USDA Practice Standard 590 for Washington State has been updated. Analysis is done to comply with manure management plans as part of USDA Farm Bill Programs will be required to use a laboratory that is successfully meeting the performance standards of the North American Proficiency Testing-Performance Assessment Program (NAPT-PAP). The Phosphorus Index calculations can be made from only Bray-P (western Washington) and Olsen-P (eastern Washington).
