Measuring Soil Moisture by Look and Feel
MEASURING SOIL MOSITURE IN THE FIELD BY LOOK and FEEL
Will Bakx of Sonoma Compost Company has a Master’s Degree in Soil Science, but when it comes to measuring compost moisture content, he treats it more like the art of cooking than science. Here’s his technique:
The ideal moisture content for composting is between 40-60%. So, how do you estimate the moisture level in your compost pile? Take a sample of compost in your hand from roughly 18 to 24” into the pile. Make sure there are no sharp objects in the sample. Squeeze tightly.
- If water flows freely out of your hand, the moisture content is 65% or higher – too wet.
- If a few drops of water are visible between your fingers, you are right at 60% - the upper limit.
- If you don’t see any water, open up your hand. If a sheen is clearly visible, moisture content will be 55 to 60%. This is the ideal starting point in the dry season, when you want more moisture in the pile.
- If no sheen is visible and a ball remains in your hand, tap the ball gently. If the ball stays intact, moisture content is 50 to 55%. This is a good maintenance moisture content for composting.
- If a ball forms, but breaks apart during tapping, moisture content will be 45-50%. As a pile moves towards the end of the composting process, let it dry out somewhat. The pile will continue to compost well. As the moisture level is reduced, the compost becomes lighter which is more appropriate for using in the garden.
- If the compost does not remain in a ball when opening your hand, moisture is 40-45%. This is a good starting point when going into the wet season. The compost pile will be able to absorb some moisture. It is also a good moisture content when entering the curing phase of the compost.
- If no ball has formed, and a dry talcum-like feeling remains on your hand after discarding the material, moisture content is likely below 40%. Too low - this level slows down the composting process.
Laboratory test of compost samples has proven these moisture ratings to match descriptions. Of course, this non-scientific technique is specific to SCC’s compost. Percentages may vary with different materials. Bakx adds, however, that experience will allow any composter to fine-tune this method to his specific product.
Reprinted with permission from BioCycle, a composting journal published monthly by The JG Press, Inc. in Emmaus, PA.