One of the primary means for organic gardeners to improve their soil is by incorporating organic material. The most common organic material is compost or peat moss, but any natural, formerly living substance may also be considered organic material. Organic material improves soil in ways that are superior to synthetic fertilizers.
Organic matter is composed of carbon compounds. It originally came from living material such as plant matter, animal remains, microbes and organisms. Organic matter may be classified as either stable organic material, which is highly decomposed and may resemble soil, or active fraction. Between 1/3 and ½ of soil organic material is stable organic material, and may have come from plants that decomposed over 100 years ago. Uncomposted kitchen scraps would be considered active fraction, as would the stubble left from barley or wheat that farmers plow back into their soil.
Organic matter that is added to soil feeds microorganisms, insects and worms that loosen soil, remove contaminants and add nutrients that plants need to grow strong and healthy. When these living things are present in the soil, the soil is loose, black and crumbly. Organic material also holds nutrients that plants need to survive, prevents erosion, aerates soil to improve root development of plants, improves water infiltration, reduces water evaporation and increases water holding capacity.
Organic material may include anything that was once living. Good examples include compost, peat moss, yard trimmings and animal manure. Most organic amendments are classified as either green or brown items. Green items are filled with nitrogen, while brown items are filled with carbon. As an organic material dies, it slowly converts from a nitrogen-filled organic material into a carbon-filled organic material. Leaves that are on a tree are an organic green; dead fall leaves are an organic brown.
Organic material has several advantages over conventional chemical means of improving soil. Organic soil amendments help to increase the buffering capacity of soil and reduce erosion by binding aggregates together. Because organic amendments add micronutrients in addition to macronutrients into soil, plants grown in organic soil are healthier than those grown using synthetic fertilizers.
Just because a soil amendment is organic does not automatically make it safe. Organic amendments such as manure may contain e-coli, while compost that was created using materials that have been treated with herb or pesticides may carry the residue of these chemicals. If contaminated organic material is placed into your soil, the contaminants can spread to the newer plants. Practicing hot composting or sterilizing organic material by baking it so that the material warms to at least 130 degrees F throughout is the best way to kill these residues.