Water Management in Sonoma County Grape Production

View the project final report

Commodities

• Fruits: grapes

Practices

• Crop Production: irrigation
• Education and Training: demonstration, extension, farmer to farmer, workshop

Water conservation in Sonoma County grape production is especially important because threatened or endangered salmonids are found in the Russian River watershed and may be deemed vulnerable. Growers must use water wisely when frost protecting and irrigating vines in order to maintain grape production while minimizing impacts on the stream flows that are critical to salmonid survival. This project was designed to provide growers with information on alternatives to frost protection using overhead sprinklers, on irrigation managements strategies to reduce water use, and on Best Management Practices for water conservation when frost protecting and irrigating grape vines.

This project had three components: 1) An evaluation of spray products on grapevines to evaluate their effectiveness in protecting against frost damage; 2) irrigation demonstrations in different soil types where irrigation scheduling and duration were determined based upon soil and plant water status measurements; and 3) grower outreach to provide Best Management Practices (BMPs) for water conservation when frost protecting and irrigating grape vines.

We conducted a trial in 2013 to evaluate frost protection spray products. A site was selected in which spring frosts had occurred on one or more days each year for the previous 19 years. Materials were provided by agricultural product retailers that are commonly requested by growers or which had been recently introduced to the market for this purpose. Unfortunately, in 2013 post bud break temperatures at the trial site remained above the critical temperature (32 °F), therefore green tissue damage of leaf blades, shoots and flower clusters did not occur. No data were collected and the efficacy of the products could not be evaluated.

We demonstrated a water management technique for drip irrigation that relies on measurements, both of soil moisture and plant moisture status. The above and below ground measurements provide an excellent picture of the moisture dynamics of the vineyard. This gives us the confidence to push our vines further into levels of controlled stress that have benefits well beyond that of water conservation. It also allows us to produce riper fruit at lower brix (data not collected but observed at many sites in the North Coast), while preventing excessive stress that could lead to reduced vineyard productivity and lower yields.

The irrigation management procedure is thus:

Observe shoot tips and plant water status measurements to delay the first irrigation events for the growing season.

Attain the target leaf water potential and stomatal conductance at or before two weeks prior to veraison and maintain those through veraison.

Use soil moisture profile data to determine active root uptake zones and depth of irrigation percolation.

Use average soil moisture in the profile to determine the duration for which moisture is returned to levels prior to each irrigation – this is the proper irrigation interval for non-deficit or surplus irrigation.

Mild water stress levels will reduce the need for irrigation, and we typically find irrigating at 18-24% of crop evapotranspiration (ET) is sufficient to maintain the canopy and crop (under mild stress conditions). Irrigation may be increased closer to harvest without negative consequences, as long as irrigation is not excessive.

Introduction

Despite naturally high levels of winter rainfall in typical years, water is a scarce resource in Sonoma County, and competition from various interests (agricultural, municipal and environmental) has increasingly become contentious. The use of water for frost protection and seasonal irrigation specifically in vineyards has come under scrutiny by California's State Water Resources Control Board (SWRCB) and the National Marine Fisheries. Either or both of these agencies could limit the use of water for frost protection of grapes in the Russian River watershed during the critical frost season.

There are almost 60,000 acres of vineyards in Sonoma County. Coho salmon in the county are listed as "endangered" under the federal Endangered Species Act (ESA). Chinook salmon and steelhead also found in the county are listed as "threatened" under the ESA. The use of water to protect grapevines from spring frosts poses risks to these species due to the instantaneous demand for water during frost events, and alleged fish takes due to stranding have occurred in association with frost events. Low flows in surface waterways pose additional risk to salmonids during summer months when there is no rainfall, yet the vines require water to irrigate.

In order to preserve grape growing in Sonoma County and protect threatened and endangered salmonids, growers need to improve water use efficiency for both frost protection and irrigation. Currently, many growers measure only ambient temperature to determine when to activate frost protection; however, knowledge of the dew point is also required to accurately determine the risk of frost damage. Growers typically use an elevated temperature threshold (35-36 degrees, for example) to trigger frost protection as a conservative approach to timing frost protection. Unfortunately, that approach often leads to unneeded or premature activation of overhead sprinkler systems and unnecessary use of water. This Western SARE funded project conducted outreach to growers via multiple methods and provided guidance for optimal decision-making for frost protection operation.

Frost protection by applications of agricultural crop sprays has been suggested as alternatives to frost water application by the SWRCB. Antibacterial sprays, often containing copper, have been shown in some crops (not grapes) to reduce the population of ice nucleating bacteria on plant surfaces, thus reducing intercellular ice formation inside the plant and subsequent tissue damage. This project attempted to conduct an objective evaluation of selected materials in a producer's vineyard that does not use overhead sprinklers for frost protection. The goal was to determine the efficacy of these materials, especially materials that do not contain copper, in order to reduce copper use in the watershed. Salmonid species are very sensitive to copper in streams and, thus, reductions in copper use can benefit salmonids. Although materials were applied each spring, there were no frost events in the project’s vineyards. This is an area for future research.

Irrigation is another major use of water by the wine grape growers of the region. It is believed that growers, though intending to be good stewards, continue to irrigate prematurely each year and may irrigate in an inefficient manner. New technologies for measuring soil and plant moisture status are available to guide more efficient irrigation. We believed, from previously executed surveys and field demonstrations, that many growers could collectively conserve 30% or more of the applied irrigation water and maintain economic yields, all the while improving wine quality.

For this project, we measured soil and plant moisture status at vineyard sites to enable grower exposure to these technologies. The project worked with a grower to fine-tune irrigation based on soil and plant water status data, vine observations and overall strategies for winegrape production. The sites were selected to represent variations of soil characteristics. Results from the demonstrations were communicated to growers through workshops and field days, newsletter articles and on the Commission website www.sonomawinegrape.org.

Sonoma County grape growers have traditionally, and enthusiastically, participated in grower educational events and programs to improve their production practices. Changes in practices have been documented for pesticide use, for example. Thus, improved management practices identified in these demonstrations are likely to result in improved efficiencies in water use for both frost protection and irrigation. The results from this project have been especially timely given the severe 2014 drought conditions in Sonoma County.

Frost Protection:

• Explore alternative methods to overhead sprinkler frost protection: demonstrate the efficacy, if any, of applied frost protection materials such as antitranspirants and copper fungicides/bactericides in a Sonoma County vineyard. Spring 2013.
• Improve the utilization of a relatively new network of weather stations to measure temperature and dew point at key locations across the county. Real-time weather data from a nearby weather station can be accessed by growers at no charge to determine when frost protection systems are needed. The system provides email or text message alarms to be set to alert growers of frost risk. In this manner, frost risks and frost water application initiation and termination can be improved and water saved. Spring 2012 and 2013. (In spring 2014, a minor Western SARE project budget revision was approved, which allowed for the purchase of a new datalogger for the Kenwood area weather station. This weather station is located in the coldest area of Kenwood, which is located in northern Sonoma Valley. This new datalogger replaced an outdated piece of equipment, which provided system information every fifteen minutes and with questionable accuracy. The new datalogger reports weather data in real-time to accurately predict frost event temperatures critical to the timing of turning on and turning off water for frost protection. This new technology also has the ability to accomodate the utilization of soil moisture probes.)
• In addition, this project looked to provide education to reduce or avoid false or early triggering of overhead sprinklers and share best management practices for the proper triggering of overhead sprinklers for frost protection to alleviate overuse during frost episodes. Spring 2012 and 2013.

Irrigation Management:

• Avoid premature applications of irrigation to vineyards by taking advantage of soil moisture storage from winter and spring precipitation. Delay the initiation of irrigation applications until soil moisture diminishes to the point where irrigation is necessary. Monitor soil moisture, plant moisture status and visual (shoot length and shoot tip) indicators of impending moisture stress to determine the decisions for initiating irrigation. Summer 2012 and 2013.
• Avoid deep percolation of irrigation, water which wastes water and has the potential for groundwater contamination. Demonstrate how to use soil moisture monitoring equipment in Sonoma County vineyards and/or vineyard blocks to determine proper volume of applied to avoid excessively deep water movement. Summer 2012 and 2013.
• Avoid excessive use of irrigation water by adjusting intervals based on need. Demonstrate the use of soil moisture monitoring equipment in Sonoma County vineyards and/or blocks and how it may be used to determine proper intervals between irrigation applications. Summer 2012 and 2013.
• Determine proper site-specific irrigation regimes. Demonstrate different irrigation practices appropriate for representative soil types and conditions in Sonoma County vineyards and/or blocks. Summer 2012 and 2013.
• Demonstrate the benefits and limitations of plant water status measurements under different climatic and soil conditions in Sonoma County vineyards. Summer 2012 through 2013.
• Demonstrate the differences in wine styles arising from different irrigation regimes applied to similar and adjacent vineyard blocks using a collaborator's commercial winery to process fruit from demonstration blocks. Fall 2012 through 2013.