RCR / Projects / A1 Soil Science

A1 - Soil Science


Vulnerability and resilience of soils under different rangeland use


Research Areas: Soil Science (W. Amelung), Ethnology (M. Bollig)

Research Locality: South Africa, (Free State, Northwestern Province)

Lead Discipline: Soil Sciences, Other Disciplines: Social Anthropology


Principal Investigators:

Prof. Dr. Wulf Amelung

Prof. Dr. Chris Du Preez


This project aims to elucidate how sensitive and to which extent soil properties respond to different rangeland management in the grassland and savannah biome of semiarid South Africa, and to figure out to which degree changes of the ecosystems are perceived and caused by farmers' decisions. We hypothesise that both ecosystems respond differently to rangeland degradation: in the savannah biome bush encroachment leads to an improvement of the soil quality, whereas in grasslands degradation of the soils proceeds with intensified management.

South Africa’s rural areas are currently undergoing rapid changes due to land tenure reform and changing patterns of land use. Sub-project A1 focuses on the mutual interdependencies of soil and (jointly with A3) vegetation dynamics as well as on the associated social change in two selected areas of South Africa:

1. grassland in the Orange Free State and

2. savannah in the Northern Cape’s/Northwestern Province’s.

Changes in the grass communities (i.e. increase in the abundance of unpalatable sour grasses) and invasions of woody plants are severely threatening the economic viability of pastoralism in both biomes. However, the causes of and the processes involved in these changes and human interactions with them remain poorly understood. Additionally, the crucial role of the soil is often disregarded.

Our aim is therefore to elucidate how and to which extent soil properties respond to different types and intensities of rangeland use in the grassland and savannah biome in semiarid South Africa. The selection of study sites will systematically take into account different tenure systems (pastures held in common property, municipal commonages, commercial farms, resettlement farms) and nature reserve areas and explore how these tenure regimes and soil/vegetation dynamics interact. Each site includes a series of different degrees of changes in species composition (grassland biome) and bush encroachment (savannah biome) as induced by different land use histories, different grazing intensities or by different restoration practices (e.g. holistic farming, herbicide application, and reseeding in the grassland biome and bush combating with fires, chaining and herbicides in the savannah biome). Soil properties are characterised by the spatial distribution of nutrients and water the aggregate stability and by the analyses of biomarkers along the selected sites of different systems of rangeland management in both biomes. The subproject ´s social science part will also document contemporary land use strategies and explore the complexities of Post-Apartheid tenure regimes. This design will allow us to answer the following questions:


I. Which soil properties reflect most sensitively the impacts of different kinds of rangeland use (early indicators)?

II. Which mechanisms control the response of soil properties to different kinds of rangeland use?

III. How do local farmers perceive changes of the local environment and how do local farmers react to legal changes in tenure rights and rapid changes of the environment?

IV. Are the changes of soil properties caused by farmers' decisions on adequate land use and if yes, to which degree?

V. Are the effects of rangeland degradation on soil properties reversible?

We hypothesise that rangeland degradation in both the grassland and the savannah biome is controlled by land use patterns and their current dynamics. It is likely, however, that the soils in both ecosystems respond differently to increased rangeland degradation. In the grassland biome soil crusts and bare soil patches prevent re-seeding of grasses and soils degrade by disaggregation, and losses of labile C and N pools that are eventually exacerbated by changes in nutrient cycling. In the savannah biome, however, the invading bush prevents such processes, likely resulting in even higher contents of soil organic matter in the degraded than in the conserved rangeland ecosystems - though at the expense of useful rangeland. Here, soil degradation might only proceed when this bush encroachment is combated. Yet, almost nothing is known on how farmers interact with the changes of the ecosystems.