Northeast Region Certified Crop Adviser (NRCCA) Study Resources

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In This Section

• Introduction
• PO 15 Fertilizer analysis conversions
• PO 16 Soil sampling
• PO 17 Variability in soil test results
• PO 18 Fertilizer recommendations
• PO 19 Soil test interpretation
• PO 20 Soil sampling strategies
• PO 21 Pre-sidedress nitrogen test
• PO 22 Plant tissue analysis
• PO 23 Plant nutrient level
• Summary

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