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Teacher Information!. Necessary materials: PowerPoint Guide. Soil Texture. Soil and Water Resources. Students will be able to…. Describe the three basic soil particles Identify the major textural classes. Soil texture. The way a soil feels - PowerPoint PPT PresentationTRANSCRIPT
Necessary materials: PowerPoint Guide
Teacher Information!
Soil Texture
Soil and Water Resources
Students will be able to… Describe the three basic soil particles Identify the major textural classes
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?
Three Fractions of Mineral Matter Sand
Silt
Clay
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?
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
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
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
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)
USDA Texture Triangle
USDA Texture TriangleExample: 60% silt 10% sand 30% clay
= silty clay loam
60% silt
30% clay
10%sand
What is a soil that is: 30% silt 0% sand 70% clay
Physical Properties of Soil Soil texture
Soil structure
Soil color
Bulk density
** Remember These properties are used for classifying soil.
Definitions Aggregate
Mass or cluster of soil particles such as a clod, crumb or granule
Soil Structure The combination or arrangement of soil particles
into aggregates
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
Bulk Density 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
Soil Color 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
Major Forms of Iron and Effect on Soil Color
Form Chemical Formula Color
Ferrous oxide FeO Gray
Ferric oxide (Hematite) Fe2O3 Red
Hydrated ferric oxide (Limonite) 2Fe2O3 3H2O Yellow
Can you… Describe the three basic soil particles Identify the major textural classes