Proficiency testing and other interactive measures to enhance analytical quality in soil and plant laboratories

Abstract

Clients are increasingly seeking enhanced accuracy and precision from soil and plant testing laboratories. Commitment to good laboratory practice is essential, but gains in analytical quality often depend upon inputs from peers through collaborative networks, proficiency programs and laboratory accreditation. Examples of laboratory networks are given, while proficiency programs receive attention with respect to scope, frequency and the statistical assessment of data. Those with a national/regional focus have proliferated with some consolidation warranted. Recent interlaboratory proficiency data from Indonesia and occasional audits of other proficiency programs have been used to reinforce the benefit of non‐parametric statistical procedures for the identification of outlying laboratories, and to suggest greater uniformity in statistical approaches. There is brief mention of formal laboratory accreditation by national providers such as the National Association of Testing Authorities (NATA) in Australia. A disappointing finding was that co‐efficients of variation (CVs) for most soil and plant methods reported in interlaboratory proficiency programs exceed predicted CVs derived from the Horwitz equation. Examples of improving method performance over time are given for two interlaboratory proficiency programs, but grand CVs associated with three successive ASPAC's soil proficiency programs remain static at around 16%. The soil and plant laboratory industry must succeed with its efforts to improve analytical performance, as failure may encourage entities outside the industry to intervene.