Monitoring Ambient Atmospheric Chemistry along a Gradient of Ammonia Emission Density in Eastern North Carolina

John T. Walker
National Risk Management Research Laboratory,
Washington, D.C. USA

During the spring and summer of 2007, an experiment was conducted near Lillington, NC to examine NH3 air-surface exchange processes in a fertilized corn field. Multiple air concentration and flux measurement techniques were used to quantify NH3 emission and deposition from pre-planting through canopy senescence. The objectives of the experiment were to: compare methods for measurement of NH3 air concentrations and fluxes; quantify NH3 emissions immediately following fertilization; quantify the cumulative flux of NH3 over the course of an entire growing season; and examine the relative importance of soil vs. foliage exchange pathways with respect to net canopy-scale fluxes. A general overview of the experiment is presented along with results illustrating temporal patterns in concentrations, fluxes, and soil/plant chemistry. Relationships between NH3 flux and soil/plant chemistry and moisture status are described. Measurements of NH4+ and H+ in the soil solution, leaf sub-stomatal cavities, and leaf surface water are used in combination with resistance modeling to examine the relationships between net canopy-scale fluxes and soil, stomatal, and cuticular exchange pathways.