Soil Texture and Textural Class

1. Soil Texture and Textural Class Laboratory #3

2. Objectives • To learn and understand the significance of the following concepts related to soil texture : • The definition of soil texture, soil separate, and textural class. The relative size of particles defined as sand, silt, and clay. • How to determine a soil's textural class using the textural triangle when the soil texture is known. • How to estimate a soil's textural class by the "feel" method. • How soil textures and textural classes relate to soil management and land use.

3. Definition • Soil texture is defined as the relative proportion of sand, silt and clay. • The ranges of diameters of the three separates are: sand (2.0- 0.05 mm), silt (0.05-.002 mm), and clay (<0.002 mm). http://science.kennesaw.edu/~jdirnber/limno/LecPhy/SiltSandClay.jpg

4. Diameter Ranges

5. Importance of Soil Texture • Soil texture is one of the most important properties of a soil, and it greatly affects land use and management. • It affects the amount of water and nutrients that a soil can hold and supply to plants. • Soil physical properties such as structure, and movement of air and water through the soil are affected by texture.

6. What affects soil texture? • The parent material, as modified by weathering and soil- forming processes, determines a soil horizon’s texture. Residuum (or bedrock) Marine Sediments http://soils.ag.uidaho.edu/soilorders/aridisols_07.htm http://soils.ag.uidaho.edu/soilorders/ultisols_01.htm

7. Can soil texture be altered? • Texture is a relatively permanent physical property under natural conditions, and, for most agricultural or forestry uses, it is not practical to change soil texture. • In intensely managed systems texture can be changed by adding coarser or finer material. http://www.gov.mb.ca/iedm/profiles/images/alfalfa_lg.jpg

8. Determining Soil Texture - Lab • Soil textures can be determined in laboratory analyses where the amount of sand, silt, and clay are measured quantitatively. • We will do this in the laboratory activities. http://earthobservatory.nasa.gov/Newsroom/NasaNews/ReleaseImages/20040730/06_LabTestingSoil.jpg

9. Determining Texture - Field • In the field, the soil's texture may be determined by the "feel" method, where we estimate the amount of sand, silt, and clay.

10. Soil Textural Class • Soil textural classes are based on the relative proportions of the various soil separates (sand, silt, and clay). • There are 12 different soil textural classes. • We use the texture triangle to determine the textural class.

11. Texture Triangle • The percentage units (0-100%) of sand, silt, and clay are listed along the sides of the triangle. • Also notice that the relative proportion of sand, silt, and clay always adds up to 100%. http://www.public.iastate.edu/~arossi/texture%20triangle.jpg

12. Texture Triangle Example #1 • Tell me what the textural class is if we have: 42% sand, 35% silt, and 23% clay. • We would have a loam!! http://www.public.iastate.edu/~arossi/texture%20triangle.jpg

13. Texture Triangle Example #2 • What would we have if we had a soil with 8% sand, 32% clay, and 60% silt?

14. Texture Triangle Answer #2 • We would have a silty clay loam!! http://www.public.iastate.edu/~arossi/texture%20triangle.jpg

15. Organics in Soil Texture • Sand, silt, and clay are the only particles used to determine soil texture. • Soil texture refers only to the mineral fraction of the soil. • Organic matter is not considered when determining texture or textural class. • A precise analysis of soil texture requires that organic matter be removed.

16. Questions??