This page gives average levels of nutrients as found by Soil Control Lab in its analyses of more than 1,600 compost samples from the southwestern U.S. The values presented in the tables below are averages, and actual nutrient levels will vary.

Compost Attribute Values
AttributeValueUnit
Organic Matter dw*42.32percent
Total Carbon dw22.19percent
Carbon/Nitrogen16.8ratio
pH7.6 
Electrical Conductivity (EC5)** dw7(w/w) mmhos/cm
Sodium (Na) dw0.28percent
Carbonates (CaCO3) dw45lb/ton
Primary Nutrients
NutrientValueUnit
Nitrogen dw1.53percent
Ammonium (NH4-N) dw 741.9mg/kg
Nitrate (NO3-N) dw291mg/kg
Potassium (K) dw1.13percent
Potassium (as K2O) dw1.36percent
Phosphorus (P) dw5900mg/kg
Phosphorus (as P2O5) dw1.34percent
Secondary Nutrients
NutrientValueUnit
Calcium (Ca) dw3.28percent
Magnesium (Mg) dw0.63percent
Sulfate (SO4) dw4384mg/kg
Micronutrients
NutrientValueUnit
Copper (Cu) dw 117mg/kg
Zinc (Zn) dw 248mg/kg
Iron (Fe) dw 15321mg/kg
Manganese (Mn) dw 291mg/kg
Boron (B) dw 51.5mg/kg
Chlorine (Cl) dw 3137mg/kg
Molybdenum (Mo) dw 4mg/kg

*dw=dry weight
**EC5 is the electrical conductivity of a slurry composed of one part compost to five parts water by weight. Compost EC5 differs from the typical electrical conductivity measurement of soil (ECe) in that it is gravimetric as opposed to volumetric, and, in most cases, requires more water to make the 1:5 slurry than what is required to make the ECe saturation paste. These differences make it such that the EC5 will almost always be lower than the ECe, and, difficult, if not impossible, to correlate the two measures."

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