1. Chapter 4: Soil Architecture and Physical Properties
Introduction to Soils
Chapter 4:
Soil Architecture and Physical Properties

2. Physical Properties
Physical Properties of the soil will deal with the particle aggregation as well as texture, colloidal properties, surface area, pore spaces, water in the soil and other physical properties.

3. SOIL COLOR
Color plays an important role in differentiating different conditions of the soil.

4. Color Classification System
Munsell color charts
1) Hue – red to yellow color of the soil
2) Chroma – brightness of the color –0 neutral gray
3) Value – lightness or darkness of the soil –0 being black

5. Color can give a clue to:
OM content
Water content
Oxidation states of iron and possibly manganese oxides.

6. Dark Soils Usually high in organic matter
Rich soils if there is not too much water

7. Light Soils
Sandy
High salts, gypsum or lime

8. Light Brown to Red
Aging soils iron – oxidizing
Drainage is fair

9. Bluish - Gray They have poor drainage
Indicates no 02 in soil and could smell rotten called - Gleying soils

10. Mottled Colors
Indicates a period of water logged and then drying out

11. The Soil Separates (USDA)
SOIL TEXTURE
the amount of sand silt and clay in the soil
The Soil Separates (USDA)
Sand – 2 mm
Silt mm
Clay less then .002mm

13. Soil Texture triangle allows the classification of the soil texture into 12 classes.

15. Determining soil texture
Ribbon test
No ribbon – sandy loam
Shorter then 1” – loam, silt, silt loam
1-2” – Sandy clay loam, silty clay loam, clay loam
2-3” – Sandy clay, silty clay clay

16. Measuring the soil separates in a jar
Can one change soil texture?

17. Surface area considerations:
It is the surface area of the soil that has the ability to hold water and be a site for chemical activity. The greater the surface area the greater the chemical activity and possible nutrient holding ability.

18. Surface area of the soils and its affect
Water holding capacity, fertility and total pore space.
Sand
Silt
Clay

20. Total pore space of the soil
Soil Porosity
Total pore space of the soil
Sand has less than clay
Determining porosity %:
Wet weight (grams) – dry weight (grams)
Soil volume (cm3) X 100 = %

21. Permeability How the water moves through the soil
Sand is rapid and clay is slow
Textural types and their characteristics ie
Soil Porosity, Permeability
a) Clayey
b) Silty
c) Sandy

22. Soil Structure Soil Structure is how the soil separates
combine to form larger aggregates

23. Types of structure peds natural formation clods caused by tillage
a. Granular- ideal agronomic structure accomplished through correct cultural practices: in the A horizon Minimum tillage, done at the correct time incorporating organic matter and encouraging microbial action
b. Platy- Usually in the lower depths of the A horizon or compacted soils
c. Blocky- in the B horizon large aggregates that slows water penetration
e. Single grain- Structure less – the absence of soil structure.
f. Massive- Structure less - concrete

25. Structure Formation Soil adhesives released by fungi and organisms
Good soil structure can be encourage through proper cultivation
Organic matter
Gypsum
Culture practices done when soil is at proper water retention
Avoid compaction
1) Equipment
2) Reduction of traffic through the field
3) Keep vegetation on the soil
a.    

27. Soil Consistence
Refers to soils ability to resist crushing and its ability to be molded.
Such as for most soil Loose, Very Friable, Friable, Firm, Very Firm and extremely firm.

28. Soil Tilth Physical condition of the soil after tillage
usually the granular form
Compaction is detrimental to good soil tilth-
Compaction causes
Reduced porosity and permeability
Reduced gas exchange
Slow percolation rate and slow drying rate.
Restricted root growth

29. Soil Particle Density As to the specific weight of the soil particles.
This is a direct correlation to the parent material and should be between 2.6 to 2.75 g/cm3

30. Bulk Density Is the weight over volume.
This will determine the amount of pore space in the soil.
Clay – 1.15
Silt – 1.35
Sand – 1.8

35. Soil Temperature Corn needs 65-70F
Germination is dependant on proper soil temperature.
Corn needs 65-70F
Most warm season crops need warm soil
Root growth is more abundant when soil temperatures
Soil Characteristics that affect temperature
Dark soils warm fast
Rocky soils warm fast
Sandy soils warm fast
Grandular loose soils warm quicker then compacted soils

36. Formation and Stabilization of Soil Aggregates:

37. Formation and Stabilization of Soil Aggregates:
Both biological and physical processes are responsible for soil aggregates
Physical Chemical Processes:
Flocculation of Clays
Clays will be the first to join together as they are attracted to each others negative and positive sides.
Together with humic acid binds together the individual particles acting like glue to bind them together.

38. Biological Processes:
Soil organisms – help bind particles together
Earth worms
Root exudates
Fungal products ie glomalin
Bacteria

39. Is the principle method of soil aggregate stabilization.OM
Is the principle method of soil aggregate stabilization.