SOIL PREPARATION

CHAPTER 7

Oakleaf and Tukulu soils generally have good physical properties due to their neocutanic B horizon and relatively high organic matter content. At higher clay contents (> 25 %), however, Saayman & Van Huyssteen (1981a) mentioned that even Oakleaf soils may suffer from compaction and will benefit from soil preparation. This can be done using a shift-delve or mix-delve plough. 7.2.6 Shallow soils on rock Two soils in this group that deserve mention because they are so common in the viticulture areas of South Africa are Mispah and Glenrosa soil forms. These two soils are generally found on higher landscapes in association with river terraces (Breede River Valley), against mountain slopes (Coastal Region) and structured shallow soils (Swartland area). Mispah soils are less developed than Glenrosas and consist of topsoil (A horizon) on hard rock. Without soil preparation Mispah soils are not suitable for perennial crops such as grapevines. In instances, however, where the underlying rock has weathered or where shale has tilted vertically and the topsoil has a depth of 30-45 cm, a Mispah can be ripped to a depth of 80 cm and successfully used for vineyards. Mispah soils generally contain large amount of salts which, after soil preparation and with irrigation, will leach to lower lying soils. Cut-off drains will be essential to remove drainage water and prevent salinisation of lower lying soils. Glenrosa soils (see Figure 2.10) can be successfully prepared using a ripper and should have a medium potential for vineyards after soil preparation. Similar to a Mispah soil, the leaching of salts from Glenrosas to lower-lying soils is a real danger and must be prevented. In the Coastal areas of the Western Cape, Glenrosas are formed both on shale and on granitic parent material, and both types generally need ameliorants such as lime or gypsum.

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