Monday, November 13, 2006

N2O Emissions from a Cultivated Organic Soil.

Philippe Rochette1, Denis Angers1, Martin Chantigny1, Nicolas Tremblay1, Leon-Etienne Parent2, and Edith Fallon1. (1) Agriculture and Agri-Food Canada, 2560, Boul. Hochelaga, Québec City, QC G1V 2J3, Canada, (2) Pavillon Comtois, Université Laval, Laval University, Dep. Soil Science & Agri-Food Engineering, Sainte-Foy, QC G1K 7P4, CANADA

Cultivation of histosols accelerates the mineralization of soil organic matter, thereby providing C and N substrates that can sustain high rates of N2O production.  The objective of our study was to quantify N2O emissions from a fertilized cultivated histosol in Eastern Canada.  Fluxes of N2O were measured during two consecutive years in plots cropped to lettuce (Lactuca sativa L.) fertilized with either 0, 50, 100 or 150 kg N /ha.  Treatments were repeated 4 times in both an irrigated and a non-irrigated field.  Concentrations in N2O up to 1300 µmol /mol were measured in the soil profile, indicating not only high rates of N2O production but also likely considerable resistance to vertical gas diffusion.  Mean annual cumulative N2O emissions were 8.6 kg /ha in 2004 and 25.6 kg N /ha in 2005.   Emissions were not affected by N fertilization rates, suggesting that nitrification and denitrification were not N-limited.  Fluxes were largely controlled by soil water content as indicated by larger emissions in 2005 (773 mm rain) than in 2004 (527 mm rain) and with emissions 15% (2004) and 25% (2005) greater in irrigated than in non-irrigated plots.  The occurrence of high N2O emissions when soil aeration was low in presence of abundant C and N substrates suggests that denitrification was a major source of soil N2O.  In summary, 1) mineral N availability did not limit N2O production in this histosol, 2) a large fraction of the emitted N2O was likely associated with denitrification events, and 3) annual emissions up to 5 times greater than the 2006 IPCC default emission factor (8 kg N2O-N /ha) indicated that the inventory of N2O emissions from histosols in Canada could be improved by the use of a country-specific emission factor for that N2O source.