Spatial assessment of optimum and sub-optimum growing areas for selected biofuel feedstocks in South Africa.
Energy production using fossil-based fuels (coal, oil and natural gas) has environmental and health effects that have the potential to endanger human welfare. Escalating oil prices and the contribution of carbon dioxide resulting from fossil fuel combustion to global climate change have focused attention on potential substitutes for current energy sources. Renewable energy is argued to improve access to clean energy, limit the use of fossil fuels and thus reduce air pollution. Biofuel is a liquid transport fuel and its production from biomass containing sugar, starch or vegetable oil is termed a first generation biofuel. The aim of these studies was to delineate areas potentially suitable for the cultivation of three first generation feedstocks (i.e. soybean, grain sorghum and sugarcane) in South Africa. Currently, these feedstocks exhibit the highest potential for biofuel production in this country. In previous studies, climatic factors were the main criteria used to map optimum growing areas for such feedstocks. However, such studies recommended that a more detailed assessment was required to provide a more realistic estimate of biofuel production potential. Thus, other mapping criteria related to edaphic, biotic and topographic factors were also considered. The approach followed is similar to other mapping methods developed by, amongst others, the Food and Agricultural Organisation. Land suitability assessment was based on crop growth requirements related to rainfall, temperature, relative humidity, soil depth and slope, which were gleaned from the available literature. These factors were then ranked and weighted according to expert opinion. A suitability score ranging from zero (unsuitable for plant growth) to one (most suitable) was derived and used to map areas optimally and sub-optimally suited to feedstock production. Relative to previous studies the inclusion of additional growth criteria decreased the land area deemed suitable for biofuel feedstock production. The results were further refined by considering current land use. For example, all areas which are deemed unsuitable for feedstock production (e.g. forest plantations and protected areas) were eliminated. The results showed that the provinces of KwaZulu-Natal, Mpumalanga, Limpopo and Free State are most suitable for soybean and grain sorghum cultivation, whilst the Eastern Cape and North-West provinces are least suitable. Similarly, KwaZulu-Natal is most suitable for sugarcane cultivation, whereas Mpumalanga, the Eastern Cape and Limpopo are least suitable. However, there are some limitations in the approach used, due mainly to the scale and accuracy of spatial datasets currently available.