Suchergebnisse

Of the greenhouse gases emitted from cropland, nitrous oxide (N2O) has the highest global warming potential. The state of California acknowledges that agriculture both contributes to and is affected by climate change, and in 2016 it adopted legislation to help growers reduce emissions of greenhouse gases, explicitly including N2O. Nitrous oxide emissions can vary widely due to environmental and agronomic factors with most emission estimates coming from temperate grain systems. There is, however, a dearth of emission estimates from perennial and vegetable cropping systems commonly found in California's Mediterranean climate. Therefore, emission factors (EFs) specific to California conditions are needed to accurately assess statewide N2O emissions and mitigation options. In this paper, we review 16 studies reporting annual and seasonal N2O emissions. This data set represents all available studies on measured emissions at the whole field scale and on an event basis. Through this series of studies, we discuss how such farm management and environmental factors influence N2O emissions from California agriculture and may serve as a basis for improved EF calculations.

California state legislation passed in 1991 mandated a phased reduction of rice straw burning in the Central Valley, to reduce air pollution. In 1993, UC Davis scientists launched an 8-year research project on the long-term effects of various alternative means of managing rice straw. Burning, incorporation into the soil, rolling, and baling and removing the straw were compared, with and without winter flooding. None of the various practices reduced grain yields on our experimental plots, but there was an increase in weeds when straw was incorporated, and in particular when the fields were not winter flooded. However, when straw is incorporated, nutrients are returned to the soil and less nitrogen fertilizer can be applied, resulting in lower production costs and less potential for water pollution. In addition, waterfowl on the Pacific Flyway benefit significantly from the wetlands created when fields are flooded during the winter.