Partitioning Direct and Indirect Emissions of N2O from 15N-Labeled Crop Residues.

Estimates of N₂O emissions in Canada are based on current IPCC methodologies which indicate that 24% of all agriculture-based emissions are associated with the use of N fertilizers and that another 17% are associated with the decomposition of crop residues. A review of greenhouse gas emissions from crop production systems in the Northern Great Plains reported that the N₂O emission factor for all N sources in this region ranges between 0.2 and 1.0% (averaging about 0.4 to 0.6%); well below the current IPCC emission factor of 1.25%. Thus, it follows that emissions from crop residues may also be lower. Residue decomposition, N mineralization and N₂O production are affected by a number of factors such as C:N ratio and chemical composition of the residue, soil type and soil water content. A bench-scale incubation study was conducted to examine the effects of soil type and water content on N₂O emissions associated with the decomposition of different crop residues. The study used soils from the Black, Dark Brown, Brown, and Gray soil zones in Saskatchewan, Canada and was conducted at both 50% and 70% water-filled pore space (WFPS); the soils were amended with ¹⁵N-labeled residues of wheat, pea, canola, and flax; and ¹⁵N₂O production was monitored using a Picarro G5101-i isotopic N₂O analyzer. Whereas both water content and soil type had an impact on N₂O production, there was a clear and consistent trend in the emission factors for the residues; i.e., emissions were always greatest for the canola residue and lowest for the wheat residue; emission factors for pea and flax were intermediate, with the pea yielding values that were often slightly—but not significantly—higher than those for the flax. Results of this research demonstrate that—under the right environmental conditions—there is considerable potential for N₂O emissions from decomposing crop residues.