Soil texture 4

BY4215

Soil texture

The proportion of sand, silt, and clay particles in a soil

Importance of soil texture

Most important physical property controlling many soil behaviors

Soil particles considered in texture

Particles smaller than 2 mm in diameter

Sand size fraction

2.0 to 0.05 mm

Silt size fraction

0.05 to 0.002 mm

Clay size fraction

Less than 0.002 mm

Surface area and texture

Smaller particles have greater surface area and higher reactivity

Clay surface area

Extremely large, controlling adsorption and nutrient holding

Sand

Large soil particles visible to the naked eye

Sand feel

Gritty and non-sticky

Sand mineralogy

Mostly quartz or mixed minerals

Sand water holding capacity

Low

Silt

Medium-sized soil particles not visible to the naked eye

Silt feel

Smooth and floury

Silt plasticity

Not sticky or plastic when wet

Silt mineralogy

Mostly quartz

Clay

Very fine soil particles formed from weathering

Clay shape

Flat plates or flakes

Clay behavior in water

Colloidal and remains suspended

Clay properties

Sticky, plastic, malleable when wet

Clay nutrient holding capacity

High

Soil texture determination

Measuring percentages of sand, silt, and clay

Laboratory texture method

Sieving and sedimentation using a hydrometer

Stokes’ Law

Used to calculate particle size during sedimentation

Field texture method

Feel or ribbon test

Feel test sandy soil

Gritty with a short ribbon

Feel test silty soil

Smooth with a crumbly ribbon

Feel test clay soil

Shiny with a long flexible ribbon

Soil textural classes

12 classes based on sand, silt, and clay content

Textural triangle

Diagram used to classify soil texture

Coarse-textured soils

Sands and loamy sands

Moderately coarse soils

Sandy loam

Medium-textured soils

Sandy loam, loam, silt loam, silt

Moderately fine soils

Sandy clay loam, clay loam, silty clay loam

Fine-textured soils

Sandy clay, silty clay, clay

Ideal loam

Balanced mixture of sand, silt, and clay

Influence of clay in loam

Small amounts strongly affect soil properties

Soil texture controls trafficability

Ease of movement by machinery

Soil texture and moisture

Regulates water retention and drainage

Soil texture and temperature

Influences soil warming and cooling

Soil texture and fertility

Affects nutrient storage and availability