Carol R. McFarland, Crop and Soil Sciences, Washington State University,
David R. Huggins, USDA-ARS, Richard T. Koenig, Associate Dean and
Director of Extension, Washington State University  FS170E.pdf (wsu.edu)  pubs.cahnrs.wsu.edu/publications/wp-content/uploads/sites/2/publications/FS170E.pdf