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practicalwinerylibrary.com Access Practical Winery & Vineyard article archives online. TECHNICAL RESOURCE FOR GROWERS & WINERIES 96 Western IPM Center speaks for growers during regulatory review of pesticides By Steve Elliott 98 Q&A with five winery compliance veterans By Ann Reynolds winegrowing Conservation tillage of cover crops in vineyard soils to improve carbon sequestration and diminish greenhouse gas emissions BY Michael Wolff, Maria del Mar Alsina and David R. Smart, UC carbon footprints, here defined as the net amount of GHGs emitted and consumed by a vineyard in production up to the vineyard gate. Davis Department of Viticulture & Enology R educing greenhouse gas emissions from agriculture and other sectors of California's economy has become one of the most important environmental concerns of state and federal regulatory organizations. This is the result of the June 2006 passage of the California Global Warming Solutions Act, Assembly Bill 32, which calls for reducing the state's greenhouse gas (GHG) production to 1993 levels by 2020; and the U.S. Environmental Protection Agency's recent endangerment finding for the primary greenhouse gases (GHGs) produced by agriculture, namely carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). The finding subjects these GHGs to regulation under the California Environmental Quality Act (CEQA). For these reasons more attention is now focused on Abstract Christine Stockert A winter barley cover crop was directly seeded to build up soil organic carbon. 84 p racti c al w i ne ry & v i n e yard NOVEMBER 20 13 Following passage of the California Global Warming Solutions Act of 2006, it is important to understand baseline greenhouse gas emissions from vineyards and examine possible mitigation options through alternative management systems. Carbon budgets that consider fuel use, crop biomass, soil carbon and greenhouse gas emissions will be important metrics of sustainability in the future. In this study, three vineyard floor treatments were maintained for nine years in a Napa Valley vineyard planted to Cabernet Sauvignon on 101-14 rootstock. Treatments were: 1) annually seeded, minimum-till barley cover crop, 2) annually seeded, incorporated and tilled barley cover crop, and 3) incorporated and tilled resident vegetation. Soil carbon analysis indicated that significant quantities of carbon were stored in the minimum-till treatment, and lowest levels were seen in the twice-yearly-tilled cover crop. Emission of soil CO2 (soil respiration) was lowest from the twice-tilled cover crop. These results suggested that twice-yearly tillage reduces the carbon sequestration benefits of seeding a barley cover crop. However, while a minimum-tilled, permanent cover crop may be preferable for carbon sequestration, vine water stress increased in this treatment, resulting in lower pruning Our ultimate goal is to lessen (mitigate) emissions of GHGs like N2O, enhance both CH4 oxidation and photosynthetic CO2 assimilation by California vineyards and foster carbon sequestration into soils, all of which can lower a system's carbon footprint, even to the point where it can be negative. There is limited knowledge available about how well current "sustainable" farming practices mitigate GHG weights and yields. Vine-root presence was higher in surface layers under minimum-till. Growers concerned with their carbon budgets may consider the fuel consumed in agricultural operations such as tillage and seeding, as we have done. In the future it will be important to more closely investigate the frequency with which cover-cropped tractor rows should be tilled in order to optimize both soil carbon sequestration (the building up of soil carbon) and vineyard productivity. The quantity and spatial and temporal distributions of nitrous oxide (N2O) emissions were studied closely. N2O is a greenhouse gas with 298 times higher climate-warming effect than CO2 per molecule. Up to half of global N2O emissions are believed to come from agricultural settings following nitrogen fertilization. Natural N2O production in the soil is heightened when soil microbes are exposed to sudden influxes of inorganic nitrogen fertilizers. Our results indicated that fertilizer-induced N2O emissions in this wine grape vineyard were small, due largely to low inputs (7.5-15 pounds per acre). Differences among tillage treatments were minor, and the majority of emissions followed precipitation. Nevertheless, all fert-irrigation systems should benefit from improved practices in the future. Methane was studied and found to play only a minor role in the carbon budget of the vineyard.