Abstract: Phosphorus addition increased mineral concentrations and improved the nutrient status of the perennial shrub Ptilotus obovatus (Cotton bush) and the ephemeral only after summer rain. In the ephemeral and the perennial species, most nutrients (N, K, Ca, Mg) were present at concentrations sufficient for herbivores except P. Concentrations of total nitrogen provide misleading estimates of the availability of crude protein for herbivores if traditional conversion factors (e.g. protein = 6.25 x N) are applied because of the presence of substantial concentrations of non-protein N in the foliage of most species. In vitro dry organic matter digestibility (IVDOMD) of Ptilotus obovatus varied seasonally from 24.71 to 51.8 % and was negatively related to concentrations of total phenolics and of condensed tannins. In unfertilised plots outside the thicket, there was no evidence that the area within the thicket was more fertile than that outside. When fertiliser P was added, the relative (to unfertilised plots) response within and outside the thicket was identical, again suggesting that fertility was not different. Further comparison with nearby grassland also suggested there were few differences in fertility.