1. The diagnostic features used to differentiate soils in USDA Soil Taxonomy are primarily macromorphological Soils can also be studied at smaller scales Colony of bacteria ~1 micron

2. Coarse fragments Silt Clay Sand Is the whole greater than the sum of its parts ?

3. http://edafologia.ugr.es/micgraf/media/desinter.gif Soil micromorphology - the study of undisturbed soil samples with the help of microscopic techniques, in order to identify small scale features and interpret how they formed.

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

7. Textural porosity Pores resulting from random arrangement of soil particles

8. Textural porosity + Structural porosity Total porosity

9. Vughs

10. Cracks

11. Channels and Chambers

12. Lots of tillage pores Few biopores Depth (cm) Origin of pores in a soil with annual moldboard plow/disk tillage

13. Fewer tillage pores Lots of biopores Depth (cm) Origin of pores in a soil with minimum tillage How were the Dutch soil scientists able to differentiate between tillage pores and biopores? Analysis of thin sections !!

14. Relationships between coarse and fine materials in soil fabrics

15. Distributions of coarse and fine materials

16. Mostly sand particles - very few fine materials

17. Bridging

18. External coatings

19. Microaggregates between sand particles

20. Coatings and microaggregates

21. Sand embedded in fine matrix

22. How much sand do you need to add to a clayey soil to make it stop acting like a clay? Massive amounts of sand are needed because sand needs to become the dominant component of the soil structure

23. < 20% sand > 50% clay >80% sand <10% clay Clay dominated soil matrix with embedded sand particles Sand dominated soil matrix with clay coatings

24. Dramatic soil textural modification is a standard part of golf course construction but is cost prohibitive (and impractical) in most other situations Play can resume 10 minutes after rain stops

25. Structural development at the microscale

26. Angular blocky structure

27. Platy structure

28. Granular crumb structure

29. Tall Grass Prairie the dominant native ecosystem in IL Clay particles

30. Multi-valent cations such as Ca +2, Al +3 and Fe +3 are important binding agents at this scale. High levels of monovalent cations such as Na + and K + cause clay domains to disperse. Domains of clay particles

31. Microbial glues are important binding agents at this scale Humic substances are also important binding agents at this scale 35,000 x Microaggregates (< 0.25 mm)

32. Macroaggregates (>0.25 mm) root micro- aggregate Networks of roots and fungal hyphae are important stabilizers of macroaggregates http://soils.usda.gov/sqi/concepts/soil_biology/images/M4_Fungi_LR_small.jpg

33. Dry soil at the end of an extended dry period http://edafologia.ugr.es/iluv/media/origen1.gif Soil processes can be studied at the microscale

34. Rain water rapidly infiltrates the surface horizon http://edafologia.ugr.es/iluv/media/origen2.gif Eluviation/Illuviation at the microscale

35. Some clay particles disperse in water filled pores http://edafologia.ugr.es/iluv/media/origen3.gif Eluviation/Illuviation at the microscale

36. Suspended clay moves downward through macropores to deeper, drier horizons http://edafologia.ugr.es/iluv/media/origen4.gif Eluviation/Illuviation at the microscale

37. Capillary action moves water outward into micropores http://edafologia.ugr.es/iluv/media/origen5.gif Eluviation/Illuviation at the microscale

38. A thin “skin” of oriented clay particles begins to accumulate on the walls of macropores http://edafologia.ugr.es/iluv/media/origen6.gif Eluviation/Illuviation at the microscale

39. Oriented clay particles coat the walls of dry macropores http://edafologia.ugr.es/iluv/media/origen7.gif Eluviation/Illuviation at the microscale

40. The process repeats itself over and over… causing illuvial clay skins to slowly increase in thickness Many years go by… http://edafologia.ugr.es/iluv/media/origen8.gif

41. Oriented clay particles also accumulate around aggregates http://edafologia.ugr.es/iluv/media/origen9.gif

42. Clay particles also orient around microorganisms.

43. http://edafologia.ugr.es/iluv/media/clas14.gif Coating

44. http://edafologia.ugr.es/iluv/media/clas15.gif Infilling

45. http://edafologia.ugr.es/iluv/media/clas12.gif Quasi-coating

46. http://edafologia.ugr.es/iluv/media/clas16.gif Fragments of illuvial features

47. http://edafologia.ugr.es/iluv/media/rec1.gif Clay skins Illuvial features at the macro-scale

48. Essential factors for significant eluviation/illuviation of clay  Alternating periods of intense rain and drought  Sufficiently high clay content in surface horizons  Sufficient macroporosity for downward transport  Relatively stable land surface

49. Most of the images in this presentation were obtained from an invaluable web resource on soil micromorphology maintained by Dr. C. Dorronsoro, Department of Pedology, University of Grenada, Spain http://edafologia.ugr.es/micgraf/indexw.htm