Every soil holds a treasure...For a long time, soil has been overlooked in international climate negotiations. Yet it is one of the bedrocks of such discussions. Thanks to plants and living organisms, soil actually represents the largest reservoir of terrestrial carbon. An estimated 1,500 Gt of carbon is stocked in the upper meter of soil, i.e. approximately twice the carbon present in the atmosphere. Every year it stores 2-3 Gt of carbon, contributing to the absorption of 20-35% of anthropogenic emissions. What if we could increase this storage capacity and offset all anthropogenic emissions?
This is the worthy aspirational target of the international “4 per 1000” initiative launched by France at the COP 21 in 2015. Its premise is as follows: by increasing the quantity of carbon in the top 30-40 centimetres of soil by 0.4% (4 per 1000), we can offset the annual increase in the atmospheric CO2 concentration due to anthropogenic emissions. In other words, even a very slight increase in the soil carbon storage will go a long way towards our goal of limiting the rise in global temperatures.
But the project doesn’t stop there. More carbon in the soil means more organic matter, boosting soil fertility and improving agricultural output. Increasing the quantity of carbon in soil will help global food security. This win-win concept has become a leading topic of discussion at the more recent international climate conferences, and the “4 for 1 000” initiative has so far been signed by more than 200 members, including 37 countries.
“ It wasn’t that long ago that soils were never even mentioned in international climate meetings. Through this project we hope to help put subsistence farming and soils at the centre of discussions. ”
UMR Eco&Sols - Montpellier SupAgro/CIRAD/INRA/IRD
A little-known service to mankind
Soil carbon sequestration is nevertheless dependant on factors including local climate, soil type, and the use and management of soil. Little research has been carried out on these factors. Lydie Lardy (UMR Eco&Sols - Montpellier SupAgro/CIRAD/INRA/IRD) explains: “the influence of these factors on the ability of soils to sequester carbon sustainably remains largely unexplored, especially for tropical subsistence farming systems which, more than anywhere else, are contending with the challenges of food security and adaptation to global warming.” Enter the SoCa (Soil Carbon) research project, coordinated by the IRD with a host of national and international partners (CIRAD, INRA, Université Abomey Calavi, IRAD (unavailable link), CNRA, Université d’Antananarivo, ICRAF, IITA).
The research will start by doing a comprehensive inventory of soil carbon flows and stocks from of agricultural plots of between 0.5 and 1 hectare in four different countries: Benin, Côte d’Ivoire, Cameroon and Madagascar. “While these pieces of farmland have different types of soil, cropping practices and socio-economic contexts, but they are all located along a north/south gradient which allows us to analyse the climate’s influence”, explains Lardy, who is the project’s coordinator.
In addition to this research on the processes involved in carbon sequestration potential and dynamics, research will be carried out on the impact of these processes on the availability of nutrients essential to growth, such as nitrogen and phosphorus. What roles do these factors play in carbon sequestration? What is their impact on agricultural output? Lastly, by comparing these plots of land the researchers hope to classify the factors that come into play, and propose with contextualised indicators to help improve local agricultural practices.
A win-win project
A component of this project is the partnership it allows with countries of the South. In addition to some 20 researchers from both France and Africa, 25 African students and farmers are involved in the research. They will be trained on how to perform carbon assessments in their countries, and informed of the actions that can help improve their food security and be part of the fight against global warming.
“By working with local stakeholders, local farmers are more accepting of recommended best agricultural practices”, says Lardy. Some of these best practices are already widely accepted: the use of intermediate crops, reusing crop residue, manuring or adding organic compost, appropriate water management, no-till techniques and agroforestry development.