Physical Properties of Soil

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Chapter 3

• Physical Properties of Soil

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Soil Texture

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

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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

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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.

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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.

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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

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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

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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.

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Soil Texture

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

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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.

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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.

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Soil Texture

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

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Soil Texture

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

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Soil Texture

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

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Soil Texture

• 2.
• 90 sand 10 clay and 25 silt
• What is it?

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Soil Texture

• 3.
• 30 sand 50 clay and 15 silt
• What is it?

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Soil Texture

• 4.
• 10 sand 80 clay and 30 silt.
• What is it?

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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?

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Soil Density and Permeability

• What is Particle Density?
• it is the density of solid particles only.

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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

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Soil Density and Permeability

• Example BD
• The core is 500 cubic cm that weighs 650 grams
• What is the answer?

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Soil Density and Permeability

• Answer
• BD 650g
• ______ 1.3 g/cm3
• 500 cm3

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Soil Density and Permeability

• Soil Porosity
• Total pore space is measured of the soil volume
  that holds air and water.
• SPwet weight(g) dry weight (g)
• _____________________ x100
• soil volume (cm3)

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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.

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Soil Density and Permeability

• Answer
• 900-650
• _________x100 50
• 500

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Soil Density and Permeability

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

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Soil Density and Permeability

• What is Hydraulic Conductivity?
• Is the measure of the rate of water movement
  through the soil

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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

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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

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Types of Soil Structures

• What is Granular structure?
• It is commonly found in A horizons
• Peds are small usually between 1to 10
  millimeters

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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.

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Types of Soil Structures

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

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Types of Soil Structures

• What is Prismatic structure?
• found in Horizon B
• Peds are large range from 10- 100 millimeters in
  size

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Soil Tilth

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

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Soil Tilth

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

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Soil Tilth

• Now you will read pages 45-50 and will take notes
  over these pages

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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

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Soil Pans

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

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Soil Pans

• Fragipans
• results from clay accumulation
• Clay will bind soil particles into hard brittle
  layer

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Soil Pans

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

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Soil Pans

• Caliche and Duripans
• Has chemicals cement soil particles together

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Soil Colors

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

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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.

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Soil Colors

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

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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

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Soil Colors

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

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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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