Interpretation of the spatial variability of soil hydraulic properties using a land system analysis.

Accurate knowledge of soil hydraulic properties is of crucial importance for reliable applications of recently developed distributed models to environmental studies and land-use planning. Use of computer models to simulate water flow and solute transport processes or to assess the hydrological response of an agricultural catchment requires non only the determination of the soil hydraulic properties in a large number of points within the area of interest, but also a detailed characterization of the spatial variability exhibited by these properties. The scope of this study is to correlate the spatial variability of soil hydraulic properties with the distribution of soils in the landscape. The experimental work was conducted in the Sauro River catchment, the main tributary of the Agri River (Basilicata Region, Italy). This catchment is located within the middle Agri valley and represents an interesting area for site-specific studies on surface erosion and land degradation. The sampled area is a hillslope oriented in the N-S direction. Undisturbed soil samples were collected from the surface layer of soil at 100 sites, spaced 50 m apart, along a 5-km long transect parallel to the main slope, ell soil cores were subjected to laboratory measurements to determine bulk density, particle density, particle-size distribution, organic carbon content, soil-water retention characteristics, and saturated hydraulic conductivity. The distribution of soils along the hillslope was analyzed by aerial photography and soil survey techniques (profile and auger pedological descriptions) with the aim of distinguishing different soil units. Relationships were evaluated between these soil units and the hydraulic properties of the cores collected along the transect. A multivariate analysis was carried out to interpret the structure of soil hydraulic property spatial variability.