SOIL PREPARATION

The control of run-off is essential on terraced soil in order to prevent erosion. Water discharged at the terrace ends must be channelled away into natural or artificial waterways and not be allowed to simply run down roads and even into lower lying cultivated land. A suitable cover crop, e.g. rye grass, should be established on the slanting slopes between terraces in order to prevent soil erosion. According to Saayman & Van Huyssteen (1981a), the terrace slope should first be covered in wet straw and the cover crop seed should then be sown in the straw. Finally, the slopes can be stabilised with a water-bitumen emulsion. It is also recommended that a cover crop be established on the terrace beds during the first winter before the vineyard is planted. A better option for the construction of terraces compared to the conventional method described above is to first prepare the soil normally and then construct narrow terraces that serve as paths for tractors and other vehicles. The grapevines are then planted on the slope between the tractor paths (Figure 5.10). This method is cheaper, simpler, and eliminates the problems of exposed subsoil and the hotter and drier conditions experienced by the outer rows of conventional terraces. The vineyard in Figure 5.10 was planted on land with a 19° slope, grapevine rows were 4.5 m apart and narrow terraces (in fact it is only a level road of ± 2 m wide for a tractor) were constructed by a small crawler tractor between rows. The area under the vine rows still has the original slope. Surface water is removed from the vineyard by the terraces that channel run-off laterally out of the vineyard to a waterway. Such a terracing system is best suited to good, well- drained soils e.g ., Tukulu and Oakleaf, which do not produce large quantities of run-off water that can cause erosion. The incline on the vine row makes this method of terracing less suitable for table grapes since easy access to the grape bunches will be more difficult than on conventional terraces. Well-drained soils that have a high water infiltration rate, i.e. erosion due to run off, is not a problem; also allow for other forms of terracing together with alternative vineyard cultivation systems. An example of such a scenario is illustrated in Figure 5.11. Terraces in the form of contour roads were constructed to allow implement traffic between several rows of narrowly- planted grapevines that will be trained on the “echalas” trellising system (stake vines). Spraying and harvesting are done from the terraces, while no implement traffic occurs between the grapevines. The soil was cross-ripped before planting and the new vineyard planted on the slope which varies between 15°-25°. Ideally, a cover crop should be grown in winter and sprayed with herbicide before bud burst of the vines to provide a soil cover that will further increase water infiltration. It is essential that adequate provision

72 | SPECIAL SOIL PREPARATION STRUCTURES