Proficiency testing of growing media, soil improvers, soils, and nutrient solutions

At Applied Plant Research two (interlaboratory) proficiency tests for (peat-based) growing media, soil improvers, soil, and nutrient solution were being organized; one for the national and one for the European methods. Data were compiled according to ISO 5725. Reports containing all data, where the laboratories were identified only by a reference number were being sent to each of the participants. In the national methods, no problems have been recognized in large variations of nitrate. It was suggested that the inexperience with the new European methods was a source of error