Urea fertilizer placement effects on soil greenhouse gas emissions and corn growth
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Agricultural soils are responsible for a majority of human caused greenhouse gas (GHG) production, such as N₂O and carbon dioxide (CO₂). Nitrous oxide is a potent GHG that stays in the atmosphere for at least 100 years. It is also an ozone-depleting gas. Carbon dioxide is problematic due to its abundance in the atmosphere. These GHGs, along with methane, have had a significant impact on climate change. Claypan soils are characterized as having a significantly higher clay content deeper in the soil profile compared to the layers directly above it. The goal of this research was to investigate the impact N fertilizer placement has on GHG emissions and corn growth. The specific research objectives were to determine the effects of urea fertilizer placement with and without a nitrification inhibitor (NI) on cumulative soil GHG emissions (N₂O and CO₂) and to assess the effects of urea fertilizer placement with and without a NI on plant N uptake, N use efficiency (NUE), and corn (Zea mays L.) production, on a poorly drained claypan soil in Northeastern Missouri. A NI helps reduce the amount of nitrous oxide produced. Field studies were conducted in 2014 and 2015. Soil greenhouse gas emissions were measured frequently throughout the growing season to determine flux and cumulative N₂O and CO₂ emissions. Soil water content and soil temperature were also assessed at each gas sampling event. Rainfall was higher than the 10-year average over the growing season for both 2014 and 2015 and possibly resulted in increased environmental N loss. Soil N₂O and CO₂ emissions were higher during the 2015 growing season. The UDB treatment produced the greatest amount of cumulative soil N₂O emissions during both growth seasons at 100 and 354 g N₂O-N ha⁻¹. Deep banded urea without a NI resulted in the highest soil CO₂ production in 2014 and UAA had the greatest cumulative CO₂ emissions in 2015 at approximately 11 and 17 kg CO₂-C ha⁻¹, respectively. Incorporating urea to a depth of 8 cm, deep banding urea, and deep banding urea with a NI all resulted in significantly higher yields of corn by as much as much as 10%. Deep banding urea with a NI provided as high as a 48% increase in grain yield compared to other treatments in 2015. The highest yields occurred in 2014 when there were lower N₂O emissions. In 2015, there were higher N₂O emissions and lower yields. This research suggests that urea fertilizer placement has an impact on GHG emissions and corn growth and this information should be provided to farmers who are interested in producing more corn and losing less N. The amount of rainfall during the growing season may also influence soil GHG emissions and corn growth. More research should be conducted to understand to what extent climatic variability impacts GHG and crop production.
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