1Until the 1990s, soil scientists had two utmost priorities: soil fertility and the protection of these heterogeneous environments, where organic elements grow alongside mineral matter under sometimes intimate forms, notably in humus, an organic matter of plant, animal and microbial origin which, as it decomposes, changes soil properties.

Decomposing organic matter.

2To study this organic matter, in the 1970s soil scientists developed innovative techniques to understand its structure and composition, as well as quantify its distribution in tropical soils. This research resulted in maps positioning soils according to their organic matter content, as well as technological developments (infrared spectrometry) making it possible to increase the number of low-cost analyses. This research also led to the identification of farming practices which sequester more organic matter in soil to enhance land fertility, providing a wealth of information which aroused growing interest in the 1990s, when the world became aware of the importance of greenhouse gases. At the interface between the atmosphere and plants, soil is a potentially important compartment for the storage of greenhouse gases (CO_2, CH₄ and N₂O). Consequently, all previously acquired knowledge has been reviewed in light of carbon and nitrogen sequestration in soil.

Peatlands accumulate organic matter, filter water and provide forage, Bolivia.

••• Certain farming practices help enhance the potential to sequester carbon in soil •••

3Researchers subsequently showed that the implementation of cultivation techniques such as conservation agriculture and agroforestry or the cessation of slash-and-burn farming could trap a significant amount of emissions over the next 20 to 30 years. This resulted in the “4 per 1,000” French initiative, the purpose of which is to increase carbon sequestration in soil by 0.4% each year, via appropriate agricultural practices.

“Organic matter in tropical soils is of paramount importance for soil fertility, all the more so as these soils are often highly altered and characterised by their low clay content and low reactivity (kaolinite). Research conducted by IRD on this issue has contributed to driving agricultural research in Burkina Faso and sub-Saharan Africa. It has been instrumental in theorising the biological functions of soil. The “Zai” technique is an excellent practical illustration of this.” 
Professor Edmond Hien, professor at the Joseph Ki-Zerbo University, Ouagadougou