France has a great plan for its soil – and it’s not just about wine

Nature’s own carbon capture and storage. Matthias Ripp, CC BY

October 5, 2015  -  French wine lovers have always taken their soil very seriously. But now the country’s government has introduced fresh reasons for the rest of the world to pay attention to their terroir.

As industrial emissions of greenhouse gases continue to increase and concerns about climate change grow, scientists and policy wonks are searching for potential solutions. Could part of the answer lie in the soil beneath our feet? French agriculture minister Stéphane Le Foll thinks so.

Soil stores vast amounts of carbon, far more than all the carbon in the world’s forests and atmosphere combined. Plants take carbon out of the atmosphere through photosynthesis and when they die the carbon they stored is returned to the soil.

This forms part of the soil’s organic matter: a mix of undecayed plant and animal tissues, transient organic molecules and more stable material often referred to as humus. It is food for organisms in the soil that play a vital role in cycling nutrients such as nitrogen and phosphorus. These organisms decompose the organic material and return much of the carbon to the atmosphere leaving only a small proportion in the soil.

In the UK alone, soils store around 10 billion tonnes of carbon – that’s about 65 times the country’s annual carbon emissions. Increasing the amount of carbon in our soils has the potential to suck CO₂ out of the atmosphere.

At a March 2015 conference on Climate Smart Agriculture, Le Foll proposed the ambitious target of increasing French soil carbon contents by 0.4% year-on-year (“4 pour mille”). How France will meet the target is currently unclear but by throwing down the gauntlet Le Foll clearly wants to stimulate French farmers and researchers into action.

A 0.4% increase might not sound like a lot but, given the scale of carbon storage in soil and the fact that small increases add up over the years, meeting the target would have a significant impact on atmospheric CO₂ concentrations.

Le Foll hopes that protecting carbon-rich soils (like those in natural bogs, permanent grassland or wetlands), better use of organic manures and farming that returns more plant biomass to the soil (such as by using cover crops and ploughing their residues into the earth) together with the use of bioenergy crops such as short rotation willow coppice, can contribute towards a 40% reduction in France’s CO₂ emissions by 2030. He plans to bring forward an international programme to promote increases in soil carbon and to propose it to the UN climate talks in Paris. Such a programme would include research, innovation and engagement with farmers.

Stuck in the mud?

There is no doubt this is a bold move. Research has shown raising soil carbon contents is not that easy due to much of the organic matter added to soils being lost to the atmosphere as it is decomposed by soil microbes. However, protecting the carbon we already have in our soils and just storing a little more could make a big difference.

In the UK most soil carbon (by far) is found in peaty soils under bogs, followed by soils under grass, woodland and arable agriculture. Protecting this carbon should be the first priority. That means maintaining and restoring bogs, avoiding conversion of grassland and forestry to arable land, or even reconverting arable land to grassland. These measures would all have a positive effect on soil carbon stocks.

Whether all this can deliver the 0.4% increase year-on-year that the French want is open to debate. What is clear though is that not only does soil offer a way to store carbon and help mitigate climate change, carbon-rich soil has numerous other benefits. It is more fertile and helps to promote food production, it improves soil’s physical properties – it protects against soil erosion and increases water-holding capacity – and it enhances biodiversity.

Promoting practices that increase soil carbon contents really is a win for both the soil and the climate.

[ John Quinton is Professor of Soil Science, Lancaster University and Executive Editor of the Journal SOIL (http://www.soil-journal.net).]