Soil is composed of inorganic minerals and organic matter, the latter consisting of the remains of plants, animals and other living organisms. As described above, the organic matter in soil is what gives it a desirable structure or tilth, retards erosion, and provides the basis for abundant and diverse soil life, which in turn fosters healthy plants. In contrast, soils with little organic content support much less life, are more prone to erosion and compaction, and generally produce less healthy plants. Thus, the major principle of soil health is to build up and maintain high levels of organic matter. This is accomplished by practices and inputs that add organic materials to the soil, on the one hand, and that minimize their dissipation, on the other.
A major source of organic matter is crop residues, such as the stalks and roots of corn or wheat, left on or in the field after harvest. Cover crops—plants that are seeded in the fall after the main crop is harvested, and killed off in the early spring—also add considerable amounts of organic matter to the soil. Crop residues are broken down to usable size and incorporated into the soil by earthworms, detritivores and innumerable soil microbes. Manure and compost are major inputs that increase the organic matter content of the soil. For over half a century, organic farmers have been the chief proponents and practitioners of what might be called “healthy soil farming,” particularly in their cultivation of cover crops and use of manure and compost rather than inorganic fertilizers.
