zero salt effect (PZSE) that occurred at pH 2.8 for the Tokomaru soil and at 4.6 for the Patua soil. The presence of permanent negative charge in the Tokomaru soil resulted in an increase in PZSE over PZC.The effect of ionic strength on adsorption varied greatly between phosphate and sulphate. For phosphate, there was a characteristic pH above which increasing ionic strength increased adsorption and below which the reverse occurred. This pH (PZSE for adsorption) was higher than the PZC of the soil and was 4.1 for the Tokomaru soil and 5.3 for the Patua soil. In contrast, increasing ionic strength always decreased sulphate adsorption and the adsorption curves obtained in solutions of different ionic strengths converged above pH 7.0. If increasing ionic strength decreases adsorption, the potential in the plane of adsorption must be positive. Also, if increasing ionic strength increases adsorption, the potential must be negative. This suggests that, depending upon pH, phosphate is adsorbed when the potential in the plane of adsorption is either positive or negative, whereas sulphate is absorbed only when the potential is positive.