WINETECH Technical Yearbook 2021

orthic topsoil and are distinguished by the type of enrichment that dominates their subsoil horizons. Groups 12 to 14 also have orthic topsoil, but are typically younger due to recent deposition, erosion or human disturbance and the subsurface enrichment is therefore weak. It is important however to remember that soil groups do not explain in-depth diagnostic differences between soil forms and cannot replace the distinction between soil forms. If cumulic soils (group 12) are looked at for example, Augrabies or Montagu soils, inter alia, must contain sufficient calcium carbonate or calcium- magnesium carbonate within 1 500 mm from the surface to effervesce visibly when treated with a cold 10% hydrochloric acid solution. Oakleaf or Tukulu soils, inter alia, on the other hand do not contain enough calcium carbonate or calcium-magnesium carbonate to effervesce visibly when treated with 10% hydrochloric acid solution. HOW DOES THIS MAKE SENSE FOR THE PRODUCER ON THE FARM? A soil scientist must often identify a large variety of soil forms on a producer’s farm, and the mass of information and different technical terms generated can be overwhelming. To make the information and its interpretation more manageable, a

soil group map should regularly be used in conjunction with a soil potential map. Soil potential takes all diagnostic criteria into account and the information that gets lost in the soil groups, will reflect on the soil potential map. The main purpose of a soil classification project is to determine the vegetative growth potential of the soil, with all the limitations considered, and to suggest block layouts according to the physical properties of the soil which create management zones. The producer receives various maps to facilitate this discussion – unique to the specific project and the producer’s needs – like farm, soil form, soil group, wetness index (drainage), natural and potential effective depth, stone percentage, recommended block layout, etcetera. Soil classification is based on the collection of scientific data and should form the foundation of establishing new vineyard blocks. The value of soil classification lies in the accurate interpretation and utilisation of this data. Considering the establishment cost per hectare, even the establishment of only one or two hectares on less suitable soil, or incorrect rootstock choices or management practices, could potentially lead to massive financial losses over time. An investment in soil classification is therefore an investment in the future.

The following photos illustrate the different soil forms that can occur in some of the soil groups:

PHOTOS 1-4. Examples of soil forms in the duplex (group 7) soil group.

PHOTOS 5-8. Examples of soil forms in the cumulic (group 12) soil group.

Contact Vinpro at 021 276 0432 for independent, precision advice to evaluate your soil health, fertilisation programme, cover crops and viticultural practices.

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