I get a lot of questions about organic matter. What is it? Why do I need to monitor my organic matter levels? What is a good result and what is bad result? What do I do if my results are bad?
Let’s begin by defining organic matter. According to the USDA, “Soil organic matter (SOM) is the organic component of soil consisting of three primary components: small (fresh) plant residues with small living soil organisms, decomposing (active) organic matter, and stable organic matter (humus).” Note that the word “organic” here means substances and organisms found in nature — not the common retail definition referring to products created without the use of pesticides, antibiotics, or synthetic fertilizers. Examples of organic matter in this context are manure, crop residue, cover crops, and compost.
Why do you need to monitor organic matter? Because without sufficient organic matter, your soil’s health will suffer. Organic matter creates an ecosystem that facilitates plants’ absorption of nutrients like those in your fertilizer applications. It also helps improve both water retention and drainage, and its effect on soil structure helps to promote beneficial microbial activity. Together these effects on soil structure will help create a healthy and strong ecosystem capable of withstanding diseases and pests that can destroy your crop.
What are good and bad levels of organic matter? Organic Matter is reported as a percentage, and healthy soils will have between 2 and 6% organic matter. If you fall below the 2% mark, take steps to improve your SOM. One step you can take is to ensure you preserve what organic material you have by implementing soil erosion measures like adopting a no-till farming regimen. You can also amend your soil with organic matter such as composts, grass clippings, and mulch among many others.
Can SOM be too high? YES! If your organic matter is too high (greater than 6%), you might have too much phosphorus. For example, if you’ve been using manure to improve your organic matter for years, your annual soil test might show a very high level of phosphorus.
Phosphorus is the leading cause of pollution in our waterways and gets into the system when farmers and homeowners apply more of it than the soil and its plants can absorb. And while the right level of phosphorus is a key to plant health, too much can actually kill plants. A surprising number of our soil test customers show toxic levels of phosphorus coming from organic lawns and gardens. Always remember – too much of a good thing can turn into a bad thing.
If you want to dive deeper into this topic, visit the USDA site for a good read.