SOIL PHYSICAL PROPERTIES

 The important physical properties of soils are

(1) soil texture

(2) soil structure

(3) soil consistency

(4) soil density

(5) soil porosity and

(6) soil color

Soil Texture and Textural Class

Soil texture is defined as the relative proportion of sand, silt, and clay.

The ranges of diameters of the three separates are: (International Soil Science Society)

• sand (2.0- 0.02 mm), 

• silt (0.02-.002 mm), and

• clay (<0.002 mm).   

                                                        

Importance of Soil Texture
Soil texture is one of the most important properties of 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.

Texture and the Use of Soils

• Plasticity, water permeability, ease of tillage, fertility, and

productivity are all closely related to soil texture

• Many clay soils expand and shrink with wetting and drying,

causing cracks in walls and foundations of buildings

• Conversely, many red-colored tropical soils have clay particles

composed mainly of kaolinite and oxides of iron and aluminum.

These particles have little capacity to develop stickiness and to

expand and contract on wetting and drying. Such soils may have a

high clay content and show little evidence of stickiness when wet,

or expansion and contraction with wetting and drying

What affects soil texture?

• The parent material, as modified by weathering and

soil-forming processes, determine a soil horizon’s

texture.

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.

• s,ls, sl, l, sc, scl

• si, sil,sicl,sic

• cl, c

We use the texture triangle to determine the

textural class.

Textural classes:

           A. Sandy soil: 1. Sand

                        2. Loamy sand

          B. Loamy soil: 1. sandy loam

                         2. Loam

                         3. Silt loam

                         4. Silt

                         5. Sandy clay loam

                         6. Silt clay loam

                         7. Clay loam

C. Clay soil : 1. Sandy clay

                      2. Silty clay

                      3. Clay

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%.

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!!