HILLSLOPE SOIL LANDSCAPES

With ongoing attempts to model climate change impacts on the water resources particularly in arid areas, there is increasing need to determine the scale and variability of soils in rangeland areas. All rangeland areas have been mapped mostly at a scale of 1:24,000 or greater. The broadly defined taxonomic units and compound soil mapping units common at this scale mean these maps provide only a very general picture of the soil landscape. However, the utility of the climate models is dependent on the accuracy of the soil data used. This is particularly true of hillslope soil landscapes.

Improving the accuracy of rangeland soil maps will rely on remote sensing, and digital soil mapping techniques, with the prospect of machine learning of the existing soil data as well. Challenges to improving rangeland soil mapping include identifying the scale of soil variability and characterizing subsoil properties remotely. Identifying the major drivers of soil variability and their proxies will aid in the prediction of soil landscape patterns.

We do have some conceptual models which can aid in identifying in particularly the scale and patterns of soil variability on hillslopes such as weathering limited /transport limited hillslopes, soil catenary relations and the concept of spatial and temporally controlled soil landscapes.

Spatially controlled soil landscapes are those where the soils are sufficiently stable that slope orientation slope position, and lithology exert a control on the pattern of soil variability. Temporally controlled soil landscapes are those where the main driver for soil variability is the age of the soil, common in areas with high erosion and deposition rates.

Examples of two types of soil landscapes are discussed, a geomorphically active drainage in the Southern Alps of NZ, Camp Creek, and two drainages in the foothills of the Ladrone Mts in the Rio Grande Rift.