Chapter 7 Notes - Soil as a system Soil is a complex...

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Soil as a system Soil is a complex plant-supporting system consisting of disintegrated rock, organic matter, water, gases, nutrients, and microorganisms. o Fundamental to the support of life on this planet and the provision of food fort he growing human population The composition of a region’s soil can have as much influence on the regions ecosystems as do the climate, latitude and elevation. Soil is composed of living and non living components Soil formation is slow and complex Parent material is the base of geological material in a particular location. o Can include lava or volcanic ash; rock or sediment deposited by glaciers, sediment doposited by rivers, or bedrock , the continuous mass of solid rock that makes up Earth’s crust. Weathering, erosion, and the deposition of organic matter were responsible for soil formation. Weathering describes the physical, chemical, and biological processes that breaks down rocks and minerals, turning large particles into smaller particles. Physical Weathering or mechanical weathering breaks down rock without triggering a chemical change in the parent material o Wind and rain are two main forces. o Areas with extreme temperature fluctuations experience rapid rates of physical weathering. o Water freezing and expanding in cracks in rock also causes physical weathering Chemical weathering results when water or other substances chemically interact with parent material. o Eg. Groundwater being unusually acidic. Biological weathering occurs when living things break down parent material by physical or chemical means. o Tree accelerates weathering by physical action of its root growing and rubbing against rock. Erosion is the movement of soil from one area to another o This is physical weathering o A destructive process that reduces the amount of life that a given area of land can support. Partial decomposition of organic matter creates humus a dark, spongy, crumbly mass of material made up of complex organic compounds. o Soils with high humus content hold moisture well and are productive for plant life. Soil that are dominated by partially decayed, compressed organic material are called peat . o Peat is characteristic of northern climates because cool temperatures slow the decay process, allowing great thicknesses of organic material to accumulate. 5 primary factors that influence the formation of soil (table 7.1 page 192) o Climate
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Soil forms faster in warm wet climates. Heat speeds chemical reactions and accelerates weathering, decomposition, and biological growth. o Organisms Earthworms and other animals mix and aerate soil, add organic matter. Plants add organic matter o Topograhpic relief Steeper slopes result in more runoff as an example o Parent Material Chemical and physical attributes of the parent material influence properties of the resulting soil o Time Soil formation takes decades, centuries, or mellenia Multiple factors (including the 4 above)
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Chapter 7 Notes - Soil as a system Soil is a complex...

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