Role of Summer Dormant Perennial Grasses as Intercrops in Rainfed Mediterranean Vineyards

Grass swards are increasingly used in vineyards to improve ecosystem function, reduce vine vigor, and enhance grape (Vitis vinifera L.) quality. In Mediterranean rainfed vineyards, the use of intercropping has been constrained because of excessive competition for water with the vine over summer. We aimed to test cultivars of Mediterranean forage grasses with a range of summer dormancy, which confers low competitiveness for water and high persistence. A 4-yr experiment compared a bare soil control and three perennial grass cultivars as interrows in a vineyard: orchardgrass (Dactylis glomerate L.) 'Kasbah' and 'Bacchus' and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] 'Centurion'. In the spring of 2006, Centurion had extracted water to the 150-cm depth, whereas neither orchardgrasses had extracted water beyond the 120-cm depth. In the summers of 2006 and 2007, Centurion used 30 to 50 mm more of the soil water reserve in the 0- to 150-cm soil layer than the bare soil control. Vine predawn leaf water potential, vine leaf area index (LAI), and biomass of pruned shoot and of vine fruit were also significantly affected by intercrops. The best intercrop was the least competitive cultivar, Kasbah, because of its low biomass production and complete summer dormancy. Bacchus is not summer dormant and was the least persistent. Centurion was the most competitive because of its deep root system and incomplete summer dormancy. The results raise the needs for breeding a larger range of adapted cultivars for intercropping rainfed Mediterranean vineyards.