Cynthia Kallenbach1, William Horwath2, Dennis Rolston3, Jefferey Mitchell1, and Zahangir Kabir1. (1) University of California at Davis, Department of Land, Air and Water Resources, One Shields Avenue, Davis, CA 95616, (2) University of California at Davis, LAWR, 3226 PES Building, Davis, CA 95616-8627, (3) University of California, Davis, Department of Land, Air and Water Resources, One Shields Avenue, Davis, CA 95616
Over a quarter of California’s state land is in agriculture representing a $59 billion dollar industry. California is also the second largest U.S. state emitter of greenhouse gases, of which 8% of total state carbon dioxide (CO2) and 59% of nitrous oxide emissions (N2O) are from agriculture related activities. However, some alternative agricultural management practices such as subsurface drip irrigation, conservation tillage and winter legume cover cropping have the potential to reduce the rate of soil CO2 and N2O evolution as well as sequester carbon. A field trial in California’s Central Valley, planted in processing tomatoes, was used to compare combinations of subsurface drip irrigation (SDI), conservation tillage (CT), and winter legume cover crop (WLCC) to furrow irrigation (FI), standard tillage (CT) and no cover crop (NCC) to evaluate system differences in CO2 and N2O emissions. CO2 and N2O fluxes were measured throughout the growing season every 14 days and during the winter season every three weeks. Annually, the SDI treatments had a CO2 emission rate 4% lower than that of the FI treatments. During the growing season, total CO2 flux was lower in the SDI treatments than in the FI treatments where the winter season showed no significant differences in total CO2 flux between irrigation treatments. Preliminary N2O results show that SDI had lower total N2O emissions compared to FI during the growing season. The highest N2O emissions were found in the FI-WLCC treatments in the furrow (813.60 μg m2- h-1) where the lowest N2O emissions tended to be in the SDI treatments, also in the furrow (4.87 μg m2- h-1). Of the 100 lbs N/acre fertilizer application, 18% was lost as N2O from the FI treatments compared to 4% N lost as N2O in the SDI treatments.