 Essential Question: How does soil form, and what purposes does it serve?  Objectives: 1. Describe the functions of soil 2. Describe the factors of soil formation

 Upper layer of Earth in which plants grow.  Formed by weathering, erosion, and the combining of those rock particles with air, water, and organic material  It can take 100 to 600 years or more for nature to make one inch of topsoil

 Parent Material  Climate  Organisms  Topography  Time

 Provides support and anchorage for vegetation  Medium for plant growth and crop production  Primary cleansing and recycling medium  Sustains biological activity, diversity and production  Stores and cycles nutrients and other elements  Allows gas exchange

 Organic matter  Water  Air  Nutrients/minerals

 Consists of the remains of plants and animals  With favorable temperature and moisture, animals and fungi break down organic matter to humus and soluble nutrients accessible to growing plants  Types of plants growing in the soil, management practices, temperature, and drainage determine the amount of organic matter

 From precipitation entering soil cracks, holes, and openings between soil particles  Used by plants  Lost to evaporation and run-off  Moves deep within the ground, inaccessible to plants

 Air in the soil contains less oxygen and more carbon dioxide than air above the soil surface  Air is pushed out of the soil as water enters  Plant roots take up oxygen for respiration  Roots die if air is unavailable for long periods of time

 18 elements essential for plant growth  Nitrogen - most important, nitrogen-fixing bacteria  Carbon, Hydrogen and Oxygen - from air and water  Iron, calcium, phosphorus, potassium, copper, sulfur, magnesium, manganese, zinc, boron, chlorine, cobalt, nickel, and molybdenum - from soil

 Permeability  Water holding capacity  Porosity

 The rate at which water moves through soil  Affected by the amount, size, and arrangement of pores.  Macropores, such as sand, can increase permeability

 The ability of a soil’s micropores to hold water for plant use  Affected by the amount, size and arrangement of pores

 Soil texture  Soil structure  Compaction  Organic matter

 The relative proportions of sand, silt and clay

 Sand - particles of 2 to.05 mm diameter  Silt - particles.05 to.0002 mm diameter  Clay - <.0002 mm diameter  Loam - contains soils whose properties consist almost equally of clay, silt, and sand separates

 The nature of the arrangement of primary particles into naturally formed secondary particles called aggregates  Profound influence on porosity and balance between large and small pores  Types  Granular  Blocky  Platy  Columnar/Prismatic

 Individual particles of sand, silt, and clay grouped together in small, nearly spherical grains  Water easily circulates  Common in surface soils with high organic matter content

 Soil particles that cling together in nearly square or angular blocks having more or less sharp edges  Resists penetration and movement of water  Common in subsoils, especially in humid regions

 Made up of soil particles aggregated in thin plates or sheets piled horizontally on one another  Plates often overlap, greatly impairing water circulation  Common with puddling or ponding of soils

 Soil particles that have formed into vertical columns or pillars separated by miniature, but definite vertical cracks  Water circulation and drainage is poor  Common in subsoils in arid and semi-arid regions

 Destroys soil quality  Reduces pore size  Less space for air and water  Difficult for plants to grow roots

 Add organic matter  Reduce trips across the area  Practice reduced-till or no till systems  Harvest when soils are not wet

 What do you think the soil profile is?  Why is it important to know about the soil profile?

 Essential Question: What are the horizons of the soil profile, and what do they contain? Objectives: 1. Describe the horizons of the soil profile. 2. Identify individual horizons of the soil profile based on their components. 3. Describe why the soil profile is important to understand.

 6 layers  O:Organic  A: Topsoil  E: Eluviated  B:Subsoil  C: Parent Material  R: Bedrock

 Organic  Top layer of soil  Made of fresh to partially decomposed organic matter  Color varies from brown to black

 Top Soil  2 nd layer  Top portion made of highly decomposed organic matter  Color ranges from brown to gray

 Eluviated  3 rd layer  Made of mostly sand and silt  Has lost most of its minerals

 Sub soil  4 th layer  More clay and bigger bedrock  Reddish brown or tan in color

 Parent Material  5 th layer  Weathered bedrock  Cracked and broken surface of the bedrock

 Bedrock  Last layer  Made of unweathered rocks