Teacher Information!

1. Teacher Information! • Necessary materials: • PowerPoint Guide

2. Soil Texture Soil and Water Resources

3. Students will be able to… • Describe the three basic soil particles • Identify the major textural classes

4. Soil texture • The way a soil feels • A name given a textural group based on the relative proportions of each size of soil particle • For example: sandy loam, silty loam, sandy clay loam • Why is soil texture important?

5. Three Fractions of Mineral Matter • Sand • Silt • Clay

6. Soil Particles • Sand • Largest of the soil particles • Feels “gritty” • Spaces between particles allow drainage and air entry • Holds little water  prone to drought • Contains fewer nutrients than smaller particles • How suitable are sandy soils for agriculture?

7. Soil Particles • Silt • Medium sized: Particle visible with microscope  0.05 mm to 0.002 mm • Feel soft, silky, or “floury” • Holds more nutrients than sand • Retains water, slower drainage than sand • Easily eroded

8. Soil Particles • Clay • Smallest particles  <0.002 mm • Feels “sticky” • Easily formed into long ribbons • High adsorption of water and chemicals • Water is not readily available for plants • Very small pore spaces • Very slow movement of water and air

9. 12 Soil Texture Classes • Sand (S) • Loamy Sand (LS) • Sandy Loam (SL) • Loam (L) • Silt Loam (SIL) • Silt (SI) • Sandy Clay Loam (SCL) • Silty Clay Loam (SICL) • Clay Loam (CL) • Sandy Clay (SC) • Silty Clay (SIC) • Clay (C) Compositions of each of the 12 texture classes is defined by the USDA Soil Triangle

10. What is loam? The Best of All Worlds • A soil type that contains all three particle sizes. • The most productive soil for farming crops • Has good water holding capacity (from clay) • Has good drainage (from sand) • Can be nutritious (from silt)

11. USDA Texture Triangle

12. USDA Texture Triangle • Example: • 60% silt • 10% sand • 30% clay • = silty clay loam 60% silt • What is a soil that is: • 30% silt • 0% sand • 70% clay 30% clay 10%sand

13. Physical Properties of Soil • Soiltexture • Soilstructure • Soilcolor • Bulkdensity ** Remember  These properties are used for classifying soil.

14. Definitions • Aggregate • Mass or cluster of soil particles such as a clod, crumb or granule • SoilStructure • The combination or arrangement of soil particles into aggregates

15. Factors that Affect Soil Structure • Kind of clay • Amount of organic matter • Freezing and thawing • Wetting and drying • Action of burrowing organisms • Growth of root systems of plants

16. BulkDensity • Determined by dividing the weight of oven-dried soil in grams by its volume in cubic centimeters • The variation in bulk density is due largely to the difference in total pore space • Influences water movement, rooting depth of plants

17. SoilColor • Indicator of different soil types • Indicator of certain physical and chemical characteristics • Due to humus content and chemical nature of the iron compounds present in the soil

18. Major Forms of Iron and Effect on Soil Color FormChemical FormulaColor Ferrous oxide FeO Gray Ferric oxide (Hematite) Fe2O3 Red Hydrated ferric oxide (Limonite) 2Fe2O33H2O Yellow

19. Can you… • Describe the three basic soil particles • Identify the major textural classes