SOIL PREPARATION

CHAPTER 7

Similar to the days of Columella, modern-day clients should make sure that the desired depth of loosening, namely 80-100 cm, is achieved when using a contractor to do soil preparation. The effective working depth can sometimes be 20-25 % less than the length of the implement shank due to soil lift (Van Huyssteen, 1983). Furthermore, the quality of the loosened soil is as important as the soil depth. This implies that large clods and unloosened banks between adjacent furrows should be absent and that the soil should have a good crumbly structure. Poor subsoil such as clay layers should not be brought to the soil surface. Good contractors will also ensure that the land surface is flat i.e. ready for planting. Although an instrument such as the penetrometer can give useful information about the depth of loosening, it is preferable that a profile pit(s) be opened in the prepared soil to assess the effectiveness of the deep tillage operation.

FIGURE 7.1: Example of the large crawler tractors used for soil preparation of vineyard soils in South Africa. Transportation requires large trucks (Photo: P. Myburgh, ARC Infruitec-Nietvoorbij). The correct choice of implement to be used for vineyard soil preparation is dictated by the soil type. Several types of implements are available in South Africa, each with a specific loosening action. A choice must be made between the following actions, which will then determine the appropriate implement: i) Loosening of the soil without mixing – ripper or wing plough. ii) Turning of the soil layers – delve plough. iii) Loosening of the soil together with a sideways displacement of the soil – shift-delve plough. iv) Mixing of the different soil layers and ameliorants – mix-delve (finger) plough.

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