Comparison of methods for measuring severity of water repellence of sandy soils and assessment of some factors that affect its measurement

Abstract

Rapid methods for measuring the severity of water repellence were assessed in 101 sandy soils from South Australia. The molarity of aqueous ethanol droplets that were absorbed by the soil in 10 s, the time of water droplet entry and the infiltration rate of water from a small ring infiltrometer were compared with the soil-water contact angle and with each other. Relationships between the tests were fitted by linear, quadratic and cubic regressions and were highly significant (100r2 = 70-92). The relationships were used to provide ratings of repellence normally found in the field. Factors which affect the measurement of repellence in the field were examined. Abrasion of sand particles during light sieving had only small effects on repellence, but more vigorous abrasion through rotational movement of the sand reduced repellence markedly. Repellence decreased with increasing temperature. Simple corrections for temperature were calculated and presented in figures as isorating charts. The moisture content of the soil had large and variable effects on the repellence tests. At moisture contents between oven and air dry (pF 5.6) there was little effect on the ethanol droplet or infiltration rate tests. Measurements by the ethanol droplet test were not reliable at moisture contents greater than air dry. At soil water contents between air dry and wilting point (pF 4.2), the infiltration rate of water was either unchanged or decreased in different soils. It then increased rapidly and reached a constant value near field capacity (pF 2.5). The infiltration rate also decreased when the time of moistening of the soil before the tests were made was extended from 20 to 168 h. It is recommended that repellence tests be made on oven- or air-dry soils. The aqueous ethanol and water droplet, and infiltration rate of water tests are all suitable for rapid assessment of repellence in the field.