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Unit C.

Unit C. Basic Principles of Agricultural/Horticultural Science. Problem Area 1. Using Basic Soil Science Principles. Understanding Soil Texture and Structure. Lesson 4. Interest Approach. Provide students with various samples of soil. One sample should be nearly all sand

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Unit C.

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  1. Unit C. Basic Principles of Agricultural/Horticultural Science

  2. Problem Area 1 Using Basic Soil Science Principles

  3. Understanding Soil Texture and Structure Lesson 4

  4. Interest Approach • Provide students with various samples of soil. • One sample should be nearly all sand • One nearly all clay • One nearly all silt. • Ask students to determine how the samples differ. • Would each sample be equally productive? • Indicate that the samples vary according to the size of soil particles. • Ask students how particle size might affect various soil properties.

  5. Learning Objectives • Describe the concept of soil texture and its importance. • Determine the texture of a soil sample. • Describe soil structure, its formation, and importance. • Identify various soil structures.

  6. Clods Loam Peds Permeability Soil structure Soil texture Soil workability Textural triangle Water-holding capacity Important Terms

  7. What is soil texture and why is it important? • Soil texture is the fineness or coarseness of a soil. • It describes the proportion of three sizes of soil particles. These are: • Sand - large particle • Silt - medium sized particle • Clay - small particle

  8. Texture is important because it affects: • Water-holding capacity the ability of a soil to retain water for use by plants • Permeability the ease with which air and water may pass through the soil.

  9. Texture is important because it affects: • Soil workability the ease with which soil may be tilled and the timing of working the soil after a rain • Ability of plants to grow some root crops like carrots and onions will have difficulty growing in a fine-textured soil

  10. How is the texture of soil determined? • Soil texture may be determined in one of two ways: • The percentages of sand, silt, and clay may be tested in the lab. • Once tested, you may determine the textural class of the soil by referring to the textural triangle. • The ribbon method.

  11. Silt Silt loam Silty clay loam Loam Sandy clay loam Loamy sand Sand Sandy loam Sandy clay Clay loam Silty clay Clay Textural Triangle – 12 basic textural classes

  12. The Ribbon Method. • Fine-textured a ribbon forms easily and remains long and flexible. • Moderately fine-textured a ribbon forms but breaks into pieces ¾ to 1 inch long. • Medium-textured no ribbon forms. • The sample breaks into pieces less than ¾ inch long. The soil feels smooth and talc-like.

  13. The Ribbon Method. • Moderately coarse-textured no ribbon forms. • The sample feels gritty and lacks smoothness. • Coarse-textured no ribbon forms. • The sample is composed almost entirely of gritty material and leaves little or no stain.

  14. What is soil structure, how does it form, and why is it important? • Soil structure is the arrangement of the soil particles into clusters or aggregates of various sizes and shapes. • Aggregates that occur naturally in the soil are referred to as peds, while clumps of soil caused by tillage are called clods.

  15. What is soil structure, how does it form, and why is it important • Structure is formed in two steps. • 1. A clump of soil particles sticks loosely together. These are created through: • Plant roots surrounding the soil and separating clumps • Freezing and thawing of soil • Soil becomes wet and then dries • The soil is tilled • Fungal activity

  16. What is soil structure, how does it form, and why is it important • 2. Weak aggregates are cemented to make them distinct and strong. • Clay, iron oxides, and organic matter may act as cements. • When soil microorganisms break down plant residues, they produce gums that also glue peds together.

  17. What is soil structure, how does it form, and why is it important • Soil structure is important for several reasons: • It improves soil tilth. • It improves permeability. • It resists the beating action of raindrops, minimizing the formation of crusts that reduce crop stands.

  18. What are the various soil structures and what do they look like? • There are eight primary types of structure. They are: • Granular • Crumb • Platy • Prismatic or Columnar • Blocky • Structureless • 1. Single grain • 2. Massive

  19. Review / Summary • Describe the concept of soil texture and its importance. • Determine the texture of a soil sample. • Describe soil structure, its formation, and importance. • Identify various soil structures.

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