Compost Nutrient Testing

Many soils labs also test compost. 

This includes nutrient and biological tests. A basic compost test may include Carbon (total), Nitrogen (total), Moisture, and pH. Additional tests can include:

  • Moisture/Total Solids
  • Phosphate
  • Potash
  • Sulfur
  • Magnesium
  • Sodium
  • Iron
  • Manganese
  • Copper
  • Zinc
  • pH
  • Total Salts
  • C/N Ratio
  • Ammoniac Nitrogen
  • Nitrate Nitrogen

Biological tests may include salmonella and E. coli.

If you wish to test compost, contact several labs to find out what they will test for, sampling and shipping procedures, and cost. 

 

Ways to test if compost is finished and stable

Over time, compost materials should become dark, soft, crumbly, have a good earthy smell, and not have any appearance of the original material. Even at this point, the compost may still be giving off ammonia or have a high carbon/nitrogen ratio that would cause plant growing  problems if used as a soil amendment.

One simple test is to show if seed will easily germinate in the compost. U

  • Use 9 large foam cups. Make three with all compost, three with half compost and half garden soil, and three with all garden soil. 
  • Place seeds that easily germinate, such as radish or lettuce, in each container and moisten. 
  • If you notice that the seeds in the compost and half and half mix don’t do as well as the all soil cups, it would be best to let the compost sit for another 1 to 2 months (longer if it’s winter) and try the experiment again.

Solvita tests

The Solvita field test measures soil respiration in fresh soil samples. It uses jars with probes to measure carbon dioxide and ammonia given off by the compost sample, along with a color chart to determine concentrations of these two gases. Results are available in a few hours. The higher the readings of these gases, the more immature the compost is.

 

To sell compost

The Test Method for the Examination of Composting and Compost  provides detailed protocols for the composting industry to verify the physical, chemical, and biological condition of composting feedstocks, material in process, and compost products at the point of sale.

Resources