SOIL PREPARATION

CHAPTER 7

7.2 Matching soil preparation with soil type Knowledge of soil types has been the basis of selecting soil preparation techniques for vineyards in South Africa. These decisions are supported by research, experience and practical observation. Despite all the knowledge available, choice of the best soil preparation method cannot be made remotely without inspecting profile pits and interpreting the properties of the particular soil. 7.2.1 Sandy soils Some sandy soils with a clay content < 6 % show low resistance to root penetration and do not need deep loosening before planting (Saayman & Van Huyssteen, 1981a). Low water and nutrient retention is the most important limitation to grapevine performance on these soils that can include Fernwood, La Motte and even deep Longlands soil forms. They occur mostly in the coastal areas of the Western Cape in association with sandstone. Deep delving is only recommended when the subsoil has to be limed. In contrast to the above-mentioned sandy soils, serious compaction and shallow root systems do occur on certain structureless sandy soils (Van Huyssteen, 1989). The high relative bulk densities and strengths of these soils are probably due to hardsetting (cementation) when dry and/or the particular mix of coarse and fine sand and the absence of medium sand. The Vaalharts area consists mainly of coarse and fine sand. These sandy soils are extremely prone to compaction due to the packing of fine sand in the pores formed by coarse sand particles. This happens after recurrent wetting and drying cycles and due to vehicle traffic (Bennie & Botha, 1986). Deep tillage, using a delve plough (shifting or mixing), will be a suitable method of soil preparation of these sands. 7.2.2 Stratified soils Stratified soils, known as Dundee soils (Figure 2.4), commonly occur along rivers in most South African vineyard areas and are associated with alluvium. They are characterised by abrupt transitions between different textural layers. In cases where the textural layers are large, water and root distribution are impeded. Such stratified soils should be well mixed using a delve plough on condition that the subsoil is not saline or high in clay content. No soil layers having poor properties should be ploughed to the surface.

7.2.3 Apedal and neocutanic red and yellow soils

In the coastal areas of the Western Cape, yellow and yellow-brown (Clovelly, Tukulu and Oakleaf) as well as red and red-brown soils (Hutton, Tukulu and Oakleaf) have a high potential for growing of perennial crops, but they usually

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