Grapes are the highest value specialty fruit crop produced in the U.S.; all grape products are valued at an estimated $162 billion each year (MKF, 2007). The dry regions of California, Oregon, and Washington account for greater than 90% of U.S. grape production and more than 9% of global grape output (4th after France, Italy and Spain). In 2005, the economic impact of California wine alone was estimated at $51.8 billion to the state. This economic activity contributes more than $3 billion annually to California’s state and local revenues from sales, excise, income, and property taxes. This grape growing region competes globally for economic sustainability. Future success will hinge on public and private policies that facilitate well-informed responses, and competitive adaptations for sustainable viticultural practices based on sound science.
Water scarcity, impaired water quality, decreased soil quality, and aberrant weather are listed among the top risks to grape production in the West. (Thrupp et al., 2008). Australia’s wine industry is feeling the impacts of drought, as several consecutive years of drought have decreased grape yields and wine production in its two primary grape producing regions, the Murray Valley and Barossa region (ABARE, 2008). In the western U.S., similar prolonged drought would have substantial impacts on the economy and food security because the agricultural productivity of this region is dependent on reliable water resources for irrigation (Service 2004; Zilberman et al., 2002) (Table 1). The majority of the West’s irrigation is used in California’s Central Valley and Washington’s Columbia Plateau (NASS 2007), two arid regions with minimal summer rainfall whose irrigation water relies upon adequate winter snowpack in the surrounding mountains. Pacific Northwest agricultural regions receive the majority of their irrigation water from snowpack runoff from the Cascades in Oregon and Washington and the Sierra Nevada in California (Service 2004). Moderate climate change predictions estimate a 60 percent reduction in Cascade snowpack that would translate into a 20-50% reduction in summer surface water (Service 2004). Recent modeling analysis by researchers from Melbourne University in Australia suggests that global warming is 37% percent responsible for recent decreases in rainfall such as the decades-long drought in Australia and a lengthy dry-spell in the Southwestern U.S.
Western states’ water allocations are established based upon centuries-old allotment guidelines, making water availability a policy issue. Governed by the prior appropriation doctrine, western states’ water rights are regulated by a “first come, first served” policy (Schlager, 2006); with allocation rules set by governors and state water agencies (Zilberman, 2001). Due to growing urban populations, climate change, and increasing ecological water demands, it is likely that agricultural water supplies will remain at low levels into the future (Schlager, 2006).
Issues of water scarcity persist beyond California: The arid Pacific Northwest also relies on irrigation water for agricultural production, and water demand in years with inadequate water supplies have negatively impacted the availability of water to farmers in that region. In 2001 and 2005, only 37 percent of the annual allocation of water was available to farmers in junior irrigation districts in Washington (Hart et al., 2001, Anderson et al., 2005). Current patterns in snowpack accumulation indicate a significant decline in irrigation water storage in the Cascades, which the inland Pacific Northwest relies upon for irrigation water availability (Mote et al., 2008).
Evidence now shows that soil salinity is increasing in major grape growing regions of the western U.S. (e.g. Battany 2007 & 2008). This emerging salinity problem is due partly to decreasing quality of irrigation water, but can be exacerbated by water deficits (i.e. agricultural vs. urban water allocations), vineyard management practices (i.e. drip and deficit irrigation), and climatic drought conditions. The salinity problem is likely to worsen under the increasing drought frequency predicted by climate change scenarios (IPCC 2007) because limited winter rainfall prevents the leaching of salts from the rootzone. The emerging salinity problem requires a whole systems research approach that will identify both short and long-term solutions for vineyard managers.
In combination with existing and predicted water availability and scarcity, water efficient crops and management practices are imperative to sustainable agriculture and minimizing water’s impact on crop production. Refining water application rates, improving scheduling of irrigation events based upon berry set, and identifying drought- or salt- tolerant grape varieties could give growers new opportunities to minimize drought damage, ultimately buffering the effects of water scarcity and poor water quality on the U.S. economy and food industry.
This multidisciplinary, regional research study combines the resources and expertise of industry stakeholders, federal scientists, university researchers and extension specialists to address critical needs of the juice, raisin, table and wine grape industries throughout the West. Our project goal is to develop water management strategies that sustain or improve vine yield and fruit quality using less irrigation water and lower quality irrigation water. These critical needs were conceptualized and developed through an iterative, face to face dialogue between our scientific and extension team and industry stakeholders.
This research will address the following six deliverables:
- Sustainable water management strategies for wine, table, raisin, and juice grape production that reduce water requirements.
- Sustainable water and soil management strategies for minimizing the impacts of drought and salinity on the root zone environment, grape yield and quality.
- Establish rootstock recommendations based on drought resistance and salinity tolerance
- Quantify the effects of various water management strategies on fruit and product composition, and sensory qualities
- Quantify the economic impacts of drought and salinity on grape production under different biophysical soil and water characteristics and alternative management strategies
- Disseminate study findings via education and outreach
In red wine grapes, red leaves are the symptoms of several possible stress disorders. One, low P in the vine, is a nutritional disorder. Two others frequently visible are related to the presence of virus disease organisms (either Leaf Roll [GLRD] or Red Blotch [GiGV]). Past research funded by the WGWRP clearly demonstrated grapevine leaf red related to low vine P status (Davenport, unpublished).
Over the past two growing seasons we have conducted field surveys of vineyards suspected of having low P due to leaf symptoms. In 2013, samples were also virus tested and GiGV showed positive on only 2 of 13 blocks tested, yet all vineyards showed leaf redness. This clearly shows that there are red wine grape vineyards in central Washington that could benefit from supplementation with P fertilizer. However, P has very low solubility and dispersion in soils (Lindsay and Velk, 1977). Thus, soil applications, even of liquids through the drip system, may or may not be as effective as foliar applications.
In addition, although there is no research that links the red discoloration seen in leaf tissue of red wine grapes infected with GiGV or GLRD with the biochemical pathway as P deficient plants, the similarity in symptoms suggests that supplemental P may alleviate the symptoms. While this is strictly a hypothesis in grapes, it has been shown that the adverse effects of little leaf virus in sweet cherry can be mitigated with supplemental zinc, a deficiency of which manifests as small leaves (Eastwell, personal communication). Thus, while it is highly unlikely that supplemental P fertilizer would overcome the symptoms of these viri, it is possible that it could at least provide some mitigation.
Objectives of the Research:
- Compare fertilizer rates and soil vs foliar application in correcting low grape P
- Evaluate impact of supplemental P fertilizers on Grape Leaf Roll (GLRD) and Red Blotch (GiGV) affected vineyards.