Introduction to Soils
Soil is a complex mixture of different materials. About half of most soils are inorganic materials, such as the products of weathered rock, including pebbles, sand, silt, and clay particles. About half of all soils are organic materials, formed from the partial breakdown and decomposition of plants and animals. The organic materials are necessary for a soil to be fertile. The organic portion provides the nutrients, such as nitrogen, needed for strong plant growth. In between the solid pieces, there are tiny spaces filled with air and water. Within the soil layer, important reactions between solid rock, liquid, water, air, and living things take place. In some soils, the organic portion could be missing, as in desert sand. Or a soil could be completely organic, such as the materials that make up peat in a bog or swamp.
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Soil Texture |
The inorganic portion of soil is made of many different size particles, and these different size particles are present in different proportions. The combination of these two factors determines some of the properties of the soil. A permeable soil allows water to flow through it easily because the spaces between the inorganic particles are large and well connected. Sandy or silty soils are considered "light" soils because they are permeable, water-draining types of soil. Soils that have lots of very small spaces are water-holding soils. For example, when clay is present in a soil, the soil is heavier, holds together more tightly, and holds water.When a soil contains a mixture of grain sizes, the soil is called a loam.
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Classification |
When soil scientists want to precisely determine soil type, they measure the percentage of sand, silt, and clay. They plot this information on a triangular diagram, with each size particle at one corner. The soil type can then be determined from the location on the diagram. At the top, a soil would be clay; at the left corner, it would be sand; at the right corner, it would be silt. Soils in the lower middle with less than 50% clay are loams.
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Course Syllabus |
This course engages the students in the study of soil as a growth medium for plants and a valuable natural resource. Topics include physical, chemical and biological properties of soil; soil-water relationships; organisms, organic matter decomposition and soil ecosystem principles; soil reactions, cation exchange and essential nutrients; synthetic and organic fertilizers; soil conservation and land management principles.
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