D. Hanson et al., SOIL ANALYSIS - WESTERN STATES PROFICIENCY TESTING PROGRAM FOR 1996, Fresenius' journal of analytical chemistry, 360(3-4), 1998, pp. 348-350
Under the auspices of the Western States Proficiency Testing Program s
oil samples were analyzed for thirty-five constituents and plant sampl
es were analyzed for fifteen constituents. Statistical evaluations usi
ng robust statistical estimation techniques were provided to individua
l laboratory participants. Analysis of samples previously analyzed in
other programs indicated that the accuracy of several soil analyses (p
H, electrical conductivity, NO3-N, extractable K and organic matter) a
re very reliable. Results of soil phosphorus independent of method and
soil organic matter by loss-on-ignition were generally unreliable. Pr
ecision, measured by a replicated sample, indicated that a majority of
laboratory participants are capable of reproducing analytical values
within 10% through a twelve month period.