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Abstract
The availability of certified reference materials (CRMs) for total concentrations of soil K, Ca, Mg, and P is contrasted with the lack of CRMs and universally accepted extradants for the measurement of extractable K, Ca, Mg, PO4, NO3, and NH4. Data are presented summarising Quality Control (QC) procedures that have been developed by a UK laboratory to address these problems. Without access to CRMs, analytical bias can be controlled by the use of homogenous internal soil reference samples. Analytical accuracy can be assessed by participation in interlaboratory comparison exercises and sample exchange schemes. QC data presented in this paper also highlight a number of problems encountered in soil analysis that cannot be solved by good laboratory QC procedures.