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  1. 1. • Soil is a layer at the surface of the earth composed of a mixture of weathered rock, organic matter, mineral fragments, water, and air which is capable of supporting the growth of plants
  2. 2. Factors of soil formation o Parent material (original type of rock- bedrock)  Residual soil: formed from local bedrock  Transported soil: parent material has been moved to a new location o Climate: most influential o Vegetation, Slope, Time, and interaction of
  3. 3. Soil composition (by volume of a healthy soil) o Weathered rock and mineral matter (dirt) (~45%): Clay and quartz most abundant minerals. Must contain potassium, phosphorus, and nitrates o Organic matter (humus) (~5%): Partially decayed plant and animal remains mixed in with soil. Supplies food for microorganisms o Air (nitrogen, oxygen, carbon dioxide) (~25%): Used by soil organisms and plants
  4. 4. o Water (~25%): A solution of water and dissolved minerals and nutrientso Pore spaces: allows for penetration spaces of roots and circulation of air and watero Soil organisms: Some decompose organic matter releasing nutrients back into the soil and some change atmosphere nitrogen into nitrogen
  5. 5. Soil Profile: as soil develops, it forms separate soil layers called horizons o “O” horizon (not a true layer): Fresh or partly decomposed organic material (humus) sitting on top of the soil (litter) and highest concentration of microorganisms
  6. 6. Soil Profile: as soil develops, it forms separate soil layers called horizons o “A” horizon: Topsoil, most weathered layer, horizon most fertile layer, high humus content (nutrients), many microorganisms, dark color due to humus, Zone of leaching (water dissolves minerals and carries them down to a lower layer), the most roots present, and the parent material unidentifiable
  7. 7. o “B” horizon: Subsoil (fill dirt), less horizon root penetration, less biological activity, compact and lighter in color, Zone of accumulation (where leached materials are deposited), many more rocks, and parent material difficult to determineo “C” horizon: Little biological activity, horizon partially weathered parent material, and more and larger rockso “R” horizon (not a true layer of soil): Bedrock and unweathered parent
  8. 8. Soil Erosion is the transportation of soil Agents  Water 1. Raindrops hit the soil and dislodge soil particles 2. Thin sheets of water (sheet flow) flowing across the surface carries away dislodged soil particles (sheet erosion) 3. Sheet flows collect in tiny channels called rills 4. Rills drain into gullies
  9. 9. 3. Gullies drain into streams 4. Streams drain into rivers 5. Rivers flow to the oceans where the soil is deposited Wind, Ice (glaciers), and Human activities
  10. 10. Soil by brainpop