Sources and Sinks: Ammonia Flux in Agricultural Ecosystems (Invited)

In the U.S., ammonia (NH3) emissions are dominated by the agricultural sector with practices such as fertilizer application and waste storage introducing significant amounts of NH3 into the atmosphere. NH3 in the air reacts with acidic gases to form ammonium-based particulate matter or returns back to land and surface waters through complex dry and wet deposition processes. The return of NH3 to an ecosystem alters nutrient dynamics and contributes to soil acidification and biodiversity changes. To improve the understanding of the cycling of NH3, field studies were conducted in agricultural ecosystems in several regions of the U.S. These studies focused on quantifying NH3 fluxes with integrated and real-time measurement techniques over a variety of crops, including corn and soybean, and over adjacent fields in proximity to waste storage units. Key meteorological variables (temperature, relative humidity, precipitation, etc.) were also monitored during each study. Results illustrated the complexity of source-sink dynamics for atmospheric NH3 in agricultural ecosystems under a variety of conditions. Bi-directional exchange of NH3 was evident in each study, but the magnitude varied with canopy and meteorological conditions, in addition to other factors.