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Understanding Soil Formation

Cover of N.C. Agric. Res. Bull. 467. Understanding Soil Formation. Mendocino Staircase. Hans Jenny (1899 - 1992). http://static.panoramio.com/photos/original/1006030.jpg. The Hans Jenny Pygmy Forest Reserve In this complex “ecological staircase,” each terrace is

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Understanding Soil Formation

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  1. Cover of N.C. Agric. Res. Bull. 467 Understanding Soil Formation

  2. Mendocino Staircase Hans Jenny (1899 - 1992)

  3. http://static.panoramio.com/photos/original/1006030.jpg

  4. The Hans Jenny Pygmy Forest Reserve In this complex “ecological staircase,” each terrace is ~ 100,000 years older than the one below it and supports a distinct association of soils, plants, animals and microbes. Pygmy forest . Giant trees The highest and oldest of five wave-cut terraces that rise from the chilly waters of the Pacific Ocean. Extremely acid and infertile soil Beach sand

  5. How is it possible that soil can naturally become so unproductive?

  6. Where is Macomb in this sequence? Dr. Jenny also studied climosequences across the Great Plains. Brady and Weil, 2002

  7. Soil = f (Cl, O, R, P, T…) H Jenny refined the ideas of Russian scientist VV Dokuchaev into the following equation: Time Relief Climate 5 factors of soil formation Organisms Parent material

  8. Organisms Climate Young Soils Older Soils Which factor is most important ??? Topography Parent material

  9. Understanding parent materials in Illinois Glacial deposits cover most of Illinois Many of these deposits are hundreds of feet thick!

  10. Retreating Glacier

  11. Depth of loess cap LOESS silt sized glacial flour, transported by wind, deposited near rivers

  12. Glaciation Primary minerals chemical weathering physical weathering dissolution chemical weathering alteration precipitation HCO3- K+ Cl- Ca+2 Na+ SO4-2 sand and silt ions in solution leaching secondary clay minerals

  13. Climatic variation Increasing rainfall Increasing temperature RR Weil

  14. Average annual precipitation in IL 1951-1990 Have precipitation levels remained constant during the last 10,000 years ? NO !

  15. N.C. Agric. Res. Bull. 467 Topographic variation Poorly drained Interstream divide Somewhat poorly drained Moderately well drained LANDSCAPE POSITIONS Well drained Poorly drained Shoulder Common in IL Valley floor SOIL DRAINAGE CLASSES Backslope

  16. Soil Associations in McDonough County, IL Topography of McDonough County, IL 800 feet above sea level A soil association is a group of soils that are found together in a landscape 470 feet above sea level

  17. Vegetative variation Grassland Forest Organic- rich A horizon From Brady and Weil, 2002

  18. How much of Illinois was originally covered by tall grass prairie ? How much of Illinois was originally covered by forest ? 13.8 million acres 22 million acres Corn and soybean dominate IL landscapes today but we know where the prairie and forest use to be because of the soils Illinois once was covered by a complex mix of prairie and forest Prairie dominated the flat expanses Forest dominated the hilly land Old growth forest in

  19. Temporal variation Lake terrace chronosequence in northeastern Michigan http://soils.umn.edu/academics/classes/soil2125/doc/s4chp4.htm

  20. Young Soil in NC Old Soil in NC Poorly Defined HorizonsLow Degree of WeatheringSlightly LeachedThin Solum Well Defined Horizons High Degree of WeatheringHighly LeachedThick Solum http://www.mo15.nrcs.usda.gov/features/gallery/

  21. Precipitation plus solutes, aerosols and particulates Additions Additions Sediment Loss of gases N2, N2O, CO2 Losses Soil forming processes Losses Sediment Capillary rise of dissolved ions E(i)lluviation of clay CaCO3 dissolved ions dissolved OM Organic residues  humus Primary  Secondary minerals minerals TRANSLOCATIONS TRANSFORMATIONS TRANSLOCATIONS Capillary rise of salts Additions Leaching of dissolved ions & OM Losses Adapted from Stewart (1990)

  22. Water driven translocations Illuviation Eluviation Illuviation Illuviation http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/soil_systems/soil_development_profiles.html

  23. Typical Florida flatwoods soil E uviation= depletion l I uviation = accumulation ll http://www.fnps.org/photos/spodosol.jpg

  24. Conceptual chronosequence http://courses.soil.ncsu.edu/resources/soil_classification_genesis/soil_formation/soil_transform.swf

  25. Chronosequence in California Foth, 8th ed.

  26. Characteristics that differentiate soil horizons Color Texture Density Structure Organic Matter content Acidity Mineral Accumulations Biological activity RR Weil

  27. Master Soil Horizons Soil horizons Most Weathered Least weathered RR Weil

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