Winetech Technical Yearbook 2022

(photo 5). These are typically young soils with stratified deposits of alluvial (river action), colluvial (gravitational action) or wind-blown (aeolian) origin. As roots grow with difficulty or not at all from a finer texture to an underlying layer with a coarser texture, root depth can be effec tively restricted through such layers. Due to the varying water-holding capacity of the different texture classes, certain layers could be dry and others oversaturated. Such stratification can be uplifted with a finger delve plough implement. COMPACTION Compaction is a common occurrence in old vineyard blocks. It can be mechanical compaction from tractors, sprayers or har vest machines, or sometimes the density can be attributed to high clay percentage, fine sand or silt content. In other cases, it results from the cementation of substances such as lime, iron or silica. Van Huysteen (1989) identified the following soil groups that are prone to compaction: • Silt-rich alluvial soils. • Sandy soils with more than 60% total sand fraction. • Topsoils with a tendency to compact. • Subsoils in which illuviation has taken place: the downward movement to an underlying soil layer consisting of material removed from the topsoil through percolating water.

PHOTO 1. Example of soil with a fluctuating water table.

PHOTO 4. Wetness is shallower than 500 mm from the surface and ridging is recommended.

PHOTO 2. Example of soil with a perched water table.

PHOTO 5. Dundee soil form.

PHOTO 6. Example of a clay horizon that must never be brought to the surface.

PHOTO 3. Drainage being installed.

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WINETECH TECHNICAL YEARBOOK 2022

WINETECH TECHNICAL YEARBOOK 2022