Contribution of Pulse Crop Residues to N2O and CO2 Emissions in a Subsequent Wheat Crop: A 13C/15N Study.

Nitrous oxide (N₂O) and carbon dioxide (CO₂) exchanges between soils and the atmosphere have drawn much attention for their important role in global warming. At present, there is considerable uncertainty regarding the contribution of crop residues to N₂O and CO₂ budgets. A field experiment was conducted at the University of Saskatchewan’s Goodale Research Farm near Saskatoon, SK, Canada, to determine the relative contributions of above-ground residue (AGR), below-ground residue (BGR), and fertilizer N to N₂O and CO₂ emissions in a subsequent wheat crop. The experiment was conducted using a dual-isotope (¹⁵N and ¹³C) labeling approach.

Five crops (chickpea, fababean, lentil, pea and wheat) were labelled with ¹³CO₂ and ¹⁵N-urea during the 2014 growing season. After harvest, AGR from the enriched and non-enriched plots were interchanged and wheat was grown on the plots in 2015. ¹⁵N₂O and ¹³CO₂ were measured once a week during the 2015 growing season using static chambers and Picarro isotopic N₂O and CO₂ analysers.   

This study elucidates the contribution of residue C and N to CO₂ and N₂O emissions. Preliminary results indicate that the proportion of ¹⁵N₂O originating from AGR, BGR and soil natural abundance was 21%, 76% and 3% respectively; while the main source of ¹³CO₂ was AGR. Dual-labelling studies can provide valuable information regarding the source of N₂O and CO₂. This is an ongoing experiment.