soil texture & structure
Post on 23-Feb-2016
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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.
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