USDA Natural Resource Conservation Service

Soil Biology

Worm your way through these questions!

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What Is Soil?

  • Soil is formed from rocks and decaying plants and animals.

  • An average soil sample is 45 percent minerals, 25 percent water, 25 percent air, and five percent organic matter.

  • Different-sized mineral particles, such as sand, silt, and clay, give soil its texture.

  • Fungi and bacteria help break down organic matter in the soil.

  • Plant roots and lichens break up rocks which become

  • part of new soil.

  • Roots loosen the soil, allowing oxygen to penetrate. This benefits animals living in the soil.

  • Roots hold soil together and help prevent erosion.

  • Five to 10 tons of animal life can live in an acre of soil.

  • Earthworms digest organic matter, recycle nutrients, and make the surface soil richer.

  • Mice take seeds and other plant materials into underground burrows, where this material eventually decays and becomes part of the soil.

  • Mice, moles, and shrews dig burrows which help aerate the soil.

The Make Up Of Soil

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Let's get dirty and learn about soil!