SOIL PREPARATION

7.2.5 Wet and dark-coloured soils Important vineyard soils falling into this group include Oakleaf, Tukulu and Westleigh forms. Westleigh soils normally occur on higher terraces along rivers and show signs of wetness. Oakleaf and Tukulu soils are found in better drained landscape positions although Tukulu soils also show signs of wetness below the B horizon. Interestingly the unique circular dark spots called heuweltjies (little hills) that occur in large areas of the Western Cape landscape (Figure 7.20) are also classified as Oakleaf soils. Heuweltjies are relic termite nests that occupy approximately 14 % to 25 % of the land surface, averaging 17 m in diameter and 1.45 m in height (Bekker et al. , 2016).

FIGURE 7.20: Heuweltjies visible as darker green spots slightly raised above the surrounding landscape occur commonly in the Western Cape of South Africa and can be seen here in the vineyard on the hill (Photo: F. Ellis).

Saayman & Van Huyssteen (1981a), from experience, recommended that Westleigh soils containing < 10 % clay are usually well-aerated and normally do not need soil preparation. The use of Westleigh soils for vineyards becomes more risky at higher clay contents and subsurface drainage will then be necessary, especially in irrigated vineyards. They doubted the success of vine growing when the clay content of Westleigh soils rise above 20-25 %.

130 | CHOICE OF IMPLEMENT FOR SOIL PREPARATION