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Why is soil important?

What is soil?

Soil is a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.

Soils are composed of solid particles, pore spaces, and organic matter. The solid particles, or mineral portion of the soil, accounts for about 45% of the soil volume. They are formed from the weathering of the parent material. These particles (not including any gravel, cobbles, or stones) are classified into three different sizes, sand, silt, and clay. Sand is the largest particle, and feels gritty when rubbed between the fingers. Silt is the medium sized particle. It feels smooth like flour. Individual silt particles are barely visible. Clay is the smallest particle and cannot be seen by the unaided eye. Clay feels sticky when wet.

Pores are the voids between the solid particles. They account for about 50% of the soil volume. These spaces are filled with air and water. These pores are extremely important to plants and other organisms that receive oxygen, water, and nutrients from the soil. The size of the pores influences the rate of movement of air and water through the soil. Sandy soils which have large pores transmit air and water more rapidly than clay soils which have very small pores.

Organic matter is comprised of dead plant and animal tissue and the micro-organisms that live in the soil. While organic matter accounts for only about 5% of the volume of the soil, it is a very important part of the soil. Organic matter has many functions including providing energy for micro-organisms, helping to stabilize the solid soil particles, providing for easier penetration of plant roots, increasing infiltration of water into the soil, and reducing runoff and soil erosion. Soil organic matter is also one place where atmospheric carbon can be sequestered, to perhaps minimize the effects of global warming.

What does soil do?

Soil performs many functions which make it a fundamental resource for life. Soil is the biologically active zone where the atmosphere, water, sunlight, and the earth's crust mix and interact, all of which affect the growth and vigor of plants. Soil provides the place where plants conduct photosynthesis, converting the sun’s radiant energy into food energy for plants and animals.

Soil controls the distribution of rain water to runoff, infiltration, or storage, which affects the movement of soluble materials, such as nitrates, nitrites, phosphorus, or pesticides. It filters and buffers impurities from our air and water. And it provides a site for waste decomposition.

Not only does soil also provide the home on which we build our structures, but it provides the foundation on which we build our civilization.

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