How to Measure the Organic Matter in Soil

Overview

Healthy, growing plants require nutrients on a regular basis. One way to get plants the nutrients they need is to provide them with plenty of organic matter in the soil that they are growing in. It is important, then, for gardeners to know just how much organic material their soil contains. One way to determine this is to heat the soil to high temperatures to burn off the organic matter and weigh the difference between the pre- and post-heated samples.

Step 1

Break apart one or two handfuls of soil and remove any large particles, debris or rocks. The finer the dirt the better so anything over 1/4 of an inch in size should be removed. Spread the soil in the clean oven pan and heat the pan in the oven to 225 degrees F and keep it at that temperature for 24 hours to dry the soil.

Step 2

Place approximately 10 grams (.35 oz.) of soil into a crucible or evaporating dish and cover it with the lid. Carefully weigh the dish with the soil and lid and mark down the exact weight.

Step 3

Put on safety goggles. Place the dish onto a metal stand, slide lid slightly ajar to allow fumes to escape and heat the dish with a propane torch. As the soil heats up, the organic matter will begin to burn off and you will see visible fumes. Heat the soil slowly being careful not to allow any particles of dirt to escape with it. If the soil is not completely dry there is a possibility that trapped moisture might build up pressure and pop compressed soil apart, so it is essential that all soil be dried completely before the test.

Step 4

Continue heating the soil for one or two minutes until there are no more visible fumes coming from the soil. Once the fumes stop, the organic matter has been burned off and the soil can be left to cool.

Step 5

Allow the soil and dish to cool completely. Weigh the container with the soil and lid again. Subtract that measurement from the measurement you took before heating the soil. The difference is the amount of organic matter that escaped during heating and the amount that was in the soil.

Things You'll Need

  • Clean oven pan
  • Oven
  • Crucible and lid or evaporating dish and cover
  • Metal stand to hold crucible or evaporating dish
  • Scale
  • Propane torch
  • Safety goggles

References

  • Rain.org: Soil Types and Testing
  • Olympia High School: Soil
  • University of Montana: Soil and Plant Growth
Keywords: measuring organic matter, organic matter in soil, evaluating soil

About this Author

Robin Lewis Montanye is a freelance artist, designer and writer. Her articles have appeared in newspapers, national magazines and on several self-help areas of the web. Montanye specializes in gardening articles with information from several universities. She has Internet articles published on Gardenguides.com, eHow.com and Suite101.com.