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Competency Area 3: Soil Testing and Plant Tissue Analysis

PO 15. Convert fertilizer analysis from elemental to oxide form and from lbs/acre to ppm and vice-versa.

Different laboratories and companies report nutrient content in different units. The most common are ppm (parts per million) and lbs/acre. In addition, the form of nutrients (particularly P and K) can either be presented in the elemental form (i.e., P or K) or the oxide form (K2O or P2O5). Conversion between the different forms and units is important, as one cannot directly compare ppm of P to lbs P2O5/acre.

  • 1 ppm = 1mg/kg = 2 lbs/acre (assuming 2 million lbs soil in one acre furrowslice)
  • 1 lb K = 1.20 lb K2O
  • 1 lb K2O = 0.83 lb K
  • 1 lb P = 2.29 lb P2O5
  • 1 lb P2O5 = 0.44 lb P