Soil Texture & Structure

Soil Texture

What is Soil Texture? It is the proportion of three sizes of soil

particles. The fineness or coarseness of the soil.The three soil particles are:

• Sand (Large)• Silt (Medium)• Clay (Small)

Soil Texture – Particle Sizes

Soil Texture

Effects of Particle Size?Soil particle size affects two important

soil features:They are internal surface area The numbers and size of the pore

spaces

Soil Texture What is the internal surface area?

It is the total surface area of the particles in the soil.

So the smaller the soil particles, the greater the internal surface area will be.

Soil Texture

Pore size and number: This depends on the particle size.So there are more pores that are found

between the larger particles.

Soil Texture What is Sand?

It is the largest soil particle. It is further divided into four subcategories.

Very coarse sandCoarse sandMedium sandFine Sand

Soil Texture

All About Sand: It is the largest soil separate and is

composed mainly of weathered grains of quartz.

Sand is also gritty to the touch.Sand grains will not stick to each other.

Soil Texture

Why is Sand important to have in the soil?It will improve the soil by improving

the water infiltration and aeration.

Soil Texture

SiltThe medium sized soil separate.Silt particles are silky or powdery to the

touchSilt grains will not stick to one another

just like sand grains.Silt is the best soil as it has the ability to

hold large amounts of water in a form plants can use.

Soil Texture

Clay The smallest size soil separate. It is composed of tiny crystals. Clay is formed by chemical reactions between

weathered minerals to form tiny particles of new minerals.

Clay will hold more plant nutrients than any other separate.

Clay grains will stick to one another.

Soil Texture

There are 12 textural classes which can be seen in the next slide.

Soil Texture

Pass out picture of triangle and lets see if we can classify some soils.

Soil Texture

1.40% sand 22% clay and 38% siltWhat is the soil classified as?

Soil Texture

2.65% sand 10 % clay and 25 % silt

What is it?

Soil Texture

3.35% sand 50 % clay and 15% silt

What is it?

Soil Texture

4.10% sand 30% clay and 60% silt.

What is it?

How to Texture

Step 1Get and moisten samplePlace some soil in your palm and

moisten it.Once the soil is moist try to form a ball

(then proceed to step 2, if not proceed to step 5.)

How to Texture

Step 2 (The test for clay)A. If the soil…

• Really sticky• Hard to squeeze• Stains your hand• Forms a long ribbon (5cm +)• Call it clay and proceed to step 3 or go to

B

Soil Texture

Step 2 (The test for clay) ContinuedB. If the soil…

Is somewhat stickyIs somewhat hard to squeezeForms a medium ribbon (2-5 cm)Call it clay loam and go to step threeOr go to C

Soil Texture Step 2

C. If the soil…Is SoftIs SmoothIs easy to squeezeIs slightly stickyForms a short ribbon (Less than 2 cm)Call it a loam and go to step 3Or go to D

Soil Texture

Step 2D. If the soil forms a ribbon but no ball

go to step 4

Soil Texture Step 3

Take a new sample from your soil and wet it just a little.

If the soil: Feels very gritty, go to EFeels very smooth, with no gritty feeling,

go to FFeels only a little gritty, go to G

Soil Texture Step 3

E. Add the word sandy to the initial classification.

Soil texture is (check one): • sandy clay, • sandy clay loam, • sandy loam • At this point you have textured your soil.

Soil Texture Step 3

F. Add the word silt or silty to the initial classification

Soil texture is (check one): • silty clay, • silty clay loam, • silt loam • At this point you have textured your soil.

Soil Texture Step 3

G. Leave the original classification of (check one): clay, clay loam, loam At this point you have textured your

soil.

SOIL STRUCTURE The physical arrangement of the particles. How the particles clump and hold together.

Soil Structure Some words to describe soil structure are

blocky, wedge, prismatic, blocky, platy, granular, columnar.

Soil Structure

Soil Structure Structure can be

altered by tillage. Adding Organic

Matter usually improves soil structure.