Download SOIL PROPERTIES

SOIL PROPERTIES
OBJECTIVES
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Describe soil by physical, chemical, and
biological properties of the soil.
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Distinguish among physical, chemical,
and biological properties of the soil.
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Distinguish between homogenous and
heterogeneous mixtures in soil.
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: (Cont’d)
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Topsoil - The upper part of the soil profile that is
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Subsoil - the area in the soil profile below the
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Subsoiling - A method of breaking up the compacted
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Tillage pan - areas of compacted soil in the plant
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Mottling - Spots of color in the soil that indicates
normally cultivated
topsoil which accumulates clay
layers of the soil that restrict air and water movement
and root growth using farm machinery
zone created by repeated plowing of heavy soils
especially when wet; also called a plow pan
internal drainage and aeration
root
Texture
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physical property of soil considered rather
permanent
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refers to the relative percentages of the
three types of soil particles
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Sand
Silt
Clay
Determining Soil Texture
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Sensing the feel
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It is the varying amount of each soil particle
type that gives soil its texture or feel.
Mechanical analysis
Textural Triangle

used to obtain a soil
textural name for a
sample after it has
been mechanically
analyzed
Light Soils vs Heavy Soils
Light Soils - sandy or coarse texture
 Heavy Soils - clay or fine texture
 Loamy Soils - medium textured
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more desirable characteristics usually
associated with highly productive soils that are
easier to manage
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
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
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Single grained soils like sand
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Solid massive condition with no noticeable
peds
Internal Soil Drainage
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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
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: (Cont’d)
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
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Light textured soil
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Loamy textured soil
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Oats
peanuts
beets
majority of Louisiana crops grow best in a loamy
textured soil.
Heavy textured soil
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Flooded rice
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requires a heavy fine textured soil to prevent loss of
surface water
Sugarcane
Determination of Soil Structure
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determined by the way the particles of
sand, silt, and clay are grouped together
in aggregates
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Peds - naturally formed groups of soil
particles
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Clods - are artificially formed groups of
soil particles
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
Destruction of Soil Structure
Soil structure can be destroyed by:
 working the soil when it is wet
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repeated movement of equipment or livestock
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repeated use of equipment at the same depth in
the soil
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continual flooding of the soil
Improving Soil Structure
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Leaving it alone, in time it will repair itself
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Planting a green manure crop
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Incorporating plant residue into the soil
Infiltration and Percolation Rates
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Rapid - spheroidal structure and single
grained structure less soils
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Moderate - blocky and prismatic
structure
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Slow - platy structure or massive
structure less soil
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.
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reduces the movement of air, water, and roots
and therefore limits crop yields.
Fragipans
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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.
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
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refers to the living organisms found in
the soil
includes both the micro and macro plants
and animals.
Plants
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Micro
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Bacteria
Fungi
Actinomycetes
Macro – roots of higher plants
Biological Properties of Soil
Animals
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Micro
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Nematodes
Protozoa
Macro
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Earthworms
Rodents (prairie dogs, moles, gophers, etc.)
Arthropods (mites, insects, spiders, etc.)
Gastropods (slugs, snails, etc.)
Biological Properties of Soil – Food Web
Chemical Properties of Soil
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The ability of soil to provide the essential
elements needed for plant growth
includes:
the availability of these elements
other chemical properties
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clay minerals present
humus content
cation exchange
soil reaction (pH).
Objective 3: TERMS TO KNOW:
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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
Objective 3: TERMS TO KNOW: (cont’d)
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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
Objective 3: TERMS TO KNOW: (cont’d)
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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
Homogenous Soil Mixtures
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Sand
Silt
Clay
Heterogeneous Soil Mixtures
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Any combination and proportion of
sand, silt, or clay