Anthropogenic erosion-induced small-scale soil heterogeneity in South African rangelands

Land-use-induced soil erosion in semi-arid drylands induced by land-use changes creates patchworks of soils and vegetation different from those of natural conditions. Knowledge of the highly dynamic spatial heterogeneity in soil properties, not depicted in conventional soil maps, is important for managing land uses sustainably, and for understanding soil-climate interactions. This study carries out analysis of soil redistribution in a degraded rangeland in South Africa, to assess the significance of anthropogenic soil heterogeneity within a small catchment with a silted-up reservoir. Surface soil (N = 51) and soil profile (N = 29) samples were collected from areas of various degrees of degradation and analysed for texture, pH, total nitrogen (TN), total organic carbon (TOC), available phosphorus (P), and potassium (K). Diverse vegetation cover is reflected in a high soil heterogeneity, showing differences in soil texture. Average surface soil nutrient content was significantly higher in vegetated areas (grassland: TOC 1.08 %, TN 0.10 %, P 20.12 mg kg −1 , mixed vegetation: TOC 0.93 %, TN 0.08 %, P 13.54 mg kg −1 , depositional: TOC 1.68 %, TN 0.18 %, P 34.67 mg kg −1 ) than at degraded sites (TOC 0.47 %, TN 0.06 %, P 7.52 mg kg −1 ). K content was low to moderate but did not show any significant difference between landscape units. Potential exists for the formation of distinct young anthropogenic soils on the silted-up reservoir where deposited sediments differed in TOC, TN, P, and profile depth from the shallow natural soils. Consequently, azonal soils on dam-deposits are different from those occurring naturally, and not depicted on conventional soil maps. Their different water and nutrient cycling may affect vegetation and biogeochemical fluxes. Land-use management should consider such soils, as they play an important role in rangeland ecology.