Quality Assurance and Quality Control in Forest Soil Analysis: 5th FSCC Interlaboratory Comparison

A total of 48 laboratories reported their results in the 5th FSCC Interlaboratory Comparison 2007. Nine laboratories reported outliers and stragglers for more than 20 % of the total; five based on the between-laboratory variability, and eight laboratories based on the within-laboratory variability.
Problem parameters are (1) exchangeable elements, especially Na, Ca, free H+, Mg, Acidity and Fe, (2) the heavy metals Hg and Cd extracted by Aqua Regia, Extractable Al and Mg, (3) carbon content in sample D with low organic carbon content and (4) the pH determination of a peat sample. In general there are more problems when the concentration of the concerning element is relatively low.
Compared to the 4th FSCC interlaboratory comparison in 2005, the coefficients of variation of all groups of analysis have improved or remained at a similar level. The CV of the blind sample B improved by 20% mainly because of a large improvement of the analysis of the Aqua Regia extractable elements.
The application of the data integrity expert rules could have been better. Several laboratories reported data which violated the rules. The rules might need further refinement, especially concerning peat layers e.g. for pH.