Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Geography & Environmental Studies

Faculty/School

Faculty of Arts

First Advisor

Michael English

Advisor Role

Thesis Supervisor

Second Advisor

Richard Petrone

Advisor Role

Thesis Supervisor

Abstract

This research examines spatial and temporal variations in N2O flux from agricultural clay loam in corn-wheat and corn-oat rotations in southern Ontario. Gas samples are collected by the chamber method following significant precipitation events, thaw events, fertilization events, and otherwise every two weeks over a two-year period. Crop type appears to influence the magnitude of N2O emisions, whereas N2O fluxes do not otherwise seem to vary by landscape position. The seasonal pattern of in situ N2O flux at Strawberry Creek (SC) indicates that the highest N2O emissions are occuring during the spring and growing season. Soil moisture and fertilization appear to be the prevailing flux drivers at these times. This pattern is common to most of the literature, although SC fluxes are up to two orders of magnitude lower than those from several studies in similar agricultural regions. Although field data appear to indicate that N2O fluxes are insignificant during the winter, other researchers, in southern Quebec and in northern Europe, have found significant winter N2O fluxes, especially during winter thaws. Soil temperature appears to be the predominant driver of N2O flux during the winter and fall.

The SC field data is compared to that collected during an intensive non-growing season simulation, whereby intact soil mesocosms are exposed to winter and spring temperatures in a laboratory environment, and gas samples are collected daily. Increases and decreases in N2O flux parallel fluctuations in soil temperature through 0°C during the winter simulation. N2O fluxes quickly drop off following an initial spike in emissions as soil temperature increases during the spring simulation. The laboratory fluxes from the situation exceed those from the field by up to two orders of magnitude. It may be that high N2O fluxes exist during in situ winter thaws, but are undetected because of the timing of field sampling. It is also possible that the laboratory methodology created extreme and rapid soil temperature changes, which may not be representative of typical in situ conditions. Dramatic increases and decreases in soil temperature may cause a high level of physical, chemical and/or microbiological disturbance to the soil cores, which, in turn, may drive higher N2O fluxes.

Strong SC correlations between N2O flux and binned soil temperature data, by soil moisture category, may allow general predictions of N2O flux based on readily available records, or estimates, of these two parameters. Derived N2O flux estimates may be reliable predictors of N2O emissions in northern temperature regions, from agricultural clay loams growing corn and grains. Predictive models would likely be improved by increasing the intensity of empirical measurements during winter and spring thaw conditions, and by incorporating antecedent soil temperature and soil moisture terms into the models.

Convocation Year

2010

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