1. Soil Physics 2010 Outline Quiz 2 answers Finishing up particle sizes Particle size distributions Clay

2. Soil Physics 2010 Quiz 2 answers Water rises higher in a capillary tube with a (larger / smaller) interior diameter. Water is (more / less) viscous when it is hot. A mineral salt (e.g., NaCl) will dissolve more readily in a liquid with a (low / high) dielectric permittivity.

3. Soil Physics 2010 Measuring soil particle sizes: Sedimentation Assumptions: Particles are smooth spheres Particles fall slowly (laminar flow) All particles have the same density Dilute: particles don’t affect each other Fluid is otherwise at rest Terminal velocity is reached instantly

4. Soil Physics 2010 Volume? Surface area? Projected area? Longest transect? Largest inscribed sphere? Smallest circumscribed sphere? Largest circle inscribed in projection? Smallest circle circumscribing projection? …? What is the “equivalent sphere” in Stokes settling? Measuring soil particle sizes: Sedimentation 90% 70% 40% After Matthews, 1991 Settling velocity, % of sphere Oblate (lentil) Prolate (rice) What are the effects of roughness & shape?

5. Measuring soil particle sizes: Laser diffraction Small particle Large particle Soil Physics 2010

6. Measuring soil particle sizes: Laser diffraction Soil Physics 2010

7. Measuring soil particle sizes: Laser diffraction Soil Physics 2010

8. Measuring soil particle sizes: Laser diffraction Fast No calibration Wide size range Good repeatability Expensive equipment Soil Physics 2010 Equivalent radius?

9. Soil Physics 2010 Measuring soil particle sizes: Image analysis Volume? Surface area? Projected area? Longest transect? Feret diameter? Sauter mean diameter? Largest inscribed sphere? Smallest circumscribed sphere? Largest circle inscribed in projection? Smallest circle circumscribing projection? …?

10. Soil Physics 2010 Particle size distributions Sand Silt Clay Start with a continuum of sizes…

11. Soil Physics 2010 Particle size distributions Break it in half * and bend it over… Sand Silt Clay * about halfway on a log scale

12. Soil Physics 2010 Particle size distributions …and you have the “texture triangle” Quick and easy, but not really a distribution Sand Silt Clay

13. About size distributions Soil Physics 2010 Calculated by: Mass? Volume? Number? Do we assume some mathematical model? What use is this distribution? Pedology Fert/Chem Hydrology

14. Soil Physics 2010 Distributions? ?!?

15. Cumulative distributions Soil Physics 2010 % depends on bin size

16. Soil Physics 2010 equal spacing in linear space ≠ equal spacing in log space Cumulative graph stays the same Cumulative distributions Variable bin size?!

17. Displaying particle size distributions Cumulative distribution must be Continuous & Monotonic Usually shown as: Log x-axis (size) Linear y-axis (  %) ? Soil Physics 2010 Sieving Stokes settling ?

18. 10 1 10 0 10 -1 10 -2 10 -3 10 -4 More particle size distributions Soil Physics 2010 Gradual Abrupt Poorly graded

19. Clay Soil Physics 2010 Kaolin: “china clay” from Chinese Kao-ling, transliteration of the name of a mountain in Jiangxi, China (near which it was originally dug up), from Chinese gao “high” + ling “mountain, hill.”

20. Soil Physics 2010 Key things about clay Small < 2  m Secondary mineral platy shape Large surface area Soil strength & structure Porosity & permeability