Jonathan Vick, University of California, Davis, Davis, CA, Martin Burger, Dept. LAWR, University of California-Davis, Winters, CA and William R. Horwath, One Shields Avenue, University of California-Davis, Davis, CA
Large peaks in nitrous oxide (N2O), a potent greenhouse gas, are commonly observed following the rewetting of dried soil. Field observations indicated that as much as 15% of seasonal N2O emissions were caused by initial fall rains following the dry summer months. A lab incubation with varying levels of nitrate (0, 30, and 60 mg nitrate-N kg-1 soil) and glucose (0, 5, 10, 20 mg glucose-C kg-1) additions was performed to parse out how denitrification substrates might influence the magnitude of the N2O emission peak observed when dry soil is rewet. Dry soil (approximately 0.02 g H2O g-1 soil) collected from the fallow alley way of a vineyard was rewet at 100% of water holding capacity and N2O emissions were tracked until a return baseline emissions 4 days after rewetting. Additionally, levels of oxygen were tracked using a non-invasive fiber optic oxygen sensor. Emissions exhibited positive responses to additions of both nitrate and glucose, with highest emissions observed when 10 mg glucose-C kg-1 soil was added along with 30 mg nitrate-N kg-1. The effect of glucose on N2O emissions varied between the levels of nitrate additions. There was a weak but significant correlation (R2 = 0.439, p = 0.02) between lowest O2 levels observed through the incubation and total N2O emissions for each treatment. Additional incubation samples were destructively sampled for each time point, providing a picture of the changes in soil inorganic N and labile organic C over the course of the incubation.