1. Unit 8: Soils characteristics
Spring 2010

2. Objectives Understand what soil is and how it is created
Describe soil layers and how they differ
Discuss how plants depend on soils for growth
List five soil forming factors
Describe how soils develop
What are soil horizons
List soil components
What creates soil texture
Identify the chemical properties of soil
Use the soil texture triangle to name soil
Describe soil particle sizes
Discuss how iron and organic material influence the color of some soils
Identify the pH of neutral, acidic, and alkaline soil
Discuss the effect of organic material on soil
Name three ways soils are classified

3. Vocabulary Alluvial soil *Oxidation reduction
Chemical weathering *Parent material
Delta *Pedon
Eluviation *Physical weathering
Eolian Depost *Plow layer
Floodplains *Polypedon
Frost wedging *Root wedging
Glacial drift *Sedimentary rock
Glacial outwash *Soil horizon
Glacial till *Soil profile
Hydrolysis *Soil series
Igneous rock *Subsoil
Illuviation *Topography
Leaching *Topsoil
Levee *Weathering
Marine sediment *Acidic
Master horizon *Alkaline
Metamorphic rock *Bulk density
Mineral soil *Neutral
Organic soil * Soil texture
Soil structure *pH

4. Entry Task
What do you think soil is made of?

5. What is soil?
Soil is a collection of natural bodies of earth’s surface, in places modified or even made by man or earthy materials, containing living matter and supporting or capable of supporting plants outdoors.

6. Physical properties of soil
Composition
What is the 5% organic composition made of?
What is the 45% mineral composition made of?
Soil microbes make a small portion of the
organic make up. For example worms
Texture
Sand >>>>>>>large>>>>>>rough
Silt>>>>>>>>medium>>>>medium
Clay>>>>>>>small>>>>>>fine/soft
Soil texture is measured by size of soil particles
Soil texture determines the amount and size of spaces between soil particles. This controls how quickly water moves through the soil profile and how much water the soil holds.

7. Soil Texture Triangle
The soil texture triangle is used to determine the textural name of a soil by mechanical analysis.
Measures the percentage of sand, silt, and clay present in soil.
Once percentages have been found, these amounts are plotted on the triangle.
This is done by projecting lines inward from the point on each side of the triangle, which represents the percentage of that particular type of soil.

8. Physical Properties continued
Structure: refers to the arrangement of soil particles.
Granular
Platy
Wedge
Columnar
The best soil structure is high in proportion of medium sized aggregates and a significant number of large pores through which water and air can move.
Structure is important in both A and B horizons

9. Physical Properties continued
Bulk density: the dry weight of the soil divided by soil volume.
This is used to calculate the amount of density between the dried soil weight and the volume of the soil when pores were present.
Finer texture soils have a smaller bulk density.
Coarse textured soils have a high bulk density.
Bulk density influences engineering properties, water movement, rooting depth of plants, and many other physical limitiations.

10. Physical Properties continued
Soil Depth: Total depth of topsoil subsoil, and parent material.
This allows for root growth to occur.
Soil depth will affect the yield of crop production
For example a plant that enjoys deep soils to set large long roots, would not grow well in shallow soil
Soil Color: helps in recognizing the different soil types but color is also an indicator of certain physical and chemical characteristics.
Color is due to two factors
Humus content (organic matter)
Chemical nature of iron compounds present in soil

11. Physical Properties continued
Water holding capacity:
Larger the pore space the less water the soil holds
Smaller the pore space the more water the soil holds

12. Soil Profile
Refers to the arrangement and properties of the various soil layers.
Layers are horizontal and formed during the development of the soil.
Topsoil
Surface or very top layer. This may be a few inches or a few feet.
Very dark with organic matter
Subsoil
Just under topsoil
Lighter in color and nutrient value
Parent Material
Lower layer.
Layer in which the sub and top soil develop from.
Broken into Horizons

13. Soil texture
Procedure
Checking of soil texture is done by Hydrometer method or Pipette method. For a huge lawn gather samples at equally spaced gaps in the area. Then mix these to form a composite sample. For accurate analysis rake up a couple of inches and make a hole six inches in depth. This enables us to check the soil from the root area rather than the surface. Free the sample of rocks and debris and make it dry in a day or two. Then sift the sample by using a wire- mesh or an old colander to separate small stones and roots and to break lumps of soil if present. Now take a cupful of the sifted soil in a jar and add to it a tablespoon of powdered detergent to keep the soil particles separate to achieve an accurate checking. Add water and mix these three materials completely. Ensure that no soil gets attached to the sides of the jar. Let the sediment settle. During sedimentation it is observed that sand settles the first, followed by silt and clay needs a couple of days. The layer of sand has a coarse texture than the silt. The layer of clay is the finest. Now measure the height of each layer with a ruler. Divide height of each layer multiplied by 100, by the total height of all three layers to get the percent of each layer. Now transfer your percentages to the soil texture triangle and deduce the soil texture.

17. Organic matter
Soil organic matter consists of plant and animal residues in various stages of decay.
Adequate levels benefit soil in four ways
Improves physical condition and structure
Increase water infiltration
Decreases erosion losses
Supplies plant nutrients
Organic matter contains up to 5% of Nitrogen

18. Chemical Properties Soil pH
Is based on the amount of hydrogen ions present in the soil.
Soils will either be
Acidic: pH less than 7.0 (more H+)
Neutral: at 7.0
Alkaline: pH more than 7.0 (more hydroxyl OH-)
Acidic
Alkaline
We have the ability to change the color of certain flowers by manipulating the pH of the soil.

19. Entry Task
How do you detect nitrogen deficiency in a plant?

20. Essential nutrients
16 chemical elements have been found to be needed for plants to grow and mature properly.
These 16 elements are considered the Essential Plant Nutrients
Nonmineral: Carbon, Hydrogen, Oxygen
Primary: Nitrogen, Phosphorus, Potassium
Secondary Mineral: Calcium, Magnesium, Sulfur
Micronutrient: Boron, Chlorine, Copper, Iron, Manganese, Moylbdenum, Zinc
When these nutrients are deficient the plant will express specific symptoms

21. Nitrogen One of the earths most abundant and mobile nutrients.
Part of every single plant cell.
N is vital for photosynthesis to occur. When plants don’t have N their leaves lose their normal green color and turn yellow.
This occurs in the lower leaves first.
N comes in three different forms, but only one form can be taken into a plant Nitrate (NO-3)
Nitrification is the process of bacteria converting ammonium nitrogen into nitrate, the usable form of N.

22. What happens to N in the soil?
Taken in by a plant
Leaching: Moves through the soil profile and is taken out of soil horizons
Erosion: N is lost through erosion in association with either water or sediment.
Denitrification: When soils become saturated with water, air is removed from soil pores. Without O bacteria increase and more N is lost to the atmosphere.
Volatilization: Loss of N into the air

23. Nitrogen Cycle

24. Nitrogen fixation is the process whereby elemental nitrogen is removed from the atmosphere by soil bacteria called rhizobia.
These bacteria live in the nodules on roots of legume plants such as alfalfa, clover, peas, beans, and vetch.
Organic matter is composed of decomposed plants in the soil.
The amount of N available to the plant depends on the carbon:nitrogen ratio of the decaying material.

25. Phosphorus and potassium
Very immobile in the soil.
Many plants respond to phosphorus being placed near the roots or the seed.
Potassium
Is second to N in the amounts used by plants.
Not much leaching occurs

26. How does pH levels affect soil composition and plant health?
What is inorganic fertilizer?
Which is more effective organic or inorganic fertilizer?
How can you tell if a plant is experiencing a lack of Potassium?
How can you tell if a plant is experiencing a lack of Phosphorus?
How can you increase and decrease the soil pH?

28. Coneflower *Verbena
Swiss Chard *Petunia
Lettuce *Waxy Begonia
Artichoke *Impatiens
Squash *Calibrachoa
Cucumber *Cabbage
Zonal Geranium *Broccoli
African Daisy *Pumpkin
Zones
Height
Sun Exposure
Bloom Time
Use
Fertilizing needs

29. How soils are made
Soils are created through a variety of processes and over long periods of time.
Heating and cooling
Water and wind
Pedology is the study of soil formation, also known as soil genesis and soil classification and mapping.
Not all soils can be dug up and studied…..instead soils are studied in small segments called Pedons.
Pedons : 1x1 meter

30. What do these questions have in common
Entry Task
What do these questions have in common
Where is the best place to build a building?
What types of crops will grow best in a particular field?
Will the basement of a house flood when it rains?
How can the quality of the groundwater in the area be improved?

31. Soils develop on top of Earth's land surface as a thin layer, known as the pedosphere
Soils hold nutrients and water for plants and animals
Change the chemistry of water
Changes the amount of recharge that reaches groundwater or what returns to the atmosphere to form rain. How does soil have this ability?
Provides the ability to have paper, buildings, and clothing.
Affect air temperature.

32. 5 Soil Forming Factors
Parent Material: material from which the soil was formed. Generally deposited by wind, water, glaciers, volcanoes, or gravity
Climate: Heat, rain, ice, snow, wind, sunshine break down parent material. Also affects organic break down.
Organisms: Soil is often home to many microorganisms. These organisms help in the process of decomposition.
Topography: Affects how much water a soil will retain.
Time: the amount of time that the other 4 factors have been interacting with each other affects the physical properties of soil

33. Gelisols Alfisols Histosols Inceptisols Mollisols Spodosols Entisols
These are various soil classifications. Research these soil types and make a poster that represents the data. Ideas….what its composed of, what can be grown on it, where is it located, color, texture, how it was made, soil profile picture, map of location
Gelisols Alfisols Histosols Inceptisols Mollisols Spodosols
Entisols
Oxisols
Ultisols
Vertisols
Aridisols
Andisols

34. Questions
What are some key factors that influence the composition of soils around the world?
From studying these images, can you infer some of the processes that have formed particular soil profiles?
What are some of the characteristics of soils in the United States and how do these relate to the kinds of vegetation occurring on them?
Why is it important to know the soil structure of a particular area? Give several reasons.
What types of soil are in your area?

35. Entry Task
What physical characteristics do scientist use to classify soil profiles

36. Soil classification
Which soil is primarily located in Northern South America and the middle section of Africa?
Which soil type can grow rice and cocoa?
Which soil is used for cultivated field crops?
Which soil is composed of silicate and organic matter?
Which soil is a black or dark brown color because of organic material located in the upper layer?
Which soil has a high content of iron and clay?
Which soil is sparsely located around the world?
Which soil is formed by volcanic ash?

37. Soil Classification
Which soil is predominantly located in northern parts of Russia and North America?
Which soils are mostly located in the Pacific Northwest?
Which soil has parent material deposited by volcanic ash?
Which soil profile contains an eluvial horizon?
Which soil has a large deposit located in the northern region of South America?
Which soils were formed by weathering processes that stripped organic matter combined with aluminum?
Which soils are composed of quartz, kaolin, clay, and OM?
Which soil is the texture of clay?
Which soil has parent material deposited by glaciers?
Which soil classification can grow tall blue stem, indian corn, soybean, and grass?