Conclusions of a blind proficiency testing scheme in manure analysis

Cugnon, Thibaut [UCL] Ferber,F. Mahillon, J. Lambert, Richard [UCL]

In order to test the complete analytical process in laboratories, a “blind” PT was organized by the REQUASUD PTprovider. The Pt items distributed to the laboratories were indistinguishable from normal customer samples. Two different samples of liquid manures were prepared and distributed to six different laboratories. Each laboratory received three samples of six liters volume: one sample of a liquid cow manure and two samples of the same and homogenous liquid pig manure, in order to test the repeatability of the laboratories. No problem was identified for the cow manure that had a quite high dry matter content (11%). The dry matter of the pig manure was relatively low, as were his content in phosphorus and magnesium. Several unsatisfactory results were observed for the pig manure on following parameters: dry matter, nitrogen, phosphorus and magnesium. The post-analysis of the results, in collaboration with the unsatisfactory laboratories, highlighted that insufficient homogenization of the sample before subsampling was the cause of theses unsatisfactory results. This observation shows the benefit of “blind PTS” in order to assess the whole analytical process in laboratories, including subsampling and homogenization.