Soil Testing Laboratory Analytical Performance - Results of the ISTA-LAP Program.

Soil testing is a critical component of nutrient management in the United States. The Illinois Soil Testing Association (ISTA), established a Laboratory Accreditation Program in 2011 for soil testing labs serving the state of Illinois and surrounding states. The program is based on a statistical assessment of soil test proficiency results of five soils from the ALP program submitted three times annually for soil analysis pH, phosphorus (three methods) and potassium (two methods). A participating lab is required to meet a minimum 80% performance score for each test method to become accredited. Failing laboratories must pass a retest with to maintain accreditation. Twenty-six labs are enrolled in the ISTA-LAP program and results indicate soil pH is the most consistent across laboratories, whereas Mehlich 3 extractable K the least. Five laboratories account for more than 50% of the soil test method failures (scores < 80%). Results will be presented on soil test method, individual laboratory and whole industry performance for sixty soils analyzed for the period 2012-2017.