NH3 Emission from Fertilizer Application: A Collaborative Study in the Midwestern U.S.

Atmospheric ammonia (NH₃) is a precursor for secondary particulate matter and a contributor to soil acidification and eutrophication when deposited to land and surface waters. Fertilizer application is a major source of atmospheric NH₃, particularly in intensive agricultural regions such as the Midwestern U.S. Quantification of NH₃ emission from fertilized crops remains highly uncertain, which limits the representativeness of NH₃ emissions that are used in air quality models. A collaborative study to improve understanding of NH₃ emission from fertilizer application focused on [1] measurement of above-canopy NH₃ fluxes from a fertilized corn field in Illinois using the relaxed eddy accumulation (REA) and flux gradient methods and in-canopy fluxes with the inverse Lagrangian dispersion analysis method, [2] estimation of NH₃ emissions at the regional scale using a process-based approach with available archived independent variables, and the currently used top-down approach, in order to compare and determine differences in predicted spatial and temporal variability of NH₃ emissions, and [3] performance of spatial analysis to determine spatial and temporal patterns of ammonia emissions and relate them to independent variables characteristic of land use, soil, meteorology, and agricultural management practices. NH₃ flux was measured over and within a maize canopy from pre-cultivation through senescence (May-September 2014) at the University of Illinois at Urbana-Champaign (UIUC) Energy Biosciences Institute Energy Farm, and data from the field study was incorporated into models to facilitate connection of local emissions with the regional scale and to improve understanding of the processes that drive emission and deposition.