At their Vineyard Water Conservation Field Day on Friday August 16, Sonoma County Winegrape Commission presented research results in water conservation for viticulture by Rhonda Smith, UCCE (University of California Corporative Extension) Viticulture Farm Advisor, and Mark Greenspan, Advanced Viticulture, at 4001 Cellars in Alexander Valley. The research focused on the efficient use of water to protect and produce grapes without excessive watering.
After a welcome by Nick Frey, Pamela Jeane, Sonoma County Water Agency, presented an update on the current state of the water supply in the Russian River Basin and Lake Mendocino. She stressed the need for water conservation as reservoir storage levels are lower than they have been in recent years, and there are no guaranties that rainfall in the winter will replenish the water levels sufficiently to provide enough water for regular rate payers, spring frost protection, and irrigation.
Many of the regions vineyards use water sprinklers in the early spring to protect their buds from frost. Rhonda Smith presented ongoing research results from UCCE’s frost protection projects, which include real-time weather data collection to provide effective frost protection, and accurate predictions for when sprinkler frost protection should be turned on. A formula based on the Dew Point and Wet-bulb temperature relations shows when frost protecting sprinklers are needed to keep the 30.2 F wet-bulb safe temperature (see chart).
Wind machines which protect vines from frost by circulating the heat in the air, can yield considerable water savings. However, effective inversion is highly dependent on local conditions, so UCCE has put up towers to measure temperature inversion conditions at 65 locations throughout Sonoma, San Luis Obispo, and Santa Barbara. This data can help vineyards determine whether wind machines are a viable option to protect against frost in their location. Visit UCCE’s website to learn more about their frost protection projects.
Mark Greenspan reported on his Western SARE (Sustainable Agriculture Research & Education) supported research on water use efficiency. The findings included avoiding premature irrigation and watering outside the root zone. Greenspan warned against a tendency to early season irrigation, and said that by delaying irrigation and putting particularly red grapes under stress before veraison stimulates the enzyme production in the grapes that help with ripening later on yielding a better result.
Greenspan also stressed the importance of site specific irrigation regimes based on the soil type and conditions of the individual vineyard block and sometimes within the block. A Sandy Loam layer on top of a rocky layer can have strong matrix potential that keeps the water in the surface and channels it out laterally instead of allowing a deeper penetration. This means that prolonged irrigation is useless and that a shorter more frequent regime is called for.
By Kim Johannsen