Spatial and temporal changes to the water regime of a Mediterranean vineyard due to the adoption of cover cropping

The use of cover cropping is currently increasing in vineyards but its development remains hampered in Mediterranean regions because of the possibility of severe competition for resources. However, recent studies on intercropping in vineyards have shown that in some situations, water stress may not be greater than that prevailing in bare soil vineyards. Over a 4-year period, we studied the effects of introducing a cover crop in terms of temporal and spatial (i.e. row vs. inter-row) changes to the water regime of a Mediterranean vineyard. The experiments compared the water dynamics prevailing under three different treatments: a perennial cover crop, annual cover crop or the use of chemical weed control. A compensatory growth of the grapevine root system was revealed, thus partly prevented direct competition for resources between it and the intercrop. The rooting of a permanent cover crop was deeper than that of an annual crop, with a higher root density. Consequently, the soil compartment dried by the cover crop was larger and the grapevine was forced to explore deeper soil layers. In the presence of a cover crop on the inter-row, the grapevine also concentrated its root system below the row and dried out this soil compartment more intensively. Overall, associating grapevine with a cover crop led to a spatial distinction of soil zones exploited by the two species. The present study provides evidence that this spatial shift mainly resulted from a temporal shift in the dynamics of resource uptake by the associated species. Indeed, cover crops began to take up water before grapevine budbreak and had almost completely dried out the soil compartment they explored before grapevine water uptake became significant. This led the grapevine to modify its rooting and explore other soil zones. This phenomenon is possible in deep soils and limits competition for water between the grapevine and cover crop. Such competition is also reduced because of better soil water replenishment during the winter in the presence of a cover crop. Nevertheless, our experiments showed that this additional water mainly benefited the intercrop and did not totally compensate for transpiration by the grass cover. In conclusion, this work shows how cover cropping can spatially and temporally modify the water regime of a vineyard, and how grapevine can partially adapt to limit water competition under certain conditions. These findings provide a clearer understanding of the water dynamics prevailing in such a system, and an opportunity to model these dynamics.