Did you know that the soils we walk on every day are one of the key levers in the fight against climate change? Isn’t that surprising? As part of the celebrations of World Soil Day, seize the opportunity to follow IRD specialists in East Africa, Southern Africa and the Indian Ocean, as they study the potential for carbon sequestration in the soils of the area.

Significant emissions of greenhouse gases, particularly carbon dioxide (CO2), due to human activities are causing global warming. In Southern Africa, East Africa and the Indian Ocean, the effects of this warming are already being felt by the environment and the people, i.e. through droughts and changes to rainfall patterns.

Yet this atmospheric carbon could in part be absorbed and stored right there, in the soils beneath our feet, and thus reduce global warming. Plants assimilate carbon for their growth during the photosynthesis process. This organic carbon, stored in all parts of the plant (stems, leaves, roots, etc.), will end up in the soil when the plants die, when the leaves fall or when the roots are renewed. A part of the carbon will be decomposed by microorganisms in the soil and released into the atmosphere, while the rest will be added to the stock of organic matter in the soil, making it more fertile. Carbon sequestration can thus play a crucial role in ensuring food security.


The international initiative “4 per 1000”, launched during COP21 in 2015, has made carbon sequestration in soils a priority in the fight against climate change. The objective is to increase the carbon stock in the first 30 to 40 centimetres of the soil by 0.4% per year, or 4 per 1000, in order to significantly reduce the concentration of CO2 in the atmosphere.

With their partners in the region, IRD scientists spare no efforts in achieving this goal, by trying to better understand the biophysical mechanisms of carbon release from soils and its storage, by developing techniques to measure it and identify agricultural and management practices that facilitate carbon storage in soils, among others. They also keep in mind the needs of local populations, from the plot to the farm, to village and territorial levels.


Embark with them and discover their reality!

Measuring the soil CO2 emissions during conservation agriculture trials in Zimbabwe.

© Cirad - Rémi Cardinael

Measuring the soil CO2 emissions during conservation agriculture trials in Zimbabwe.

Assessing and mapping

Assessing the current situation is the first step in encouraging carbon sequestration in the soils of an area. Scientists work hard to determine how the soils are used (agricultural plots, forests, housing, grassland, etc.) and how much carbon they store.

Soil sampling in Zimbabwe.

© Cirad - Rémi Cardinael

Let us have a look in the field. IRD is implementing the DSCATT project in four countries: Kenya, Zimbabwe, Senegal and France. In Zimbabwe, the project’s partners CIRAD and the University of Zimbabwe compare different systems, such as plots in conservation agriculture and plots in conventional agriculture, and quantify CO2 and N2O emissions and the amount of carbon stored in those systems. They drill the soils of plots where farmers implement different practices, at different times, to measure their impact on the amount of organic matter stored. They also set up measurement chambers on these plots, in order to collect and analyse the gases emitted by the soil.


Rémi Cardinael is a CIRAD researcher and coordinator of the project in Zimbabwe: “We also have access to data from long-term trials in all of the project’s countries. These tests started several years ago and show the evolution of carbon stocks according to the type of soil and the techniques used. This information is very valuable."

Mapping of soil types in Reunion Island.

© IRD - Alain Albrecht

Assessing carbon stocks also means mapping them and making information accessible to all. Alain Albrecht, an IRD soil scientist based in Reunion Island, is the regional coordinator of the 4 per 1000 project for overseas territories. The objective is to comprehensively assess land use and carbon stocks in all overseas territories and to list current agricultural practices and possible alternatives to foster carbon sequestration in soils.

Mapping of soil carbon stocks in Reunion island, at the island scale, the municipality scale and the field scale.

© IRD - Alain Albrecht

The project started a few weeks ago and will provide a database accessible not only to researchers, but also to policy-makers. “This initiative follows the 2CARMA project (cartography of soil carbon in Madagascar), which compiled information on land use and on the island's carbon stock in a complete database, made available to users”, Alain Albrecht explains. “Managing our soils better requires us to have perfect knowledge of them."

Quantifying organic matter in soils also requires efficient and low-cost methods. Researchers at the Eco & Sols research unit have recently developed a methodology to characterize soils thanks to infrared spectroscopy. This allows for quick analysis of soil carbon content.

Melon plantation in Tunisia.

© IRD - Christian Lamontagne

Melon plantation in Tunisia.

Optimizing agricultural practices

Once the inventory has been drawn up, how can we increase the amount of carbon stored in the soils of the region? This is where farmers and their practices come into play. Among all the solutions identified, it is crucial to find those that are best suited to agricultural stakeholders and that are the most effective, depending on the type of soil and climate.


IRD scientists and their partners test the varied solutions by comparing plots managed in a conventional manner and those where new practices were introduced. These new practices include conservation agriculture which encourages minimum tillage; agroforestry which associates trees with crops; the contributions of organic amendments and soil cover and crop rotation.

The choice of crops can also have an impact. Vincent Chaplot, a soil scientist at IRD, is a long-time partner of South African researchers. Leading numerous projects on the topic, they recently analysed global data to determine which crops store more carbon in soils. Maize, rye and rice lead the race. “These plants transfer a greater proportion of carbon to the soil than wheat and barley, for example. We believe this is due to the extent of their root network,” the scientist explains.

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© Cirad - Rémi Cardinael

Measuring the soil density in Zimbabwe.

In Kenya and Zimbabwe, researchers carry out experiments to better understand carbon storage processes associated with organic amendment or conservation agriculture. Dominique Masse is a soil specialist. He coordinates the ongoing DSCATT project: “We collaborate with local partners and other international institutes on these long-term experiments, in order to develop mathematical and computer models. These models help us to simulate the functioning of the soil-plant system and to better predict the influence of the farmers’ choices on carbon storage in their soil."

Soil preparation by cows before sowing the field with maize, in the foothills of Drakensberg, South Africa.

© IRD - Vincent Chaplot

In South Africa, the solution to carbon sequestration may well come from pastures, which cover no less than 50% of the surface of this large country. Soil stocks have been severely degraded by poor management. Animals used to move to graze, but humans have forced them to be closed in and have also started to burn the grasslands. This has greatly impoverished the soil and resulted in significant greenhouse gas emissions. “South African farmers have the means to use ephemeral intensive grazing: moving a large amount of herbivores over the grasslands, over short periods of time, in order to maximize plant activity. We estimate that this would increase the carbon stock by 35 per thousand per year, well beyond the recommended 4 per 1000," Vincent Chaplot explains.


The choice of species and ephemeral intensive grazing are thus part of the solutions studied by the IRD and its partners in Southern and Eastern Africa and in the Indian Ocean, along with the input of organic matter. A recent study on the soils of Madagascar showed that adding organic matter, such as manure or compost, was highly effective. Alain Albrecht is based in Reunion: “Our measurements show that the more carbon we bring to the soil, the more it will be able to store. This requires farmers to be able to buy or produce manure themselves. This solution is readily available, but we have to think of the entire territory in order to be able to implement it on a large scale and at low cost."


The various tools put in place by the researchers and their partners are thus intended to support the decisions of the stakeholders, by allowing them to choose the best compromise among the multiple solutions that exist.

Restitution of soil research in South Africa.

© IRD - Vincent Chaplot

Restitution of soil research in South Africa.

Co-building and adapting to each context

We have seen that many solutions exist and that the soils of the region will soon reveal all their secrets to the scientists. But climatic, social, economic and political contexts play a crucial role in the evolution of agricultural practices. Improving the food security of an area through carbon-rich soils, which are more fertile, means thinking in the long-term.

How can one improve one’s agricultural practices when droughts are more and more frequent? Why would a farmer switch crops if customers only buy the usual crop, at the usual price? How do you get manure without access to land or cash? Taking these constraints into account is the key to successful carbon sequestration policies.

Let us go back to South Africa, where the IRD and its partners study possible scenarios to achieve the 4 per 1000 target, while taking into account climate change and limited water resources. “Combining certain species might produce win-win situations, both for carbon sequestration and for the production of cereals and biomass, while using the minimum amount of water. We test and compare existing cultivars of maize, spring wheat, sorghum and pearl millet from different parts of South Africa,” Vincent Chaplot says.


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© Cirad - Rémi Cardinael

Discussing soil fertility restauration with farmers and local players in Zimbabwe.

To succeed in the carbon sequestration challenge, it is also essential to establish a constant dialogue among all the players involved: farmers, local and national decision-makers, local populations. Researchers participating in the DSCATT project meet Kenyan and Zimbabwean farmers through sociological surveys and participatory workshops. The objective is to understand their constraints, their customs and to develop collaborative scenarios associating better land productivity with carbon storage.

In Reunion, the scientists put emphasis on the need to provide policy-makers with decision-making tools. "The Paris Agreement and the Territorial Climate Air Energy Plans (PCAET) in France require a clear strategy for reducing greenhouse gases and sequestering carbon. Scientists are preparing clear and intuitive tools to assist decision-makers in designing this strategy,” Alain Albrecht explains. The coming SEQCOI project will create a group of junior experts, involving research institutes and public organisations, in Reunion Island, Madagascar and Rodrigues. Policy-makers will also have access to a tool with which they can test different land use scenarios on their territory.

Students of the Unviersity of KwaZulu-Natal, in South Africa, measuring the soil density, one of the variables used to know the carbon stocks.

© IRD - Vincent Chaplot

Last but not least, carrying out research on carbon sequestration involves training local stakeholders, who are fully aware of local constraints. Researchers and local training organizations are developing many training modules for farmers, policy-makers and researchers. In Madagascar, IRD contributed to the development of the radioisotope laboratory more than 15 years ago. Following a project on carbon sinks on the island, a team was created at the University of Madagascar. Since then, dozens of doctoral students, now researchers or decision-makers, have become soil and carbon specialists and are training the next generation.


East Africa, Southern Africa and the Indian Ocean thus provide multiple grounds for testing and implementing measures promoting carbon sequestration in soils. The IRD and its partners believe that soils have a role to play in mitigating climate change, adapting local agriculture to global warming, and ensuring food security for populations in the region.

However, greenhouse gas emissions are far too high today. Mitigating climate change must also include reducing the emissions because soils are not be able to absorb everything.

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