UC Riverside

In California, agriculture contributes about 9% of the state’s greenhouse gas (GHG) and 72% of ammonia (NH3) emissions due to fertilizer application, livestock manure management, and enteric fermentation. California climate legislation seeks to achieve carbon neutrality and reduce GHG emissions by 85% below 1990 levels by 2045. State legislation also emphasizes the importance of increasing carbon sequestration and reducing GHG flux from natural and working lands as well as reducing emissions in the dairy and livestock sector. Ensuring the success of these policies requires further research to determine the impact of management strategies on GHG fluxes. First, I conducted seasonal field measurements of methane (CH4) on the manure storage complex of a dairy farm in the San Joaquin Valley with a mobile platform before and after anaerobic digester installation. Digester implementation strongly reduced CH4 emissions by 45.8 to 91.2% compared to pre-digester levels and show temporal variability due to differences in meteorology, on farm management practices, and digester operation. The next study analyzes soil trace gas emissions from land application of liquid dairy manure and the effect of varying soil properties, manure NH4+, and moisture conditions across California. Nitrous oxide (N2O) and ammonia (NH3) emissions ranged from 0.01 to 1.9 μg N2O-N g soil-1 and 0.3 to 32.9 μg NH3-N g soil-1 respectively and were controlled by variability in soil properties. Soil moisture conditions and manure NH4+ interacted to increase emissions. Finally, I examine greenhouse gas emissions from the soil application of solid dairy manure across soil properties and temperature conditions and compare emissions after manure biochar application and to co-application with liquid manure. Manure biochar application saw 1.9-2.5 times less normalized carbon dioxide (CO2) emissions and 4.0-4.4 times less N2O emissions compared to conventional dried solid manure application while N2O emissions were 1.6-2.2 times greater with co-application with liquid manure anaerobic digestate depending on the soil. These findings indicate how several factors interact to impact trace gas emissions from these systems and the importance of these measurements to quantify the impact of changing management practices set to better air quality and mitigate climate change.