The ENVASSO project (Environmental assessment of soil for monitoring) aims to harmonise the European soil monitoring networks. As part of this project, we made a review, the most exhaustive to date, on the sampling strategies used in the different networks.

Soil monitoring networks exist in all the 27 European countries, most of them being members of the European Union. Nevertheless, their strategies are very heterogeneous (selection of monitoring sites, site area, number of sub-samples, time step, soil sampling). Therefore, harmonisation of the strategies remains a difficult issue: indeed most of the changes would make the comparison with the results of the previous campaigns quite impossible. Yet, harmonisation is necessary in order to compare the different European monitoring networks, and from this perspective, some recommendations have been made in that way. We estimate that more than 4000 additional sites should be selected in order to reach an acceptable level of cover age for the European soils. The areas of the sites should preferably be comprised between 100 m² and 1 ha. The minimal number of sub-samples should be 4, and should be adapted with regards to the within-site variability. A time step of ca 10 yr is recommended. Advices are also formulated for the vertical sampling strategy, the bulk density determination, samples preparation and archiving. However, this harmonisation would require considerable efforts and some countries may not be able to achieve all of these recommendations. Nevertheless, the framework provided in the ENVASSO project can be used to reach a common acceptable level of soil monitoring in Europe.