Assessment and management of the risk of land subsidence, from the individual plot to the national level

The physical degradation of agricultural and forest soils caused by compaction resulting from the passage of machinery is a major concern for those involved in agriculture and forestry. Indeed, soil compaction can affect both agricultural and forestry production and the environment by promoting soil erosion, denitrification and a decline in biodiversity. In this context, the DST project (Physical Degradation of Agricultural and Forest Soils due to Compaction) proposed five research strands: impact, prediction, prevention, monitoring and mapping of compaction in mainland France. It relied on the use of soil compaction models and soil-plant system functioning models to study the consequences for crops and the environment, via changes in soil properties (storage, transfer and mechanical properties). Its main findings concern: (i) the impact of compaction, highlighting a threshold for the structural void index (0.15 m³·m⁻³) beyond which crop performance and hydrodynamic properties are undoubtedly affected; (ii) modelling, with the project leading to the development of a 2-D model for predicting soil deformation, (iii) monitoring, involving the evaluation of non-destructive geophysical methods for mapping compacted areas, (iv) prevention, through the development of a tool for forecasting soil moisture and available days, and (v) the mapping of risk areas in France.