Canadian Forest Service Publications
Inter-laboratory variation in the chemical analysis of acidic forest soil reference samples from eastern North America. 2015. Ross, D.S.; Bailey, S.W.; Briggs, R.D.; Curry, J.; Fernandez, I.J.; Fredriksen, G.; Goodale, C.L.; Hazlett, P.W.; Heine, P.R.; Johnson, C.E.; Larson, J.T.; Lawrence, G.B.; Kolka, R.K.; Ouimet, R.; Paré, D.; Richter, D.D.; Schirmer, C.D.; Warby, R.A. Ecosphere 6: Article 73.
Issued by: Laurentian Forestry Centre
Catalog ID: 35939
Availability: PDF (request by e-mail)
Long-term forest soil monitoring and research often requires a comparison of laboratory data generated at different times and in different laboratories. Quantifying the uncertainty associated with these analyses is necessary to assess temporal changes in soil properties. Forest soil chemical properties, and methods to measure these properties, often differ from agronomic and horticultural soils. Soil proficiency programs do not generally include forest soil samples that are highly acidic, high in extractable Al, low in extractable Ca and often high in carbon. To determine the uncertainty associated with specific analytical methods for forest soils, we collected and distributed samples from two soil horizons (Oa and Bs) to 15 laboratories in the eastern United States and Canada. Soil properties measured included total organic carbon and nitrogen, pH and exchangeable cations. Overall, results were consistent despite some differences in methodology. We calculated the median absolute deviation (MAD) for each measurement and considered the acceptable range to be the median ± 2.5 x MAD. Variability among laboratories was usually as low as the typical variability within a laboratory. A few areas of concern include a lack of consistency in the measurement and expression of results on a dry weight basis, relatively high variability in the C/N ratio in the Bs horizon, challenges associated with determining exchangeable cations at concentrations near the lower reporting range of some laboratories and the operationally defined nature of aluminum extractability. Recommendations include a continuation of reference forest soil exchange programs to quantify the uncertainty associated with these analyses in conjunction with ongoing efforts to review and standardize laboratory methods.
Plain Language Summary
In this study, the researchers compared soil analyses performed in 15 laboratories in the eastern United States and Canada. Despite a few differences in the methods used, the results were comparable from one laboratory to another, and the variations observed were not larger than those found within a laboratory itself.
Many research studies establish forest soil monitoring systems. It is therefore important for soil analyses to be performed as uniformly as possible between laboratories and over time.
In light of these results, the researchers conclude that collaboration on the analysis of soil data may continue, which does not however preclude pursuing efforts to standardize laboratory methods.