Enriching carbon soils to combat climate change
As the Cop 24 opens in Poland today, a track is mobilizing many scientists, gathered under the 4p1000 project. Behind this code name, it is to relieve the atmosphere of a part of its CO2 by slightly increasing the carbon storage in the first layers of the soil.
And if we store more carbon in the soil? While the level of CO2 in the atmosphere and in the oceans still worries researchers and populations, this idea is gaining momentum. The 4p1000 initiative thus encourages actions to to increase 0,4% per year, 4 for 1 000, carbon capture in the first 40 cm of soil depth through certain agroecological practices.
Launched 1 December 2015 at the COP21 in Paris by Stéphane Le Foll, then Minister of Agriculture, Agri-Food and Forestry, this international initiative is now supported by more 250 partners from 39 country. As we approach COP24 (24e Annual Conference of the United Nations Framework Convention on Climate Change), which opens on 3 December in Katowice, Poland, it could constitute a beginning of solution to the question of climate change ...
The 0,4% figure owes nothing to chance. It corresponds to approximately 80% of the increase in the atmospheric concentration of CO2 over the 2017 year, ie 6 billion tons per year. Given that soils already contain 1 500 billion tonnes of carbon in the form of organic matter, achieving and meeting this target would help offset the continued rise in anthropogenic carbon emissions.
Better yet: it would improve agricultural production, the presence of carbon in soils making them more fertile. However, the FAO estimates that half of the world's fields are now degraded, that is to say that their yields are decreasing, leading to an overall decrease of around 10%.
Thierry Heulin, CNRS research director and director of the Eccorev1 laboratory, is a member of the scientific committee of 4p1000.
He had already been campaigning for scientists to organize and coordinate on these issues. "My work concerns the use of cultivated plants to increase interactions with rhizosphere bacteria and the storage of carbon in the soil, which is directly related to the speech of Stéphane le Foll. "
He emphasizes the dual purpose of 4p1000: combat climate change while ensuring food security. Indeed, this increase in the carbon content of soils does not only make them more fertile but also more stable in order to limit their erosion.
"Some soils are very poor, as in the Sahel because of their very sandy texture, complete Thierry Heulin. Enriching them would make it possible to cultivate previously undeveloped land. "
For the climate and harvests
Other soils have in fact been degraded by human activities and still see their carbon levels decline. This is due to changes in agricultural practices, such as the reduction in the number of "multi-crop-livestock" farms, which limits the intake of plant and animal organic matter. Tillage, like deep plowing, accelerates the mineralization of carbon, leading to its evacuation in the form of CO2. "We are not only trying to increase the carbon content in the soil, says Thierry Heulin, but also to avoid losing it! "
Milk lines were studied at the Laboratory of Microbial Ecology of the Rhizosphere and Extreme Environments, in collaboration with the Research Institute for Development in Montpellier and Dakar, for their ability to structure the soil around their plants. roots, thanks to the activity of bacteria. These transform simple sugars exuded by the roots into polysaccharides, which allow better storage of water in the soil.
The importance of performance
"Farmers are aware that the maintenance, or even the increase, of the carbon content in soils is a real issue, explains Thierry Heulin. Although mitigation of CO2 in the atmosphere is not a priority, they know that it can improve soil fertility. The selection of more rustic varieties, which improves their root architecture and the associated microbiota, becomes a real challenge.
"The yield of wheat in France has for example gone from 20 quintals to the hectare after the war to 100 quintals today, says Thierry Heulin. The selection of seedlings was essentially based on yield criteria. This may have been to the detriment of other properties, such as the ability to inject carbon into soils. The researchers hope to influence farmers' choices, while remaining aware of the difficulties.
- Biochar.jpg (103.85 Kio) Accessed 4247 times
Obtained from household waste, biochar, "organic charcoal", stabilizes organic substances in the soil when it is combined with compost.
"We biologists always think we have the right solution, but we are never safe from a" false good idea, "admits the researcher. The solutions must be proposed in consultation to the actors of the field. " Choices can indeed lose more on one side than win on the other.
"We hope that, since the 4p1000 initiative was launched by a minister in office, the associated research effort will be supported by major incentive programs," says Thierry Heulin. By launching Sète's appeal at the beginning of November, the members of the 4p1000 scientific council underline its potential contribution to the goal, set by the Paris agreement, of not allowing global warming to exceed 2 ° C.
Cornelia Rumpel, president of the scientific and technical committee of the international 4p1000 initiative and CNRS research director at the Institute of Ecology and Environmental Sciences in Paris, is one of fifty signatories. "I've been studying soil stabilization and sequestration processes for over twenty years," she says. Now that we know these mechanisms pretty well, it's time to act. She stresses the need to apply beneficial soil enrichment methods, while adapting them to the many climates, ecosystems and farming practices.
With about 570 million farms and more than 3 billion rural people in the world, it is hard to hope that a small handful of solutions would suit everyone. The 4p1000 initiative also aims to reach wetlands, forests, protected areas ...
Among the solutions, Cornelia Rumpel cites the management of organic waste, in particular increased reuse of household waste. Biochar, the "biological carbon" obtained by pyrolysis of biomass, thus participates in stabilizing organic substances in the soil when it is combined with compost.
Employment ofGreener fertilizers would at the same time help to reduce nitrous oxide emissions to the greenhouse effect three hundred times stronger, at equal mass, than CO2.
A transdisciplinary initiative
"Scientific barriers still exist, we still do not know exactly the details of the carbon cycle, nitrogen and other elements in the soilsays Cornelia Rumpel. Carbon storage limits are also unknown. How far can we go? " And before increasing storage, it is better to first try to maintain it. The largest stocks of carbon are found in peatlands, forcing researchers to focus on certain well-identified hot spots.
"In any case, we need more interdisciplinary studies, we need to involve areas beyond the base formed by soil sciences, hydrology and ecology," she says. The socio-economic environment must also be taken into account to make the different actors of the territories work together. "
Agathe Euzen, CNRS research director at the Technical Laboratory, Territories and Societies3, scientific assistant director of the Ecology and Environment Institute of the CNRS and member of the scientific council of 4p1000, agrees. "This type of initiative can not be envisaged without taking into consideration the perceptions of the actors and their relations to the territory, their social and cultural specificities. They must be further considered upstream so that the results lead to real practices, which farmers will be able to appropriate. "
Here again, the diversity of situations complicates the task. In addition to the issue of climate and places, agriculture is also experiencing extreme scale changes: food parcels, industrial exploitation, national agricultural policies and beyond ... "The commitment of actors necessarily requires knowledge of the diversity of cultural practices according to the contexts, the environmental and socio-economic local issues, insists Agathe Euzen. The dialogue promotes the exchange of knowledge between farmers and researchers, this is how the mechanism can be sustainable, equitable and viable and thus be considered as one of the possible solutions to meet the objectives of the Paris Agreement on the climate. "
The entanglement of local and global issues is always delicate and often leads to the question of political intervention. Like many other actions in the fight against climate change, 4p1000 will therefore use the springboard of COP24 hoping to bring its message to the general public, researchers, farmers and policy makers.
Source and references: https://lejournal.cnrs.fr/articles/enri ... climatique
