California has a long history with droughts, across its extensive landscape it faces a range of abnormally dry patches and even severe drought. Since 2000, California has experienced the longest duration of drought and 63% of the state’s population currently lives in a drought. This clearly has a very large impact on the functionality of vineyards, however Napa Valley is in a region characterized as abnormally dry, which means it faces short-term dryness that slows planting and the growth of crops, however it is not in a full drought. In lieu of this problem, there has been an emphasis placed on the discussion of water management amongst the viticulture community. In 2016, the American Society of Enology and Viticulture held a symposium which gathered internationally recognized speakers to discuss water policy, salinity management and plant physiology. One of the speakers, Rick Snyder, discussed how irrigation accounts for most of the water inputs, therefore the water lost to evaporation from soil and plants is the primary mechanism of water loss in California vineyards (Fidelibus). There are equations to estimate evapotranspiration (ETc), which have been widely adopted by growers throughout California in order to identify the vineyard water uses and incorporate this information into their irrigation management strategies to reduce water loss.
Many vineyards faced difficulties in 2018 after the California Department of Water Resources declared in May that “14 groundwater basins across the state face threats to groundwater, and this should be reprioritized under the Sustainable Groundwater Management Act (SGMA)” (Weiser). Four of these 14 basins are located in Napa and Sonoma county wine-growing valleys, and are vital sources of irrigation water for grape growing. These wine regions are now confronted with costly groundwater regulations. Sonoma County has budgeted up to $2.7 million to fund groundwater agencies for each of the basins in order to help regulate and control the water sources. The main concern and strategy of vineyard owners is to maximize the benefits of winter rainfall during their dry growing seasons. To make the most of the rainwater, they need to maximize the capacity of the soil reservoir, which is characterized by two factors–the volume of soil available to hold moisture and the intensity of moisture holding within that volume (Lodi Growers). Through preplant deep tillages, which improve both storage capacity and conductance, growers are able to maximize the value of soil reservoir prior to planting. Tillage “alleviates soil compaction, shatters semi pervious subsoil layers, and disrupts distinct boundaries between some subsoil layers…it also allows vine root systems to extend and access moisture in larger volumes of soil” (Lodi Growers).
After planting, it is recommended to deep till, amend and utilize cover crops to maintain root zone conditions that favor vine water acquisition and use efficiency (Lodi Growers). Management practices to enhance this process include sustaining healthy leaves by limiting their number to 12-20 per shoot with two clusters and increasing sunlight exposure. Well-nourished grapevines under moderate water stress use water more efficiently for growth and fruit production so it is important to practice a regulated deficit irrigation schedule. This should sustain moderate grapevine water stress after canopies fully develop. Along with water storage and water use, vineyard managers should also consider water delivery to increase effectiveness of their vineyard water management systems. It is recommended that vineyards install and maintain an irrigation system that uniformly applies water across the vineyard to match the rate of soil intake when wet (Lodi Growers). In practice, these irrigations should be scheduled regularly and for durations that match vine water needs—it is important to avoid over saturating the root zones and exceeding their capacity to hold moisture.
Citations
“Comprehensive Vineyard Water Management.” Lodi Growers, www.lodigrowers.com/comprehensive-vineyard-water-management/.
Fidelibus, Matthew. “Managing Water In California Vineyards.” Growing Produce, 23 Aug. 2016, www.growingproduce.com/fruits/grapes/managing-water-in-california-vineyards/.
Weiser, Matt. “New Groundwater Woes, and Regulations, in California Wine Country.” Oceans, News Deeply, 9 July 2018, www.newsdeeply.com/water/articles/2018/07/02/new-groundwater-woes-and-regulations-in-california-wine-country.