Soil Science

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Soil Science

• Faculty of Agricultural and
• Applied Biological Sciences
• Ghent University

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Why Study Soil Science?

• Land is a Natural Resource
• It provides raw materials
• Enables us to produce food fiber
• Stores collects water for use
• Is the primary source of habitat for wildlife

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Soil Classification

• Capability Classes
• Developed by the USDA
• Identifies land by its characteristics
• Class I-IV Can be used for cropland
• Class V-VII Non-cropland agricultural use
• Class VIII Used for wildlife recreation

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Soil Profile

• Top layer often decaying organic material
• Topsoil (A Horizon) Most developed part of a
  soil
• Sub-soil (B Horizon) Layer of soil below the
  layer that is usually tilled
• Parent Material (C Horizon) Weathered material
  that often restricts root development

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Soil Factors

• Used to Determine Land Classification
• Texture
• Surface
• Subsurface
• Depth of Soil
• Slope
• Erosion

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Soil Texture

• Determined by the amount of each soil separate
  within a given sample

• Soil Separates
• Sand
• Silt
• Clay

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Soil Separates

• Sand
• .002 to .08 inches
• Feels gritty
• Silt
• .00008 to .002 inches
• Feels smooth when wet
• Clay
• Less than .00008 inch
• Feels sticky when wet

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Soil Texture

• Is broken into five categories
• Coarse- over 70 sand
• Moderately Coarse- over 50 sand
• Medium
• Moderately Fine- 20 to 40 clay
• Fine- at least 40 clay

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Depth of Soil

• The total thickness of material available for
  plant root growth
• The thickness above any layer which restricts
  root development.
• Very important in locating buildings, crop
  fields, ponds, and sewage systems.

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Depth of Soil

• Deep- more than 40 inches
• Moderately Deep- 20 to 40 inches
• Shallow- 10 to 20 inches
• Very Shallow- less than 10 inches

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Slope

• Refers to the steepness of a given area of land.
• Affects the management and use of the land.
• Is directly related to the hazard of erosion.
• As slope increases, agricultural suitability
  decreases.

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Slope

• Determined by the rise or fall of the land from
  one point to another point 100 feet away.
• Simple equation is Rise/RunSlope
• 4 Feet / 100 Feet 4 Slope

4 feet
100 Feet
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Classes of Slope

• Nearly Level Less than 1
• Gently Sloping 1 to 3
• Moderately Sloping 3 to 5
• Strongly Sloping 5 to 8
• Steep 8 to 15
• Very Steep Greater than 15

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Erosion

• Process that causes the loss of soil by the
  action of water or wind.
• The three types of erosion are
• Sheet Results from the splash of rain.
• Rill Small channels cut into soil by running
  water, are easily smoothed by tillage.
• Gully Caused by concentrated running water
  cutting deep into the soil.

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Erosion

• Process that removes the finer, more fertile soil
  materials.
• Can be controlled by
• Conservation tillage
• No-till
• Reduced till
• Leaving Crop Residues
• Contour Tillage
• Terracing
• Vegetative Waterways

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Erosion

• Determined by
• Subtracting the current top soil depth from the
  original top soil depth.
• Dividing the difference by the original depth.
• Converting to a percentage.
• Tells the of soil lost.

• Original Depth 25 inches
• Current Depth 20 inches

25 20 5 inches 5 / 25 .20 .20 20 Erosion
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Levels of Erosion

• None to slight Less than 25 and no gullies.
• Moderate 25 to 75. May have small, occasional,
  crossable gullies.
• Severe Greater than 75. May have frequent
  crossable gullies or occasional uncrossable
  gullies.
• Very Severe Greater than 75. Has frequent
  uncrossable gullies.