1. What is Soil?

2. 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

3. Factors of soil formation
Parent material (original type of rock)
Residual soil: formed from local bedrock
Transported soil: parent material has been moved to a new location
Climate: most influential
Vegetation, Slope, Time, and interaction of all factors

4. Soil composition (by volume of a healthy soil)
Weathered rock and mineral matter (dirt)(~45%): Clay and quartz most abundant minerals. Must contain potassium, phosphorus, and nitrates
Organic matter (humus) (~5%): Partially decayed plant and animal remains mixed in with soil. Supplies food for microorganisms
Air (nitrogen, oxygen, carbon dioxide) (~25%): Used by soil organisms and plants

5. Water (~25%): A solution of water and dissolved minerals and nutrients
Pore spaces: allows for penetration of roots and circulation of air and water
Soil organisms: Some decompose organic matter releasing nutrients back into the soil and some change atmosphere nitrogen into nitrogen compounds (nitrates)

6. Soil Profile: as soil develops, it forms separate soil layers called horizons
“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

7. Soil Profile: as soil develops, it forms separate soil layers called horizons
“A” horizon: Topsoil, most weathered layer, 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

9. “B” horizon: Subsoil (fill dirt), less 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 determine
“C” horizon: Little biological activity, partially weathered parent material, and more and larger rocks
“R” horizon (not a true layer of soil): Bedrock and unweathered parent material

11. Soil Erosion is the transportation of soil
Agents
Water
Raindrops hit the soil and dislodge soil particles
Thin sheets of water (sheet flow) flowing across the surface carries away dislodged soil particles (sheet erosion)
Sheet flows collect in tiny channels called rills
Rills drain into gullies

12. Gullies drain into streams
Streams drain into rivers
Rivers flow to the oceans where the soil is deposited
Wind, Ice (glaciers), and Human activities

13. Special Soils
Laterites (Brick Soil): Thick red soils form in the wet tropics and subtropics and is the end product of extreme chemical weathering

14. Special Soils
Tundra: Soils near the Artic Ocean, thin soil with little humus, and supports only small plants, no trees

15. Soil by brainpop