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46 Wines&Vines January 2015 grapegrowing irrigation early and often, and parts that rarely need water until after véraison." Such flexibility requires him to keep track of several variables at once. For the vine, he considers variety, transpira- tion, rootstock, root structure and depth. For the vineyard, he evaluates evaporation, soil field capacity, soil type and permanent wilting point. The evapotranspiration rate helps him de- termine how much water to add to the root zone to replenish the vineyard block. Soil type and root depth tells him how many hours to irrigate. "It might take three hours at 1 gallon per hour to saturate coarse-textured soil or six hours to saturate heavy clay soil," he says. Rocky soil could receive two sets of three hours each, while clay soil could absorb one six-hour set. "The same holds true for soil depth," he says. "I irrigate shallow soils at a higher frequency and lower volume, and vice versa for deeper soils." Rootstocks affect the volume and irriga- tion rate, too. "Some rootstocks like 039-16 are very vigorous, but if you stress them too much they shut down and never recover," he says. "Drought-tolerant, high-vigor root- stocks like 140Ru and 1103P can handle stress, and are typically used on low-vigor sites because of their potential for vegetative growth where resources are plentiful." His ability to gather data on each vineyard block and calculate a water budget from an evapotranspiration rate, RDI coefficient, vine spacing, rainfall and irrigation patterns that reflect the character of a vineyard allow him to prescribe an efficient irrigation rate for each estate. This year, he irrigated Rockaway Ranch at 40% of its evapotranspiration rate saving 56 acre-feet or nearly 18 million gallons of water across the 130 acre hillside vineyard. Taking into account that the evapotranspiration rate and the RDI coefficient can vary widely from vineyard to vineyard, Rodney Strong Wine Estates saved approximately 430 acre-feet or 140 million gallons of water this season. A mountaintop or hillside vineyard like Rockaway Ranch contains several soil types. Alexander's Crown soil on slopes and ridges can be rocky and shallow—holding less water. (707) 431–9342 westectank.com