Seasonal nutrient fluctuation in selected plant species in the Kalahari

Abstract

Seasonal changes in crude protein, phosphorus and calcium contents of five common plant species in the south-western Kalahari were investigated. Three species that are browsed by springbok (Acacia erioloba, Grewia flava and Rhigozum trichotomum) and two grass species (Schmidtia kalahariensis and Stipagrostis obtusa), were included in the study. Browse species had higher crude protein, phosphorus and calcium contents than the grass species, but the fluctuation range was similar to that of the grass species. In general, the crude protein content of the food plant species sampled in the present study was above the level required by African ungulates for maintenance. However, the diet of springbok in the south-western Kalahari appeared to be phosphorus deficient. Crude protein and phosphorus levels in plant food were especially low during the cold-dry season, when the crude protein content of the grass species was at or below that which is required by springbok for sustenance. The phosphorus content was below ruminant requirements in all plant species in all habitats during the cold-dry season. Faecal crude protein and phosphorus percentages higher than that of the selected plant species investigated imply that springbok have the ability to select the most nutrient-rich plant species and plant parts available. The Ca:P ratio of the plant species that were sampled in the present study fell outside the range that is considered to be healthy for ruminants in all instances, with calcium in excess.

Keywords: calcium, Kalahari, nitrogen content, nutritional value, phosphorus, seasonal variation

African Journal of Range & Forage Science 2008, 25(3): 111–119