Conservation Tillage of Cover Crops as a Means of Improving Carbon Sequestration and Diminishing Greenhouse Gas Emissions in California Vineyards Soils
Reducing 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 1) the passage of the California Global Warming Solutions Act, Assembly Bill 32 (AB32) in June of 2006, 2) the US EPA?s recent endangerment finding for GHGs of CO2, N2O and CH4 (http://www.epa.gov/climatechange/). This project represents the culmination of an overarching effort to accurately quantify CO2, N2O and CH4 emissions from vineyards, soil carbon (C) sequestration, and above- and belowground annual net primary productivity of C. The project coordinates with efforts by Dr. William Salas (Applied Geosolutions LLC), Dr. Changsheng Li (University of New Hampshire, Institute for the Study of Earth, Oceans and Space) and Alison Jordan of the Wine Institute to calibrate the DeNitrification DeComposition model (DNDC). The model will be embedded into a decision support system (DSS) for use by grape growers and other practitioners for carbon assessments (http://www.wineinstitute.org/ ghgprotocol). The modeling exercises will allow us to test multiple management practices in order to lessen (mitigate) N2O emissions from California vineyards. The data is being made available to Dr. Alissa Kendall and Sonja Brodt of the Department of Agricultural and Environmental Engineering and Agricultural Sustainability Institute to assemble life cycle analyses for carbon footprints of vineyards and orchards. We are quickly approaching that objective for a conventionally managed vineyard and a vineyard managed under minimum-till conditions to increase soil C sequestration. There is currently tremendous uncertainty concerning the quantity of GHGs produced and consumed in vineyards (Carlisle et al., 2008). It is estimated that in vineyard land managed under no-till, soil carbon sequestration would greatly increase (Kroodsma and Field, 2006) but little data exists to support this contention. Our research led to working budgets of GHGs and C sequestration in a Napa Valley vineyard being managed with three tillage treatments. These treatments were: (1) minimum-tillage with a barley cover crop (no-till); (2) conventional tillage with the same barley cover crop; and, (3) conventional tillage of weeds, where conventional tillage refers to disked and disked and rolled twice yearly in spring and fall (2 x 2 passes). The major research success of this project concerns a comprehensive carbon footprint for a Napa Valley vineyard under minimum tillage (no-till) conditions. The deliverable results included a number of important observations that emerged from quantifying variables needed for a footprint assessment. These are: (1) long-term increase of soil carbon under the minimum tilled cover crop; (2) slightly higher rates of N2O loss from minimum tillage cover crop; (3) apparent loss of soil carbon in the conventional tilled cover crop; (4) soil carbon sequestration potential observable at depth (1.2 meters); (5) methane oxidation and therefore GHG offsets under all treatment conditions; (6) a shift in root distribution under minimum tillage that resulted in higher carbon deposition; (7) successful spatial modeling of N2O emissions in the area around N¬fertigation drip emitter to increase accuracy of scaling emissions; (8) temporal constraint of N2O emissions to an annual budget for assessing offsets; and, (9) observation of desirable vine de¬vigoration under the minimum tillage treatment.