Understanding Soil Texture and Structure

1. Understanding Soil Texture and Structure

2. 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.

3. Soil Texture • Soil Texture: • Fineness or coarseness of a soil • What are the three soil particles? • Sand • Silt • Clay

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

5. Determine Soil Texture • What would you do to determine the texture of a soil sample? • You can feel it

6. 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?

7. 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

8. Sand: 20% Silt: 30% Clay: 50% Sand: 40% Silt: 45% Clay: 15% Sand: 17% Silt: 44% Clay: 39%

9. 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

10. Activity – The Ribbon Test Watch the video

11. Activity – The Ribbon Test • 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?

12. 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

13. Soil Structure, Function, Importance • Two waysto 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

14. Why is Soil Structure Important? • Soil structure: • Affects tilth • Affects permeability • Determines whether it resists beating action of raindrops or not • Minimizes formation of crusts

15. 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

16. Identify Soil Structures • 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

17. 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

18. Soil Structure affect on water