Chapter 7
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Department
Environmental Science
Course
EESA01H3
Professor
Carl Mitchell
Semester
Fall

Description
Chapter 7Soil and Agriculture Soil as a System y Soil is not merely loose material derived from rock it is a complex plantsupporting system consisting of disintegrated rock organic matter water gases nutrients and microorganisms y Soil is also fundamental to the support of life on this planet and the provision of food for the growing human population Soil formation is slow and complex y The formation of soil plays a key role in terrestrial primary succession which begins when the lithospheres parent material is exposed to the effects of the atmosphere hydrosphere and biosphere y Parental material is the base geological material in a particular location y Bedrock the continuous mass of solid rock that makes up Earths crust y The process most responsible for soil formation are weathering erosion and the deposition and decomposition of organic matter o Weathering describes the physical chemical and biological processes that break down rocks and minerals turning large particles into smaller particles These small particles of mineral matter called regolith are the precursors of soil y Physical weather or mechanical weathering breaks rock down without triggering a chemical change in the parent material y Chemical weathering results when water or other substances chemically interact with parent material y Biological weathering occurs when living things break down parent material by physical or chemical meansy Another process often involved is erosion the movement of soil from one area to another y Partial decomposition of organic matter creates hummus a dark spongy crumbly mass of material made up on complex organic compounds y Soils that are dominated by partially decayed compressed organic materiallike the soil at Mer Bleueare called peat A soil profile consists of layers known as horizons y Each layer of soil is known as a horizon and the cross section as a wile from surface to bedrock is known as soil profiley Five major horizons are O A B C and R horizonsy Many soil profiles include an uppermost layer consisting mostly or organic matter such as decomposing branches leaves and animal waste This thin layer is designated the O horizon O for organic or litter layer y Distinctions are also made among LF and H horizons which are organic horizons derived from the accumulation of forest litter in various stages of decomposition y Just below the organic horizon lies the A horizon consisting of inorganic mineral components with organic matter and humus from above mixed in The A horizon is often referred to as topsoil that portion of the soil that is
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