Soil water dynamics and drought stress response of Vitis vinifera L. in steep slope vineyard systems

The accessibility to water is a crucial factor for grapevine performance in vineyards. A sufficient supply of water favors vegetative growth, yield formation and fruit ripening. Under a changing climate, especially steep slope wine-growing regions may face severe problems in soil moisture conservation due to oftentimes lower soil water holding capacity and a larger radiation intake on the, usually South-facing, hill slopes, which causes a higher evaporative demand compared to vineyards in the flat. The impact of two steep slope vineyard management systems on water retention and drought stress response of grapevines was assessed. Soil water dynamics in the inter-vine space of steep slope sites planted downslope (control, C) and of terraces (T) were compared. Terraced vineyards were capable to retain up to a 40 % higher relative percentage of winter precipitation, compared to the control. Vines in the early years of their adaption phase planted on terraced vineyards generally displayed a higher drought stress response, showed lower vigour, lower yield and lower sugar yield. The older the terrace system, the better the performance compared to C became. This suggests a high competition of young grapevines to the cover cropped embankments of terraced vineyards. Therefore, means to improve root development and to reduce water and nutrient competition in the early years of terrace construction are crucial for successful grapevine adaptation, for the increase of resilience to abiotic stress factors and finally for the maintenance of valuable steep slope vineyard sites for grapevine cultivation.