Soil and manure testing is an important component in agricultural research. The North American Proficiency Testing (NAPT) Program, the Agricultural Laboratory Proficiency (ALP) Program, and the University of Wisconsin provide soil proficiency samples to laboratories. The Minnesota Department of Agriculture provides manure proficiency samples to laboratories. How are the proficiency samples prepared, and what are the program differences? What is considered normal variability in laboratory results for soil and manure for various analytical tests? How do laboratories make use of proficiency data?

In addition, Wisconsin, Iowa, Minnesota, Missouri, and Nebraska utilize proficiency data to certify laboratories for soil or manure testing and the Illinois Soil Testing Association also evaluates laboratory performance based on proficiency testing. What criteria do the various certification programs use to certify laboratory for soil testing or manure testing? What percentages of laboratories participating in the various proficiency programs meet certification requirements? Does the certifying agency allow reruns for laboratories failing to meet certification requirements?