Soil Science Faculty of Agricultural and Applied Biological Sciences Ghent University

November 19, 2002Informatics2 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

November 19, 2002Informatics3 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

November 19, 2002Informatics4 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

November 19, 2002Informatics5 Soil Factors Used to Determine Land Classification Texture Surface Subsurface Depth of Soil Slope Erosion

November 19, 2002Informatics6 Soil Texture Determined by the amount of each soil separate within a given sample Soil Separates Sand Silt Clay

November 19, 2002Informatics7 Soil Separates Sand.002 to.08 inches Feels gritty Silt to.002 inches Feels smooth when wet Clay Less than inch Feels sticky when wet

November 19, 2002Informatics8 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

November 19, 2002Informatics9 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.

November 19, 2002Informatics10 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

November 19, 2002Informatics11 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.

November 19, 2002Informatics12 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

November 19, 2002Informatics13 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%

November 19, 2002Informatics14 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.

November 19, 2002Informatics15 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

November 19, 2002Informatics16 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% Erosion

November 19, 2002Informatics17 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.