Although we tend to take it for granted, human society is principally possible only because the earth’s crust is “dusted” with a thin and often fragile layer of life-supporting material on which we can grow food: the soil. Two distinct parts of the soil—the biotic and abiotic components—function together to form a stable system.
The biotic, or living (or that which was once alive) component is comprised largely of living plants, living organisms (macro and micro), and organic matter (plant and animal residues), which can be fresh, partially decomposed, or fully stabilized (humus). Soil’s abiotic component is made up of minerals, air, and water.
By understanding the soil’s ecosystem, growers can harness and promote the biotic components with judicious additions of compost and “green manures” (cover crops worked into the soil) to create a healthy environment for plant growth, and thus virtually eliminate the need to apply purchased fertilizer. This can lower costs—both out of pocket and environmental.
This supplement introduces the soil’s four basic components and three major properties, discusses how these interact, and describes ways that gardeners and farmers can improve their soils by learning how to become “biological growers.”
Organic matter (5%, + or -): Organic matter is made up of a wide range of organic (carbon-containing) substances, including living organisms, plant biomass, and the carbonaceous remains of organisms and plants. Some soil microorganisms break down the remains of plants, animals, and other microorganisms; others synthesize new substances. 3.
Soil air (25%): Soil air occupies the interstitial spaces between soil particles. Its primary role is to provide oxygen to fuel the aerobic (oxygenrequiring) activities of microorganisms and plant roots. Soil bacteria that associate with roots of legumes such a beans and peas use the nitrogen component of soil air to “fix” nitrogen in a form that plant roots can assimilate.