Understanding Soil Texture and Structure. Objectives: Describe the concept of soil texture and its...
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Transcript of Understanding Soil Texture and Structure. Objectives: Describe the concept of soil texture and its...
Understanding Soil Texture and Structure
Understanding Soil Texture and Structure
Objectives:• Describe the concept of soil texture and its
importance;• Determine the texture of a soil sample;• Describe soil structure, its formation, and
importance; and • Identify various soil structures.
Soil TextureSoil Texture:
Fineness or coarseness of a soil
What are the three soil particles?◦Sand ◦Silt ◦Clay
Soil TextureWhy is soil texture important?
◦It affects Water-holding Capacity Permeability Soil Workability Ability of plants to grow
Determine Soil TextureWhat would you do to determine
the texture of a soil sample?◦You can feel it
Determine the TextureCan be tested in a lab
◦The lab results will be in the form of percentages of the three soil particles.
So let’s say we had:◦40% sand◦10% clay◦50 % silt
How would this sample feel?
Determine the Texture
What do you do with those percentages?◦40% sand◦10% clay◦50 % silt
Use the Textural Triangle to determine the textural class
Sand: 20%Silt: 30%Clay: 50%
Sand: 40%Silt: 45%Clay: 15%
Sand: 17%Silt: 44%Clay: 39%
Determine the TextureWhat if you can’t send it to a lab?What would you do?
The Ribbon Test◦You can find 5 texture classes in the
field with this method Fine-textured Moderately fine-textured Medium textured Moderately coarse-textured Coarse textured
Activity – The Ribbon Test
Watch the video
Activity – The Ribbon Test
You need:◦ Soil◦ Water
Now roll your sleeves up
Put a small amount of your soil in your hand
Moisten itSqueezeDoes it stay together?
• Roll it into a ball• Will it stay in a ball?
• Form a ribbon• Will it?
• How long before it breaks?
• What soil texture do you have?
Soil Structure, Function, ImportanceWhat is Soil Structure?
◦Arrangement of soil particles into aggregates. (clusters)
◦Many different sizes and shapesPeds
◦Naturally occurring aggregatesClods
◦Aggregates formed by tilling
Two ways to form soil structure◦Clumps of soil particles stick together
Plant roots surround soil and break up clumps Freezing and thawing of soil Soil gets wet and then dries out Soil is tilled Fungal activity
◦Weak aggregates are cemented together making them distinct and strong. Clay, iron oxides, and organic matter act as
cement Also gums produced by microorganisms
Soil Structure, Function, Importance
Soil structure:◦Affects tilth◦Affects permeability◦Determines whether it resists
beating action of raindrops or not Minimizes formation of crusts
Why is Soil Structure Important?
Identify Soil StructuresEight of them
Granular◦Aggregates are small, non-porous,
and strongly held togetherCrumb
◦Aggregates are small, porous and weakly held together
Platy◦Aggregates are flat, plates overlap
causing slow permeabilityPrismatic/Columnar
◦Aggregates are prism-like with the vertical axis greater than the horizontal;
◦Prismatic – flat caps◦Columnar – rounded caps
Identify Soil Structures
Blocky◦Aggregates are block-like, with six or
more sides; all three dimensions are about the same
Structureless◦No apparent structure – 2 forms◦Single grain
Soil particles are individual and do not form aggregates
◦Massive Soil particles cling together in large uniform
masses
Identify Soil Structures
Soil Structure affect on water