Characteristics of Topsoil
Topsoil is a combination of minerals, decayed plant matter and ecological activity that supports a wide variety of life, including plant roots, burrowing animals, bacteria and insects. Humans use topsoil to fertilize barren areas in gardens or crop fields, but without it, few plants on the Earth could survive.
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Definition
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Topsoil is so named because it lies on the top of the Earth, a crust-like layer that serves as a covering to the deeper foundations of bedrock below. In some locations, topsoil may reach down hundreds of feet, while in other places, such as the tundra, topsoils may only be a few inches deep before frozen soil takes its place. Topsoil is a vital part of plant growth--it is where plants grow their roots, taking in moisture, nutrients and oxygen. Without topsoil, life on the Earth could not exist.
Formation
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Topsoil is an extremely complex mixture of different substances. Its base elements are formed from various kinds of rock, worn down into dust from years of wind, rain and glacier activity. This dust, once moist, attracted various forms of plant and animal life, and when the plants and animals died, their matter was absorbed into the dust and became a part of it. After hundreds of years of this cycle, layers of topsoil are finally born, consisting of minerals, plant and animal matter, water, and many different kinds of life living in the soil, including worms, which consistently add nutrients as the soil passes through their bodies. In this way, soil can be seen as an environment, more than a substance.
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Composition
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What kinds of nutrients are in soil and what color and texture it has depends entirely on where it is. The type of rock nearby, the channels from which minerals could have originally come, the type of water brought by the rain and the plants and animals living in the area all make up the composition of soil. Generally, topsoil has several different layers, the first being a mixture of loam made mostly of leaves and other matter from surrounding plants. This loamy layer combines with a deeper mineral layer rich in nutrients, which rests on the third layer, worn bedrock that provided minerals for the soil to begin formation.
Uses
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Topsoil is used most often by humans in gardening applications. Bags of it are frequently sold, and trucks of topsoil are hauled in for large landscaping projects. Sometimes, the soil is just spread around plants that are already growing to add new nutrients, while other times topsoil is added to a barren area so plants or seeds can be planted as landscapers desire. Generally, the richest and most expensive topsoil is black, but there are many different kinds and the most useful type depends on the plants to be grown in it.
Process
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Plants extend their roots down into topsoil and put out thousands and thousands of tiny hairs that absorb the minerals and nutrients found there. For this reason, good, rich topsoil is relatively loose, allowing easier penetration by plants. As the plants draw nutrients, the topsoil is gradually drained and may lose its effectiveness if not renewed. Naturally, drained topsoil must be left alone for at least several years to regain its former potency.
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