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Soils

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  1. Soils Ag I

  2. Objectives* Outline the process involved in soil formation Describe a mature soil profile Discuss the 8 land capability classes

  3. Soil The top layer of the Earth’s surface which is suitable for the growth of plant life

  4. Soil Formation Slow Forms from parent materials- mineral & rocks, glacial deposits, loess deposits, alluvial and marine deposits, organic deposits

  5. Parent Material • Materials underlying the soil from which it was formed • 5 categories • Mineral and rocks • Glacial deposits • Loess deposits • Alluvial and marine deposits • Organic deposits

  6. Minerals & Rocks • Minerals • Solid • Inorganic • chemically uniform • Feldspars, micas, silica, iron oxides, calcium carbonates • Rocks • Aggregates of minerals • 3 groups-Igneous, Sedimentary, Metamorphic

  7. Glacial Deposits Deposits of rock, parent material and already formed soils that were left behind as the glaciers moved across the northern hemisphere Soils found in much of the Midwestern US were formed from glacial deposits

  8. Loess Deposits Wind-blown silt Make up much of the soil in the eastern Mississippi Valley

  9. Alluvial & Marine Deposits • Alluvial Deposits • Left by moving fresh water • Marine Deposits • Formed on ancient ocean floors • Both are found in the forms of flood plains and deltas

  10. Organic Deposits Form as vegetation dies and falls into the water where it decays slowly Muck Soils- plants are decayed to the point they are no longer recognizable Peat Soils- plant materials are still recognizable

  11. Weathering

  12. Major Forces Temperature change Water action Plant roots Ice expansion Mechanical grinding

  13. Process Continuous Even as erosion is occurring, parent material is breaking down forming new soil Biggest problem is balance—actions of erosion happen much more quickly

  14. Soil Organic Matter

  15. Make-Up • Decaying plants and animals • 2 forms • Original Tissue- organic matter that is still recognizable • Ex- Leaves and twigs on a forest floor • Humus-organic matter that has decomposed beyond recognition. • Gives topsoil its brown color

  16. Functions Affects soil structure by acting as a cementing agent Returns nutrients to the soil- most notably phosphorous, sulfur and nitrogen Helps store soil moisture Makes soil more tillable Provides food for soil microorganisms which make the soil capable of plant production

  17. Physical, Chemical and Biological Characteristics

  18. Soil Profile 4 or more horizons O A B C

  19. C Horizon • Parent material • Stores and releases water to the upper layers • Doesn’t contribute much to plant nutrition • Contains larger soil particles • Substantial amounts of gravel or rock • Layer below is bedrock

  20. B Horizon Subsoil Mineral content is similar to the A Horizon but particle sizes and properties differ Less organic matter than in the O and A horizons Lighter in color than A horizon

  21. A Horizon Topsoil Near the surface Contains desirable proportions of organic matter, and sand, silt and clay Generally supports plant growth

  22. O Horizon Surface Composed of organic matter and a small amount of mineral matter

  23. Land Capability Classes

  24. Capability Classes Developed by the USDA and NRCS to classify lands based on their limitations. 8 classes

  25. Class I Very good, productive land Can be safely cultivated with minimal erosion control methods Nearly level Well drained Deep Medium textured Not subject to erosion or flooding Easily cultivated Very little land falls into Class I even in the most productive farming areas.

  26. Class II • Good for all types of farming • Has some limitations • Gentle slope • Suffers from past effects of erosion • May have less than ideal soil depth and drainage problems that can be corrected by installation of drainage systems • Land requires careful soil adjustment to prevent erosion damage

  27. Class III Moderately good land May be cultivated and farmed regularly as long as limitations are followed May be highly susceptible to erosion or have problems with drainage Needs to be farmed with great care to control erosion

  28. Class IV • Severe limitations but can be cultivated with careful soil management • May have a strong slope and be subject to severe erosion • May suffer from past erosion • May be very shallow, very dry or very wet • If wet, even extensive drainage systems may still allow occasional water logging

  29. Class V Nearly level but has some properties that make it unsuitable for cultivation May be in a frequent floodplain May be very wet, dry or rocky Swampy areas frequently are Class 5 Best suited for pasture, wildlife habitat, or forest production

  30. Class VI Serious limitations May have very rocky or shallow usable surface soil Tree production, permanent pasture and wildlife habitat are the best uses

  31. Class VII Severely limiting properties May be very steep or severely eroded with large gullies May have very course soil combined with strong slopes Using native grasses for controlled grazing is the best use Can also be used for forest production, wildlife and recreation

  32. Class VIII • One or more extreme limitations • Rock outcroppings, areas of almost solid surface rock • Best examples are river washes, streambeds, lake bottoms, sand dunes and other nearly barren areas • Little agricultural value • Best preserved in its natural state for recreation and wildlife

  33. Summary* The Earths naturally occurring rocks and minerals are broken down into parent material by weathering forces. Parent materials combine with organic matter through further weathering into soil. Soils may be classified based on the lands capability to produce plants while resisting erosion. There are 8 capability classes- class I is the best and class VIII is the worst from the standpoint of plant production Classes I-IV are tillable, classes V-VIII are generally not considered tillable.