1. Ch. 4 continued
Soil Properties

2. Soil Color Munsell Color system:
Hue value/chroma  color lightness/brightness
Ex: 10YR 5/6 is
Lighter than
10YR 3/6; and
brighter than
10YR 5/2

3. Causes or sources of color in soil
Humus or decomposed organic matter  black
Wet soils are darker than dry soils
Oxidized Fe oxides (Fe+3) are redder and brighter than reduced Fe minerals (Fe+2)  gleyed
Carbonates, gypsum, salts  white masses or nodules in soil and overall lighter values
Mn oxides  black; usually associated with red Fe oxides
Other minerals  yellow, green, white, etc…

4. Color as indicator of environment
Bright colors indicate oxidized (aerobic or oxygen-rich) environment
Dull, grayed or bluish colors indicate reduced (anaerobic or water-logged) environment
Pale yellow jarosite indicates oxidized (and now acidified) sulfidic soils

5. Soil Texture (proportion of different-sized particles)

6. Basic Soil Property Because it is not readily subject to change
Master Variable Because it affects so many other soil properties and variables
Basic Soil Property
Because it is not readily subject to change

7. Soil Separates Figure 4.1, page 96, Brady and Weil, 2004
“fine earth fraction (< 2-mm)”
“coarse fraction (> 2-mm)”
Soil Separates
Figure 4.1, page 96, Brady and Weil, 2004

8. What does particle size tell us about mineralogy?
Sand and silt contain primary minerals such as quartz & feldspars
Clay is dominated by secondary minerals, formed from the weathering of primary minerals

9. Sand and silt are largely chemically inert, while clay is chemically active (charged)
Mainly because of size, shape, and chemical characteristics of clay
Cations (+) stick to clay particles because of negative charges on the clay

10. Heavy or Light Soils These terms actually refer to texture, not weight
A heavy soil is a clayey soil
called ‘heavy’ because of the soil's ability to retain moisture and the difficulty in working the soil (and it’s heavy after rain or irrigation)
A light soil is a sandy soil
called ‘light’ because it is usually easy to work in the field and drains quickly
Actually, a clayey soil weighs less than a sandy soil when dry

11. Calculate: (1) total surface area of original cube (uncut) and
8cm x 8cm x 8cm
8cm
2 x 2 x 2
2 x 2 x 2
Calculate: (1) total surface area of original cube (uncut) and
(2) total surface area after cutting it into smaller cube of the given sizes
8cm
4 cm x 4cm x 4cm
8cm

12. Specific surface area
2 cm
2 cm
2 cm
Each cube is 2 cm on each side, the same mass of material would now be present as 64 smaller cubes
Surface area for one face of a small cube = 2 x 2 = 4 cm2
Surface area for each cube (6 faces, 4 cm2 per face) = 6 x 4 = 24 cm2
Total surface area (64 cubes, 24 cm2 per cube) = 64 x 24 = 1536 cm2
Surface area for each face (8 x 8) = 64 cm2
A cube has six faces
Total surface area (6 faces 64 cm2 per face) = 6 x 64 = 384 cm2

13. Clay vs Silt vs Sand:
The surface area to volume ratio greatly increases as the particle size decreases and the shape changes from rounded to plate like
As the surface area increases, so does the ability to adsorb compounds and interact with the soil solution:
more chemical reactions,
more biological interactions,
more surface for water to cling to

14. How particle size affects soil properties
Specific surface area
CEC
Sorption capacity
Stickiness
Plasticity
Cohesion
Bulk density
Porosity
Water holding cap.
Colloidal Clay Silt Sand
clay

15. How particle size affects soil properties
Soil separates
Property
Clay
Silt
Sand
Size
Specific surface area
Water holding capacity
Stickiness/plasticity
Cation exchange capacity
Chemical sorption
Porosity amount
Pore size
Bulk Density
Puddling
Tillage
<0.002 mm
Very high
High
Small
Low
Hard mm
Moderate
Medium mm
Very low
Large
Easy

16. Soil Texture Texture influences most other soil properties
Soil texture does not change in nature over a short period of time
Adding organic matter may improve characteristics of soils but not change texture
Large quantities of sand, silt, or clay must be added and thoroughly mixed before the texture significantly changes
Mixing media for potting soil, golf greens, etc. is generally the only time when textural modification is economically feasible