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Chapter 3

Chapter 3. Physical Properties of Soil. Soil Texture. What is Soil Texture? It is the proportion of three sizes of soil particles. Which are: Sand (Large) Silt (Medium) Clay (Small). Soil Texture. Effects of Particle Size? Soil particle size affects two important soil features:

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Chapter 3

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  1. Chapter 3 Physical Properties of Soil

  2. Soil Texture • What is Soil Texture? • It is the proportion of three sizes of soil particles. • Which are: • Sand (Large) • Silt (Medium) • Clay (Small)

  3. 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

  4. Soil Texture • What is the internal surface area ? • It is the area of soil that the total surface are of the particles in the soil. • So the smaller the soil particles the greater the internal surface area will be.

  5. Soil Texture • Pore size and number: • this depends on the particle size. • So there are more pores that are found between the larger particles. • See page 34 for example.

  6. Soil Texture • What is a Soil Separates? • They are categories that scientist have divided up into three groups • The three groups are: • Sand • Silt • Clay

  7. Soil Texture • What is Sand? • It is the largest and is further divided into four subcategories. • They are: • Very coarse sand • Coarse sand • Medium sand • Fine Sand

  8. Soil Texture • Sand • it is the larges 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.

  9. Soil Texture • Sand • What will sand do to the soil? • It will improve the soil by improving the water infiltration and aeration

  10. Soil Texture • Silt • is the medium sized soil separated. • Silt particles are silky or powdery to the touch • Silt 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.

  11. Soil Texture • Clay • is the smallest size soil separate. • It is composed of tiny crystals • Clay is formed by chemical reactions between weathered minerals to form tiny particle of new minerals. • Clay will hold more plant nutrients than any other separate. • Clay grains will stick to one another.

  12. Soil Texture • There are 12 textural classes which can be seen in the next slide.

  13. Soil Texture • Pass out picture of triangle and lets see if we can classify some soils.

  14. Soil Texture • 1. • 40% sand 22% clay and 38% silt • What is the soil classified as?

  15. Soil Texture • 2. • 90% sand 10 % clay and 25 % silt • What is it?

  16. Soil Texture • 3. • 30% sand 50 % clay and 15% silt • What is it?

  17. Soil Texture • 4. • 10 % sand 80% clay and 30% silt. • What is it?

  18. Soil Texture • Lets go and texture some of the kits that we have. • See if you can make a ribbon and with which one? • Which one feels grittiest? • Which one feel powdery?

  19. Soil Density and Permeability • What is Particle Density? • it is the density of solid particles only.

  20. Soil Density and Permeability • What is Bulk Density? • It is the mass of a volume of undisturbed oven dry soil • BD= Weight dry soil ___________= __G__ Volume dry soil cm3

  21. Soil Density and Permeability • Example BD: • The core is 500 cubic cm that weighs 650 grams • What is the answer?

  22. Soil Density and Permeability • Answer: • BD= 650g ______ = 1.3 g/cm3 500 cm3

  23. Soil Density and Permeability • Soil Porosity • Total pore space is measured of the soil volume that holds air and water. • SP=wet weight(g) – dry weight (g) _____________________ x100 soil volume (cm3)

  24. Soil Density and Permeability • Example: • The soil core before had a volume of 500 cubic centimeters and weighed 650 grams when dry. When wet the same core weighed 900 grams. • Calculate Porosity.

  25. Soil Density and Permeability • Answer: 900-650 _________x100 =50% 500

  26. Soil Density and Permeability • What is Permeability? • is the ease of which air, water, and roots move through the soil

  27. Soil Density and Permeability • What is Hydraulic Conductivity? • Is the measure of the rate of water movement through the soil

  28. Soil Structures • What is Soil Aggregates? • It is aggregates that occur naturally in the soil are called peds. While clumps of soil caused by tillage are called clods

  29. Types of Soil Structures • Before we discuss these turn to pg 43. • There are four types of soil structures. • They are: • Granular structure • Platy structure • Blocky structure • Prismatic structure

  30. Types of Soil Structures • What is Granular structure? • It is commonly found in A horizons • Peds are small usually between 1to 10 millimeters

  31. Types of Soil Structures • What is Platy Structures? • Usually found in E horizons • Peds are large but tin, platelike and arranged in overlapping horizontal layers.

  32. Types of Soil Structures • What is Blocky Structures? • This is the typical of my B horizons • Peds are large about 5 to 50 millimeters

  33. Types of Soil Structures • What is Prismatic structure? • found in Horizon B • Peds are large range from 10- 100 millimeters in size

  34. Soil Tilth • What is Soil Tilth? • is a general term for the physical conditions of a tilled soil.

  35. Soil Tilth • What is compaction? • It is the result when pressure is applied to the soil surface.

  36. Soil Tilth • Now you will read pages 45-50 and will take notes over these pages

  37. Soil Pans • What is a pan? • It is any layer of hardened soil. • There are four types of pans: • Clay pan • Fragipans • Plinthite • Caliche and duripans

  38. Soil Pans • Claypans: • Has a very high clay content in the subsoil layer. This layer is very dense

  39. Soil Pans • Fragipans: • results from clay accumulation • Clay will bind soil particles into hard brittle layer

  40. Soil Pans • Plinthite • Layers are cemented by a special type of clay common to the tropics • These soils are very poor for Agriculture uses.

  41. Soil Pans • Caliche and Duripans • Has chemicals cement soil particles together

  42. Soil Colors • Dark Brown to Black • dark colors result from organic matter or dark parent material.

  43. Soil Colors • White to Light Gray • color indicates that chemicals that color soil have leached out • May also be a result of a large amount of lime in one place for the white appearance.

  44. Soil Colors • Light brown, Yellow to Red: • These are the colors of oxidized iron minerals, chemically similar to rust • Red indicates good drainage

  45. Soil Colors • Bluish Gray • this is the color of less oxidized iron and indicates a lack of oxygen in the soil • So this is an indication of poor drainage

  46. Soil Colors • Mottled Colors: • Will show different colors often spots of rust, yellow, and gray.

  47. Soil Colors • Hue- • is the color such as red and yellow • Value- • Is the lightness or darkness of the hue 0-10 and 0 being the darkest and 10 the lightest • Chroma- is the purity of the dominant color and is also number

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