The effective establishment of cover crops is essential. A cover crop that is not of good grade or not giving good density will not be effective for weed control which leads to weeds dominating the cover crop.
There is much value in a good grade cover crop (Photo 1). The most important benefits of cover crops, are moisture retention by means of dead plant residues, weed control, increased water infiltration, improvement of soil structure, limitation of run-off and evaporation, and a certain degree of nutrient distribution. It is therefore essential to ensure a longer growing season for the cover crop and ideal to sow the cover crop before middle April (Photos 2 and 3). Ensure that the establishment of cover crops is done effectively, because a weak grade crop will mean that the cover crop is not effective (Photo 4). Examples of cover crops that can be sown in vineyards, include barley (Photo 5), vetches and triticale, sometimes mixed (Photo 6) and rye grass, to name a few.
Basic principles to keep in mind when establishing cover crops:
Use good quality seeds.
Sow early to extend the growing season of the cover crop and ensure maximum production of dry material.
Start preparing the seed bed at the end of March.
Use a cover crop that will flatten by itself once it has been sprayed with a herbicide (clovers, vetches and barley) or drag it flat (Photo 7).
Leave the dead plant residues on the surface.
Spray ridges with a herbicide in the middle of winter over a one metre wide strip in the vine rows.
Spray the cover crops with a herbicide just before bud break.
Know the cultivation requirements of the cover crop, in other words which soil type is more suitable for a specific cover crop.
Cover crops have a stabilising effect on soil structure, because:
Dead plant material is an energy source to soil microbes which form structure stabilising bonds from it.
Cover crops contribute to the organic material content of the soil and promote formation of new structural units.
Cover crops protect the soil against the impact of water and raindrops.
There are various ways to handle cover crops before the new growing season:
Working them into the soil with a ghrop or disc plough so that they may serve as a soil fertiliser (Photo 8).
Spraying them with a chemical herbicide at the beginning of the growing season and flattening or cutting them so that plant residues remain on the surface to obtain maximum moisture retention (Photo 9).
Destroying them mechanically with a disc plough, slasher or rotovator without working them into the soil.
Keeping them short using a slasher.
Leaving cover crops or natural weeds to grow in the vineyards and die naturally.
Ideally cover crops seed before budding, then die naturally and germinate and grow the following winter.
Problems that may be encountered with cover crops:
The carpet of dead plant residues from the previous year is destroyed when the seedbed is prepared to sow the following year’s cover crop (a cover crop that re-establishes itself is ideal).
A cover crop cannot be established successfully using drip irrigation, because moisture distribution to the middle of the row is insufficient.
In winter cover crops offer snails a place to hide while serving as a source of nutrition.
When switching from clean cultivation to minimum cultivation, there may be a slight decline in yield, but this may be rectified with additional fertilising (70 kg N/ha per annum).
If cover crops are sown at an early stage, germination problems may be experienced in high trellising systems (gables and factory roof) as a result of overshadowing.
Problematic grasses or weeds will not be suppressed by cover crops.
Certain cover crops exude toxic substances which may impede the growth of grapevine roots.
The large quantity of dry material creates a fire hazard in the dry summer months.
(Photos: Francois Viljoen)
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