What is soil?

Soil is the loose surface material that covers most land. In short, soil is a mixture of minerals, dead and living organisms (organic materials), air, and water. These four ingredients react with one another in amazing ways, making soil one of our planet’s most dynamic and important natural resources.

How does soils form?

Dig down deep into any soil, and you’ll see that it is made of layers, or horizons. Put the horizons together, and they form a soil profile. Like a biography, each profile tells a story about the life of the soil. Soil is formed through the mechanisms of weathering and erosion. The natural processes of weathering and erosion that take place in nature, aid in soil formation. Soil is created from the rock when weathering breaks up the bedrock deep in the ground. Tree roots and animals mix these broken rock pieces, breaking them down into even smaller fragments. As the pieces get smaller, they make their way up closer to the surface of the earth. Through the process of leaching, water and dissolved minerals from above, mix with the rock fragments and become part of the soil. The soil near the surface of the earth is made from rich nutrients, from the breakdown of organic plant material and animal matter. Bacteria and fungi help the organic matter to decay. Small animals mix this nutrient-rich soil with rock and mineral fragments. Their mixing also creates space for air and water to enter. When all of these steps take place over time, and the rock and mineral fragments, organic matter, water, and air have combined, new soil is created. How is soil made? It is made through a complex multi-step process that takes a very long time to complete.

The organic layer (also called the humus layer) is a thick layer of plant remains such as leaves and twigs.

Topsoil is considered the "A" horizon. It is a fairly thin layer (5 to 10 inches thick) composed of organic matter and minerals. This layer is the primary layer where plants and organisms live.

Subsoil is considered the "B" horizon. This layer is made primarily of clay, iron, and organic matter which accumulated through a process called illuviation.

The parent material layer is considered the "C" horizon. This layer is called the parent material because the upper layers developed from this layer. It is made up mostly of large rocks.

Bedrock

The bottom layer is several feet below the surface. The bedrock is made up of a large solid mass of rock.

The particles that make-up soil are categorized into three groups by size – sand, silt, and clay. Sand particles are the largest and clay particles are the smallest. Most soils are a combination of the three. The relative percentages of sand, silt, and clay are what give soil its texture. A clay loam texture soil, for example, has nearly equal parts of sand, silt, and clay. These textural separates result from the weathering process

How Color affects soil

Color can tell us about the soil’s mineral content. Soils high in iron are deep orange-brown to yellowish-brown. Those with lots of organic material are dark brown or black; in fact, organic matter masks all other coloring agents.

Color can also tell us how a soil behaves. A soil that drains well is brightly colored. One that is often wet and soggy has an uneven (mottled) pattern of grays, reds, and yellows.

How does Soil affect Biomes

Ecologists group large geographic regions with similar environments and distinctive plant and animal communities into biomes. The environmental factors influencing biomes include latitude, the general climate and topography of the region, and soil. Soil is the foundation of every terrestrial ecosystem. Each biome has soils with characteristics unique to it.

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