During the last decade, carbon emissions caused by human activities averaged 4.9 gigatons per year. Limiting climate change requires reducing our greenhouse gas emissions. Thanks to the organic matter they contain (from plants, microorganisms), the soils of terrestrial ecosystems store two to three times more carbon than the atmosphere. Increasing the carbon pool of agricultural soils each year by 0.4% (or 4 per 1000) in the upper 40 centimeters of the soil would, in theory, be equivalent to the increase in annual carbon emissions caused by human activities. This is the objective that is at the origin of the initiative "4 per 1000" launched by France during COP 21 in 2015 and which aims to promote the increase of carbon storage in soils through sustainable agricultural practices. .

Currently, the degradation of agricultural soils has become a major risk for food security, especially in developing countries, because soils that are too degraded (poor in organic carbon) are no longer fertile. But the implementation of sustainable agricultural practices (soil conservation agriculture, agroforestry, etc.) could stop this degradation. Adding organic matter to degraded soils, in addition to increasing carbon stocks, would lead to more stable and fertile soils for agriculture that are more resistant to climate change. The authors of the study put the issue back on the agenda by analyzing the environmental and socioeconomic conditions that must be taken into account in different regions of the world through concrete examples from Europe, the United States. , Australia or southern Africa. In this way, they present a strategy to effectively use the potential of agricultural soils to contribute to the fight against climate change.

Need for local measures to promote carbon sequestration in soils

The general implementation of this plan faces the disparity in the quality and properties of the soils of the different sites, and too different cultivation practices. This diversity requires specific and local measures to promote carbon sequestration in the soil. Unfortunately, knowledge about the state of the soil is very uneven. For this reason, scientists recommend the establishment of databases that record the state of the land, a model of possible yield gains and the use of fertilizers necessary for this. While these data are available in European countries such as Germany, France or Belgium thanks to high resolution soil mapping, there is a glaring lack of information in developing countries. In these countries, measures to restore agricultural soils can be established locally through the involvement of farmers and stakeholders who are generally well informed about the condition of their soils.

One of the key points to be implemented to promote sustainable soil management measures is to develop measurement tools, such as integrated platforms to predictively measure and model the evolution of carbon stocks to help policy makers. decisions your approach. In the United States, the University of Colorado is developing and testing a prototype.

The most effective economic and social measures to establish soil carbon sequestration programs have turned out to be those that involve the collaboration of multiple stakeholders, such as NGOs, private companies and local actors. In response to consumer demand, many multinational agricultural companies are committed to significantly reducing their greenhouse gas emissions. Therefore, the large industrial groups involved in the 4 per 1000 initiative can influence the transition to sustainable agriculture of large-scale agricultural spaces. Local initiatives are also important, such as that of a Dutch foundation that has developed around twenty camps around the world to raise awareness and train local actors in a region in ecosystem restoration and sustainable agricultural practices. Through the study of numerous examples, scientists have identified 3 points to consider so that future measures are effective:

• the participation of agricultural markets and related industries in these measures, 
• the promotion of small-scale actions involving various local actors, 
• improve local soil management capacities.