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SOIL PHYSICAL PROPERTIES Chapter 4

SOIL PHYSICAL PROPERTIES Chapter 4. Color. Color. Thus, red = oxidized = aerated but gray = reduced = anoxic, poorly aerated. The oxidation state of Fe in Fe 2 O 3 and Fe 2 O 3 H 2 O is + 3. Color. This surface horizon is dark due to enrich- ment in organic matter from grass roots and

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SOIL PHYSICAL PROPERTIES Chapter 4

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  1. SOIL PHYSICAL PROPERTIES Chapter 4

  2. Color

  3. Color Thus, red = oxidized = aerated but gray = reduced = anoxic, poorly aerated. The oxidation state of Fe in Fe2O3 and Fe2O3 H2O is + 3.

  4. Color This surface horizon is dark due to enrich- ment in organic matter from grass roots and surface residue. Common feature of prairie soils is high organic matter content to appreciable depth (see inches).

  5. Color  

  6. Color These colors, certainly, but also gray color generally indicate poor drainage and aeration. Colors of chroma 2 or 1 indicate gley.

  7. Color These secondary colors modify one’s interpretation based on the main (matrix) color –like yellow or gray within an otherwise oxidized matrix say drainage and aeration are not uniformly good. And visa-versa –red mottles against gray matrix = some veins that are well drained / aerated.

  8. Texture Illustration of how surface area increases with decreasing size. If you prefer algebra, for a cube, A = 6s2 and V = s3, so A / V = 6 / s. The smaller the cubes, the greater the surface area per volume (or per mass, since mass is proportional to volume through density).

  9. Texture All these are surface phenomena, therefore, increase with increasing particle surface area. On the other hand, pulling an implement through a clayey soil is much harder than through a sandy soil, no?

  10. Answer, sandy clay.

  11. Texture

  12. FUP = Bouyant + Drag FDOWN = Gravity FBouyant = 1/6 π d3ρL g FDrag = 3 π d μ V FGravity = 1/6 π d3ρS g At equilibrium, i.e., terminal velocity, forces balance

  13. Texture Smaller d means smaller v, no? So comparing the largest clay (d = 0.002 mm) to largest sand (d = 2 mm), vclay / vsand = 0.0022 / 22 = 1 / 1,000,000.

  14. Texture Express velocity as distance / time, rearrange and find time need for smallest sand to settle a prescribed distance. So, aliquot taken above this depth contains no sand, only silt and clay. Do same calculation for smallest silt, take aliquot at that time and it contains only clay.

  15. Texture Your times may vary depending on density and viscosity of the medium (see equation). Besides any solutes added to aid dispersion of particles, temperature affects these parameters.

  16. Texture Depending on the nature of the soil, more extensive methods may be necessary to disperse particles.

  17. Sure, erosion can change texture at a location but barring gross erosion, this is slow. Certainly, internal translocation of clay will make the topsoil more sandy but this is very, very slow. Unless you move a lot of dirt around, texture is effectively a fixed property.

  18. Structure Munsell book give guide.

  19. Probably blocky because the large pores between aggregates are more vertically oriented than in soil with platy structure. Obviously, the tiny pores in a massive clay conduct water very slowly.

  20. The organics jointly adhere to surfaces of adjacent mineral particles. Cations like Ca2+ tend to be closely associated with particle surfaces, bridging adjacent minerals. Shrink-swell clays tend to give persistent internal fissures.

  21. X is better drained. You know this because the color indicates oxidized Fe, Fe3+, which exists under a prevailing oxidized (oxic, aerated) environment. On the other hand, gray color is due to chemically reduced Fe, Fe2+, that occurs under anoxic conditions.

  22. The one with the greatest surface area, clay, of course.

  23. The four types of geometric structure are spherical (all dimensions about the same with radial orientation, one dimension short compared to the other two, i.e., flat = platy, one dimension long compared to the other two, i.e., elongated = prism-like and all dimensions about the same but with x-y-z orientation, i.e., cubic = blocky.

  24. It couldn’t hurt to remember these and the subtypes of spherical structure.

  25. Structure Crust = dense, i.e., low porosity and pores are small so that infiltration is greatly reduced. Bad.

  26. Structure Sure, there are large pores between clods but the large pores that previously existed throughout are gone. Bad.

  27. Structure Protecting an otherwise bare surface from raindrop impact will preserve surface aggregation, thus, preserve good infiltration, soil water conservation and limit runoff, erosion and downhill degradation of surface water quality. Adding organic matter aids structure stability and redevelopment if degraded.

  28. Besides color, texture and structure, this is another feature included in horizon descriptions.

  29. PARTICLE DENSITY ρs = mass soil solids / volume solids (g / cm3) Depends on mineralogy to some extent

  30. Well, it can vary depending on whether a very low density mineral predominates, however, this is usually not the case and common soil minerals have densities that are about 2.65 g cm-3.

  31. BULK DENSITY ρb = mass of soil solids / total volume occupied by solids (g / cm3) Is ρb greater than or less than ρs?

  32. You are dealing with a solution. Recall that solutes elevate the boiling point.

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