Conservation Tillage of Cover Crops as a Means of Improving Carbon Sequestration and Diminishing Greenhouse Gas Emissions in California Vineyard Soils
Recent legislation, specifically, The California Global Warming Solutions Act of 2006, or AB 32, as well as marketing demands, have placed a tremendous emphasis on sustainable production practices, including those defined in terms of diminishing carbon footprints in vineyards. A carbon footprint can be defined as a comprehensive measure of the amount of greenhouse gases (GHGs) we are producing and consuming, and provides an indication of whether or not we are contributing to the increase of GHGs in the atmosphere and therefore to global climatic change. There is currently tremendous uncertainty concerning the quantity of GHGs produced and consumed in vineyards (Carlisle et al., 2008). In a recent report it was estimated that if vineyard land was managed under no-till or conservation tillage conditions, soil carbon sequestration would greatly increase, and thus diminish the overall C-footprint (Kroodsma and Field, 2006). Our research aims to construct working budgets of GHGs and carbon sequestration in a Napa Valley vineyard being managed under ?conservation? and conventional tillage practices, with cover crops. The GHGs being studied are those defined by the International Panel on Climate Change?s 2006 Assessment (IPCC, 2006) and consist of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). It is essential that we improve understanding of vineyards? role in promulgating or absorbing these gases. Little research is so far available on these topics for California vineyards (Carlisle et al., 2008). Our definition of conservation tillage (minimum-till) consists of surface disking (2.5 cm) in fall when needed to prepare a seed bed for cover crops, and deep tillage (15-20 cm) each 5th year to alleviate issues related to de-vigoration of vines. We are currently in the first year of work on a block with three five-year-old tillage treatments. These treatments are: (1) Minimum-Till with a barley cover crop; (2) Conventional Till with a barley cover crop; and (3) Conventional Till with resident vegetation. The Minimum-Till treatment was disked heavily for the first time during October of 2008 (year 5), adhering to decisions that many viticulturalists might make with a long-established conservation-tilled cover crop. Several important results have emerged from our measurements, which require further experimentation. These are: (1) vine devigoration in Min-Till rows; (2) apparently low carbon sequestration in the Conventional Till-cover cropped treatment; and (3) Deep carbon sequestration potential observable at depth (1.2 meters).