Soil Texture and Textural Soil Texture and Textural ClassClass

Laboratory #3Laboratory #3

ObjectivesObjectives

To learn and understand the significance of the To learn and understand the significance of the following concepts related to soil texture : following concepts related to soil texture : The definition of soil texture, soil separate, and The definition of soil texture, soil separate, and

textural class. The relative size of particles textural class. The relative size of particles defined defined as sand, silt, and clay.as sand, silt, and clay.

How to determine a soil's textural class using the How to determine a soil's textural class using the textural triangle when the soil texture is known.textural triangle when the soil texture is known.

How to estimate a soil's textural class by the "feel" How to estimate a soil's textural class by the "feel" method.method.

How soil textures and textural classes relate to soil How soil textures and textural classes relate to soil management and land use.management and land use.

DefinitionDefinition

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

The ranges of diameters The ranges of diameters of the three separates of the three separates are: sand (2.0- 0.05 are: sand (2.0- 0.05 mm), silt (0.05-.002 mm), silt (0.05-.002 mm), and clay (<0.002 mm), and clay (<0.002 mm). mm).

http://science.kennesaw.edu/~jdirnber/limno/LecPhy/SiltSandClay.jpg

Diameter RangesDiameter RangesSoil Soil

FractionFractionSoil Separate Soil Separate Diameter Diameter

(mm)(mm)

SandSand Very coarse Very coarse sand sand

1 to 21 to 2

Coarse sandCoarse sand 0.5 to 10.5 to 1

Medium sandMedium sand 0.25 to 0.50.25 to 0.5

Fine sandFine sand 0.1 to 0.250.1 to 0.25

Very fine sandVery fine sand 0.05 to 0.10.05 to 0.1

SiltSilt SiltSilt 0.002 to 0.05 0.002 to 0.05

ClayClay ClayClay < 0.002 < 0.002

Importance of Soil TextureImportance of Soil Texture

Soil texture is one of the most important Soil texture is one of the most important properties of a soil, and it greatly affects properties of a soil, and it greatly affects land use and management. land use and management.

It affects the amount of water and It affects the amount of water and nutrients that a soil can hold and supply to nutrients that a soil can hold and supply to plants. plants.

Soil physical properties such as structure, Soil physical properties such as structure, and movement of air and water through and movement of air and water through the soil are affected by texture. the soil are affected by texture.

What affects soil texture?What affects soil texture? The parent material, as modified by The parent material, as modified by

weathering and soil- forming processes, weathering and soil- forming processes, determines a soil horizon’s texture. determines a soil horizon’s texture.

http://soils.ag.uidaho.edu/soilorders/aridisols_07.htm

http://soils.ag.uidaho.edu/soilorders/ultisols_01.htm

Residuum (or bedrock)

Marine Sediments

Can soil texture be altered?Can soil texture be altered?

Texture is a relatively Texture is a relatively permanent physical permanent physical property under natural property under natural conditions, and, for most conditions, and, for most agricultural or forestry agricultural or forestry uses, it is not practical to uses, it is not practical to change soil texture. change soil texture.

In intensely managed In intensely managed systems texture can be systems texture can be changed by adding changed by adding coarser or finer material.coarser or finer material.

http://www.gov.mb.ca/iedm/profiles/images/alfalfa_lg.jpg

Determining Soil Texture - Determining Soil Texture - LabLab

Soil textures can be determined in laboratory Soil textures can be determined in laboratory analyses where the amount of sand, silt, and analyses where the amount of sand, silt, and clay are measured quantitatively.clay are measured quantitatively.

We will do this in the laboratory activities.We will do this in the laboratory activities.

http://earthobservatory.nasa.gov/Newsroom/NasaNews/ReleaseImages/20040730/06_LabTestingSoil.jpg

Determining Texture - FieldDetermining Texture - Field

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

Soil Textural ClassSoil Textural Class

Soil textural classes are based on Soil textural classes are based on the relative proportions of the the relative proportions of the various soil separates (sand, silt, and various soil separates (sand, silt, and clay). clay).

There are 12 different soil textural There are 12 different soil textural classes.classes.

We use the texture triangle to We use the texture triangle to determine the textural class. determine the textural class.

Texture TriangleTexture Triangle

The percentage The percentage units (0-100%) of units (0-100%) of sand, silt, and clay sand, silt, and clay are listed along the are listed along the sides of the sides of the triangle. triangle.

Also notice that the Also notice that the relative proportion relative proportion of sand, silt, and of sand, silt, and clay always adds up clay always adds up to 100%. to 100%.

http://www.public.iastate.edu/~arossi/texture%20triangle.jpg

Texture Triangle Example Texture Triangle Example #1#1

Tell me what the Tell me what the textural class is if textural class is if we have: 42% we have: 42% sand, 35% silt, and sand, 35% silt, and 23% clay.23% clay.

We would have a We would have a loamloam!!!!

http://www.public.iastate.edu/~arossi/texture%20triangle.jpg

Texture Triangle Example Texture Triangle Example #2#2

What would we have if we had a soil What would we have if we had a soil with 8% sand, 32% clay, and 60% with 8% sand, 32% clay, and 60% silt? silt?

Texture Triangle Answer #2Texture Triangle Answer #2

We would have a We would have a silty clay loamsilty clay loam!!!!

http://www.public.iastate.edu/~arossi/texture%20triangle.jpg

Organics in Soil TextureOrganics in Soil Texture

Sand, silt, and clay are the only particles Sand, silt, and clay are the only particles used to determine soil texture. used to determine soil texture.

Soil texture refers only to the mineral Soil texture refers only to the mineral fraction of the soil. fraction of the soil.

Organic matter is not considered when Organic matter is not considered when determining texture or textural class. determining texture or textural class.

A precise analysis of soil texture requires A precise analysis of soil texture requires that organic matter be removed.that organic matter be removed.

Questions??Questions??