Dirt is dirt, but not all dirt is created equal. Good, organic soil has a good composition of organic matter, with the appropriate balance of clay, silt and sand. A good understanding of what organic soil is composed of will help any gardener grow healthier plants.
Stabilized Organic Matter
Stabilized organic matter is matter that is not decomposing. According to the University of Minnesota, this composition is made up of complex compounds from years of decomposition that will no longer degrade. Stabilized organic matter makes up 1/3 of organic soil. Stabilized organic matter is made up of plants that grew centuries ago, acting like a sponge that absorbs water.
Fresh organic matter that is decomposing is called the active fraction of soil, and makes up 15 percent of organic soil. This may be new plants grown in the soil, or composted material. This decomposing material does not make nutrients in the soil, but rather releases it in the soil as the material decomposes. The addition of active fraction materials must be greater than the rate of decline to prevent soil degradation.
Living Organisms and Fresh Organic Residue
Living organisms make up around 20 percent of a soil's composition. These materials are important, as when they die or produce waste, they provide further organic material. They also hold the soil together, preventing erosion that strips away topsoil.