1. Chapter 4 Physical Properties of Soil

2. Texture Density Permeability Porosity Structure Tilth Compaction Temperature Color Soil physical properties are characteristics that you can see or feel

3. Texture refers to the proportion of sand, silt, and clay The most important property for determining the behavior of a soil Texture affects water holding capacity, compaction, the ability of plant roots to penetrate soil, the amount of nutrients that can be “held”, etc.

4. Loam: medium soil texture class where sand, silt, and clay are pretty equally distributed and contribute to soil properties There are 12 textural classes based upon percentages of sand, silt, and clay

5. Sand Largest mineral particle - weathered grains of quartz Visible to the naked eye Gritty to the touch Do not stick to one another Good for soil infiltration Too much can increase leaching and decrease water holding capacity

6. Silt Medium sized mineral particle Silky or powdery to the touch - like baby powder Best water holding capacity for use by plants From Alaska

7. Clay Smallest mineral particle Tiny, sheet-like crystals From rock crumbling into very fine pieces and reacting with water and other particles Stick to one another Microscopic clay particles

8. Three major soil mineral sizes: Sand2.0 - 0.05 mm Silt0.05 - 0.002 mm Clay< 0.002 mm Other materials greater than 2 mm: gravels2mm - 3 in cobbles3 in - 10 in stones10 in - 24 in boulders>24 in

9. Coarse textured soils (sands, loamy sands): Hold low amounts of water and nutrients - may have to irrigate and fertilize frequently Not very erosive - allows water to infiltrate; less runoff Very permeable - good for waste disposal only if a deep soil

10. Fine textured soils (clays, sandy clays, silty clays) Hold large amounts of nutrients and water - but may hold things too tightly Erosion - slow infiltration; high runoff means greater erosion. Slow permeability - often unacceptable for septic tanks

11. Structure refers to the way soil particles clump together into larger units (aggregates) The second most important property for determining the behavior of a soil Naturally occurring aggregates are called peds. Aggregates that develop due to soil tillage are called clods Aggregates contain an abundance of macro and micro pores

12. Five basic types of structural units 1.Platy 2.Prismatic/Columnar 3.Blocky 4.Granular 5.Structureless (single grain)

13. Granular Structure: found usually in upper soil layer small rounded peds (pieces) increases total pore space and lowers bulk density think “cookie crumbs”

14. Platy Structure usually found in middle soil layer large, thin, plate-like peds arranged in overlapping horizontal layers discontinuous pores…reduce penetration of air, roots and water…water moves laterally can occur in upper soil layer due to compaction…topsoil crushed into thin layers

15. Blocky Structure usually found in middle soil layer large block-like peds, may be angular medium permeability think “cloddy”

16. Columnar or Prismatic Structure usually found in lower soil layers large peds (as much as 4 inches) if top is pointed or flat - prismatic if rounded - columnar

17. Out of these areas, where would you find a structureless soil??

18. Color is an indicator of soil conditions; based on parent materials, organic matter, weathering, etc light colored soils dark topsoils reddish soils bluish, gray soils Color typically measured using Munsell color chart (last slide)

19. Dark Brown to Black usually indicates high organic matter also common in waterlogged soils, but smell will be noticeable Mottling grayish, often speckled with other colors indicating occasional waterlogging often found in wetlands

20. White to Light Gray indicates leaching or an accumulation of lime, gypsum, or salts

21. Light Brown and Yellow to Red presence of iron materials indicates lots of oxidation usually indicates good drainage - enough oxygen to rust!

22. Bluish-Gray presence of iron, but with lack of oxygen indicates poor drainage referred to as “Gleying”

23. Munsell Book/System: colors defined by three variables Hue (color), such as red or yellow Value---lightness or darkness of the hue. 0-10 system where 0 is black and 10 is white Chroma—designating purity of the dominant color…also by a number. For example: 10YR 3/6 10 is the ‘hue’ of yellow/red (very common) 3 is the value (dark) 6 is the chroma