Proficiency Test on soil improver maturity tests

Evira and Proftest SYKE carried out this proficiency test in November-December 2012 for sample phytotoxicity and aerobic biological activity by determining the effect of soil improver samples on germination and root growth of cress, sample CO2-production or oxygen uptake and sample dry weight and organic matter content. In total 11 laboratories took part in this test. Sample material was soil improver (S1) and soil improver and peat based growing medium (S2). Standard methods were used to determinate the properties from the samples, except for CO2 evolution rate analysis for which no standard exist. The robust means of the reported results by the participants were used as the assigned values for measurements. The evaluation of performance was based on the z scores which were calculated using the standard deviation for proficiency assessment. z scores were not calculated for CO2 (S2), CO2 production per bottle, and root length index (RI; S1), oxygen consumption (Oc) and oxygen uptake rate (OUR). In total, 91 % of the results were satisfactory when the deviations of 4-80 % from the as-signed values were accepted. It seems further guidance in some of the methods is needed. According to the results many laboratories have good practices and manage these analyses well. Other laboratories still need more experience. In future rounds of proficiency tests also pretreatment practices will be taken into account