1.3.2.b Soil cover: biomass production and soil protection

Planting cover crops is recommended on a resting plot for several reasons:

• To protect the soil: the microorganisms and organic matter in the soil are sensitive to the sun's UV rays: a bare soil is more directly in contact with UV-A and B rays than a covered soil. Extended exposure can destroy certain bacteria and microorganisms beneficial to soil life.

• To protect the soil against nematodes: some species have nematicidal properties and can potentially fight againt an infestation that caused the grubbing up in the first place. Some examples of crops would be : alfalfa, oats, hairy vetch, coriander.... Barley is also said to have protective properties against root rot. According to the IFV, seedlings sold as nematode-resistant are not necessarily effective against the Xiphinema Index species, also known as the California dagger nematode, which is the main vector of Gravevine Fan leaf virus, since the rooting depth does not exceed 150 cm. However, they are proven to be effective against other species of nematodes, which are responsible for direct damage to the plants.

• Soil aeration, soil structure and limiting erosion risks such as water runoff and nutrient leaching (e.g. nitrates): the installation of cover crops aerates and structures the soil on the surface horizon due to the development of the plant's roots. A mixture or a combination of different varieties inhabit the soil in diverse ways. This structuring work is done progressively and in a flexible manner, which is less traumatic for the soil. Additionally, there are no counter effects, as opposed to deep ploughing for example (formation of hardpans).

• To produce biomass. This boosts soil life and helps break down organic matter. As long as the cover crops are mowed down or sheathed at the right time, the biomass amassed in these plants is returned to the soil, naturally fertilising both the soil and the future vines. These plants are also known as "green manure", as they are grown to increase soil fertility, not for their crop. However, the species and varieties must be adapted to the type of soil and all needs: a grass can have a structuring effect while crucifers will return more of the captured potassium and phosphorus to the soil.