Evaluating agricultural potential of a Cape Metropolitan Catchment : a fuzzy logic approach

[摘要] Sustainable use of the earth's resources is seen by many authorities as critical to ensure the planet'ssurvival. In this regard agriculture is seen as a major role player and fundamental link in the chainof sustainability. South Africa, a country with relatively little favourable agricultural land, shouldtherefore preserve high potential areas for agricultural purposes. The Western Cape, with 75% of allmedium-potential arable land in South Africa, is a valuable asset. One region targeted fordevelopment and where uncertainty prevails regarding its agricultural potential, is the G21Bcatchment in the Atlantis Growth Corridor (AGC). The AGC is envisaged as long-term growth axisfor the Cape Metropole, but conflicting opinions exist on its agricultural possibilities and suitabilityto absorb urban growth.Consequently, the aim of this project was to evaluate the suitability of this catchment for a numberof agricultural landuses. Fuzzy logic, a modification of the land evaluation approach originallydeveloped by the Food and Agricultural Organization of the United Nations (FAO), was used toaddress this problem. Input data consisted of a soil map and digital elevation model (DEM) of thearea. Parameters identified from these sources and applicable to the study were soil texture of thefirst, second and third horizons, as well as coarse fragments in the top soil, wetness, weathered rock,average pH, effective root depth, and slope. These parameters were compared to the requirementsof six landuses, i.e. wheat, wine grapes, potatoes, tomatoes, onions, and citrus, and a fuzzyrepresentation for every landuse was constructed. Expert opinion aided in a weighting processwhereby the relative weights of parameters were computed and incorporated into the evaluation.Results showed extensive areas with a relatively high agricultural potential for potatoes and winegrapes. In addition, areas with potential were also identified for wheat, citrus, and tomatoes, albeiton more limited scale. Large areas, however, were deemed unsuitable for the aforementionedagricultural crops and would therefore be suitable to absorb metropolitan growth or to bemaintained as conservation areas.The fuzzy logic approach provided insightful results. Problematic parameters were easily identifiedand no information was lost in the evaluation process. It also allowed for an objective quantitativecomparison between crops. This provided freedom in deciding which landuse should be practiced,especially if the focus is on a sustainable rather than the most productive crop.

[发布机构] Stellenbosch University