Tennessee Brown Phosphate
(0-6-0, 22% total P2O5) The consistency of rich soil. Comes from the washing piles left behind when high-grade ore was extracted to produce superphosphate in the early 20th century. When tested in several midwestern states’ labs, concentrations of available phosphate were regularly over 6%. Lowest concentration of heavy metals of any phosphate source. Recommended by soil gurus Phil Callahan and Mark Fulford.