soil science faculty of agricultural and applied biological sciences ghent university

Soil Science

Faculty of Agricultural and Applied Biological Sciences

Ghent University

November 19, 2002 Informatics 2

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


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


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


Soil Factors

Used to Determine Land Classification Texture

Surface Subsurface

Depth of Soil Slope Erosion


Soil Texture

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

Soil Separates Sand Silt Clay


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


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


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.


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


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.


Slope

Determined by the rise or fall of the land from one point to another point 100 feet away.

Simple equation is: Rise/Run=%Slope

4 Feet / 100 Feet = 4% Slope

100 Feet

4 feet


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%


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.


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


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


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.

soil science faculty of agricultural and applied biological sciences ghent university

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