46011soil1

46011soil1 - Soil as an Ecological Factor 1. Significance...

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Soil as an Ecological Factor 1. Significance of soil: “It’s just dirt,” is a statement that not only perturbs soil scientists and geologists but which defies reality. Soils are complex materials, not simple stuff, and they are central to much of the Earth’s contemporary life. Terrestrial organisms, directly or indirectly, receive water and inorganic nutrients from soils. Soils offer part or all of the habitat for a variety of plant, microbial, and animal species 2. Components of soil a. Mineral materials derived from the weathering of parent materials b. Organic materials derived from biological activities c. Water held within the matrix of mineral and organic materials and containing solutes i. Capillary water: water within soil pores that is largely available to plants ii. Hygroscopic water: that portion tightly held by adsorptive forces and not available iii. Gravitational water: that transitory water moving through the soil due to gravity d. Gases, i.e., a soil atmosphere, which is to some degree different from the overlying atmosphere e. Because of their intimate association, soil organisms are sometimes listed as a fifth component. 3. Depending on the soil, varying amounts of inorganic nutrients can become available from these sources: a. Nutrients dissolved in the soil solution: These are easily available for plant uptake but represent a small fraction of the total nutrient pool, which is replenished with ongoing slow dissolution and decomposition. b. Nutrients adsorbed as ions on ion exchange surfaces: These too are readily available and represent a small, renewable nutrient fraction. c. Mineral material:
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46011soil1 - Soil as an Ecological Factor 1. Significance...

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