QUALITY ASSURANCE FOR SOIL NUTRIENT ANALYSIS - A CASE-STUDY

The availability of certified reference materials (CRMs) for total con centrations of soil K, Ca, Mg, and P is contrasted with the lack of CR Ms and universally accepted extractants for the measurement of extract able K, Ca, Mg, PO4, NO3, and NH4. Data are presented summarising Qual ity Control (QC) procedures that have been developed by a UK laborator y to address these problems. Without access to CRMs, analytical bias c an be controlled by the use of homogenous internal soil reference samp les. Analytical accuracy can be assessed by participation in interlabo ratory comparison exercises and sample exchange schemes. QC data prese nted in this paper also highlight a number of problems encountered in soil analysis that cannot be solved by good laboratory QC procedures.