Understanding Soil Texture and Structure

Soil Texture Soil Texture:  Fineness or coarseness of a soil What are the three soil particles? ◦ Sand ◦ Silt ◦ Clay

Soil Texture Why is soil texture important? ◦ It affects  Water-holding Capacity  Permeability  Soil Workability  Ability of plants to grow

Determine Soil Texture What would you do to determine the texture of a soil sample?

Determine the Texture Can 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 Texture What 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 videovideo

You need: ◦ Soil ◦ Water Now roll your sleeves up Put a small amount of your soil in your hand Moisten it Squeeze Does 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? Activity – The Ribbon Test

Soil Structure, Function, Importance What is Soil Structure? ◦ Arrangement of soil particles into aggregates. (clusters) ◦ Many different sizes and shapes Peds ◦ Naturally occurring aggregates Clods ◦ Aggregates formed by tilling

Two steps to forming 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: ◦ Improves tilth ◦ Improves permeability ◦ Resists beating action of raindrops  Minimizes formation of crusts Why is Soil Structure Important?

Identify Soil Structures Eight of them Granular ◦ Aggregates are small, non-porous, and strongly held together Crumb ◦ Aggregates are small, porous and weakly held together

Platy ◦ Aggregates are flat, plates overlap causing slow permeability Prismatic/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