Water repellency in soils of humid subtropical climate of Rio Grande do Sul, Brazil

In this study, the effects of soil bulk density, total porosity, organic matter content, aluminium saturation and cation exchange capacity (CEC) on water and ethanol sorptivity and hydro-repellency index of various sized aggregates of horizons A and B were investigated. Soil samples were taken from horizons A and B in 17 different locations of Rio Grande do Sul, Brazil. Three samples were collected from each of the horizons for the determination of soil sorptivity in water and ethanol. Soil sorptivity was determined by a steady-state flow using a mini-infiltrometer. Hydro-repellency of samples was estimated from the ethanol/water sorptivity values. Aggregates from most soil samples exhibited low hydro-repellency index, R (1.24–3.12), except for luvisol and vertisol, which had R ≥ 5.79. The very low coefficients of determination, r2 = 0.18 and 0.22 at p = 0.01 between hydro-repellency index and organic matter content, and between angle of contact and organic matter content, respectively is an indication that the quantity of organic matter have little influence on hydro-repellency, but the composition of organic matter and other soil properties. The mean pH of sampled soils ranged from 3.90 and 5.50 in both horizons A and B but presents no significant effect on the hydro-repellency of soil at p = 0.01. The results show that soil hydraulic and sorptivity properties are dependent on interaction between aggregate sizes, which is mainly a function of the soil clay minerals.