Life in the Soil and Landscape
An incredible diversity of organisms makes up the soil food web. These organisms range in size from the tiniest one-celled bacteria, algae, fungi, and protozoa to more complex nematodes and microarthropods, as well as visible earthworms, insects, small vertebrates, and plants.
As these organisms eat, grow, and move through the soil, they help support healthy plants, healthy soil, moderated water flow, clean water, and clean air.
There are many ways in which the soil food web is an integral part of landscape processes. Soil organisms decompose organic compounds, including manure, plant residue, and pesticides, preventing them from entering water and becoming pollutants.
They store nitrogen and other nutrients that might otherwise enter groundwater, and they fix nitrogen from the atmosphere, making it available to plants. Many organisms enhance soil aggregation and porosity, thereby increasing infiltration and reducing runoff. Soil organisms prey on crop pests and serve as food for above-ground animals.
Organisms and Their Interactions
The soil food web is a community of organisms that live all or part of their lives in the soil. A series of energy and nutrient conversions, as one organism eats another, demonstrates the activity of the soil food web.
All food webs are fueled by primary producers: plants, lichens, mosses, photosynthetic bacteria, and algae that use the sun’s energy to fix carbon dioxide from the atmosphere. Most other soil organisms obtain energy by consuming plants, other organisms, or waste by-products. A few bacteria, called chemoautotrophs, obtain energy from nitrogen, sulfur, or iron compounds rather than from carbon compounds or sunlight.
As organisms decompose complex materials or consume other organisms, nutrients are converted from one form to another and are made available to plants and other soil organisms. All plants, including grasses, trees, shrubs, and agricultural crops, depend on the food web for their nutrition.
Growing and reproducing are the primary activities of all living organisms. As individual plants and soil organisms work to survive, they depend on interactions with one another. By-products from growing roots and plant residues feed soil organisms. In turn, soil organisms support plant health as they decompose organic matter, cycle nutrients, enhance soil structure, and control populations of soil organisms, including crop pests.