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