1. Soils
Mrs. Gill

2. Components of the soil profile
 The "A" horizon
 The "B" horizon
 The "C" horizon

3. Characteristics of the soil horizons
The "C" horizon
Generally called parent material
It is the deepest of the three major horizons
Usually very low in organic matter
Usually no structure

4. Characteristics of the soil horizons
The "B" horizon
Generally called the subsoil
Usually lower in organic matter and lighter in color than "A" horizon
Usually red or yellowish in color
Structure is less desirable than the "A" horizon; it may have a blocky or prismatic structure
Frequently heavier texture than "A" horizon

5. Characteristics of the soil horizons
The "A" horizon
It includes the upper part of the profile in which life is most active; generally called the topsoil
It is the most productive horizon because of its normally high organic matter content and is usually dark colored
May be from a few inches to a foot or more deep
Lighter in texture than the "B" or "C" horizons
More likely to have granular structure than the other horizons

6. Importance of soils Plants grow in and on soil
Plants support animal life
Plants and animals support human life
World population is rapidly increasing and/or has inadequate nutrition
Supply of productive soil is limited
Improved soil management could feed more people

7. Function of soil as related to plant growth, development and maintenance
Media for seed germination
Media for support of plants
Storehouse of plant nutrients
Storehouse of water for the plant

8. Soil composition
TM 3

9. Soil composition Solids--Approximately 50%
Mineral matter
Organic matter
Living organisms
Pore space--Approximately 50%
Water
Air

10. Factors affecting soil formation
Parent materials
Residual
Igneous--Derived from molten materials in the center of the earth's crust (granitic, basaltic)
Metamorphic--Formed from the pre-existing rocks through the action of extreme heat and pressures (quartzite, schist)
Sedimentary--Formed from sediments deposited by wind, water or ice (shale, sandstone, limestone)

11. Factors affecting soil formation
Parent Material
Transported
Wind (loess)
Water (alluvial)
Glaciers (glacial drift)
Gravity (colluvial)

12. Factors affecting soil formation
Decomposition by weathering
Physical weathering
Wind
Plants and animals
Heating and cooling
Freezing and thawing
Wetting and drying
Chemical weathering--Chemical reactions of water, oxygen and carbon dioxide
Biological weathering--Micro-organisms secrete a gummy substance which aids in decomposing rocks

13. Factors affecting soil formation
Climate
Temperature
Rainfall
Vegetation and organisms
Plant--Lichens, mosses, weeds, grasses, shrubs, trees
Animal--Bacteria, fungi, large animals (cattle, horses, etc.) birds, man

14. Factors affecting soil formation
Slope and drainage
Hillsides
Thin topsoil due to soil loss by erosion
Reduced plant growth
Low organic matter
Less leaching (due to runoff)
Flat lands
Deeper topsoil
More vegetation
High organic matter
Greater leaching

15. Explore the physical properties of soil
A. Soil texture
B. Soil structure
C. Soil depth
D. Soil color

16. Soil particles Sand Diameter--2.00 to 0.05 mm Coarse and gritty
When moist, individual grains can be seen
Its presence decreases water-holding capacity
Its presence decreases nutrient holding capacity

17. Soil particles Silt Diameter--.05 to .002 mm
Its presence increases water-holding capacity
Its presence increases nutrient holding capacity
Moderate to high exchange capacity
Feels smooth and velvety

18. Soil particles Clay Diameter--less than .002 mm
Its presence increases water-holding capacity
Its presence increases nutrient holding capacity
High to very high exchange capacity

19. Determine soil texture
Mechanical analysis
A mechanical analysis of a soil reports the percentage of each of the soil particles (sand, silt and clay)
Percentages can be applied to the texture triangle to determine the texture of a soil

20. Determine soil texture
Feel method
Texture is determined by moistening the soil and rubbing between thumb and fingers
The wet sample is worked into a ball and placed between thumb and index finger, the thumb is pushed gradually forward in an attempt to form the soil into a ribbon (clayey soil)
If the wet sample will not form a ribbon, evaluate for grittiness (sandy soil)
Evaluate wet sample to determine if it feels velvety and slick, but will not ribbon (silty soil)

21. Soil Texture
Descriptions of soils of different texture using the feel method
Sandy soil
Coarse and gritty
When moist, individual grains can be seen
Called a "light" soil
Silty soil
Feels smooth, flowing when dry
Feels velvety or slick when wet
Clayey soil
Sticky and will form a ribbon when wet
Very hard when dry
Called a "heavy" soil 

22. Soil Structure
Granular (sphere shaped) -- Ideal for plant growth

23. Soil Structure Blocky (sharp and angular faces) Water storage good
Circulation of air and water is poor

24. Soil Structure
Platy (flat, horizontal, plate-like)--Poor permeability

25. Soil Structure
Prismatic and columnar (column-like)--Poor air-water relationship

26. Soil Structure
Massive

27. Color and importance
Color is an important characteristic used in the identification of soil conditions that affect the value of land for agricultural uses
Influenced mainly by organic matter content; benefits of organic matter include
Makes soil porous 
Supplies nitrogen and other nutrients to the plant
Holds water in the soil
Reduces leaching
Improves soil structure

28. Soil colors
Dark brown to black--Regarded as the most productive; usually contains a higher organic matter content
 Red or reddish brown--Usually less fertile than black or dark brown soils; may contain a high iron content
Yellow or gray--Usually caused by imperfect drainage

29. Acidity or alkalinity
The acidity or alkalinity of the soil solution is determined by the relative number of hydrogen (H+) ions and hydroxyl (OH-) ions
When a soil solution contains more H+ ions than OH- ions, it is acidic.
When the OH- ions are more abundant, the solution is alkaline.
A neutral solution has an equal amount of H+ and OH- ions

30. pH pH ranges on a scale from 1 to 14 1 to 7--Acidic soil
7--Neutral soil
7 to 14--Alkaline soil

33. Liming soils Soil acidity can be corrected by adding lime to the soil.
The function of lime is to neutralize the hydrogen (H+) ions that cause soil acidity

34. Liming soils Amount of lime to apply depends on
The degree of acidity of the soil
The crops to be grown
The grade or purity of the lime materials
The frequency of application
Soil texture
Soil exchange capacity

35. Types of alkali soils
Saline--Soils in which there has been an accumulation of soluble salts, for example: NaCl (table salt); these are referred to as "white alkali" soils
Sodic--Soils in which there has been an accumulation of sodium (Na); sodium affected soils have low permeability to water
Saline-sodic--Both salty and sodic affected

36. Reclamation of alkali soils
Saline
Flood with water and leach out salts
Install drainage tiles to remove accumulated salts
Grow salt tolerant crops
Sodic
Apply gypsum (CaSO4)
Grow sodic tolerant crops
Saline-sodic
First correct sodic
Then correct salt problem