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Transcript
Soil Soil in Our Environment What is soil? Or is it Dirt? “Gold’s father is dirt, yet it regards itself as noble.” Yiddish Proverb Is it alive? Is it fragile? Formations of Soils How much time does it take to form about 1” of topsoil? About 1,000 years! Destruction of Soils How long does it take to deplete about 1” of topsoil? In a few short years – less than 5 years in some areas Destruction of Soils What forces of nature do you suppose cause the largest amounts of erosion? A hint . . . Uh Huh . . . Wind! What Else? Another hint? That’s Right . . . Water! Destruction of Soils So what do you suppose causes soil, on a large scale, to be so susceptible to wind and/or water erosion? Destruction of Soils Mismanagement . . . poor agricultural practices Carelessness Neglect Leads to . . . (and the magic word is?) Erosion – wind and water Soil loss through plowing The Outcome? How about the failure of the local civilization? What about from a landscape perspective? Do we still see erosion? What about soil fertility? And plant health and vigor? Chapter 1 Soil Composition and Importance Pages 1 – 24 What is soil? The uppermost layer of the Earth’s surface – the tectonic plates . . . The tectonic plates? Tectonic Plates ? What is soil . . . . . . A product of? Geologic processes weathered rock – parent materials Weathering? Physical and chemical process Physical process . . . freeze-thaw tumbling down hills and streams Weathering? Chemical process . . . chemical reactions between rocks and water Decomposition of parent materials/rocks End product are soils What is soil composed of? Minerals . . . altered physically and chemically from original bedrock Organic chemicals Biomass Gasses – air, water Dissolved materials Soil Composition . . . Made up of three fractions . . . mineral fraction organic fraction gasses and water Mineral fraction Sand – 2mm to 0.05mm Silt – 0.05mm to 0.002mm Clay - <0.002mm Analogy – compare a basketball to a baseball to a BB Organic fraction . . . Living organisms including: plants and plant roots bacteria & fungi worms, insects, etc. dead/decomposing organisms Organic fraction . . . Organic materials provide a reservoir of plant nutrients Nutrients are continually recycled as organic materials Gasses and water . . . Oxygen (O) Carbon dioxide (CO2) Nitrogen (N), etc. H2 O Gasses and water . . . Fills in pore spaces between the soil particles Larger pore spaces contain more gasses Smaller pore spaces contain more water Soil pore spaces can take up to 50% of the volume of a given soil sample Soil texture What did we say made up the mineral fraction? Sand . . . Silt and . . . Clay So soil texture is . . . The percentage (%) of . . . Sand . . . Silt and . . . Clay . . . By volume We’ll come back to that later. . . . Name 2 reasons soils are studied? Agricultural reasons . . . ability to support plant life soil fertility Structural reasons . . . building construction ability to support foundations, footings, etc. Some definitions Actually, a whole bunch of definitions . . . Rocks . . . What are rocks? consolidated mass of minerals Minerals . . . And minerals? unique, repeatable combination of elements stable consistent hardness, melting point, etc. Elements . . . What about elements? found on the periodic table . . . unique combination of protons and neutrons in a nucleus . . . surrounded by electrons The nucleus . . . Nucleus of an atom contains . . . protons (+) neutrons (-) and electrons Three types of rocks . . Rocks are found in three forms . . . igneous - divided into two groups metamorphic sedimentary Igneous rocks Extrusive igneous rock - lava volcanic in nature formed by being pushed out of the Earth’s crust small to no crystals caused by rapid solidification when exposed to air or water ex. basalt Igneous rocks Intrusive igneous rock forms as magma cools within the crust can form large, distinct crystals caused by slow cooling under ground ex. granite (Sierra Nevada mountains, Southern California batholiths) Sedimentary rock Made from sediments eroded igneous, metamorphic or sedimentary materials deposited horizontally by wind or water solidifies over time and as sediments continue to build over time Sedimentary rock typically softer than igneous or metamorphic rock ex. sandstone (western Rocky Mountains, Utah, Grand Canyon) Metamorphic rock The name implies change . . . igneous, sedimentary or other metamorphic rock changed by being subjected to heat and or pressure hard, strong and resistant to weathering Tropical region soils . . . Often subjected to much leaching Basalts – minerals leached out settle out as clays Tropical region soils . . . Clay soils in tropical areas start out fairly fertile leaching from rainfall . . . high temperatures . . . extensive plant growth . . . they loose fertility Tropical region soils . . . Tropical clay soils tend to be shallow erode quickly when disturbed . . . by clearing of vegetation and agriculture Temperate region soils Often granitic, sandy soils fertility varies soil depth vary Parent materials It’s all about the rock! Rocks weather How? Physical and chemical weathering Decomposition of rocks creates soils Geography & local weather Affect: soil formation development of plant species and varieties Organic soils Formed exclusively from organic matter formed as peat bogs dry out peat soils muck soils Ex. areas of the Sacramento River Delta Soil horizons . . . Separate and distinct layers of soil down to parent materials and basement rock Examples: O-Horizon A-Horizon B-Horizon C-Horizon Soil horizons . . . Soil horizon layers and content . . . very much based on their surroundings ex. topography deposition history local weather, etc. Hatch Act of 1887 Set aside land around the country for agricultural studies Created series of agricultural experimental stations Provides funds for Land Grant schools founded under the Morrill Act 1862 USNRCS US Natural Resource Conservation Service formerly: US Soil Conservation Service under the United States Department of Agriculture (USDA) part of the Executive Branch of the US Government USNRCS Provides an interactive website with regional soil maps http://www.nrcs.usda.gov/ Topography . . . Study and graphic representation of changes of relief features . . . in surface configurations of a given area Indicates changes in elevations and positions on a map Alluvial fans . . . Distinct fan-shaped formation of soil deposition . . . Found at base of hills or downstream ends of rivers