A reference soil system for the monitoring of soil nutrient status and metallic trace elements contaminations in agricultural soils.

Among other soil characteristics, those related to the nutrient status and the content in metallic trace elements (MTE) originate from both natural factors and land management. A methodological framework has thus been set up to evaluate the importance of natural driving factors -the so-called pedo-geochemical background- of the spatial distribution of mineral elements in soils and also to compare the current levels of MTE content in agricultural soils with natural values. References for natural, typical, and suspicious values are stated in a Reference Soil System (RSS) which is based on the identification of relationships between geology, relief, and soil, and on the consideration of soil volumes. It integers the land cover and also takes into account the spatial dependance between measurement points in order to estimate the change detection sensibility. Thanks to a comparison-based methodology, to the existence of a detailed soil map, and to the integration of various spatial representation techniques, an image of the state of the soils has been drawn and can serve as a reference for the prediction and the interpretation of point values, for the evaluation of a particular land utilization type, and as a base for the monitoring of soil quality. The reference values about natural and usual content in MTEs for various soil horizons that are proposed reveal especially a relatively weak level of contamination for agricultural soils.