Abstract:
Aspects, which influence the choice of species for the rehabilitation of degraded arid areas, were studied. Although only one trial was established in the target area (transition area between the Succulent and Nama Karoo) seed of the indigenous species used was collected from this area. In the initial trials the effect of rumen digestion on the germination of fodder shrubs was observed. Species included the exotic Atriplex nummularia and Cassia sturtii, and the indigenous Sutherlandia microphylla, Tetragonia calycina, Tripteris sinuatum and Salsola glabrescens. No seed of T. calycina germinated. In T. sinuatum and S. glabrescens rumen digestion prevented germination while in the other species percentage germination was reduced. In the establishment trial with A. nummularia and C. sturtti, on a bare area onfarm, in the arid Northern Cape Province, no seed germinated. Observations showed that, for both species, protection is essential, where the risk of herbivory is high. Of the two species, C. sturtti shrubs appeared to be more drought tolerant. A further trial addressed the intra-species variation in the palatability of A. nummularia. Established shrubs of the F1 “elite” generation were browsed by sheep. The most palatable shrubs were identified and seed from these shrubs will be used to produce seedlings that will go into further selection trials. The final section of this study was a comparison, in terms of quantity, quality and re-growth, of C. sturtii, T. sinuatum and S. microphylla, at, and subsequent to, five different harvest dates. In the first three harvests no significant differences were observed in the total plant material produced, between the three species. In Harvest 5 both indigenous species had produced more edible material (leaf and <3mm stem material) than C. sturtii. The edible material of Harvests 1, 3 and 5, was analysed for crude protein content, in vitro digestibility and mineral concentrations. All three species had sufficient crude protein as well as calcium, phosphorus and magnesium, to meet maintenance requirements of sheep. Trace minerals, manganese and copper, were present in adequate amounts and toxicity could be more of a concern. The concentrations of zinc in all three species, however, were only sufficient in material obtained in Harvests 1 and 3. Re-growth of all shrubs 21 weeks after Harvest 5 was assessed in terms of survival, healthiness, leafiness, volume and dry matter production. C. sturtii shrubs harvested at a later stage in the initial trial had the best survival. For most re-growth periods, C. sturtii shrubs also appeared healthier and leafier than the indigenous species. S. microphylla seedlings had, however, established in the S. microphylla plots, which was a plus for that species. Copyright
