Anisotropy of Soil Hydraulic Properties Along Arable Slopes

The spatial variations of the soil hydraulic properties were mainly considered in vertical direction.The objectives of this study were to measure water-retention curves,θ(ψ),and unsaturated hydraulic conductivity functions,K(ψ),of the soils sampled at different slope positions in three directions,namely,in vertical direction,along the slope and along the contour,and to determine the effects of sampling direction and slope position of two soil catenas.At the upper slope positions,the surface soils(0-10 cm) sampled in the vertical direction had a lower soil water content,θ,at a certain soil water potential(-1500 kPa < ψ <-10 kPa) and had the greatest unsaturated hydraulic conductivity,K,at ψ > -10 kPa.At the lower slope positions,K at ψ > -10 kPa was smaller in the vertical direction than in the direction along the slope.The deep soils(100-110 cm) had similar soil hydraulic properties in all the three directions.The anisotropic variations of the hydraulic properties of the surface soils were ascribed to the effects of natural wetting and drying cycles on the structural heterogeneity.These results suggested that the anisotropy of soil hydraulic properties might be significant in inffuencing soil water movement along the slope and need to be considered in modeling.