Spatial and temporal variability of physical properties of Aquands under different land uses in southern Chile

The aquands found in southern Chile are derived from volcanic ash and contain high levels of organic matter. Due to the presence of an impermeable stratum, they have shallow soil profiles, which induce waterlogging for several months each year. These fragile soils, locally known as 'Nadi', cover an area of 475 000 hectares and have undergone intensive land use changes, which have affected the soil physical properties. These are still not well understood but are relevant for the design of efficient drainage systems. The aim of this research was to analyse the impact of the land use change in Nadi soils on the spatial and temporal variability of their soil physical properties. For the land use change from secondary native forest (sNF) to naturalized grassland (NG), the effective soil depth was measured at defined points. Time-and space-dependent changes of water-table depth and penetration resistance were recorded. Volumetric water content and soil temperature were measured with sensors installed at three depths and the water retention curve and air permeability at these depths were also determined. The changes in land use over time have induced a reduction in soil depth. Soils under NG showed a smaller soil water storage capacity, air capacity and permeability compared with soils under sNF, as well as waterlogging during winter and greater mechanical strength and soil profile temperatures during summer. Therefore, the land use change affected the spatial and temporal variability of soil physical functions across the field.