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What is a soil pedon ?

What is a soil pedon ?. A pedon is a natural body of soil that is large enough to allow classification of the soil. Horizons. classification. Brady and Weil, 2002. Soil scientists have developed detailed terminology for describing soil pedons.

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What is a soil pedon ?

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  1. What is a soil pedon ? A pedon is a natural body of soil that is large enough to allow classification of the soil. Horizons classification Brady and Weil, 2002

  2. Soil scientists have developed detailed terminology for describing soil pedons. We will learn many of these terms later in the semester. Today we will think about “pedons personified”. http://www.britannica.com/ebi/art-19380

  3. Parts of a soil body skin skeleton stomach connective tissues respiratory system circulatory system

  4. Sand and silt are the bones of the soil skeleton http://www.ecogrowth.com.au/soil.htm Soil skeletons

  5. Clay and humus are the soil skin and connective tissues Brady and Weil (2002) http://www.ccma.csic.es/dpts/suelos/ clay minerals humus

  6. Why is the soil skin important ? • Adsorption of water films • Adsorption of organic and inorganic chemicals • Ion exchange • Catalysis of chemical reactions • Habitat for bacteria

  7. What is humus ???? • While it is unlikely that any 2 humus molecules are identical… the diverse products of “humification” have many common characteristics: • Extreme chemical complexity • Resistance to further decomposition • High specific surface and negative charge • Dark color

  8. What is texture ??

  9. 12 textural classes Textural triangle http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

  10. 12 textural classes Textural triangle http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

  11. 12 textural classes Textural triangle http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

  12. 12 textural classes Textural triangle How much sand, silt and clay is represented by this location ? http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

  13. Why do the textural class zones have such strange assymetrical shapes ? Soils within each zone behave similiarly

  14. 12 textural classes Textural triangle What do these textural classes have in common? http://www.oneplan.org/Images/soilMst/SoilTriangle.gif

  15. They are all “loamy” ! ! Loam soils have favorable physical properties for agriculture

  16. Granular crumb structure Compacted soil The soil fabric How are the primary particles arranged in real soils ? http://www.grdc.com.au/growers/gc/gc48/conference1.htm

  17. Granular crumb structure

  18. 20 years of bluegrass sod followed by 5 years of corn with moldboard tillage 25 years of corn with moldboard tillage

  19. After adding water Water stable aggregates 25 yrs of conventional corn 20 yrs of bluegrass, then 5 yrs conventional corn

  20. How do these soils differ ?? manure cover crops crop residues crop residues 20 years of similar tillage but different types of organic inputs Rodale Institute Farming Systems Trial

  21. Contrasting stands of corn in the NC tillage systems experiment Fall plow/ spring disk No-till

  22. Plasticity vs. Friability Friable soils crumble easily when subjected to mechanical stress. Tillage requires less draft !

  23. Angular blocky structure enhances drainage and root growth below the plow layer Ray Weil

  24. habitat !! Soil is The Furrow

  25. The Soil Stomach • Bacteria • Fungi • Algae • Protozoa • Nematodes • Microarthropods • Enchytraeids • Earthworms • Ants, termites, spiders • Mollusks • Others: rodents, snakes, • voles, amphibians, etc. Body size increasing Microflora Microfauna Mesofauna Macrofauna Megafauna

  26. SSSA BACTERIA cocci bacillus filamentous spirilla

  27. FUNGI

  28. The fence post principle Schriefer (2000)

  29. The fence post principle Schriefer (2000)

  30. The soil pore network serves as a respiratory and circulatory system http://www.mtm.kuleuven.ac.be/Research/NDT/IDO_SHerman_final.ppt

  31. Texture affects the pore network

  32. Tillage affects the pore network white zones are pores plow pan No-till soil Tilled soil (Young and Ritz, 2000)

  33. Intensive tillage Long term no-till plow pan network of biopores Ontario Ministry of Ag and Food

  34. NO Traffic affects the pore network Brady and Weil (2002)

  35. Crusts impede seedling emergence, infiltration of water and gas exchange http://www.oznet.ksu.edu/soybeanscene/may24.htm

  36. high residue high infiltration

  37. Soil circulatory system Pore diameter Drainage pores 10-30 μm Field Capacity Most available Plant available water Permanent wilting point 0.2 μm Hygroscopic water Adapted from Buol (2000)

  38. Why do crops on tiled-drained land tend to be more drought resistant ? Ontario Ministry of Ag and Food

  39. What’s in the soil soup ?? Ca+2 Cu+3 DOM NO3- Ca+2 Mg+2 NO3- H2PO4- Ca+2 Zn+2 soil water DOM K+ NO3- K+ Mg+2 Ca+2 NO3- Mg+2 Fe+3 DOM Ca+2 SO4-2 Adapted from Brady and Weil (2002)

  40. Plants take up mostly inorganic forms of nutrients when inorganic forms of nutrients are readily available In some natural ecosystems (e.g., tundra), organic forms of nutrients are very important

  41. What are these guys up to ?

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