Frozen soils might be major emitter

A University of Manitoba study has discovered 
the previously overlooked emissions

Frozen cropland may be a larger source of nitrous oxide emissions than previously understood.

A new study suggests global greenhouse emission calculations have overlooked an important aspect of the agricultural sector.

Emissions, especially of the key gas nitrous oxide, may in fact be about 17 to 28 per cent greater for cultivated soils frozen in winter than currently thought.

Mario Tenuta, professor in applied soil ecology at the University of Manitoba, and his colleagues from the University of Guelph led by Claudia Wagner-Riddle, published their findings in Nature Geoscience this week.

Their paper, “Globally important nitrous oxide emissions from croplands induced by freeze-thaw cycles,” argues that current calculations do not account for freeze-thaw emissions.

Every winter seasonal freezing induces large thaw emissions of nitrous oxide (N2O). Nitrous oxide is a trace gas that contributes to stratospheric ozone destruction and atmospheric warming. Cropland soils are by far the largest anthropogenic source of nitrous oxide, the paper says.

This gas was overlooked because prior to this study it was not quantified. The U of M and Guelph team monitored emissions every 30 minutes at sites in Ontario and Manitoba over 14 and nine years, respectively. They validated their Canadian data with emissions data from 11 additional cold-climate sites from around the world.

“We hope revision to the estimate of N2O emissions from seasonally frozen cultivated soils will encourage research and use of cropping practices to lower greenhouse gases from agriculture,” Tenuta says.

Nitrous oxide makes up just six per cent of greenhouse gas emissions, but its impact is said to be 300 times that of carbon dioxide.

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