South Africa Wine Technical Yearbook 2025

conversion depends on the fineness of the lime and the amount of water that moved through the profile. What influences the breakdown or transfer process of herbicides? Large quantities of manure additions can increase the salt load in the topsoil, which in turn can lead to a decreased prevalence of the bacteria that help to break down herbicides in the soil. Herbicides can break down faster in balanced, healthy soil than in soil with limitations like poor aeration or drainage. Should I keep the material on the surface or remove it after establishing cover crops? What is visible above the soil surface is only a part of the remains of cover crops and largely serves as soil cover. The cover crop roots beneath the soil surface are where organic material is built up when the roots break down. If the roots are retained and minimum tillage is applied, they will eventually convert to organic material. In short: make sure you keep the roots. Does plant material protect the soil surface? Visualise raindrops and how hard they hit the surface. If you have a protective layer on the surface, the soil will not be stirred up, washed away or blown away when it rains or the wind blows. The disadvantage, however, is that the top layer or hay under the berm will keep the soil cool. If the farm has a history of cold soil, it is not advisable to have a thick layer of organic material on the berms. What also needs to be considered, is that the top layer takes up nitrogen during the breakdown process. This can cause a nitrogen-negative period, during which micro-organisms use the available nitrogen in the soil to break down organic material, leading to nitrogen deficiency for the vineyard. The top layer can also have a water-absorbing sponge effect, especially if the drippers are lifted. Why is organic material important in the soil? I can talk about this all day. Organic material in the soil influences everything, from water- and nutrient-retention capacity, to the sponginess of soil and how forgiving your soil is towards environmental factors. Soil with higher levels of organic material will also be less prone to compaction. How important is copper (Cu) in the plant tissue? Copper improves disease tolerance and is regarded as the “disease nutrient”. Copper is involved in the synthesis of lignin, which helps to strengthen cell walls and offer resistance against pathogens. If you experience problems with disease pressure, it is a good idea to check your soil and plant’s copper levels. If you can increase the copper levels, the crop will have a natural resistance against diseases. Copper also improves the flexibility of vine shoots. The gap between sufficient copper and a deficiency is very narrow; however, toxic concentrations are not much higher than normal levels.

PHOTO 4. Example of poor aeration and delayed water infiltration rate.

PHOTO 5. Lime is calcium carbonate or magnesium carbonate.

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TECHNICAL YEARBOOK 2025