2. 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.
3. 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
4. Objective 1: TERMS TO KNOW: (Cont’d)
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
5. Texture
physical property of soil considered rather
permanent
refers to the relative percentages of the
three types of soil particles
Sand
Silt
Clay
6. 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
7. Textural Triangle
used to obtain a soil
textural name for a
sample after it has
been mechanically
analyzed
8. 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
9. 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
10. 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
11. Two Types of Structureless Soils
Single grained soils like sand
Solid massive condition with no noticeable
peds
12. 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
13. 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
14. 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
15. 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
16. 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
17. 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
18. 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
19. Improving Soil Structure
Leaving it alone, in time it will repair itself
Planting a green manure crop
Incorporating plant residue into the soil
20. 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
21. 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.
22. 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.
23. 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.
24. 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
27. 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).
28. 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
29. Objective 3: TERMS TO KNOW: (cont’d)
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
30. Objective 3: TERMS TO KNOW: (cont’d)
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
