Unit 8: Soils characteristicsSpring 2010

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

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

Entry Task

•What do you think soil is made of?

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.

Physical properties of soil•CompositionWhat is the 5% organic composition made of?What is the 45% mineral composition made of?

▫ Soil microbes make a small portion of theorganic 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.

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.

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

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.

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

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

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

Soil textureProcedure

• 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.

Organic matter•Soil organic matter consists of plant and

animal residues in various stages of decay.

•Adequate levels benefit soil in four ways1. Improves physical condition and structure2. Increase water infiltration3. Decreases erosion losses4. Supplies plant nutrients

Organic matter contains up to 5% of Nitrogen

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-)

We have the ability to change the color of certain flowers by manipulating the pH of the soil.

Acidic Alkaline

Entry Task•How do you detect nitrogen deficiency in

a plant?

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

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.

What happens to N in the soil?1. Taken in by a plant2. Leaching: Moves through the soil profile

and is taken out of soil horizons3. Erosion: N is lost through erosion in

association with either water or sediment. 4. 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.

5. Volatilization: Loss of N into the air

Nitrogen Cycle

•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.

Phosphorus and potassium•Phosphorus

▫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

•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?

• 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

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

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?

•Soils develop on top of Earth's land surface as a thin layer, known as the pedosphere

•Soils:▫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.

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

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 locationGelisolsAlfisolsHistosolsInceptisolsMollisolsSpodosols

EntisolsOxisolsUltisolsVertisolsAridisolsAndisols

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?

Entry Task

•What physical characteristics do scientist use to classify soil profiles

Soil classification1. Which soil is primarily located in Northern

South America and the middle section of Africa?

2. Which soil type can grow rice and cocoa?3. Which soil is used for cultivated field crops?4. Which soil is composed of silicate and organic

matter?5. Which soil is a black or dark brown color

because of organic material located in the upper layer?

6. Which soil has a high content of iron and clay?7. Which soil is sparsely located around the

world?8. Which soil is formed by volcanic ash?

Soil Classification1. Which soil is predominantly located in northern parts of

Russia and North America?2. Which soils are mostly located in the Pacific Northwest?3. Which soil has parent material deposited by volcanic ash?4. Which soil profile contains an eluvial horizon?5. Which soil has a large deposit located in the northern

region of South America?6. Which soils were formed by weathering processes that

stripped organic matter combined with aluminum?7. Which soils are composed of quartz, kaolin, clay, and OM?8. Which soil is the texture of clay?9. Which soil has parent material deposited by glaciers?10. Which soil classification can grow tall blue stem, indian

corn, soybean, and grass?