SOME BACKGROUND ON THE SOIL OF DE TRAFFORD
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It is a well known fact that the slopes of the Helderberg are very well suited for growing high quality grapes. This is due to the granitic origin of it's soils which contain a high clay content with excelent water retention qualities while at the same time free draining (see wetness index map)
In 2020, an in depth soil survey was conducted in our vineyards. As part of the analysis, 27 profile holes of 1,2m deep each were dug and it was found that in the 5ha of our farm that is under vine, there are 5 different soil groups and 9 different soil forms. This diversity in the soil gets translated into the fruit that it produces and in turn contributes to the complexity found in every bottle of De Trafford wine.
The map below shows a satellite image of the farm with an overlay of the different soil groups. Each yellow cross represents one of the 27 profile holes. Click on them to see what the soil looks like at that site. There are also links to other maps that highlight the soil forms, wetness and soil potential respectively.
The table below has a more in depth analysis of each block and their various limitations as well as the soil preparation actions that need to be implemented.
*VH - Very High Vigour Potential
H - High Vigour Potential
MH - Medium High Vigour Potential
There are 5 different soil groups that are found throughout or vineyards, namely: Cumulic, Plinthic, Oxidic, Lithic and Humic. Each of these soil groups have differing characteristics and origins. These soil groups contain 9 different soil forms.
These soils are youthful (in geological terms) having formed as a result of unconsolidated sediments such as colluvium (material that accumulates at the foot of a steep slope), alluvium (material that accumulates as a result of its movement in water) and aeolian (materials deposited as a result of wind).
Younger soils are usually deep and are potentially highly productive although water movement can be problematic in root zones. This can however be solved by correct soil preparations when establishing a block.
Cumulic soil forms at De Trafford:
Plinthic soils occur in areas with a rainfall of more than about 450 mm per annum. They form under conditions of a fluctuating water table where the underlying material is semi-permeable to water. During the rainy season a temporary water table forms in the soil above the semi-permeable layer, which leads to reductive conditions. Later, it drains away, leading to oxidative conditions. These conditions lead to movement of iron in the soil, which accumulates as yellow and/or red and/or black flecks, mottling or nodules in this horizon. When dry periods occur between these cycles, it could harden to a hard plinthic horizon (also known as oubank, ouklip or laterite).
These soils have the ability to store ground water effectively and later make it available to plants. However, hard plinthic can be extremely hard and dense, and become impermeable to roots if not broken during soil preparation actions. This horizon also has sponge-like properties with water-holding capacity.
Plinthic soil form at De Trafford:
Within this soil group, the dominating process is the accumulation of iron oxides.The iron oxides are strong colouring agents that cling to the soil particles and give the soil a red or yellow colour. Haematite is a red iron oxide, and when it dominates, it indicates a freely drained soil with adequate oxygen (thus very little water saturation). Goethite is the yellow and more reduced form of iron oxide, and when it dominates, it indicates a well-drained soil with a bit less oxygen than in the case of red soils (thus slightly more water saturation). This occurs when the soil remains wet for longer periods and does not drain as quickly as in the case of the red soils. It is the same process as a piece of iron that lies under water and then rusts to a yellowish colour. Oxidic soils are well drained and therefore occur in drained positions in the landscape. This soil is very well suited for strong root development.
Oxidic soil forms at De Trafford:
Getting a feel for the oxidic soil at profile hole 2
These soils are youthful either because of limited rock weathering or because of rejuvenation through natural erosion on steeper, convex slopes, ensuring intimate contact between a surface horizon that is maintained by biological activity and the underlying rock. Penetration of roots and water is typically non-uniform and restricted to spaces between fragments of rock.These soils are derived from in situ (at the site) weathering of parent material.
Lithic soil form at De Trafford:
In this soil group, the dominant process is the accumulation of organic matter in old landscapes in the cool, high rainfall areas of South Africa. Good drainage, accumulation of iron and aluminium oxides, and low pH conditions, which inhibit microbe activity, are essential for the formation of Humic soils. The conditions under which Humic soils form, give rise to highly weathered soils. The high organic material content gives rise to a low density therefore these soils are less prone to compaction. In general, this soil group is highly productive when used for crop production.
Due to the leaching and acidity, large quantities of lime are necessary to prepare the soil for crop production. Humic soils are stable therefore less susceptible to erosion.
Break down of the organic matter provides large quantities of nitrogen for plant growth, but also degrades the soil in the long term.
Humic soil forms foud at De Trafford.