SOIL PREPARATION

CHAPTER 7

not be used when heavy clay layers are present within 80 cm from the soil surface since the danger of destroying the internal drainage of the soil profile is then too great. The excavator is always working backwards, irrespective of the technique that is employed. Large excavators can reach the required depth in one scoop, but care should always be taken not to turn the soil over either when it is mixed or when it is shifted. When too small an excavator is used, the topsoil has to be removed first, before the subsoil can be dug up and placed back in a manner that will ensure its mixing with the necessary ameliorants. The topsoil must then be returned to cover the subsoil. The speed of a one-action excavation delving, compared to instances where the topsoil has to be removed before the subsoil is loosened, makes the latter approach very attractive to contractors and farmers alike.

FIGURE 7.15: Excavator busy with soil preparation (“handjie-dol”) (Photo: J.E. Hoffman, Stellenbosch University).

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