SOIL PROPERTIES

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SOIL PROPERTIES
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OBJECTIVES

• Describe soil by physical, chemical, and
  biological properties of the soil.
• Distinguish among physical, chemical, and
  biological properties of the soil.
• Distinguish between homogenous and heterogeneous
  mixtures in soil.

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Objective 1 TERMS TO KNOW

• Clay- The smallest soil particle
• Sand - The largest soil particle
• Silt - An intermediate sized soil particle
• Structure - The way individual soil particles
  are grouped together
• Texture - A physical property of the soil
  referring to the relative percentages of sand,
  silt, and clay

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Objective 1 TERMS TO KNOW (Contd)

• Topsoil - The upper part of the soil profile that
  is normally cultivated
• Subsoil - the area in the soil profile below the
  topsoil which accumulates clay
• Subsoiling - A method of breaking up the
  compacted layers of the soil that restrict air
  and water movement and root growth using farm
  machinery
• Tillage pan - areas of compacted soil in the
  plant root zone created by repeated plowing of
  heavy soils especially when wet also called a
  plow pan
• Mottling - Spots of color in the soil that
  indicates internal drainage and aeration

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Texture

• physical property of soil considered rather
  permanent
• refers to the relative percentages of the three
  types of soil particles
• Sand
• Silt
• Clay

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Determining Soil Texture

• Sensing the feel
• It is the varying amount of each soil particle
  type that gives soil its texture or feel.
• Mechanical analysis

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Textural Triangle

• used to obtain a soil textural name for a sample
  after it has been mechanically analyzed

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Light Soils vs Heavy Soils

• Light Soils - sandy or coarse texture
• Heavy Soils - clay or fine texture
• Loamy Soils - medium textured
• more desirable characteristics usually associated
  with highly productive soils that are easier to
  manage

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Light Soils vs Heavy Soils

• When comparing light soils to heavy soils, the
  light soil will
• require less energy to cultivate
• heat and cool faster
• usually lighter in color
• wet and dry faster
• usually subject to greater erosion
• usually lower in fertility

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Four Main Types of Soil Structure

• Platy - thin horizontal sheets overlapping each
  other
• Prismatic - long vertical columns without
  rounded tops
• Block-like - irregular shaped cubes
• Spheroidal - rounded and often referred to as
  granular or crumb usually found in the topsoil

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Two Types of Structureless Soils

• Single grained soils like sand
• Solid massive condition with no noticeable peds

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Internal Soil Drainage

• important for proper plant growth
• Permeability can be determined by the color of
  the subsoil.
• Grey with some red or yellow streaks - poorly
  drained soils
• Yellowish-brown or reddish brown with some grey
  mottling - as internal drainage improves
• Uniform bright color with few or no grey streaks
  or mottling good internal drainage and aeration

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Objective 2 TERMS TO KNOW

• Infiltration - The movement of water into the
  soil
• Percolation - The movement of water through the
  soil
• No-till planting - The planting of a crop into
  the previous crop stubble or a cover crop,
  disturbing only the immediate seed zone

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Objective 2 TERMS TO KNOW (Contd)

• Reduced-tillage - The elimination of one or more
  operational procedures from a conventional
  system of working the soil
• Permeability - the characteristics of a soil
  which permits variations in the speed of air and
  water movement

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Soil Types Influence Crop Selection

• Light textured soil
• Oats
• peanuts
• beets
• Loamy textured soil
• majority of Louisiana crops grow best in a loamy
  textured soil.
• Heavy textured soil
• Flooded rice
• requires a heavy fine textured soil to prevent
  loss of surface water
• Sugarcane

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Determination of Soil Structure

• determined by the way the particles of sand,
  silt, and clay are grouped together in aggregates
• Peds - naturally formed groups of soil particles
• Clods - are artificially formed groups of soil
  particles

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Structured Soil

• more desirable because it
• is easier to cultivate
• allows more water intake
• does not restrict root growth
• encourages better drainage within pore spaces
• allows entry of oxygen into the pore spaces after
  the water has drained
• facilitates organic matter decomposition and the
  release of plant nutrients

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Destruction of Soil Structure

• Soil structure can be destroyed by
• working the soil when it is wet
• repeated movement of equipment or livestock
• repeated use of equipment at the same depth in
  the soil
• continual flooding of the soil

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Improving Soil Structure

• Leaving it alone, in time it will repair itself
• Planting a green manure crop
• Incorporating plant residue into the soil

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Infiltration and Percolation Rates

• Rapid - spheroidal structure and single grained
  structure less soils
• Moderate - blocky and prismatic structure
• Slow - platy structure or massive structure less
  soil

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Tillage Pans and Traffic Pans

• Tillage pans - areas of compacted soil in the
  plant root zone caused by repeated plowing at the
  same depth.
• Tillage and traffic pans are serious problems in
  many parts of the country because the area of
  root restriction is generally in the topsoil.
• reduces the movement of air, water, and roots
  and therefore limits crop yields.

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Fragipans

• Fragipans (silt pans) and clay pans can occur
  naturally in or near the subsoil. A fragipan is
  the result of too much silt in or near the B
  horizon, and is not the result of mans actions.

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Alleviating Traffic or Tillage Pans

• Subsoiling breaks up or shatters compacted layers
  using deep plowing equipment.
• Reduced or minimum tillage means less movement
  over the soil which results in less compaction of
  the soil. Deep Subsoiling should precede reduced
  or minimum till operations.
• No till reduces the formation of traffic pans
  because planting is done directly in the stubble
  of the previous crop.

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Biological Properties of Soil

• refers to the living organisms found in the soil
  
• includes both the micro and macro plants and
  animals.
• Plants
• Micro
• Bacteria
• Fungi
• Actinomycetes
• Macro roots of higher plants

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Biological Properties of Soil

• Animals
• Micro
• Nematodes
• Protozoa
• Macro
• Earthworms
• Rodents (prairie dogs, moles, gophers, etc.)
• Arthropods (mites, insects, spiders, etc.)
• Gastropods (slugs, snails, etc.)

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Biological Properties of Soil Food Web
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Chemical Properties of Soil

• The ability of soil to provide the essential
  elements needed for plant growth includes
• the availability of these elements
• other chemical properties
• clay minerals present
• humus content
• cation exchange
• soil reaction (pH).

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Objective 3 TERMS TO KNOW

• Homogenous mixtures soil mixtures that contain
  the same type of soil particles
• Heterogeneous mixtures soil mixtures that
  contain different types of soil particles
• Aerobic occurring only in the presence of free
  oxygen
• Algae soil plant microorganisms capable of
  photosynthesis
• Anaerobic growing or occurring in the absence
  of free oxygen

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Objective 3 TERMS TO KNOW (contd)

• Bacteria single-celled soil plant
  microorganisms, some of which are responsible for
  organic matter decomposition, while others are
  responsible for nitrogen fixation
• Fungi soil plant microorganisms responsible for
  organic matter decomposition, especially the
  cellulose, lignin and gum
• Microorganisms life forms too small to be seen
  with the unaided eye or barely visible
• Nematodes - soil animal microorganisms that are
  responsible for the decomposition of organic
  mater, consumption of other animal microorganisms
  and parasitism on the roots of certain higher
  plants

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Objective 3 TERMS TO KNOW (contd)

• Nitrogen cycle the biochemical changes
  undergone by this atmospheric gas from its use
  by living organisms to decomposition and
  conversion back to the atmosphere
• Organic matter soil materials including plant
  and animal residues at various stages of
  decomposition
• Rodents small gnawing animals such as rats and
  mice
• Acid soil one having a pH below 7.0 on a scale
  from 0 to 14
• Alkaline soil one having a pH below 7.0 on a
  scale from 0 to 14
• Ion charged atoms or groups of charged atoms
• pH a numerical measure of the degree of acidity
  or alkalinity of the soil solution

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Homogenous Soil Mixtures

• Sand
• Silt
• Clay

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Heterogeneous Soil Mixtures

• Any combination and proportion of sand, silt, or
  clay