Parts per million (ppm) and percent (%)

If you saw potassium at 23,000 ppm in a leaf nutrient analysis (tissue test), would you be worried about possible potassium toxicity? If that test reported manganese at 0.007%, should you be concerned about a manganese deficiency? The answer to both of these questions is no. These are normal values expressed in atypical units. I was reminded of how what seems like a large value when expressed in ppm seems innocuous when expressed as percent in a recent conversation about…