Semester of Graduation
First Major Professor
Master of Science (MS)
Nitrate loss from leaching can adversely affect human health and the environment. Nitrification inhibitors such as nitrapyrin and dicyandiamide (DCD) have the capability of slowing the nitrification process by hindering the ability of Nitrosomonas sp. bacteria to oxidize ammonium, thereby slowing the conversion of ammonium to nitrate. However, DCD is needed in large quantities to serve as an effective nitrification inhibitor. While there are products available as a urea coating containing DCD, there are questions about if urea can be coated with enough DCD to adequately slow nitrification.
Using soil columns and urea as a nitrogen source, 3 rates of DCD were tested against the standard rate of nitrapyrin, Super U® (urea containing DCD and a urease inhibitor which are distributed throughout the granule), and urea without nitrification inhibitors. To determine if enough DCD can be added to urea to be effective, soil columns were tested for ammonium and nitrate concentrations over 3 sample times and 6 depths (15.25 cm increments) each time. Sample times were determined by calculating Growing Degree Days (GDDs). This study was conducted twice in 2019 and 2020.
Sample time targets were 400, 800, and 1200 GDDs respectively. Ammonium oxidation was complete by the first sample timing in 2019. However, significant differences in nitrate concentrations in the 0-15.25 cm depth were observed to draw conclusions. Differences in nitrate values at this depth suggest that there were differences in nitrification rates based on the amount of nitrate that has remained at this depth. Nitrate-N concentrations were greatest to least from Super U® (132 ppm) > Nitrapyrin (129 ppm) > DCD High (115 ppm) > Urea + NBPT (106 ppm) > Urea (94 ppm) > DCD Med (88 ppm) > DCD Low (86 ppm) > Control (36 ppm). Sample timings were moved in 2020 to earlier targets (100, 200, and 400 GDDs) which allowed for nitrification to be observed. While moving the sample timings did make it possible to make these observations, the 2019 results were not verified.
The method of using soil columns shows promise in future nitrification and nitrogen movement studies. Alterations in this method can be made to best suit what exactly is being studied. Potential also exists for the study of other aspects of soil science with this method.
Embargo Period (admin only)
Moore, Kevin, "Determining an Effective Rate of Dicyandiamide as a Nitrification Inhibitor: A Soil Column Study" (2021). Creative Components. 773.