Freezing and thawing cycles have been shown to induce soil physical and biological changes such as disruption of structure (aggregate stability) and stimulation of denitrification. The latter is a major process involved in production of nitrous oxide (N2O), a greenhouse gas. The increase in denitrification following freezing may be attributed to the diffusion of newly available organic substrates from disrupted aggregates to denitrifying micro-organisms. However, agricultural practices influence the aggregate stability (resistance to physical disruption), the macro-porosity and the organic matter content of soil.
The objective of this study was to evaluate the effect of freezing and thawing cycle on N2O production in a Kamouraska clay soil submitted to different crop rotations and tillage practices. Experiments were conducted in soil slurries (without addition of C substrates) to favor substrate diffusion and in undisturbed soil cores to simulate field conditions.
In slurries, a freezing and thawing cycle increased denitrification rates by 44% in a no-till treatment and by 25% in a moldboard tillage plowing in comparison to an unfrozen treatment. In soil cores, N2O production was increased after thawing and was also related to agricultural practices. Relationships involved between denitrification, soil structure and C release from organic matter are discussed with respect to the contribution of agriculture to N2O emissions during cold season. The effect of freezing and thawing on N2O production in macro-aggregates of different sizes is currently under investigation.
Dr. Danielle Prevost Soils and Crops Research and Development Centre Agriculture and Agri-Food Canada 2560 Hochelaga Blvd. Sainte-Foy, Quebec G1V 2J3 Canada Telephone: 418 - 657 7980 Fax: 418 - 648 2402 E-mail: prevostd@em.agr.ca Eric van Bochove E-mail: VANBOCHOVEE@EM.AGR.CA