Selenium concentration of maize grain in South Africa and possible factors influencing the concentration
A total of 896 maize grain samples were obtained from all the maize silos throughout South Africa (231 silos) and analysed for selenium (Se) content. This information was used to compile a regional distribution map of the Se content of maize grain in South Africa. Of the samples analysed, 94% contained below 50 μg selenium/kg DM and can thus be classified as deficient from an animal and human nutritional point of view. Maize grain in South Africa is therefore a poor source of Se for animals and humans. The geographical distribution of Se values of maize grain is consistent with that of previous studies on the Se status of herbivores in South Africa, suggesting that plants growing in most of the maize-producing areas of the country contain low concentrations of Se. However, these findings contradict those of the soil Se status in the country as reported by the Agricultural Research Council’s Institute for Soil, Water and Climate, which states that the eastern part of the maize-producing areas of the country tends to have adequate to high soil Se levels and the western areas to have low levels. These contradictory results can be explained to a large extent by the varying soil pH throughout the country. Soil pH plays a primary role in the availability of selenium to plants. Although the eastern parts of the country tend to have high Se concentration in the soil, it is not available to the maize plant owing to a low soil pH, while in the western parts of the country, where soil pH may be suitable for Se uptake by plants, there seems to be an inadequate concentration of available Se in the soil.
Keywords: Geographical map, soil pH, white maize, yellow maize