Introduction to Soils

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Introduction to Soils

• Chapter 4
• Soil Architecture and Physical Properties

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Physical Properties

• Physical Properties of the soil will deal with
  the particle aggregation as well as texture,
  colloidal properties, surface area, pore spaces,
  water in the soil and other physical properties.

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SOIL COLOR

• Color plays an important role in differentiating
  different conditions of the soil.

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Color Classification System

• Munsell color charts
• 1) Hue red to yellow color of the soil
• 2) Chroma brightness of the color 0 neutral
  gray
• 3) Value lightness or darkness of the soil 0
  being black

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Color can give a clue to

• OM content
• Water content
• Oxidation states of iron and possibly manganese
  oxides.

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Dark Soils

• Usually high in organic matter
• Rich soils if there is not too much water

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Light Soils

• Sandy
• High salts, gypsum or lime

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Light Brown to Red

• Aging soils iron oxidizing
• Drainage is fair

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Bluish - Gray

• They have poor drainage
• Indicates no 02 in soil and could smell rotten
  called - Gleying soils

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Mottled Colors

• Indicates a period of water logged and then
  drying out

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SOIL TEXTURE

• the amount of sand silt and clay in the soil
• The Soil Separates (USDA)
• Sand - .05 2 mm
• Silt .05 - .002 mm
• Clay less then .002mm

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• Soil Texture triangle allows the classification
  of the soil texture into 12 classes.

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Determining soil texture

• Ribbon test
• No ribbon sandy loam
• Shorter then 1 loam, silt, silt loam
• 1-2 Sandy clay loam, silty clay loam,
  clay loam
• 2-3 Sandy clay, silty clay clay

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Measuring the soil separates in a jar

• Can one change soil texture?

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Surface area considerations

• It is the surface area of the soil that has the
  ability to hold water and be a site for chemical
  activity. The greater the surface area the
  greater the chemical activity and possible
  nutrient holding ability.
•  

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Surface area of the soils and its affect

• Water holding capacity, fertility and total pore
  space.
• Sand
• Silt
• Clay

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Soil Porosity

• Total pore space of the soil
• Sand has less than clay
• Determining porosity
• Wet weight (grams) dry weight (grams)
• Soil volume (cm3)
  X 100

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Permeability

• How the water moves through the soil
• Sand is rapid and clay is slow
• Textural types and their characteristics ie
• Soil Porosity, Permeability
• a) Clayey
• b) Silty
• c) Sandy

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Soil Structure

• Soil Structure is how the soil separates
• combine to form larger aggregates

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Types of structure

• peds natural formation clods caused by tillage
• a. Granular- ideal agronomic structure
  accomplished through correct cultural practices
  in the A horizon Minimum tillage, done at the
  correct time incorporating organic matter and
  encouraging microbial action
• b. Platy- Usually in the lower depths of the A
  horizon or compacted soils
• c. Blocky- in the B horizon large aggregates that
  slows water penetration
• e. Single grain- Structure less the absence of
  soil structure.
• f. Massive- Structure less - concrete

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Structure Formation

• Soil adhesives released by fungi and organisms
• Good soil structure can be encourage through
  proper cultivation
• Organic matter
• Gypsum
• Culture practices done when soil is at proper
  water retention
• Avoid compaction
• 1) Equipment
• 2) Reduction of traffic through the field
• 3) Keep vegetation on the soil

a.    
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Soil Consistence

• Refers to soils ability to resist crushing and
  its ability to be molded.
• Such as for most soil Loose, Very Friable,
  Friable, Firm, Very Firm and extremely firm.

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Soil Tilth

• Physical condition of the soil after tillage
• usually the granular form
• Compaction is detrimental to good soil tilth-
• Compaction causes
• Reduced porosity and permeability
• Reduced gas exchange
• Slow percolation rate and slow drying rate.
• Restricted root growth

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Soil Particle Density

• As to the specific weight of the soil particles.
• This is a direct correlation to the parent
  material and should be between 2.6 to 2.75 g/cm3

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Bulk Density

• Is the weight over volume.
• This will determine the amount of pore space in
  the soil.
• Clay 1.15
• Silt 1.35
• Sand 1.8

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Soil Temperature

• Germination is dependant on proper soil
  temperature.
• Corn needs 65?-70?F
• Most warm season crops need warm soil
• Root growth is more abundant when soil
  temperatures
• Soil Characteristics that affect temperature
• Dark soils warm fast
• Rocky soils warm fast
• Sandy soils warm fast
• Grandular loose soils warm quicker then compacted
  soils

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Formation and Stabilization of Soil Aggregates
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Formation and Stabilization of Soil
Aggregates Both biological and physical
processes are responsible for soil aggregates

• Physical Chemical Processes
• Flocculation of Clays
• Clays will be the first to join together as they
  are attracted to each others negative and
  positive sides.
• Together with humic acid binds together the
  individual particles acting like glue to bind
  them together.

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• Biological Processes
• Soil organisms help bind particles together
• Earth worms
• Root exudates
• Fungal products ie glomalin
• Bacteria

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OM Is the principle method of soil aggregate
stabilization.