SOIL PREPARATION

SUMMARY MATCHING SOIL TYPE WITH METHOD OF DEEP TILLAGE • Guidelines can be given regarding the best soil preparation method per soil type, but inspection and interpretation of the soil profile will be decisive. • Some sandy soils ( e.g. Fernwood and deep Longlands) do not need soil preparation except when lim- ing of the subsoil is necessary. Sandy soils that contain a large percentage of coarse and fine sand are prone to compaction and must be prepared using a mix-delve or a shift-delve plough. • Stratified soils (Dundee) must be well mixed using a mix-delve plough except when some of the subsoil layers are saline or high in clay. • Apedal (structureless) and neocu- tanic red and yellow soils (Hutton, Clovelly, Avalon, Tukulu and Oak- leaf) of the Cape coastal areas are normally compact and low in pH. They respond well to deep tillage and liming. Shift-delving is the recommended method of preparation for these soils. Sin- gle-direction delving should result in adequate mixing of lime with the soil provided that the correct cutting width and implements were used. • Red and yellow soils of the dry inland viticulture areas of South

Africa often contain hardpans in the subsoil. Depending on the de- gree of cementation, rippers or delve ploughs can be employed to remove the impeding layers. Blade delving is also effective on these soils. • Dry duplex soils with a relatively thin clay layer that overlies better material can be loosened with a wing plough or a shift-delve plough. If the clay is deeper than 50 cm, these soils can still be loosened by using a plough that penetrates 20-30 cm into the clay when the clay is in a dry condi- tion. Ridging should be considered when the clay layers are thick and shallow (< 40 cm deep). • Wet duplex soils should be drained if they are deep enough. Soil preparation must aim to break up continuously cemented concretion layers and to incorporate lime and P into the leached E horizon. The clay subsoil of duplex soils must not be ploughed to the surface. Ridging is the only solution to ren- der shallow wet duplex soils fit for grape growing. • Oakleaf and Tukulu soils may not always need soil preparation except when their clay contents are higher than 25 %, in which

132 | CHOICE OF IMPLEMENT FOR SOIL PREPARATION