Impacts of Climate and Land Use Change on Soil Trace Gas Fluxes

Steve Del Grosso
USDA ARS NPA SPNR, 2150 Centre Ave, Building D, Suite 100, Fort Collins, CO

Bill Parton
NREL-CSU, 1231 East Drive, Fort Collins, CO

Agricultural soils are responsible for the majority of nitrous oxide (N2O) emissions in the US and are also an important source of ammonia (NH3) and nitric oxide and nitrogen dioxide (NOx) emissions. With a global warming potential of ~300 times that of carbon dioxide (CO2), N2O is an important greenhouse gas while NH3 and NOx contribute to ammonium (NH4) and nitrate (NO3) in precipitation. The major factors that control soil trace gas emissions are nitrogen (N) inputs, vegetation cover, soil type, weather, and land management. To address how climate and land use change impact soil trace gas fluxes, the DAYCENT biogeochemical model was used to simulate N2O, NO3, and NH3 emissions for native vegetation and cropping under current climate and projected climate change. Under current climate, DAYCENT estimated N gas emissions are typically 4 to 8 times higher for intensive cropping than for native vegetation. Projecting until the end of the present century, DAYCENT simulations suggest that N gas emissions from corn/soy bean cropping in the central US will be 20-25% higher than under current weather and CO2 levels. However, the potential to mitigate emissions from agricultural soils is very strong. Recent data from irrigated corn cropping in Colorado suggests that using nitrification inhibitors and time released fertilizer can reduce N2O emissions by 50% or more compared to application of urea or urea ammonium nitrate, which are the most common forms of N fertilizer. Reduced tillage intensity provides an additional opportunity to mitigate soil greenhouse gas emissions by storing carbon in soil.