SOIL PREPARATION

FIGURE 7.14: Blade delving a ‘dorbank’ soil in the vicinity of Vredendal along the Olifants River (Photos: ARC Infruitec-Nietvoorbij).

In the drier parts of South Africa, especially In the Olifants River and Bonnievale areas, special soil challenges exist such as lime “heuweltjies” (little hills) and heavy clay patches that need to be mixed thoroughly with the surrounding and/or overlying soil. In such cases, growers went to the extreme practice of “blade delving” (lemdol) which entails removal of the topsoil, breaking up of the subsoil with a ripper followed by moving and mixing the soil using the tractor blade (Figure 7.14). Finally the topsoil is moved back. Blade delving is also applied when “dorbank” (hardpan) is thick and the topsoil is removed in order to break up the “dorbank”. This is obviously a very expensive practice, but the improvement is permanent, and excellent grapevine performance is obtained on such soils. Soil preparation using excavators (Figure 7.15) is also conducted in South Africa. Excavators fit better into small spaces between existing vineyard blocks and can work closer to roads and the edges of vineyards than large crawler tractors equipped with ploughs. Two techniques, aimed at different end results, are being used with excavator delving (“handjie-dol”). Both techniques require the opening of a short trench to the required depth whereafter the soil is scooped out from bottom to top against the trench wall closest to the machine operator. The first technique, which aims at both loosening and mixing, requires that the soil is carefully shaken out against the furthest trench wall. Good operators will let the soil fall down from the scoop from some height to ensure good mixing, but prevent turning the soil layers upside down. The second technique entails the loosening and shifting of the soil towards the back of the trench. In this case the excavator scoop remains at ground level and the different soil layers remain in place and minimum mixing takes place. The importance of a skilful operator cannot be over-emphasized in obtaining the sought-after effect with excavator delving. Excavator delving should, however,

120 | CHOICE OF IMPLEMENT FOR SOIL PREPARATION