Soil formation and soil profiles

1. Soil formation and soil profiles Unit 5: Biosphere Ms. Thind

2. Formation of Soil • Decaying vegetation: • In areas of favorable climate for vegetation growth • Decaying organic matter is broken down  dark, sticky partly decomposed layer at soil surface  humus • Very fertile • Ideal for agriculture

3. 2. Leaching: • Layer of weathered rock particles and decaying organic matter allow water to pass through  dissolved minerals are carried deep into rock particles • process of water soluble minerals transported through the soil • Tropical wet climate

4. 3. Capillary action: • Occurs in dry desert and grassland regions • Surface layers so dry that water is transferred deep in the ground to the surface • Capillary action brings water and dissolved minerals close to the surface • Very fertile

5. 4. Translocation • Movement of solid material from one place to another • Transport of material occurs on the surface or downward through the soil and carried by water • Soil animals play a role eg: worms, burrowing animals

6. Formation of a soil profile Soil layers or soil profile begin to appear form: weathering organic debris parent material  Soil that forms in areas with rainfall and vegetation have distinct soil layers  horizons

7. Soil Profile: 3 Horizons A-horizon: topsoil layer, darker = more humus = more fertile B- horizon: subsoil, brown/red  clay and iron oxide through translocation. In areas of heavy precipitation. Excessive leaching  transports soluble materials into bottom layers. C-horizon: rock partially weathered, above parent material or bedrock.

8. Soil types 5 main soil types: • Chernozem soils • Podzol soils • Laterite soils • Sierozem soils • Tundra soils

9. Chernozem soils • Temperate prairie grasslands  “breadbasket” areas of the world • North America Prairies, Russian Steppe • Very fertile  thick, dark humus layer • Dry summers  leaching not a problem  capillary action brings nutrients to the surface • Cold winters  freezes soil  burrowing animals important to mix up soil

10. Laterite soils • Topical low pressure belt • Very deep and red due to high iron oxide content • Leaf litter adds nutrients to soil • Trees have shallow root system to capture nutrients in top layer • Infertile soil

11. Podzol soils • Coniferous forests • Humid Continental  cold winters, warm summers (due to lack of ocean influence) • Heavily leached and very acidic • Thin humus layer of decaying evergreen needles

12. Sierozem soils • Desert soils  areas of little precipitation • Limited vegetation • Organic content is low • Little rainfall = poorly defined soil layers • Can be fertile when irrigated  stirring the soil  capillary action brings nutrients to surface layer

13. Tundra soils • Permafrost limits the circulation of water in soil = layers not well defined • Low temperatures  decomposition of vegetation is slow  small decomposing organic layer