Soil is often thought of as an inert substrate, useful in propping up plants and a mere vehicle for applied fertilizer and water. It is, in reality, a distinct ecosystem, defined as a system formed by the interactions of a community of organisms with their physical environment.
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.”
Soil’s Four Components When you pick up a handful of soil, only half of that volume is solid material (minerals and organic matter). The other half should be pore space occupied by air (25%) and water (25%). Thus soil consists of four basic components: 1. Mineral (45%, + or -, by volume): The mineral component of soil consists of rocks ground down over geologic time as a result of physical, chemical and biological actions. Think of it as rock or stone “flour.”