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Science
| 01/24/18

Researchers find limits to global soil carbon plan

TCE

A global effort to boost carbon stocks in soil to mitigate greenhouse gas (GHG) emissions may not be as practical as first imagined, say scientists who pored over 150 years of data and found major limitations.

Signatories to the “4 per 1000” initiative of the French government have committed to increasing the amount of carbon that enters the soil via the decomposition of plants and animals, also known as soil organic carbon or SOC. If they could boost this by just 0.4 percent a year (or four parts per thousand, hence 4 per 1000) for 20 years, French researchers had theorized this would compensate for the world’s annual CO2 emissions from fossil fuels.

Scientists with Rothamsted Research in the UK, the world’s oldest agricultural research institute, assessed more than a century and a half’s worth of data from long-term field experiments at three sites in southern England. While the soil types and climates are geographically representative only of temperate regions globally, what amounted to the largest concentration of long-term SOC data in the world, much of it never before published, was sufficient to get a real-world sense of whether the 4 per 1000 goal was practical.

In research published in Global Change Biology, they conclude that most techniques were able to achieve the French goal—and then some. Indeed, almost two-thirds demonstrated they could hit 7 parts per 1000.

But many techniques would be challenging to put into practice, the researchers note. In other cases, they are already being deployed.

Applying manure far in excess of the norm worked well, for example, but few farmers have access to such amounts, and even if they did, this would result in substantial nitrogen and phosphorus pollution.

Upping synthetic nitrogen fertilizer application would likewise increase nitrogen pollution and, worse still, release of nitrous oxide, a lesser known GHG.

Application of sewage sludge and food waste compost to fields were successful, and unwanted food otherwise ends up in landfills where decomposition returns CO2 and methane to the atmosphere. However, these resources could be used to produce biogas instead.

Stuart Smyth, an agronomist at the University of Saskatchewan whose research focuses on sustainable innovation techniques in agriculture, wondered why they had not investigated reducing tillage.

“The biggest observation I have is the question of ploughing,” he told the Climate Examiner. “All that manure has to be incorporated somehow, but reducing tillage slows the release of carbon back into the atmosphere.”

In Canada, low-tillage or no-tillage techniques have been the norm within agriculture for at least 15 years, and increasing since 1985 in Saskatchewan, thanks to efficient weed control.

“So what would be interesting is to take what they’ve done in the paper and run the analysis again if possible complementing this with low-tillage,” he added.

One agricultural innovation that could also complement the most feasible options for storage of SOC uptake, which Smyth calls a “game-changer” for climate mitigation, is gene-editing crops to increase their incorporation of carbon into plant structures, and then as a result upon decomposition, increasing SOC stocks. Woburn, Massachusetts-based Yield10 Bioscience, with facilities in Saskatoon, began field trials with corn along these lines two years ago, upping carbon absorption of the plants by 40 percent. The corn could be on the market within three years, reckons Smyth.

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France's '4 per 1000' soil carbon initiative sounded great, but there are practical limits to achieving the goal, researchers have found

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