As winters warm, fields left fallow are becoming a major source of greenhouse gas emissions

By | November 21, 2020

National Observer reports:

Each September, Ashala Daniel sows her fields with winter rye, hoping the seed takes root before the first snows fall. It’s a ritual that could help save the planet.

Fields are among Canada’s largest emitters of agricultural greenhouse gases (GHGs), emissions that are at their highest levels in winter. During the freeze-thaw cycle, increased levels of nitrous oxide (N2O) and methane, both potent GHGs, are pumped from barren fields into the atmosphere. The natural phenomenon is expected to become more common as winters warm.

“It’s part of why I cover crop,” said Daniel, who owns Solstedt Organics, an organic vegetable farm and orchard near Lytton, B.C.

Cover cropping is the practice of planting a field with a crop, like winter rye, after the growing season is over. It is common on organic farms because it helps build soil fertility and reduce erosion.

However, the practice isn’t widely used on most Canadian fields, particularly if they’re managed for industrial agriculture.

That could be a problem: A study published last month in the scientific journal Nature revealed that nitrogen fertilizers, essential to industrial agriculture, and the N2O they release are driving agricultural emissions globally. Without major transformation to farming systems globally, these emissions will send global temperatures soaring far above the 1.5 C “safe” limit agreed to in the 2015 Paris Agreement.

Freeze-thaw cycles play a major role in this process, explained Carson Li, lab and research co-ordinator for the University of British Columbia’s sustainable agricultural landscapes lab and a researcher who studies N2O in agriculture.

“Normally, people think that where N2O comes from is the warm-weather agricultural regions,” but that’s not what’s happening, he said. Instead, his team and others have found that between 17 and 28 per cent of field-based emissions are taking place in the winter, after crops have been harvested and the fields left fallow. It’s an unexpected process they trace back to the freeze-thaw cycle. [Continue reading…]

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