GEMAS: Boron as a geochemical proxy for weathering of European agricultural soil

About a century ago, B was recognised as an essential element for the normal growth of plants and terrestrial organisms. Limitations for plant development have been recognised in agricultural systems, particularly in highly weathered soil. Boron is rarely analysed in whole rock or soil analysis, as it requires specific analytical techniques. It is often determined, after partial extraction (aqua regia or Casingle bondCl), usually on a limited number of samples. Many more questions than answers exist about the environmental behaviour of B. We present B contents in agricultural soil samples (0–10 cm) collected in 33 European countries (5.6 million km2) during the GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) continental-scale project. The B content, determined by ICP-MS following hot aqua regia extraction, varies in European agricultural soil from 0.5 to 49 mg/kg (median 2.42 mg/kg, n = 2108), which is somewhat similar to total B estimates for the Upper Continental Crust (17–47 mg/kg). Its spatial distribution in agricultural soil shows a patchy pattern with low values in regions with granitic bedrock and high contents in soil formed over limestone and in volcanic areas. Boron geochemical behaviour in soil is strongly dependent on other factors such as pH, CEC, presence of organic matter, clay and secondary oxides and hydroxides. Boron geochemical mapping at the continental scale in arable soil allows investigations of plant health, i.e., the beneficial and adverse effects due to the nutritional status of boron.