Adapting cover crop soil coverage to soil depth to limit competition for water in a Mediterranean vineyard

Cover crops could provide many interesting environmental services for vineyards, but French Mediterranean winegrowers mostly avoid permanent cover cropping because they fear too much competition and consequently a reduction in grapevine yield. To better understand the effect of cover cropping management on vine growth and yield, we carried out our study in a vineyard of Shiraz (Vitis vinifera L.) in the Mediterranean region of France over three consecutive years. Three cover crop strategies were monitored (30CC, 60CC and 100CC corresponding respectively to 30%, 60% and 100% of cover crop soil coverage) on two types of soils (shallow and deep), and compared with bare soil (0CC corresponding to 0% cover crop, controlled with chemical weeding). Grapevine growth, yield and soil moisture were measured and the fraction of transpirable soil water (FTSW) was simulated using a water balance model. Grapevine yields decreased as the cover crop soil coverage increased, and these yield reductions were found to be more severe in the shallow soil. Nevertheless, the 30CC treatment appeared to be both feasible and useful for ecosystem services such as soil protection whatever the soil depth. Moreover, FTSW was found to be relevant as an early yield indicator that could be useful to adapt the cover crop strategy to seasonal climate characteristics. The findings support the feasibility of a cover crop-based strategy, even in the Mediterranean region, as an effective measure to reduce the use of herbicides and fossil fuels without significantly decreasing the grape yield, provided that the winegrowers adapt their strategy to the soil depth and to the seasonal climatic conditions.