Exam Schedule

1. Exam Schedule Exam I: Friday, May 22nd Exam II: Friday June 5th Exam III: Friday June 19th Review sessions will be on the Thursday preceding the exam.

2. Soil Texture Three separates: Sand, Silt, Clay Importance: indicator of pore size, surface area, water movement, reactivity There are 12 textural classes based on relative abundance of sand, silt, clay Florida soils tend to range from sandy to sandy clay textures Texture-by-feel assesses grittiness, smoothness, plasticity to estimate texture Laboratory analysis relies on sedimentation of soil particles in water Stokes’ Law determines the settling rates of particles from water Large particles (sand) settle quickly, small particles slowly. A hydrometer measures the density of a soil suspension Based on the density, the mass of particles remaining suspended is determined

3. Texture Particle Size Large/coarseMedium Fine/Small Sand Loamy Sand Sandy Loam Sandy clay Loam Silty clay Loam Silt Loam Loam Clay Loam Sandy Clay Silty Clay Clay Pore Size LargeMediumSmall Reactivity WeakModerate Strong

4. Texture and Civilization?

5. Earliest Civilizations Tigris-Euphrates Nile

6. Year-round supply of water Enduring Sunlight Trustworthy harvests Building materials Population increases Substantial homes Relative Safety, peace Civilization Nile Jordan Tigris Euphrates Neolithic Founder Crops Wheat Barley Flax Chick Pea Lentil cows, goats, sheep, and pigs Periodic Flooding

7. Flooding

8. Flooding and Soil Texture Sand 2.0-.05 mm Silt 0.05 – 0.002 mm Clay < 0.002 mm Clay

9. Stokes’ Law: V = kD2 K = 11,241 cm-1 sec-1 Sand 1 mm V = 112 cm/sec Silt 0.05 mm V = 0.281 cm/sec Clay 0.002 mm V = 0.0004 cm/sec

10. Sedimentation Sand Clays/Silts River channel Flooding slows flow

11. The Nile Blue Nile Kenya Uganda Tanzania Flood peaks in mid-September

12. Mesopotamia Alluvial Plain Flood: March through June Euphrates

13. Agriculture and Irrigation Irrigation Canals Dikes Weirs Reservoirs channels

14. History and Soil Texture (knowledge from clay and stone)

15. Stone Clay Stone and Clay Egypt Sumer

16. Architecture and Sculpture Egypt

17. Sumerian The Language of Power sacred, ceremonial, literary, and scientific language

18. Soil Structure, Density, Porosity

19. Soil Structure Arrangement or grouping of individual soil particles into secondary units.

20. Soil Structure Peds Aggregates Units of soil Structure

21. Soil Structure Formation Chemical Processes – electrostatic attraction between clay particles and between organic particles. Biological Processes -macro-organisms (burrowing, tunneling,wastes) -roots, fungal hyphae (compression, fibers, exudates) -microorganisms (organic residues)

22. Importance Effects on porosity, water retention, water movement Large pores Inter-aggregate pores Small pores (between) Intra-aggregate pores (within) Water moves easily and is poorly retained in inter-aggregate pores Water moves slowly and is strongly retained in intra-aggregate pores

23. Soil Structure is Desirable Poor soil structure can inhibit infiltration of water, water movement, growth of roots.

24. Summary Structure is the arrangement or grouping of individual soil particles into larger secondary units. Clays and organic matter possess natural electrical Charge which can electrostatically bind particles together. Macro-organisms and microorganisms can aid in binding of individual particles into larger aggregates.. Aggregation allows for both movement and retention of water via macropores and micropores, respectively.. Poor soil structure can inhibit infiltration of water, water movement, growth of roots.

25. Soil Density

26. Density g cm3 ) Density = Mass Volume ( 2.65 g/cm3

27. Soil Bulk Density x • Density of soil including the particles and the pore spaces y BD = mass OD soil volume solids + pores z Volume = xyz B.D. ranges between 1.1 and 1.6 g/cm3 (for mineral soil with 1 – 5% organic matter)

28. Bulk vs. Particle Density Bulk density measures the mass of the soil solids in relation to the volume of the soil solids and the soil pores. Bulk density = mass solids volume xyz x y Mass of particle Particle density = Volume of particle z No pores BD = 1.6 g/cm3 PD = 2.65 g/cm3

29. Known Volume Sampling for Density

30. Known Volume Dry and Weigh: mass/volume = Bulk Density

31. Factors Affecting Bulk Density Porosity (pores are weightless) • organic matter • aggregation • arrangement of particles • compaction • depth in profile

32. Organic Matter Factors Affecting Bulk Density Typical 1-5% organic matter Mineral Soil: bulk density = 1.1 –1.6 g/cm3 Organic Soils: > 20% organic matter bulk density = 0.1 – 0.6 g/cm3

33. Aggregation One aggregate of Clay sized particles One sand grain (Zero porosity) (50% porosity) Aggregation generally increases overall porosity, decreases density

34. Arrangement (compaction) Sorting Packing Arrangement Discrete particle size classes Continuum of particle sizes Particle Size

35. Depth in Profile Lower organic matter Fewer roots Compaction from above => Higher bulk density Aggregation can mitigate Some of these effects.

36. Summary Bulk densities of typical mineral soils range between 1.0 and 1.6 g/cm3. Organic matter increases porosity, decreases BD Organic soils can have BD as low as 0.1 g/cm3. Compaction decreases porosity, increases BD Aggregation increases porosity, decreases BD Depth in profile decreases porosity, increases BD

37. Porosity

38. [ ) ] ( BD PD % Porosity = 1 - X 100 Porosity 100% Bulk Density (g/cm3) 0 2.65 Bulk density high porosity low Bulk density low porosity high Bulk Density and Total Porosity 2.65 g/cm3

39. A E Bulk Density and Porosity B A E B BD = 1.1 g/cm3 BD = 1.15 g/cm3 BD = 1.6 g/cm3 P = 59 % P = 57% P = 40 %

40. Pore Size Distribution Macropores > 0.8 mm in diameter large, freely draining sands, inter-aggregate pores Micropores < 0.8 mm in diameter small, storage of water clays, intra-aggregate pores

41. The effect of total porosity and of pore size distribution is largely related to the movement and retention of water as well as the movement of soil gases Knowledge of texture, structure, bulk density, and porosity allow deduction of the patterns of movement of water and gases in soils Next: Water in Soils