Soil maps are critical for various land use applications and form the basis for the successful implementation of precision agriculture in crop production. Soil maps provide the spatial distribution of important soil physical and chemical properties to a farmer. The farmer uses this information to make critical management decisions for profitable and sustainable food production. South Africa is a water scarce country where rainfall is mainly seasonal and unreliable. Under these circumstances, knowing the soil’s physical properties is increasingly important for the management of soil water for successful crop production. The current South African conventional method for determining the spatial distribution of the soils physical and chemical properties are a grid survey, which include soil classification and the sampling of the top soil for chemical analysis. This way of determining the spatial distribution of the soil is labour intensive, slow and thus costly. Advances in the fields of digital soil mapping and remote sensing allows experts to create timeous and cost effective soil maps. In this study aerial and proximal gamma-ray spectrometry was used to determine the distribution of soil physical and chemical properties of two fields within an important summer rain crop production area in South Africa. At both study areas a conventional grid soil survey was done, where soils were classified and samples analysed for pH, electrical conductivity (EC), exchangeable cations, phosphate, elemental composition with a portable XRF instrument, and particle size analysis. These values were correlated to the gamma-ray spectrometry values obtained. The different soil textures in the study areas show correlation with the soil gamma radiation. The gamma-ray data was also able to delineate the different soil types/bodies identified with the soil survey. This study shows that gamma-ray spectrometry data acquired can be efficient for rapid and affordable zoning of different soil types to produce useable soil maps for precision agriculture.
