A Modeling Analysis of Ammonia Fluxes from a Maize Canopy in Illinois

Although emissions from fertilized agricultural fields constitute a major source of ammonia (NH₃) to the atmosphere, the quantification of such emissions remains highly uncertain due to its dependence on a variety of environmental and socio-economic variables, as well as the bi-directional nature of NH₃ fluxes between the biosphere and atmosphere. During Summer 2014, NH₃ concentrations and fluxes were measured using multiple instruments, methods and temporal resolutions within and above a maize canopy located on the University of Illinois Energy Farm near Urbana, Illinois. NH₃ measurements at the site began prior to initial fertilization and planting and continued throughout the growing season until harvest. In this work, the unique dataset obtained in this field experiment is analyzed using two independent process modeling systems designed specifically for NH₃ flux simulation over fertilized crops. In particular, we examine the temporal behavior of fluxes after initial fertilization and as the maize crop grows, matures and reaches senescence. Further, we estimate how the canopy interacts with NH₃ emissions from the soil and how this interaction changes over the growing season and as a function of critical environmental variables, thereby impacting the total flux of NH₃ to the atmosphere from the maize field.