California Department of Resources Recycling and Recovery (CalRecycle) 

Organic Materials Management

Average Levels of Compost Nutrients

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
Attribute Value Unit
Organic Matter dw* 42.32 percent
Total Carbon dw 22.19 percent
Carbon/Nitrogen 16.8 ratio
pH 7.6
Electrical Conductivity (EC5)** dw 7 (w/w) mmhos/cm
Sodium (Na) dw 0.28 percent
Carbonates (CaCO3) dw 45 lb/ton
Primary Nutrients
Nutrient Value Unit
Nitrogen dw 1.53 percent
Ammonium (NH4-N) dw  741.9 mg/kg
Nitrate (NO3-N) dw 291 mg/kg
Potassium (K) dw 1.13 percent
Potassium (as K2O) dw 1.36 percent
Phosphorus (P) dw 5900 mg/kg
Phosphorus (as P2O5) dw 1.34 percent
Secondary Nutrients
Nutrient Value Unit
Calcium (Ca) dw 3.28 percent
Magnesium (Mg) dw 0.63 percent
Sulfate (SO4) dw 4384 mg/kg
Nutrient Value Unit
Copper (Cu) dw 117 mg/kg
Zinc (Zn) dw 248 mg/kg
Iron (Fe) dw 15321 mg/kg
Manganese (Mn) dw 291 mg/kg
Boron (B) dw 51.5 mg/kg
Chlorine (Cl) dw 3137 mg/kg
Molybdenum (Mo) dw 4 mg/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."

Compost Use in Agriculture

Last updated: August 19, 2013
Organic Materials Management