Nitrous Oxide Emissions From California Silage Corn Cropping Systems: I. Sampling Techniques and Preliminary Results.

In California, 55 % of all nitrous oxide (N₂O) emissions have been estimated to come from agricultural soil. The California Global Warming Solutions Act of 2006 (AB 32) mandates that the State develops comprehensive strategies to reduce greenhouse gas emissions. The main objective of this project was to determine detailed time series of N₂O fluxes and underlying factors at crucial management events (irrigation, fertilization, etc.) in the production of silage corn grown on dairies in the Central Valley of California. In this presentation we review the sampling techniques and the preliminary results obtained from measurements conducted late Summer and early Fall 2010. Procedures involving the use of static flux chambers and a Photoacoustic Field Gas-Monitor 1412 (INNOVA AirTech Instruments) for N₂O emissions will be discussed. Field observations, such as crop biomass and yield, soil climate, SOC storage dynamics, soil ammonium and nitrate contents, and emissions of N₂O, will be utilized to calibrate and validate a processed based NUtrient and Greenhouse Gas Evaluation Tool (NUGGET) model. Decomposition, nitrification, denitrification and other processes related to soil C and N transformations will be simulated by NUGGET-DNDC (Denitrification-Decomposition), and the modeled dynamics of the processes will be compared with field results to interpreting the observations.  Thus, the understandings gained from the field measurements regarding the interactions among climate/soil conditions, management practices, SOC dynamics and N₂O emissions will be synthesized in NUGGET-DNDC. The NUGGET will be important for evaluating the short- and long-term impact of these management practices on crop yields, soil biogeochemical processes, soil fertility (organic carbon and organic matter) and environmental impacts (i.e., greenhouse gas emissions, nitrate leaching and ammonia volatilization).