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)