International database on organic carbon stocks in cropland soils

National and European public policies on the storage of soil organic carbon (SOC) are increasingly being developed, seeking to improve soil health, protect biodiversity, and mitigate climate change by increasing the carbon captured in agricultural soils. Their success depends on the availability of models that can simulate and predict shifts in soil carbon stocks caused by agricultural practices and variations in the climate. To develop, calibrate and test these models, scientists require real data on the evolution of carbon stocks and, given the relatively slow dynamics of organic carbon in agricultural soils, such data are generally acquired through long-term experimental projects (extending over more than 10 years). Until now, only a small number of long-term experimental sites (LTEs) have been identified and engaged in their delivery. 

This situation inspired the scientists from INRAE and the CNRS to develop a project for an international database that could bring together measurements from a wider number of agricultural LTEs. Beginning in France, with 23 sites, the project has gradually expanded to include data from European, Australian, and North and South American experimental sites. The database currently incorporates data from a total of 34 field-trial sites in temperate climates, the oldest of which has been in operation for 97 years, and the most recent for seven. Carbon inputs to the soil were calculated using information from crop yields, non-harvested biomass residues returned to the soil, and the application of organic matter (manures, composts etc). The dataset also includes daily climate data from each study site. The team has worked to harmonise the data across the 34 sites and has established an organisational template and a shared methodology for the measurement of carbon stocks, making it possible for other sites in temperate zones to make use of the database. 

This is the first such database on the long-term evolution of soil organic carbon stocks in temperate croplands to be built and made freely available. The database will become a first-order evaluation tool for models of soil organic carbon stocks, and is expected to expand gradually as other sites join the initiative. A similar project for a database for the evolution of soil organic carbon stocks in tropical croplands is currently in hand. 

‘Maintaining long-term agronomic testing is critical for our understanding of the effects of agricultural practices on soil properties. By valorising the work of these test sites using the FAIR approach (Findable, Accessible, Interoperable, Reusable), this database constitutes a key resource that can now be used by model developers to evaluate modelling of the dynamics of soil carbon’
Kenji Fujisaki, a Research Engineer at INRAE and lead author of the study.