Developing sustainable irrigation practices in Cabernet Sauvignon and Concord vineyards in central Washington

Thesis (Ph.D.), Department of Crop and Soil Sciences, Washington State UniversityRegulated deficit irrigation (RDI) is a management technique used in wine grape (Vitis vinifera L.) production to control vegetative growth and improve fruit quality. However, the severity of the deficit imposed varies widely among growers. RDI also has the potential to reduce water use in juice grape (Vitis labrusca L.Bailey) production, as current strategy is to fully irrigate throughout the season. The objectives of this project were to evaluate the effects of a range of deficit irrigation treatments on: (a) the temporal and spatial variation in soil water content, (b) the yield and quality of `Cabernet Sauvignon' wine grapes, and (c) the yield and quality of `Concord' juice grapes.Field study was conducted over four years in both a commercial `Cabernet Sauvignon' and `Concord' vineyard. The `Cabernet Sauvignon' trial increased the water application by one third of the current practice (extreme deficit) based on grapevine phenology, while the `Concord' treatments reduced the amount of water applied from bloom to veraison. Soil was intensively sampled three times during the growing season to determine seasonal and spatial variation in water availability. Shoot growth and shaded area under the canopy were measured as plant stress indicators. Yield and fruit quality were analyzed for differences between treatments.Soil water distribution data indicated that increased distance from the drip emitter decreased soil water content. The majority of the plant available water was within 50 cm of the emitter. In the `Cabernet Sauvignon' increasing the amount of water applied increased yield, but not significantly. However, reducing water in the `Concord' grapes resulted in a significant decrease in yield, but after a period of adaptation, the yield of the RDI vines was the same as the control. There were no statistical differences in the quality of either the `Cabernet Sauvignon' or `Concord' grapes.RDI significantly reduced soil water availability at veraison, but the deficit was replenished by the end of the season. Water use efficiency was maximized in `Cabernet Sauvignon' when additional water was applied post-veraison. RDI in `Concord' initially reduced yields, but the vines adapted over time.Department of Crop and Soil Sciences, Washington State Universit