Agriculture Maps of South Africa

Generalized Soil Patterns of South Africa 2003

The land type survey is a reconnaissance survey that followed an inventory rather than a fixed legend approach. The soils were subsequently reorganized based on pedogenesis and land use capability and grouped into 19 generalized soil patterns to produce a map with a scale of 1:1,000,000. In this process, wherever possible, polygons smaller than 0.25 square centimeters (3,900 hectares) were incorporated into the largest bordering polygon with similar characteristics. International soil classification standards were also followed where possible.

Grazing Capacity of South Africa

This map refined a draft grazing capacity map by correlating the maximum normalized difference vegetation index (NDVI) image of 200 with animal unit values from earlier grazing capacity maps. Refinements took the form of incorporating land cover and tree density data. The integration of tree density data was based on a number of underlying assumptions: that a linear relationship exists between tree density and biomass production as measured by NDVI, 0–10 percent tree density can be regarded as having no influence on biomass production, at 75 percent tree density there would be very low to no biomass production, and the influence would not be the same for all tree species. The long-term NDVI map with tree density integrated was converted into grazing capacity values. Where overlapping occurs with transformed rangeland, the grazing capacity values were masked with land cover classes (cultivated land, forest plantations, mines and quarries, urban and water bodies). Adjustment of NDVI values was not attempted.

Land Capability of South Africa

The classic eight-class land capability system was adapted for use with GIS in South Africa taking data availability into account. Land capability classes are interpretive groupings of land units with similar potentials and continuing limitations or hazards. Land capability is a more general term than land suitability and more conservation oriented. It involves consideration of the risks of land damage from erosion and other causes and the difficulties in land use owing to physical land characteristics including climate. Social and economic variables are not considered.

Susceptibility to Wind Erosion in South Africa

In the western and northwestern cultivation districts of the Western Cape, North West and Free State Provinces, wind erosion is an acknowledged problem. This is because of the prevalence of sandy soils, high winds, cultivation practices, and low rainfall resulting in low plant biomass production and low soil organic material. Wind erosion is the loss of fine materials (fine silt and clay) from topsoil in the form of dust. By losing fine material, the soil loses much of its ability to provide plants with water and nutrients. The main factors determining susceptibility to wind erosion are particle size distribution of the topsoil, wind speed, topography, soil cover, soil water content, and aggregation of soil particles. In producing this coverage, the emphasis was on particle size distribution as the prime permanent factor rendering land susceptible to wind erosion. It follows that the higher the sand (especially fine and very fine sand) fractions, the more susceptible the soil is to wind erosion. Silt could not be used as a parameter because of lack of data.