The NAPT Program and Its Use for Monitoring Laboratory Proficiency.

The North American Proficiency Testing (NAPT) program is an outgrowth of several proficiency testing programs which were developed to meet the needs of soil testing labs for industry-wide quality control.  The goal of the NAPT program is to assist soil, plant, and water testing laboratories in their performance through inter-laboratory sample exchanges and a statistical evaluation of the analytical data.  The results of the quarterly exchanges of five soil, three plant, and/or three water samples from all laboratories are compiled and labs are informed of how they compare to their peers.  Laboratories can use their quarterly reports to determine how they performed in that quarter’s exchange and also follow their results over time to find problems in their laboratories; for example, the lab may realize they are consistently low on one analyte through several quarters.  Because one soil is repeated each quarter, the four results for the year by each laboratory for that soil are tabulated and the variance determined so the lab can observe how they are performing throughout the year.  Samples used in the program are also available for purchase so a lab can monitor their own performance on a regular basis in the lab.  Outside agencies and individuals make use of the NAPT program to monitor laboratory performance through blind submission of NAPT QC samples to the lab.  The NAPT-PAP program was developed for the NRCS to monitor soil testing labs, particularly in the Pacific Northwest where phosphorus analysis has received close scrutiny.  Additional ways in which the NAPT program plans to help laboratories is through workshops, articles, and videos directed at improving laboratory performance.