1 / 86

Soil properties

Soil properties. A. Texture B. Adhesive-Cohesive properties (Plasticity/Stickiness) C. Structure D. Density E. Porosity F. Color. A. Texture. Relative proportion of sand, silt, clay sized particles in a soil Does not change (in human lifetime)

lsavell
Download Presentation

Soil properties

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Soil properties A. Texture B. Adhesive-Cohesive properties (Plasticity/Stickiness) C. Structure D. Density E. Porosity F. Color

  2. A. Texture • Relative proportion of sand, silt, clay sized particles in a soil • Does not change (in human lifetime) • Important for agricultural and engineering uses of soil

  3. Fine earth fraction only • Does not include coarse fragments: • Boulders: > 600 mm • Stones: 250 – 600 • Cobbles: 75 – 250 • Gravels : 2 - 75

  4. USDA fine earth fraction (“soil separates”): • Sand 0.05 – 2.0 mm • Very coarse 1.0 – 2.0 • Coarse 0.5 – 1.0 • Medium 0.25 – 0.5 • Fine 0.1 – 0.25 • Very fine 0.05 – 0.1 • Silt 0.05 – 0.002 • Clay <0.002

  5. sand • Naked eye • Gritty • Predominantly quartz • Round

  6. silt • Light microscope • Cannot feel individual grains; slippery • Predominantly quartz and other primary minerals • In between round and flat

  7. clay • Electron microscope • Wide variety of minerals • Flat

  8. Properties that vary with particle size: • Surface area • Geometry of pore spaces • Adhesive / Cohesive properties; Plasticity / Stickiness

  9. Surface area • (site of water adsorption, gas adsorption, mineral weathering, nutrients) • Very coarse sand: • Particles per gram = 90 • Surface area = 11 cm2 / gm • Clay : • Particles per gram = 90,260,853,000 • Surface area = 8,000,000 cm2 /gm

  10. Pore space geometry • Sand has large pores between grains • Highly permeable • Silt has relatively small pores • Less permeable • Clay has very small pore spaces • Least permeable

  11. B.Adhesive/Cohesive properties • Adhesion: force with which something clings to other surfaces • Soil and water • Cohesion: force with which something clings to itself • Soil particles

  12. Plasticity/Stickiness • Plasticity is ability to be molded; force required to deform soil in wet pliable condition • Make a “worm” of soil; see how thin the worm can be and still support its own weight on end • Indicates cohesiveness

  13. Stickiness is force required to pull soil apart when wetted (beyond plastic) • Press moist soil between thumb and forefinger and see how much sticks to fingers • Indicates adhesiveness

  14. Non-sticky

  15. Slightly sticky

  16. Very sticky

  17. Shape governs extent of contact between adhering and cohering surfaces • Greatest contact occurs when flat surfaces lie parallel to one another (as in clay) • e.g. cohesiveness makes some clays turn into hard clods when dry and become very sticky when wet

  18. Sand has a large particle size and round shape • Limited contact with other surfaces • not sticky, not plastic • Silt is more cohesive and adhesive than sand, but has only limited plasticity and stickiness • Can be crushed when dry

  19. C. Structure • Way in which soil particles are assembled in aggregate form • Results from pedogenic processes • Structural unit is ped • e.g., blocky soil has blocks as peds • Ped: < cm to several cm

  20. Structures: • Platy: flat horizontal units; diverse sizes

  21. 2. Prismlike: tall peds with flat sides Prismatic: flat tops Columnar: rounded tops

  22. 3. Blocky Angular: flat faces, sharp corners Subangular: faces and corners are rounded

  23. Subangular blocky Angular blocky columnar prismatic

  24. 4. Granular: roughly spherical; porous

  25. 5. wedge-shaped peds form in clays where cracking and swelling cause soils to slide along planes

  26. 6. Structureless single-grained massive

  27. Importance of structure • Movement of air and water • Root penetration

  28. What gives structure to soil? • Organic gums (HUMUS!) • Decay products • Shrink and crack on drying • Shrink-swell clays • Roots • Freeze/thaw cycles • Soil animals • Fungal hyphae

  29. compaction

  30. Pan structures • Dense layers, diverse origins

  31. Clay pan Clay accumulation; usually B Duripan cemented by ppt silica , iron oxides, and/or CaCO3 Fragipan hard, brittle dense and compact, but breaks apart when taken out Caliche white layer of CaCO3 (soft or hard); arid near surface

  32. 5. Plinthite (laterite) sesquioxides, usually B tropical, weathered soft when wet; brick hard when dry 6. Plowpan compaction from weight of implements

  33. Clay pan

  34. duripan

  35. fragipan

  36. caliche

More Related