Compost Testing Yields Good Results

Since the start of this semester, it has been my goal to put some science behind the composting that goes on at Washington College, and yes, we do compost by the way. Mid-September, I met with Dr. Sherman, associate professor of chemistry at Washington College who specializes in soil chemistry. She agreed to guide me through the testing and soon I was on my way to determining the quality of our compost.


The procedures were taken from the manual Test Methods for the Examination of Composting and Compost (TMECC), developed by the U.S. Composting Council. The purpose of following these procedures rather than our own is to have the ability to analyze our compost according to widely used standards. Also, in the future we may want to market our compost to the public, and following the TMECC procedures will allow us to put a Seal of Testing Assurance on our compost.

So far, three tests have been performed on the compost from last year, which finished decomposing over the summer. It has been tested for pH, conductivity (soluble salt concentration), and moisture. It is still in the process of being tested for organic matter, which will tell us the percentage of carbon-based materials in the compost. This does not, however, tell us the carbon to nitrogen ratio which is most important during the process of composting, determining the ability for the pile to decompose aerobically and at the correct temperature. This test is quite complicated, so we must send samples to select labs with the proper equipment.

These are the results:

pH: 7.43
Conductivity: 10.83 dS/m
Percent Moisture: 42.8%

Analysis of the results:

A pH within the range of 6.0 and 7.5 is optimum for compost according to the TMECC. In this range, necessary nutrients are available for microbes and the compost can decompose readily. If the pH were below or above this range, necessary biological processes would not occur. A pH within this range indicates that nutrients necessary for plant growth are available. The presence of toxic metals is also an important factor in compost quality. Toxic metals are indicated by a pH less than 5, so we do not need to be concerned about toxic metals in our compost.

Electrical conductivity measures the soluble salt concentration in a sample. Salts are important factors in compost quality because high concentrations can damage seedlings, prevent or delay germination, and decrease nutrient availability. Low concentrations may indicate low fertility levels. Typical compost samples have a conductivity of 1.0 to 10.0 dS/m, and although our reading was slightly higher, it is not excessively high and will not likely damage plants when mixed in with soil.

The percent moisture measures the amount of water in the sample. Percent moisture does not really affect its quality, but rather its ease of handling and transportation. A preferred moisture range is 40-50%, so our compost should be easy to handle.

By the end of the semester we should have results for the organic matter tests as well as results from a sample being sent to a soil analysis lab to determine carbon/nitrogen ratio.

You may be wondering about the actual application of the compost on campus. Some of the compost from last year’s pile has just been applied in front of Daly Hall. Now with these data we can rest assured that the plants are growing in quality compost. Look for signs in front of Daly indicating the use of the compost and be on the lookout for more signs in other areas in the future!