Effects of irrigation regime on canopy water use and dry matter production of ‘Tempranillo’ grapevines in the semi-arid climate of Southern Oregon, USA

Abstract

Vine water use and dry matter production were measured in a Vitis vinifera L. cv. ‘Tempranillo’ vineyard in Southern Oregon, USA, a semi-arid region. Whole-canopy chambers were custom-built for gas exchange measurements at two phenological stages, pre-véraison and post-véraison, on mature grapevines that were irrigated at three different levels: (i) full irrigation, where 100% of crop evapotranspiration (ETc) was provided (FI); (ii) sustained deficit irrigation, where 50% ETc was provided for the remainder of the season once a specific threshold of vine water status was reached (SDI); and, (iii) regulated deficit irrigation, where 30% ETc was provided once the same threshold was reached until véraison and increased to 50% ETc during the post-véraison to harvest period (RDI). Soil moisture was monitored continuously in all treatments, and vine water status was measured bi-weekly. Despite similar environmental conditions at both timepoints, differences in whole-vine gas exchange were not apparent between irrigation treatments at pre-véraison but were marked post-véraison when vine water status differences were greater. Vine water use and dry matter production were both positively-related to irrigation level. Instantaneous water use efficiency peaked early in the day but was not higher on a daily basis in deficit-irrigated vines likely due to their higher dark respiration rates. Nocturnal transpiration was also positively-related to irrigation level and represented nearly one-third of daily water use in the FI vines but near zero in the RDI vines. These results are discussed in the context of common deficit irrigation scheduling practices in vineyards and shed light on the limitations of ETc-based approaches.