Soil, Environmental and Atmospheric Sciences electronic theses and dissertations (MU)
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The items in this collection are the theses and dissertations written by students of the Department of Soil, Environmental and Atmospheric Sciences. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item Impacts of nitrogen fertilizers and nitrification inhibitors on greenhouse gas emissions from soil(University of Missouri--Columbia, 2024) Frossard, Dean Michael; Davis, Morgan P.This thesis investigates the impact of nitrification inhibitors and varying fertilizer rates on greenhouse gas emissions and crop yield in agricultural systems. Fertilized agricultural soils can experience notable losses of nitrogen gases, such as nitrous oxide (N2O) and ammonia (NH3) after the application of nitrogen (N) fertilizers. In the Midwest U.S., anhydrous ammonia and urea are common nitrogen sources used in corn cropping systems. Nitrification inhibitors pronitridine and dicyandiamide (DCD) have demonstrated potential to enhance corn grain yield when applied with N fertilizer. The first chapter explores the efficacy of pronitridine in reducing N2O and NH3 emissions from corn fields fertilized with anhydrous ammonia. Results from field trials conducted in Northeast Missouri over two growing seasons indicated that while pronitridine did not significantly reduce cumulative NH3 emissions in both seasons, it lowered N2O emissions from higher fertilizer rates in the 2023 growing season. Grain yield increased with fertilizer rate and the addition of pronitridine. Overall, we found that pronitridine did not affect cumulative N2O and NH3 emissions (outside of 202N fertilizer rate for N2O in 2023) but has the potential to increase grain yield. The second chapter examines the effects of urea fertilizer and DCD on N2O, NH3, carbon dioxide (CO2), and methane (CH4) in bare soil. Findings revealed that increased fertilizer rates led to higher NH3 emissions, while DCD application had a marginal effect on reducing N2O emissions, with greater reductions observed at higher DCD rates. Our data supports other work concluding DCD has the potential to reduce N2O emissions but highlights the potential for greater reductions through increased DCD rates.Item Cycles and drivers of spatiotemporal variation of forest soil respiration at the intra-landform scale(University of Missouri--Columbia, 2024) Seubert, Hunter Anton; Wood, Jeffrey D.Spatiotemporal variability of soil respiration (RS) is a primary driver of large uncertainties associated with forest carbon budgets. However, most studies focus on either spatial or temporal variations, not both. As the frequency and severity of extreme weather events, such as heavy rain and drought, increase it is crucial to understand how these stressors affect the spatial variation of RS to reduce uncertainties in carbon budgets. We analyzed a decades-long data set of continuous chamber measurements from a temperate deciduous forest in the central USA to examine spatiotemporal variations of RS and the influence of water status on these patterns. Our findings reveal that spatial variation of RS changes seasonally and is significantly affected by water status. During drought conditions, the mean daily spatial variation of summer RS increased from a CV of RS of 16.6 percent to a CV of RS of 28.1 percent, and the daily amplitude also rose. A power analysis indicated that spatial variation observed at the MOFLUX forest prevented detection of changes in RS between MOFLUX and a hypothetical forest. Spatial variability peaked at soil water content levels of 0.2 m^3 m^-3 and 0.5 m^3 m^-3, indicating that in the extremes, soil water content drives spatial variation. Additionally, our analysis showed that soil water content (SWC) and soil temperature (Tsoil) are key drivers of spatial variation of RS, with the influence of these drivers shifting seasonally. During the non-growing season, soil climatic variables explained more of the spatial variation among chambers compared to the growing season. These results highlight the seasonality in the drivers of spatial variation of RS, where soil climatic variables have greater explanatory power during the non-growing season. Our results demonstrate that both seasonality and extreme water conditions significantly influence the spatiotemporal variability of RS, providing valuable insights for improving understanding of forest RS spatial variation.Item Drought impacts on forest responses to precipitation and biological drivers of the surface energy imbalance(University of Missouri--Columbia, 2024) Cochran, Emma Grace; Wood, Jeffrey D.The eddy covariance (EC) technique is used across the world to study the interaction between the biosphere and the atmosphere. This thesis consists of two research chapters, one devoted to analyzing historical EC data to gain new insights into how drought shapes forest responses to precipitation, and another study aimed at advancing scientific understanding of the surface energy imbalance (SEI). For both research chapters, historical ecosystem gas and heat flux data from the Missouri Ozark AmeriFlux site (MOFLUX) were analyzed. The first study focused on drought impacts on forest responses to precipitation. By analyzing predawn leaf water potentials ([psi]pd) to quantify drought and focusing on short-term responses (timescales [less than] 1 week) of latent and sensible heat fluxes (LE and H, respectively), as well as net ecosystem carbon dioxide (CO2) exchange (NEE), this study determined that the forest was most responsive to precipitation while under moderate antecedent drought stress (-1 [less than] [psi] pd [less than] -0.5 MPa). The second study focuses on the SEI, an issue apparent at EC sites globally whereby we cannot account for all energy within an ecosystem using EC measurements, introducing biases into the data and how we interpret it. Drought impacts forest heat fluxes and also ecosystem level photosynthesis, therefore affecting transient energy storages associated with photosynthetic energy. These energy storages are often neglected in surface energy budget studies and may be responsible for a portion of the SEI. Using Random Forest regression and Shapley Additive Explanations, both machine learning tools, NEE was identified as a primary driver of SEI, pointing towards the possible importance of biochemical and photochemical energy storages in surface energy closure. Taken together, this thesis advanced scientific understanding of forest drought responses and the SEI problem that has plagued the EC community for decades.Item Evaluation of soil properties in log landings after subsoiling and biochar amendments(University of Missouri--Columbia, 2024) Rumpf, William Richard; Davis, Morgan P.Log landings are a necessary component of timber harvest infrastructure that decrease overall impact of harvest activities by concentrating management operations to a small area. However, the soil on the landings themselves can be significantly degraded as a result of heavy machine traffic. This study evaluates the efficacy of biochar application and subsoiling used singly and in combination to reduce compaction and improve soil fertility as a means to improving vegetation reestablishment. Fifteen landing sites were selected across Hoosier National Forest in Indiana, Mark Twain National Forest in Missouri, and Shawnee National Forest in Illinois. Landings were divided into treatment plots of biochar at 22.4 Mg ha-1 , subsoiling to a depth of 20in, a combination treatment, and control, with seeded and unseeded subplots. One-year post treatment findings show that surface applications of biochar reduce compaction by ~18-19 percent in the top 10cm of soil regardless of seeding or subsoiling (P < 0.05). The biochar amended soils also saw a significant increase in active carbon, potassium, magnesium, and plant available phosphorous, as well as marginal increases in total carbon and nitrogen. Comparison to pretreatment data showed that removal of slash and mulch on landings reduced bulk density (P = 0.001) regardless of treatment by allowing vegetation and removal of insulation that attenuates freeze thaw cycles.Item Identifying cold-air damming in the region of the Ozark Plateau(University of Missouri--Columbia, 2024) Bongard, Jonathon Thomas; Market, PatrickFollowing the events of March 2014 in which icy, hazardous conditions stranded motorists along the roadways and interstate highways of eastern Arkansas, an investigation is launched to determine if the event was the result of cold-air damming occurring in the region. This investigation led to a larger three-phase study on cold-air damming events in the region of the Ozark Plateau. First, the initial phase studies the marquee event of March 2014 and what atmospheric conditions led to the event. Second, a 5-year study to find the frequency and intensity of cold-air damming events in the region. Finally, a numerical analysis using the WRF model to study the effects of terrain height on cold-air damming cases. The objective analysis, results, and conclusions will be showcased including chart analysis, numerical analysis utilizing the Froude number, and WRF output analysis.