Gas emissions on irrigated soil overestimated

OUTLOOK, Sask. — Canada’s national inventory of greenhouse gases overestimates how much irrigated crops are emitting from prairie soil.

But that’s not a surprise to Dr. Reynald Lemke, who was involved in setting inventory levels in the first place. He said emissions were based on general moisture regimes in certain regions.

For the brown soil zone, for example, there is, on average, a high moisture deficit so emissions are assumed to be low. Adding water would lead to another assumption that emissions are higher.

“At the time that that methodology was developed we were pretty sure we were wrong,” he said in an interview.

But there wasn’t any data to work with when it came to irrigation systems on the semi-arid Prairies.

He and University of Saskatchewan collaborators have now published a field-scale study comparing an irrigated field to a dryland field. While there are management differences the comparison is as close as possible.

Total emissions and seasonal patterns were examined, and nitrous oxide, carbon dioxide and methane were measured.

The study found that higher rates of nitrogen used in the irrigated system didn’t substantially increase nitrous oxide emissions.

“For our conditions, you cannot irrigate enough to remove the moisture deficit; you’re just limiting the moisture deficit,” Lemke said.

Nitrous oxide emissions were higher on the irrigated area overall, but that can be offset by higher yields.

“If we calculate (emissions) on a yield intensity basis, units of greenhouse gas versus units of product produced, then that is a much closer comparison,” he said.

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