Study Evaluates Impact of Vineyards

UC Davis researchers developing web application to help grapegrowers mitigate GHG emissions

by Jon Tourney
kerry steenwerth uc davis
Dr. Kerri Steenwerth discusses a project to help Napa and Lodi growers evaluate their carbon footprints March 15 in Davis, Calif.
Davis, Calif.—A research project to help grapegrowers manage their carbon footprints and greenhouse gas (GHG) emissions is expected to yield results this year. Data from the study will be used to develop an online application to help vineyard managers maximize soil carbon storage and minimize GHG emissions. Researchers with the University of California, Davis, presented information about the project at the Recent Advances in Viticulture and Enology (RAVE) meeting on March 15.

Management surveys and soil sampling were conducted with 19 Napa, Calif., growers across 72 vineyard blocks, and seven Lodi, Calif., growers across 20 vineyard blocks. The project evaluates the interaction of soil and organic matter, landscape factors and vineyard management practices to determine the environmental footprints of vineyards. Soil scientist Dr. Kerri Steenwerth, who works for the USDA Agricultural Research Service and is an adjunct professor at UC Davis, is the principal investigator for the project, which also involves regional life cycle assessments. The California Department of Food and Agriculture’s Specialty Crops Block Grant program is funding the project.
    What's being measured

    The project presented by Dr. Kerri Steenwerth at the Recent Advances in Viticulture and Enology (RAVE) will evaluate several vineyard site systems. The overall biological system includes soil type, water availability, GHG and topography. Within this is the technical system that includes:

    Technical inputs: materials, fuel and vineyard machinery

    Vineyard setup inputs: land preparation, trellis and irrigation systems and vine planting

    Management inputs: harvest and transportation, water, nutrients, weed and canopy management and the effects of unplanted acreage

    These create outputs: the grape product and emissions to air, water and soil, which lead to environmental impacts.

    Steenwerth observed, “Assessing environmental impacts may sound negative in tone, but this is actually a positive thing, because it will allow growers to identify inputs and practices to reduce their environmental footprints.”

Steenwerth defined life cycle assessment (LCA) as “the assessment of the environmental impact of a given product throughout its lifespan.” While assessments are more commonly done for manufacturing and processing facilities, she said, “For our study, the vineyard is the factory, and the grape is the product, and we’re looking at the environmental impact of all the inputs used to produce the grape.”

The LCA will use data from Napa and Lodi to compare the environmental impacts of winegrape production practices, determine how these impacts vary across management regimes, topography, soil type and land-use history in these regions. Researchers will look at the relative contributions that select practices (such as tillage) have on these impacts and determine which practices may reduce negative impacts and the overall carbon footprint.

Data will be incorporated into an LCA project that the Wine Institute and California Sustainable Winegrowing Alliance (CSWA) are conducting to assess the entire wine production process including winery practices and distribution. The CSWA recently announced that it has developed an online performance metrics tool to help growers and winemakers lower GHG emissions related to energy use.

Measuring GHG emissions
To measure GHG emissions, a PVC collar with a lid (20 cm in diameter) is hammered about 5 cm into the soil to trap soil gas emissions. Readings of carbon dioxide (CO2) and nitrous oxide (N2O) emissions are taken twice per week. In Lodi, GHG emissions were sampled across three soil types at nine sites, with a collar placed in the vine row under the drip line and in the alley between rows at each site. Initial data indicates that sandy soils tended to have lower emissions than clay soils. Steenwerth cautioned, “This doesn’t necessarily mean clay soils will have greater levels of GHG emissions. Clay soils usually hold more organic matter and may have potential to store more carbon, so this should be evaluated over a longer period of time to determine overall impacts.”

The three main GHGs in agriculture are CO2, N2O and methane (CH4). The global warming potential of nitrous oxide is 300 times that of CO2. Total estimated N2O emissions in the United States are much lower than CO2, and an estimated 80% of N2O comes from agricultural lands. N2O emissions increase when nitrogen fertilizers are added to soil. Winegrape vineyards generally use much less nitrogen fertilizer compared with other crops, including raisins and table grapes, and methane is more of an issue with livestock operations.

The study will identify practices to mitigate GHG emissions across the entire vineyard operation, but it is generally believed that the sources of most winegrape vineyard GHGs are the burning of fossil fuels in vineyard machinery and the planting and replanting of vineyards that disturbs soils, releasing soil carbon and GHGs.

GHG regulatory and marketing issues
Under the California Global Warming Solutions Act of 2006, the California Air Resources Board (CARB) will regulate industries and sources of GHG emissions. California estimates of GHG production from agriculture and forestry operations account for just 8.3% of total statewide production of CO2-equivalent metric tons.

UC Davis associate professor Dr. David Smart, a plant physiologist who researches the effects of climate change on vineyards, noted that California agriculture likely will have less regulation from CARB than other industries, but CARB has stated that more data must be provided to assess the impacts of agriculture. Smart also cited recent reports of nitrate contamination in the water wells of some California farm communities related to nitrogen fertilizer applications, which could lead to regulatory action on nitrogen use.

The issue also has marketing implications for vineyards and wineries, as sustainability and carbon neutrality are concerns to more consumers. Smart suggested that some U.S. retailers and export markets in Europe might demand proof of carbon neutrality.

Smart and graduate student researcher Michel Wolff gave a RAVE poster presentation based on several years of data comparing vineyard GHG emissions and global warming potential in different tillage and cover crop systems. The researchers concluded that fuel emissions from equipment, methods and frequency of tillage, and the final disposal of vineyard biomass are the major controls for winegrape vineyard global warming potential.

Smart cited figures for CO2 emissions from tractor operations in vineyards that increased between 2009 and 2010, and he suggested the trend to more vineyard mechanization might require looking at carbon offsets in other vineyard practices.

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