Organic matter: The living, the dead, and the very dead
Three different types of organic matter defined.
Soil health, specifically soil organic matter has been on the minds of farmers in the past few years. Farmers are testing their soil and comparing its soil health on the grounds of increase of soil organic matter. Most tests that farmers use measure total soil organic matter. Soil organic matter, however, is broken up into three different categories: living, dead, and the very dead. The ratio of these three is also a good measure of the health of your soil.
Soil organic matter that is classified as the living is the easiest for us to quantify. This type encompasses all microbiological organisms, plant roots, residues, manure, compost, etc. that are in the soil. We can determine the microbiological population of our soil by weight. In tilled fields bacteria outweigh fungi. In contrast, in a forest system fungi outweigh the bacteria. The weight of worms, roots and other plant residue can be determined and compared to various tillage practices.
The dead is what we call the active carbon pool. Active carbon is very important to a healthy soil. This pool is where nutrient and aggregate glues are found. It also supplies food for the microbial population. Decrease in organic matter due to farm practices usually equates to a reduction in the active carbon, dead, pool. Fortunately, this is the area where we can see an increase in soil organic matter when we use conservation practices. The Ohio State University Extension has developed an in-field soil health kit that can assess the active carbon in the soil.
The very dead is what we call soil humus. Soil aggregation as well as the cation exchange capacity is dependent on the amount of humus found in the soil. This pool does not decompose quickly and is labeled as stable soil organic matter. Management practices have a minimal short-term impact on this portion of soil organic matter but there can be a long-term positive or negative effect depending on farm management practices.