What is Soil?
Soil is a thin layer of material that covers the surface of most of the dry land on Earth. If one reaches down and picks up a handful of soil, it sifts away through the fingers. It appears to be a collection of small lifeless particles.
Soil is anything but lifeless—it does contain small particles of rock (called gravel, sand, loam, clay etc. based on the particle size) but ground up rock alone is not soil. Soil forms as a result of the activities of living things—plants and animals grow, die, and decay, leaving their minerals and organic material in the soil. Various creatures live in the soil, breaking down decaying organic matter, moving soil, mixing it, and making it their home. These living things, their waste products, and the remains of other living things are all part of soil.
Why is Soil Important?
In Tree: A Life Story, David Suzuki and Wayne Grady wrote: “soil is the terrestrial ocean. Both soil and ocean are the cradles of photosynthetic life” (Vancouver: Greystone, 2004). Soil provides the nutrients and environment for plants to grow, and plants, in turn, provide the environment where animals make their homes. Where soil is removed or degraded, very little can live.
What are Live Species Doing in Soil?
All of the species that live in soil have a part to play in their ecosystem. Not all soils are alike, and different soils support different species. Here are some species commonly found in soil:
- Lichens: lichens actually play an important role in breaking down rocks to provide the particles that determine the texture of soil. Lichens also remove nitrogen from air and water, adding it to the soil when they break down, and help stabilize soil.
- Fungi: Fungi grow on and break down dead organic material. Fungi produce spores in order to spread and reproduce, and many fungal spores are found in soil.
- Bacteria: Bacteria help to break down organic material and draw nitrogen from the air, making it available to plants in the soil.
- Arthropods: Insects, arachnids, and insect-like creatures called springtails live in the soil in massive numbers. Some of them prey on others, while many of them break down animal feces, dead plants and animals, and other organic materials, which speeds decomposition by other species such as bacteria and fungi. Arthropods also add their wastes and dead bodies to the soil.
- Earthworms: Earthworms are constantly moving through the soil, mixing and loosening it, and feeding on the plant and animal material there. With their tilling, earthworms make it easier for plants to grow, and improve the texture and drainage. They help break down decaying organic materials and increase soil fertility with their waste products.
In addition, soil contains many transient life forms that are passing from one stage of their lives to another: plants seeds await the right circumstances to begin growth or spread to new places; parasitic eggs and cysts await the arrival of their next host; insect larvae pupate and develop to adults—it may look lifeless, but there’s a lot going on in soil.
Sources:
10 Minute Ecologist. Janovy, John Jr. New York: St. Martin’s Press, 1997.
The Earthworm Book. Minnich, Jerry. Emmaus, PA: Rodale Press, 1977.
Tree: A Life Story. Suzuki, David, and Wayne Grady. Vancouver: Greystone, 2004.
