Date of Award
1-1-2024
Document Type
Thesis
Degree Name
M.S. in Biological Science
First Advisor
Jason Hoeksema
Second Advisor
Jason Taylor
Third Advisor
Colin Jackson
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Increased nitrogen (N) fertilizer use and cultivation of N-fixing crops have dramatically increased agricultural N inputs to the global N cycle. Excess N on agricultural lands is highly susceptible to loss through runoff or atmospheric emissions, potentially as a greenhouse gas (GHG). Nitrous oxide (N2O), a GHG with a warming potential ~300 times that of carbon dioxide (CO2), primarily enters the atmosphere through denitrification, which converts bioavailable nitrate (NO3-) to inert nitrogen gas (N2), with N2O as an intermediate. Wetlands are crucial for de-nitrification and N regulation due to their wet, anoxic soils, but have declined worldwide, including substantial losses in the Mississippi Alluvial Valley (MAV). Shallow flooding of fallow crop fields potentially restores some nutrient regulation and habitat functions once provided by natural wetlands in the MAV. Post-harvest flooding in the Mississippi Delta provides a management option for migratory shorebird habitat, yet little is known about N2O production relative to N2 (N2O yield) associated with wetland processes that are potentially activated by this practice. We measured N2 and N2O production in flooded crop fields throughout fall and winter 2023–2024 to assess seasonal and spatial variation. Sampling included continuous flooded zone monitoring across three treatment fields flooded for either fall, winter, or fall and winter, plus additional sampling of intermediate and dry zones to evaluate floodwater level effects. We observed very low N2O yield and flux values overall, with yield decreasing with soil phosphorus (P) and flux increasing with dissolved NO3-. N2 flux decreased with longer flood duration and with higher temperatures and decreased in the winter field relative to the others. Fall floodwater gradient sampling revealed that N2O yield decreased with dissolved ammonium (NH4+), and that flood-water level and time interactions influenced N2O flux. In winter gradient sampling, N2O yield changed with incubator sampling time, with the second of three samplings having the lowest and the only negative yield out of the three. The same trend was observed with N2O flux, which also increased with increased soil NO3-. Additionally, N2 flux decreased with higher soil NH4+ in winter gradient sampling, with no predictive importance from any factors in the fall. These results suggest that despite stimulating denitrification, this water management practice is not a meaningful contributor to N2O emissions and may reduce nitrate loads to downstream ecosystems with-out releasing a potent GHG.
Recommended Citation
Rosson, Andrew, "Effects of Off-Season Fall-Winter Farm Field Flooding on Nitrogen Gas Production" (2024). Electronic Theses and Dissertations. 3028.
https://egrove.olemiss.edu/etd/3028
