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