The evaluation of different technologies to restore old cultivated lands

Thesis (M.Sc. (Environmental Science and Management)--North-West University, Potchefstroom Campus, 2008.

As production costs for the cultivation of cash crops increased and government subsidies for farmers decreased and eventually stopped, the farmers stopped to cultivate the marginal to lower potential soils. The higher input costs could not be recouped form these lands and today, many of these old cultivated lands have been lying fallow for years. This resulted in unproductive land that could neither been used for the cultivation of crops nor for the grazing of livestock, as they have low grazing capacity value (economical value). The following restoration technologies were evaluated to restore old cultivated lands in two row spacings (0.75m and 1.5M), with and without the application of Roundup (herbicide): control; rip; rip and the application of organic matter (cow dung); rip and re-seeding with a seed mixture; rip, re-seeding with a seed mixture and the application of organic matter (cow dung); rip and re-seeding with only Digitaria eriantha seed and the establishment of conventional Digitaria eriantha cultivated pasture. The old cultivated lands used in this study lay fallow for approximately ten years and the species composition was mainly made up of species such as Aristida congesta and Eragrostis lehmanniana. Other perennial species, such as Themeda triandra and Cynodon hirsutus did occur in patches over the study area. The purity, of the seed used in the re-seeded restoration technologies, varied as follows Cenchrus cilliaris (97.9%), Digitaria eriantha (96.0%), Eragrostis curvula (95.4%), Eragrostis chloromelas (91.3%), Chloris gayana (85.6%), Panicum maximum (84.3%), Themeda triandra (72.5%) and Cymbopogon excavatus (44.7%) and the germination also varied: Eragrostis curvula (86%), Themeda triandra (76%), Eragrostis chloromelas (48%), Cenchrus cilliaris (35%), Chloris gayana (29%), Digitaria eriantha (19%), Cymbopogon excavatus (13%) and Panicum maximum (4%). The rip action (for both row widths) did have a positive influence on the growth and establishing of existing and re-seeded seedlings of the perennial species. The re-seeded species that were established the most successfully were Themeda triandra, Digitaria eriantha and Eragrostis curvula. The application of organic material did help the initial establishment of the re-seeded grass species, but the affect did decrease over the three seasons. The narrow row spacing benefited the re-seeded grass species, while the wide row spacing did benefit the natural occurring grass species, such as Eragrostis lehmanniana. The establishment of the conventional cultivated Digitaria eriantha pasture were unsuccessful and could not be explained. The application of the herbicide (Roundup) did help to minimise the inter-species competition between the seedlings of the re-seeded grass species and the natural occurring species, thus bettering the seedlings survival rate. The natural occurring perennial grass species, such as Themeda triandra were also killed by the Roundup. Herbicide should not be applied if the old cultivated land already has a good stand of palatable grass species. It can be used to minimise the inter species competition, if there are lots of annual species present in the plant community of the old cultivated land, to be restored. The farmer's available budget is an important factor when considering the type of restoration technology to restore old cultivated lands. The rip and re-seeding with Digitaria eriantha alone is highly recommended as it is a relatively cheap restoration technology. If the species diversity of the old cultivated land is to be enhanced more expensive technologies must be used, like the rip and re-seeding with a seed mixture (Themeda triandra, Digitaria eriantha and Eragrostis curvula). This technology was one of the cheapest, especially if no Roundup was applied. Themeda triandra is a naturally occurring species and its seed was not commercially available, making it difficult to come by in the trade and the seeds must be harvested in the veld near the old arable land that is to be restored, to minimise the effect of ecotypes. The following shortcomings were identified during the executing of this study and need further research: * The potential increase in the farmers income, with the increased grazing capacity must be included in the economical analyses, * The influence of an over supply or lack of plant nutrients and the influence of soil organisms must be researched, * The threshold point where a restoration action will not better the veld condition further must be determined, * The plant surveys must be done over the whole restored area in order to determine the true veld condition and not only on the rip furrows, * The influence of grazing on the vegetation of the restored old cultivated lands must be researched and * A survey technique or apparatus must be developed to distinguish between the re-seeded individual and the natural occurring plants of the same species in a restoration technique.

Masters