What are the advantages of plant cover? How do the plants compete with the vines? Which species should I choose? This article answers the winegrower’s questions about the use of plant cover in the vineyard.
1. What is plant cover?
Plant cover means planting vegetation between the rows of vines.
2. What are the advantages of plant cover?
Plant cover provides an important source of organic matter that promotes biological activity and life in the soil. It also has a structuring role, increasing the stability, porosity and bearing capacity of the soil. Good plant cover will also protect plots from runoff and its negative consequences. Plant cover limits erosion as well as the transfer of pesticides caused by rainfall. This technique therefore represents a significant advantage for biodiversity and offers an array of services for the environment.
3. How do the plants compete with the vines?
Plant cover competes with the vines for water and nitrogen, which can lead to a reduction in vigour and possibly a reduction in yields for the vine. Climate, soil, the type of plant and the type of vine all play a role in this process. The climate plays a major role as it differs from one region to another or from one year to the next, depending on the amount of sunshine and rainfall. Soil also has a strong impact due to its capacity to retain water, its organic matter content and its depth. The type of plant cover will have consequences that vary depending on the species chosen and its life cycle in correlation with the age of the vine, its vigour, its yield and the management techniques used.
4. Which species of plant should I choose?
Over the last twenty years, numerous trials have been conducted and the findings reveal that the least competitive species for vines are the annual species (legumes and grasses). These plants complete their cycle early in the year (in May) and disappear during the summer season, avoiding competition at the most opportune time. They return in autumn but this seasonality makes them very dependent on climatic variations and they do not generally last more than two years.
The choice of species has to be considered in the light of the soil and climate situation and the qualitative objectives pursued. Depending on whether you want to use green manure, in-row plant cover, to focus on biodiversity, aesthetics or even having plant cover on the headlands, there is a wide range of plant species to choose from. Mixes of species are available to winegrowers, and the choice must be made in consultation with the technician. Legumes (clover, alfalfa) are experiencing renewed interest and studies are being continued.
5. What about spontaneous plant cover?
Spontaneous plant cover, which is often the simplest option, should not be neglected: no sowing is required and the species are, by definition, adapted to the climate and the soil. They are easy to kill, which is also an advantage in managing competition and facilitates overall technical management.
6. How do I choose which plant cover to use?
The decision to establish plant cover must be made plot by plot and the objectives sought (competition, soil structure, erosion, etc.) defined in advance. Once established, these objectives will determine the percentage of area to be planted and the choice of species to be sown if you have not opted for natural plant cover.
The species must be chosen first and foremost on the basis of the degree of competition desired or acceptable on the plot; the other criteria allow the choice to be narrowed down. It is often interesting to sow a mixture rather than a single species. This choice guarantees a better establishment of the plant cover.
7. When should you sow your plant cover?
It is preferable to sow in the autumn, as early as possible after the harvest (or even earlier in a Mediterranean climate). Spring sowing is also possible but will be more difficult to establish. Before sowing, carry out shallow soil milling to break up the soil and eliminate weeds. If the vine needs fertilizing, the fertilizer should be applied in-row or carried out by foliar application between the flowering and closing stages of the bunch.
8. Plant cover or no plant cover?
The level of competition depends mainly on the vintage and rainfall. Over several years, we can see that the rainiest vintages are those that result in the least competition from the plant cover. The objective is therefore to adapt depending on the rainfall of the vintage. Irrigation limits competition from plant cover. If you cannot irrigate, the solution lies in destroying the plant cover, but you have to know when and how to do it depending on the year and the winter rains.
9. What are the future prospects for plant cover?
The aim of current research is to rethink vineyard management techniques by including in-row plant cover. The aim is to develop herbicide-free techniques with reduced plant cover (around 30% of the surface area) solely under the vine rows, to avoid excessive competition. We need to know if this type of technique permits simpler row maintenance than mechanical weeding, reducing or even completely eliminating the need for mowing depending on the species. The results of trials conducted in recent years support the researchers’ belief that if the area under plant cover is reduced to a minimum, there is little to no competition. They are now turning their attention to the mechanisation of these operations. The solution could come from robotics, which will completely change vineyard management techniques by requiring less manpower and shorter mowing periods, which could further reduce competition from grass.
10. Why do we see little plant cover in Mediterranean vineyards?
A recent study of 334 winegrowers in Languedoc-Roussillon showed that the main obstacle to establishing plant cover was the fear of excessive competition for the vines. A large majority of the respondents express the same doubts about potential water stress and yield reduction. These fears are indeed verified, as plant cover can lead to a reduction in vine vigour and yield, to a greater or lesser extent. The aim is therefore to find the right amount and method of plant cover, depending on the geographical area and individual needs. The ultimate goal is that each plot of vine should be able to enjoy the benefits of plant cover, while reducing competition from the plants to a minimum.
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