Organic composition and living organisms

In addition to nematode activity, the bacteria and fungi present in the soil decompose all sorts of organic material, such as leaves, dead roots, and animal carcasses. Living organisms and their organs, such as roots, produce carbon dioxide, which combines with water and forms an acid. The acidic nature results in a higher dissolving rate for the minerals present in the soil. Bacteria, fungi, nematodes, birds, ants and other burrowing insects all serve as composters for topsoil. As these organisms alter the soil through their activities, they add to it with their wastes and the decomposition of their bodies when they die. The organic composition of soil depends on external factors, such as location and water resources. If an area is constantly wet, and oxygen is limited or lacking in the soil, the microorganism activity may be quite low and the organic content may be as high as 90%. Thus the organic content in that soil will be quite high. On average, topsoil might be composed of 25% air, 25% water, 48% minerals, and 2% organic material. Furthermore, with the exception of legumes and a few other plants, almost all of the nitrogen needed by growing plants, and most of the phosphorus and sulfur come from the decomposition of organic matter. As the decomposition progresses, the acid content increases which in turn increases the breakdown of minerals which will be carried into solution into growing plants.