Proficiency testing for improving analytical performance in soil testing laboratories: A summary of results from the council's soil and plant analysis proficiency testing programs

Abstract

In 1994, the Soil and Plant Analysis Council initiated a Proficiency Testing program for soil testing laboratories in the United States and Canada. The program consists of a semi‐annual (January and July) exchange of five soil samples. Participating laboratories can test the samples for up to ten different analytes following analytical methods recommended by geographic region. The data is collected and subjected to statistical analysis and data summaries are provided to the participants. Data summaries are reported here from results of the January, 1995 exchange. Of the analytes tested, the least variability was found for water and buffer pH while greatest variability was found for chloride and soluble salts. Variability of test results for phosphorus was greater than that of the other macronutrients regardless of soil test procedure employed. On the average, 53 to 80% of the participating laboratories had results that were within +/‐1 standard deviation of the mean for the analytes tested while 76 to 100 % had results that were within +/‐ 2 standard deviations of the mean. Future improvements of the Council's Proficiency Program will include the addition of micronutrients (B, Fe, Mn, Zn, and Cu) as well as the implementation of a Plant Tissue Proficiency Testing Program.

Notes

Agricultural Analytical Services Laboratory, The Pennsylvania State University, University Park, PA, 16802–1100.