Research on Agricultural Emissions & Mitigation
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California agriculture, with over 400 commodities, provides high quality food for Californians and people around the nation and the world. However, California cropland is also a primary emission source of N2O, a potent greenhouse gas (GHG) damaging climate, in the State, contributing over 50% of the state total N2O emission inventory. N2O is produced from soil through microbial processes that convert nitrogen from nitrogen fertilizers, manure, and crop residues into various nitrogen gases, including N2O. These microbial processes can be affected by environmental conditions which change constantly, leading to substantial uncertainties in N2O emission estimates. CARB’s in-house and extramural research projects investigate N2O emissions from diverse California cropping systems and explore alternative management options that can cut N2O and overall GHG emissions from California cropland and help California agriculture to be more productive and sustainable.
Below, we present just a few of our research projects on this topic.
Dairy Farm Research Projects
Characterize physical and chemical properties of manure in California dairy systems to improve greenhouse gas emission estimates (Contract 16RD002, active) Dairy farms will be selected to represent the various types of manure management systems, including scraping, flushing, solids separation, lagoon storage, covered lagoon digestion, and solids digestion, etc. Representative samples of manure will be taken from each manure pathway to determine the nutrient flow at each stage of management. Results will be compared to U.S. EPA assumptions about volatile solids in manure management systems modeled according to farm-size, temperature, and other modeled factors related to methane production.
Assessment of nitrous oxide emissions in California's dairy systems (Contract 09-325, Completed in 2013) Nitrous oxide (N2O), a greenhouse gas, is produced by soil microorganisms. Nitrogen (N) inputs, soil moisture and carbon stimulate the production of this gas, which accounts for about one third of all GHGs from California’s agriculture sector. Nitrogen inputs, crop N removal, and cumulative N2O emissions were measured from spring 2011 to fall 2012 in three dairy forage production systems receiving liquid and solid manure, as well as synthetic N fertilizer. To lower N2O emission potential, applying N incrementally in moderate doses with the irrigation water according to crop N demand is recommended.
Quantification of the emission reduction benefits of mitigation strategies for dairy silage (Contract 11-325, Completed in 2016) The focus of the research was on monitoring and modeling of volatile organic compound production using silage additives, as well as emissions mitigation via various silage storage methods, de-facing practices, and feed management approaches.
Soil and Crop Research Projects
Improving DNDC modeling capability to quantify mitigation potential of nitrous oxide from California agricultural soils (Contract 14-306) The project will develop and deliver to CARB a quantitative tool to further refine a process-based DNDC (DeNitrification-DeComposition) model based on new N2O emission data obtained from available mitigation studies and new understanding of N2O emission mechanisms. The improved capability of quantifying N2O emission reductions under a variety of management practices will bolster the State’s ability to develop greenhouse gas mitigation strategies that are essential for meeting long-term climate change goals set forth by Assembly Bill 32.
Evaluating mitigation options of nitrous oxide emissions in California cropping systems (Contract 11-313, Completed in 2016) The rates of N2O emissions depend on cropping system nitrogen (N) inputs and biophysical factors that can be influenced by soil management. Previously (Contract 08-324, see below), investigators quantified the N2O emissions in N rate trials in tomato, lettuce, wheat, and rice systems to demonstrate the reductions in emissions possible at proper N fertilization rates. In this study, investigators evaluated additional management practices related to N fertilization and irrigation that can be used as N2O emissions mitigation techniques in side-by-side on-farm field experiments that included measurements of yields and N use efficiency in tomato, corn, and lettuce.
Assessment of baseline nitrous oxide emissions in California cropping systems (Contract 08-324, Completed in 2012) Crop yields and cumulative N2O emissions were measured for two years in tomato, wheat, lettuce, and rice cropping systems fertilized at various N rates. Alfalfa was also monitored.