Soil moisture influences sorptivity and water repellency of topsoil aggregates in native grasslands

Abstract

Water repellency is associated to coating of soil particles by hydrophobic substances, usually of organic origin, affecting water dynamics in soil matrix. We analyzed the effect of water repellency on water sorptivity of topsoil aggregates of six soil types under three initial moisture conditions (10 kPa, 100 kPa, and air-dried). Undisturbed soil samples were collected to evaluate sorptivity in the 0–5 cm soil layer at different locations in Pampa Biome in southern Brazil. Disturbed soil samples were also collected for soil particle size distribution, particle density and organic matter content. Sorptivity test was conducted in a tension micro-infiltrometer, using distilled water and ethanol (95% v/v). High values of repellency index R (13.43 in Hapludert, and 8.98 in Dystrudept) of soil aggregates reduced sorptivity and restricted infiltration properties. Repellency index decreased sharply with increase in soil moisture. Therefore, for hydrophobic soils an increase in soil moisture of original air-dry soil reduces hydrophobicity and enhances sorptivity and water infiltration into soil aggregates. High values of water repellency modifies water dynamics in soil aggregates, concealing the effects of matric potential and generating different patterns of conventional water infiltration behavior, especially in dry soil conditions.