Short-term carbon dioxide and nitrous oxide flux following tillage of the clay soil in the Red River Valley in Southern Manitoba

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Koiter, Alexander J.
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There has been resurgence in the interest of conservation tillage as a way to sequester carbon from the atmosphere, to help improve soil quality, and as a means to mitigate the increasing concentration of greenhouse gases (GHGs) in the atmosphere. However, the term conservation tillage is qualitative and quite ambiguous, and refers to a wide range of tillage practices. This makes the interpretation of information gathered from different tillage systems difficult. There currently exists a need for the quantification of soil surface properties following different tillage methods because surface properties are closely linked to soil surface processes. Previous research has focused on the long-term impacts of tillage systems and their effects on soil biological processes and properties, such as soil microbial populations and activity, soil organic matter fractions and their role in the production and emission of greenhouse gases. However, the more immediate impacts of tillage on soil physical processes and properties and their role in the production and emission of GHGs are not well understood and are often overlooked. The first objective of this research addressed the need for better quantification of soil physical properties after tillage practices. This research demonstrated the use of a laser profiling system and digital imagery and image analysis software in measuring soil micro-relief and crop residue cover. Furthermore, comparisons of geostatisitical and univariate procedures of quantifying surface roughness were also investigated. There was a definite advantage in using a geostatistical approach to characterize soil topography as the indices they provide give insight into the characterisitcs of the surface roughness. Soil disturbance and the addition of corn residue were both found to be significant factors affecting the surface roughness, crop residue cover, exposed surface area, and near-surface porosity. The second objective of this research focused on the quantification and characterization of the short-term effects of soil disturbance as a result of tillage on the carbon dioxide (CO2) and nitrous oxide (N2O) flux from the clay soils of the Red River Valley, Manitoba. The short-term CO2 flux (up to 5 days) following a soil disturbance event was characterized by an immediate increase in the CO2 flux following the soil disturbance event that quickly dissipated within the first 24 hours. Both the addition of residue and soil disturbance were found to be significant factors in the cumulative CO2 loss over the 5-day observation period. However, the incorporation of the residue through the action of soil disturbance was found to be a more important factor than soil disturbance or the addition of residue alone. The effects of residue and soil disturbance on the N2O flux were highly variable. However, there was some indication that the N2O flux under soil conditions may have a response to soil disturbance similar to that of CO2. The third objective is a combination in the previous two objectives and deals with the need to better understand the underlying physical mechanisms that control the CO2 and N2O flux. This was accomplished by combining the detailed information on the changes in surface properties and the CO2 and N2O fluxes that occur due to soil disturbance. Generally, the soil disturbance treatments that resulted in a rougher surface...