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soil :
The thin, top part of the earth’s crust, composed of rock and mineral particles and, in the upper layers, mixed with decaying animal and plant matter called humus. Growing plants take water and minerals from the soil. Soil is essential to much of the life found on Earth. Soils are affected by climate and weather, by the organisms that live in them, by groundwater, by age, and by other factors. Between the topsoil and the bedrock is a layer called the subsoil, which generally has little or no humus and is not very good for plant growth. There are many different types of soils, ranging from heavy clay soils with little humus to light sandy soils with large amounts of organic materials.
