1. Soil Is Not Dirt

2. Why do We Study Soil? Essential natural resource
Snapshot of geologic, climatic,
biological, and human history
Medium of crop production
Great integrator:
all parts of ecosystem
Producer and
absorber of gases
Waste decomposer
Source material for construction,
medicine, art, etc.
Medium for plant growth
Home to organisms
(plants, animals and others)
Essential natural resource
Filter of water and wastes

3. Soil Forming Factors

4. What is Soil?
Each DISCIPLINE defines soil in a different way, depending on how soil affects it.
Wiki says soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics.

5. About ½ of the soil volume is solid particles
What’s In Soil?
About ½ of the soil volume is solid particles
About ½ of the soil volume is pore space

6. Physical and Chemical Characteristics of Soil
Physical Characteristics
Soil Texture, Consistency, & Structure
Soil Compaction (Bulk Density)
Soil Moisture
Nutrient Characteristics (Soil Chemistry)
Chemical bonding pH
Cation Exchange Capacity (CEC)
Nutrient Availability

7. Physical Characteristics
Physical Characteristics of Soil:
Texture: the mineral components
Consistency & Structure: How the mineral components are put together
Bulk Density
Soil Moisture

8. The way the soil “feels” is called the soil texture.
Soil texture depends on the amount of each size of mineral particles in the soil. 9 9

9. Sand, silt, and clay are names that describe the size of individual mineral particles in the soil. Sand are the largest particles and they fell “gritty” Silt are medium sized, and they feel soft, silky or “floury” Clay are the smallest sized particles, and they feel “sticky”

10. Soil Texture: Relative Size Comparison of Soil Particles
beachball
Sand
(feels gritty)
( mm, USDA)
( mm, ISSS)
frisbee
dime
Clay
(feels sticky)
Silt
(feels floury)
(< mm, USDA)
(< mm, ISSS)
 The way a soil “feels” is called the soil texture.
 Soil texture depends on the amount of each size of particle in the soil.
 Sand, silt, and clay are names that describe the size of individual particles in the soil.
Sandare the largest particles and they feel “gritty.”
Siltare medium sized, and they feel soft, silky or “floury.”
Clayare the smallest sized particles, and they feel “sticky” and they are hard to squeeze.
( mm, USDA)
( mm, ISSS)

11. Clay percentages are read from left to right across the triangle
Soil Texture Triangle
Clay percentages are read from left to right across the triangle 
Record the percentages of each grain size or name of soil
 Sand from lower right towards the upper left portion of the triangle 
Silt is read from the upper right to lower left 

12. 40 % clay, 50 % silt, 10% sand Soil Texture Triangle
What kind of soil do we have?

13. Again

14. Effects of Texture on Soil
Soils are more cohesive when they have more fine particles (Clays).
Soils are more loose when the have more coarse particles (Sand).
Different combinations of coarse and fine contents produce different soil textures.
A loam is a mixture of sand, silt and clay: sandy clay loam is best in landscapes - best for agriculture.
Many other inclusions, such as cobbles, boulders.

15. Soil Consistency Describes the general organization of the soil.
Hold a moist sample between the thumb and forefinger, and gently squeeze it until it falls apart.

16. The soil is classified by the following categories
Loose: You have trouble picking out a single sample and the structure falls apart before you handle it.
Friable: The sample breaks with a small amount of pressure.
Firm: The sample breaks when you apply a good amount of pressure and dents your fingers before it breaks.
Extremely Firm: The sample can't be crushed with your fingers (you need a hammer!).

17. * Soils with “single grained” structure always have loose consistence.
Soil Consistency
Soil Consistence
Loose*
Extremely Firm
Firm
Friable
* Soils with “single grained” structure always have loose consistence.

18. Soil Structure
Soil Structure: the shape that the soil takes based on its physical and chemical properties. Possible choices of soil structure are:
With structure
Without structure 2 2

19. Soil Structure: with Structure
Soil w Structure
Soil Structure: with Structure
Granular
Blocky
Prismatic
Columnar
Platy

20. Soil Structure: without Structure
Soil w/o Structure
Soil Structure: without Structure
Single Grained
Massive

21. Bulk Density Bulk Density: a measure of soil compaction
Sample is made of Solids and
Pore Spaces
1 cm. (so, there is 1 cubic centimeter of soil)
1.33 gms.

22. Basic Soil Components Basic Soil Components
Soil Particles: mineral and organic
Pore Spaces: location of air and water

23. Porosity and Permeability
Porosity: percentage of void spaces between grains in soil - effects how much water soil can hold AND how fast water can flow through layer
Permeability - measure of the ability of a porous material to allow fluids to pass through it

24. Permeability
Granular Blocky Platy

25. Movement of Fluid Through Soil
Rate depends on:
pore space (structure) and consistency
particle sizes (texture) and particle size distribution.
compaction

26. Run-off Angle and length of slopes Soil or surface type
Presence or absence of vegetation

27. Soil Horizons Soil Horizons: Horizon “C” Horizon “O” = leaf litter
Unconsolidated leaf (forest) litter
Some decomposed material
Horizon “A” = topsoil
High in minerals and nutrients
High in rich organic material called humus
Dark black material
Horizon “B” = leached zone, subsoil, zone of illuviation
Much lighter in color
Lower in minerals and nutrients
Horizon “C”
Little or no soil development
Big chunky rocks
Sits atop bed (parent) rock

28. Soil Horizons O A B C R

29. Soil Profiles

30. Soil Chemistry
Cation Exchange Capacity (CEC)
Nutrient Availability pH

31. Plant Nutrients Macronutrients: Micronutrients:
(needed in large amounts)
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Calcium (Ca)
Magnesium (Mg)
Sulfur (S)
Micronutrients:
(needed in small amounts)
Chlorine (Cl)
Cobalt (Co)
Copper (Cu)
Iron (Fe)
Manganese (Mn)
Molybdenum (Mo)
Nickel (Ni)
Zinc (Zn)

32. Where Do the Nutrients Come From?P K

33. Where Do The Nutrients Come From?
Water
Acid Zn Ca K Ni Cu Mg

34. Where Do the Nutrients Come From?
Human introduction
Fertilizer
Manure and sludge

35. Absorption and Nutrients
Absorption refers to the ability of an object to attract and hold particles on its surface.
Solid particles in soil have the ability to adsorb
Water
Nutrients and other chemicals
The most important absorbers in soil are
Clays
Organic matter

36. Anions and Cations Chlorine: Cl- Sodium: Na+
What happens when an anion meets a cation?
Anions have a negative charge (-):
Cations have a positive charge (+):
When they meet, they combine to become a molecule, the simplest compound:
NaCl (sodium chloride = table salt)
Chlorine: Cl-
Sodium: Na+

37. Common Soil Cat+ and An-ions
Common soil cations and anions, their chemical symbols and ionic forms

38. Clay Clay ¼ cup of clay has more surface area than a football field
The large surface area of clay allows it to
Absorb a lot of water
Retain nutrients
Stick to other soil particles
¼ cup

39. - - - - - - - - - - - - - - - - - - - - - - - - - - Chemistry of Clay
The Chemistry of Clay: - - - - - - - - - - - - -
Clay Particle - - - - - - - - - - - - -
Clay particles carry negative charges

40. - - + + - + - + What’s This Mean? With Magnets In Soil CLAY NH4+
Ammonium
CLAY K+
Potasium
Unlikes Attract - - + +
CLAY
NO3-
Nitrate
Likes Repel - + - +

41. Cation Retention on Clay
Calcium, +2
Magnesium, +2
Potassium, +1
Ammonium, +1
Sodium, +1
Copper, +2
Aluminum, +3
Hydrogen, +1

42. Cation Retention on Organic Material
Hydrogen
Nutrients
Increasing pH
increases cation
exchange capacity
of organic matter
Low pH, 4 - 5
(acidic soil)
Neutral pH, 7
(“sweet” soil)

43. Cation Exchange Capacity (CEC)
Cation exchange capacity (CEC) is the total amount of cations that a soil can retain
The higher the soil CEC the greater ability it has to store plant nutrients
Soil CEC increases as:
The amount of clay increases
The amount of organic matter increases
The soil pH increases (becomes more basic)

44. Negatively Charged Nutrients
Some very important plant nutrients are anions.
Soils are able to retain some of these nutrient anions.
Retention of nutrient anions varies from one anion to another 1- 2- 2- 1-
Nitrate
Phosphate
Sulfate
Chloride

45. Phosphate Retention in Soil
1. Formation of a new solid material +
Aluminum phosphate
solid
Phosphate
Aluminum
2. Anion exchange + 2-
Phosphate +

46. Phosphate Retention in Soil Con’t.
3. Adsorption on oxide surfaces
Phosphate anions -
Each held by two
chemical bonds to the
iron oxide surface
Iron oxide surface

47. Nitrate Retention in Soil
Unlike phosphate, nitrate is very weakly held by soils
Nitrate does not react to form new solids
Nitrate is not held by oxide surfaces
NO3-
If nitrate is not taken up by plants it is very likely to be lost from the soil

48. Moving Nutrients from Soil to Plants
Nutrients in soil solution
Plant
Root
Nutrients on soil clay and organic matter

49. Soil pH
pH of the soil solution is very important because soil solution carries nutrients
Ex: If the pH of the soil solution is increased above 5.5, in the form of nitrate is made available to plants.
Phosphorus is available to plants when soil pH is between 6.0 and 7.0
Can change pH by adding lime

50. What Should We Title This Slide?
Absorbed nutrients are not prone to loss in drainage water
Soil absorption capacity can be exceeded leading to greater nutrient loss
Soil consists of mineral and organic matter, air and water
Soils are able to adsorb nutrients and other chemicals
The most important absorbers are clay and organic matter
Absorbed nutrients are available to plants