1. Soil Test Method Precision, Correlations, and Trends: SSSA-NAPT Historical Data

The Soil Science Society of America’s (SSSA) North American Proficiency Testing (NAPT) operates as a not-for-profit service laboratory resource since 1998 to assist/evaluate agricultural and environmental testing laboratories with quality assurance and quality control. Soil (n5 samples each quarter), plant (n3), and/or water (n3) samples collected nationwide are submitted quarterly to ~150 participating laboratories who choose which method(s) to use for which analytes they are interested... B. Hopkins, S.V. Nelson, G. Cardon, J. Lawley, T.J. Hopkins