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Interactions among Nitrogen Input, Nitrification Inhibition, Edaphic and Environmental Conditions on N2O Fluxes and associated Biological Processes in Central Alberta Soils

  • Author / Creator
    Lin, Sisi
  • Increasing atmospheric concentration of nitrous oxide (N2O) emissions due to intensified human activities is of concern, as N2O is not only a precursor for stratospheric ozone destruction but also an important greenhouse gas. Agriculture accounted for about 82% of the anthropogenic N2O production in the world and two-thirds came from soils receiving manures or synthetic N fertilizers. Therefore, it is important to gain new knowledge by investigating the N2O production processes and their controlling factors. In the first study, field experiments were conducted from 2014 – 2017 in Edmonton and Lacombe, Alberta. We examined the effects of manure application timings (fall and spring) and nitrification inhibitors (NIs), namely nitrapyrin [2-chloro-6-(trichloromethyl) pyridine] and 3, 4‐dimethylpyrazole phosphate (DMPP) on N2O emissions and soil mineral N and investigated the potential residual effects of repeated manure additions. The annual N2O emission factor due to fall manure injection without NIs was about four times greater than that due to spring injection without NIs in 2014-2015, whilst this comparison was reversed in 2015-2016. This was mainly owing to the contrasting precipitations between the two experimental years. Residual effects became evident by the increased, divergent N2O emissions and soil NO3- concentration in the spring of 2017. The second study was a controlled laboratory study established to elucidate the impact of several soil moisture contents and NI application rate on the efficacy of two NIs [i.e., nitrapyrin and 3,4-dimethylpyrazole succinic acid isomeric mixture (DMPSA)] in reducing N2O emissions and inhibiting nitrification in Black Chernozamic (BC) and Gray Luvisolic (GL) soils. Regardless of NI application rates and soils, the emission reductions due to NIs were obvious at high moisture contents as compared to the lowest moisture content in which there was no significantly different N2O emission between the manured soils with versus without NI additions. With higher soil moisture content, greater NI application rate was required to efficiently inhibit nitrification and reduce N2O emissions for both NIs in both soils. Moreover, it seemed that the BC soil required higher NI application rate than the GL soil under the same condition, likely because higher clay and organic matter contents would cause increased surface adsorption and microbial degradation. In the third study, a mesocosm experiment was conducted to investigate the N2O production and sources from soils with different N management history (soil with (SW) and without (CT) legacy of manure additions) and three different water contents over a simulated fall-freeze-thaw cycle. Compared to the untreated control treatment, the urea-amended treatment showed greater soil-derived N2O emissions during thawing, indicating a net positive priming effect. This positive priming effect was greater in the SW soil than the CT soil. Above 83% of the N2O fluxes on the 2nd and 3rd days of thawing were produced by denitrification. In the fourth study, a process-based ecosys model was used to represent agroecosystems and predict the resultant N2O emissions from soils receiving manure (as per our first study mentioned above) and also to simulate de-watered manure additions in fall and spring seasons. The model was able to simulate well the magnitude and timing of N2O fluxes except for when the soil was very moist. The model could be further improved by refining the representation of soil water retention by implementing a simulation of snowmelt filtration and runoff in ecosys. Overall, this dissertation makes a contribution to better understand N2O production sources and drivers and provides insights into N2O emission mitigation.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-hac4-2z26
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.