Mulching helps control weeds by covering the soil. It acts as a physical barrier by limiting the light weeds need to grow.
Mulching can help retain a large quantity of water and it also limits the phenomena of leaching, surface runoff and erosion. As such, it maintains adequate humidity which in turn reduces water stress. It is also highly suitable for young trees and shrubs.
Soil fungi then slowly degrade the lignin in the mulch cover, which makes the leftover woody elements accessible for plant uptake. This also improves the pedological structure of the soil, limits the formation of a soil crust, favors soil enrichment with organic matter and minerals accessible to the vine, and increases the presence of microfauna (mainly earthworms).
Another potential benefit is that it reduces the risk of water splashing on the vine ("splash" effect) and thus reduces the risk of cryptogamic contamination.
Young shrub mulching at Château Latour
Mulch can rot and form a layer that is impermeable to water and air. This occurs when several layers of exogenous mulch have accumulated and/or been compacted repeatedly by passing farm machinery.
The degradation of exogenous mulch by microorganisms can result in what is called "nitrogen starvation". These microorganisms use the nitrogen in the soil to degrade the mulch's organic matter and this can result in a lack of nitrogen for vine growth. Mulch made of RCW seems to be the predominnant cause of this problem. Unlike straw, it is made of lignin and has a very high C/N ratio (around 80 depending on the raw material components). Consequently, a lot of nitrogen is required to break down the organic matter. The fungi that degrade the lignin need this nitrogen and take it from the soil, giving rise to intense competition for nitrogen (hence the term nitrogen starvation). If this happens, the type of mulch should be adjusted. A nitrogen fertilizer can also be applied if necessary.
Some mulches can cause machinary to slip when there is high humidity on the plots or when the plot is on a slope. In this situation, the potential loss of machine maneuverability and falling risks should be taken into account.