Mitigation of the greenhouse effect: increasing carbon stocks in French agricultural soils?

Foreward

At the Earth Summit in Johannesburg, declarations by some States raised hopes that the Kyoto Protocol could be implemented in 2003. A reduction in the human induced greenhouse gas emissions is clearly the most sustainable policy to slow down the accumulation of these gases in the atmosphere, which is causing, according to a large scientific consensus, climate change. However, in the case of CO2 emissions, possible alternatives consist in stocking for some time some additional organic carbon in the biomass and in the soil organic matter. Carbon stocks in the forest biomass (Article 3.3. of the Protocol) have already been the subject of international agreements, with strict quotas being imposed on different countries. Favouring a more or less long-term accumulation of organic matter in soils, through changes in land use and agricultural or forestry practices, is another alternative (Article 3.4.) which was accepted as a mode of application of the Kyoto Protocol. With respect to this alternative, there are no limitations as to the amounts accumulated or the land surface concerned, but no methods for verification have yet been defined. Worldwide, soils contain about 1500 gigatons of organic carbon. A relatively small increase in these stocks could therefore play a significant role in limiting the net flux of greenhouse gases towards the atmosphere. Changes in land use and agricultural production practices could contribute to this, notably by increasing the magnitude and the duration of organic carbon storage in soils. The residence time of carbon in the soil organic matter is highly variable, as it varies with the rate of carbon mineralisation, through which organic carbon is finally returned to the atmosphere in the form of . It is therefore important to determine the potential offered by this pool, as a function of soils, their uses and associated practices. In order to apply the Kyoto Protocol, it is also necessary to know how and with what precision this pool could be measured, and which incentive policies could induce additional accumulations in soils.

The approach adopted by the French Ministry for Ecology and Sustainable Development

These challenges are not negligible for France in a European context, because of its large agricultural land and surface area. For this reason, the Ministry for Ecology and Sustainable Development requested an Assessment Report from INRA, which concerns the capacity for organic carbon accumulation in agricultural soils and its time-related dynamics.

This Expert Report should be read in the context of a strategy for soil management on a national basis, bringing together the principal actors in a Scientific Interest Group (Ministry for Ecology and Sustainable Development, Ministry for Agriculture, French Institute for the Environment, Agency for the Environment and energy resources, INRA) and the implementation of a soil quality monitoring network. At the European level, this report is in line with the recommendations of the recent Communication of the European Commission on soil protection.

The main questions for this assessment have been formulated by a Steering Committee, consisting of representatives from the main public bodies concerned and from INRA, and chaired by the Director for Economic Studies and Environmental Evaluation at the MEDD. These questions are as follows:

• Can we, in France, through actions specifically targeting an increase in organic carbon accumulations in soils, contribute to reduce the greenhouse effect? The answer to this question is of direct interest to the French Interministerial Mission on the Greenhouse Effect, and France in general, so that agriculture can be taken into account in the national plan to combat the greenhouse effect.
• How could such actions meet the conditions of compliance with the Kyoto Protocol? It is necessary to propose solutions which will be technically feasible and economically viable.
• Which economic policy tools would be effective to promote the changes required? In this respect, it must be possible to integrate the tools in the Common Agricultural Policy.
• What are the needs in terms of research and references? What is required to further develop the research results and recommendations arising from MEDD pilot programmes concerning the sustainable management of soils and the impacts of climate change?

Implementation of the project by INRA

This Assessment Report was drafted by an Expert Group consisting of researchers specialised in soil sciences, agronomy, bioclimatology and public economics applied to agriculture, from INRA and from other French and foreign organisations. INRA was designated for organising the project, which was entrusted to the Scientific Assessment Unit at the Environment and to the Forestry and Agriculture Scientific Directorate. They ensured compliance of the study with the methodologies of Assessment Reports, and with the requirements from the Steering Committee. Indeed, an Assessment Report, bringing together researchers from different areas, was necessary to consider a series of complex, scientific questions which are controversial. This report, through the assessment it has enabled and without omitting any debates and uncertainties, will provide an unquestionable aid for decision-makers.

This "Synthesis", more particularly drafted for Decision-Makers, was compiled by the Scientific Assessment Unit of INRA and was validated by the scientific experts. It forms a detailed summary of the report, with cross references to the chapters of the expertise which will provide readers with a more comprehensive information. As such, we hope it will provide all those interested in this important debate for the future of the planet with the ideas necessary for their thinking on national and European initiatives.