Download ORH 1009 Soil, Water, Plant Relationships

SOS 1102 Soils and Fertilizers
Definition of a Soil
• A collection of naturally occurring, dynamic,
three dimensional bodies on the earth’s
surface.
• Consist of the upper physical, chemical, and
biological portion of the earth’s crust.
• It contains living matter and is capable of, or
has been capable of supporting plant growth.
For purposes of growing plants
Mixture of organic and
inorganic solids, air, and water
all interacting with each other
and the plant.
Man is dependant on soils for
• Habitat for crops
• construction
• sewage disposal
• recreation
Early civilization built on good
agricultural soils.
History of the study of soils
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1000 BC Homer
400 BC Xenophon
1590
Sir Hugh Platt
1600 Sir Francis Bacon
1652 Von Helmont
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1699
1727
1731
1804
1840
1850
1886
1912
Woodward
Stephen Hale
Jethro Tull
N. T.deSaussure
Von Liebig
Way & Lawes
Dokuchaiev
Coffey
Soil studies can be divided into
two disciplines
Edaphology
Pedology
Parent material
• Unconsolidated and
partially weathered
mineral and/or
organic matter from
which the upper part
of the soil is
developed by various
weathering
processes.
Three Basic Types of Rocks
• Igneous - formed when molten
lava/magma cools
• Sedimentary - formed from mineral
and/or organic fragments which are
deposited and recemented
• Metamorphic - igneous or sedimentary
rock which has been changed by heat
and pressure
Igneous rock in the making
Lava flow movie
Rock cycle
Plate tectonics
Three Classifications of Parent
Material
• Residual - rock weathered in place
• Cumulose - organic matter deposited in
place due to saturated conditions
• Transported - parent material which
have been moved before being
weathered and forming a soil
Catagories of Transported Parent
material
• Moved
• Moved
• Moved
• Moved
by
by
by
by
water
wind
ice
gravity
Parent material moved by water
Three categories moved by water
• Alluvial
• Lacustrine
• Marine
Alluvial
• Sediments deposited by flowing
water
–flood plains
–terraces
Lacustrine
• Materials deposited at the
bottom of fresh water lakes
Marine deposits
• Sediments deposited by rivers into
oceans
Parent material moved by wind
Too much of a good thing!
Parent material moved by ice
Four Types
• Terminal moraine
• Lateral moraine
• Ground moraine
• Outwash plain
Parent material moved by gravity
Colluvial materials
Weathering of parent material
• Physical
• Chemical
Physical Weathering
• Heating and
cooling
• Freezing and
thawing
• Wetting and
drying
• grinding action
Chemical weathering
• Reactions which
cause changes in
structure
hydration
hydrolysis
oxidation
carbonation
reduction
• Reactions which
cause changes in
solubility
Factors affecting soil formation
• Type of parent material
– effectiveness of weathering
processes
– nature of the plant material
• Climate
– Precipitation
– temperature
• Topography
•Biosphere - type and amount
of organic matter
•Time - younger soils tend to
be less fertile
Soil Morphology
Study of the nature and
shape of the soil profile
What is a soil profile???
• An exposed vertical
cut through the soil
body exposing the
soil horizons.
• What’s a horizon? A
zone in the soil
parallel to the
surface.
Erosion
exposed this
profile
• Erosion from a
major storm
exposed this
profile at Talbot
Island State Park
Notice the layer of black humus
Soil horizons are differentiated
by
• Color
• Soil chemistry
• texture
• consistence
• organic matter
content
• structure
Six master horizons
• O, A, E, B, C, & R
• Not every soil exhibits all horizons
• Buried ancient soils my be found
deeper in soil
• Roman numerals and subscripts
give additional information about a
horizon
O horizon
A horizon
• organic material at the
surface
• greater than 20% organic
matter
• most common in
undisturbed forested areas
or wet areas
• Oi OM identifiable
• Oa more highly
decomposed
• Is or was at or near the
surface
• mineral layer with an
accumulation of
organic matter
• loss of clay and some
nutrients
• higher in sand and silt
• develop relatively fast
E horizon
• zone of maximum loss
(eluviation)
• light color
("bleached")
• low clay, organic
matter, and nutrients
• higher in sand and silt
• take a very long time
to develop
B horizon
• zone of maximum
accumulation (illuviation)
• accumulations of clay,
iron oxides, humus
(organic matter), and/or
carbonates
• shows moderate to strong
structure development
• take a long time to
develop
C horizon
R horizon
• parent material
• loose (can dig with a
shovel)
• weak or no structure
• weatherd from
bedrock, or
transported and
deposited
• Bedrock
• Hard & solidified
Soil Taxonomy
Order12
Sub order 47
Great group
230
Sub group 1,200
Family
6,000
Series 13,000
Phase
Soil taxonomy
Order - based on major set of soil forming
processes
Sub order - temperature, vegetation, wetness
Great Group - based on soil horizons and their
arrangement
Sub group - variation around central theme
Family - based on properties important to plant
growth
Series - group of individuals uniform in
differentiating
characteristics
Phase - surface texture, stoniness, drainage,
salinity
Examples of complete
classification of several soils
Twelve Soil Orders
• Entisols
• Vertisols
• Inceptisols
• Aridisols
• Mollisols
• Andisols
• Spodosols
• Alfisols
• Ultisols
• Oxysols
• Histosols
• Gelisols
Alfisol
Have a noticeable
clay horizon, gray
to brown surface
horizon, forest
soils of north
central U.S. and
Canada
Andisols
• formed in volcanic
ash/volcanic material,
typically dominated by
hydrous oxides of
aluminum, fix large
amounts of phosphorus,
mountains of the Pacific
Northwest, portions of
Alaska and Hawaii.
Aridisols
Develop in dry
climates, low in
organic matter, B
horizon just
developing. One of
the largest soil
orders in the U.S.
Entisols
Mineral soils
with lack of
significant
profile
development,
found in a
wide range of
climates
Gelisols
contain permafrost
close to surface,
generally poorly
suited for agriculture,
difficult to build on,
polar regions, high
mountains, and
Alaska.
Histosols
Organic soils, 25%
to greater than
90% organic
matter, form
anywhere
saturated
conditions exist
Inceptisols
Young soils in
which the
profile has
developed
quickly,
Appalachia
Mollisols
Dark colored
agricultural soils of
the mid west,
granular structure,
high fertility, high
percent base
saturation
Oxysols
Most highly
weathered soil
order, have
surface horizon
dominated by
hydrous oxides of
iron and
aluminum, near
equator
Spodosols
Have a spodic
horizon, (I.e. a
subsurface
horizon
dominated by
clay) NE U.S.,
Canada, Fl. GA.
Ultisol
Moist soils that
develop in warm
climates, have a
noticeable red or
yellow clay
horizon, S.E. U.S.
Vertisols
High content of
swelling clay,
Mississippi,
Louisiana,
Texas
FL. Entisols, Ultisols, Spodosols
• Tend to be low in:
nitrogen, sulfur,
magnesium
• Low organic
matter
• Low CEC
• Mostly sandy
• Low pH
• Low organic
matter
• some Ultisols may
be deficient in
phosphorus
Florida
Histisols & calcareous Entisols
• Histisols tend to
• Calcareous
be very highly
Entisols occur in
organic, 90
coastal south
percent or
Florida areas. Low
greater. Very
CEC, high pH, 7.2
fertile however
to 8.0
are poorly drained
Land Capability Classes
• Roman
Numerals
• I - IV
suitable for
agriculture
• Roman Numerals
• V - VIII
not suitable for
agriculture but
may have
valuable functions
Poor soil conservation practices
• In the 30’s drought combined with poor soil
conservation practices to create the “dust
bowl” in Oklahoma and several other mid
western states. The social upheaval
associated with this place and time is
chronicled in John Steinbeck’s classic novel
“The Grapes of Wrath”.
Dust Bowl Movie
Importance of “topsoil”
• The dramatic increases in yield associated
with thickness of topsoil (ie. Relative
amount of erosion) is illustrated by this data
from a 3 year study done in Missouri.
The rest of the story
• Notice that yield is also associated with pH.
The lower 1/3 of the field had been
previously limed.
Not Harvested
Land capability classes
Class I-
few limitations, row crops every year
0 to 2% slope
Class II -
row crops every 2 years, terraces for slope
2 to 6% slope
Class III -
severe limitations, row crops every 3 years
6 to 10% slope
Class IV year
very severe limitations row crops forth
10 to 15% slope
Land capability classes
Class V -
not suitable for agriculture because of
special conditions (i.e.. Rocky, wet, climate)
Class VI -
severe erosion, light grazing or forestry
15 to 25% slope
Class VII -
mountainous regions, forestry, recreation
25% + slope
Class VIII - mountain peaks, coastal marshes, may be
useful for ecological areas, recreation, etc.
Land Capability Class
Subscripts
Roman Numerial
E
W
Example:
S
IIIE
C
Soil Survey
• Consist of a set of base
maps and a bulletin
• Classify the soils in an
area
• Locate the different soil
series on a base map
• Describe the nature of
the various soils as they
occur in the field
Edaphology
Soils are a 3 phase system
Ideal Soil
50% solid space & 50% pore space
Nitrogen
oxygen
carbon dioxide
Sand, silt, &
clay
1/2 available
1/2 unavailable
25 % air
25 % water
45% mineral solids
5% organic solids
Solid phase - physical properties
• Soil texture - the relative proportions of
various particle sizes in the soil
• Soil structure - the degree and nature
of how the soil particles are bound
together
Effects of soil texture
• CEC
• water holding
capacity
• infiltration and
percolation of water
• pattern of water
movement
• gas exchange
between soil and air
Soil Textural Separates
Whole soil
Sand
2.00 - 0.05mm
Silt
0.05 to 0.002 mm
Clay
less than 0.002 mm
Sand
• Low CEC
• low fertility
• Low water
holding capacity
• low plasticity and
stickiness
• Rapid infiltration
and percolation
• rapid gas
exchange
• resist compaction
• higher bulk
density
Silt
• CEC somewhat
higher than sand
• moderate plasticity
and stickiness
• infiltration and
percolation
somewhat slower
than sand
• Bulk density
intermediate
between sand
and clay
• could be best
described as
“micro” sand
Clay
• High CEC
• High fertility
• very plastic and
sticky
• high water
holding capacity
• Very slow infiltration
and percolation rate
• bulk density lower
than sand and silt
• “heavy” to cultivate
• narrow range of
moisture for
cultivation
Relative differences in textural
separates
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•
•
•
•
•
•
Very coarse sand
coarse sand
medium sand
fine sand
very fine sand
silt
clay
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8 foot beach ball
4 foot beach ball
medicine ball
basketball
softball
poker chip
flake of oatmeal
Soil textural triangle
• Soil textural class is determined by physical
analysis to determine percent composition
of sand, silt, and clay then using this
information in conjunction with the textural
triangle.
Loams
• A loam is a soil whose properties are
not dominated by a single textural
separate
• It is not an equal mixture of sand, silt,
and clay
• Relatively small quantities of clay tend
to a disproportionate affect on a soil’s
properties
Determining texture by feel
Sand
Silt
Clay
Clay forming a ribbon
Soil structure
Unstructured - single grained
soil
Structured- soil containing
aggregates
Soil structure
Importance of desirable aggregates
• Improved infiltration
and percolation
• less runoff
• less erosion
• improved drainage
• better gas exchange
Improving soil structure
• Add organic matter
• proper pH and liming practices
• avoid cultivating in wet conditions
• avoid traffic on wet soils
• manage sodium problems
Describing soil pore space
• Macropores (non-capillary) - large soil
pores which will not hold water against
the force of gravity
• Micropores (capillary) - small pores
which hold water against the force of
gravity
Calculating soil pore space
• Particle density - the weight of the
solid divided by the volume of the solid
measured in grams per cubic centimeter
(2.65 g/cm)
• Bulk density - weight of the soil divided
by the volume of the soil
Calculating soil pore space
continued
• Particle density = pd (2.65 standard
value)
• Bulk density = bd (measured in lab)
• % solid space = bd/pd X 100
• % pore space = 100 - % solid space
Properties of water
• Hydrogen bonding
Properties of water
• cohesion - the attraction of water for itself
• adhesion - the attraction of water for
charged surfaces
• surface tension - cohesive forces at work at
the waters surface
• capillarity - rise of water in small pore spaces
due to adhesion and
cohesion
Forms of soil water
• Gravitational water - water which drains
freely due to the force of gravity
• capillary water - water held in smaller soil
pores against the force of gravity
• available water - capillary water available for
plant uptake ( -1/3 atm to -15 atm)
• hygroscopic water - water held in a thin film
around the soil particle
Soil moisture constants
• Field capacity (FC) - maximum amount
of water the soil can hold against the
force of gravity, -1/3 atm tension
• permanent wilting point (PWP) - plant
can no longer obtain water from the
soil, - 15 atm
• Soil saturation - gravitational water
present above -1/3 bars
The range of soil moisture
Determining soil moisture
• Tension tables are used to develop soil
moisture release curves
Generalized soil moisture release
curve
Generalized soil moisture release
curve
Soil moisture & plant growth
Methods of measuring soil
moisture
• gravimetric
Resistance method/Gypsum
blocks
Suction method
(tensiometers)
Time Domain Reflectometry
TDR
• A signal is sent down a metal probe, the
time it takes for the signal to return to a
sensor allows calculation of soil moisture.
• Gives volumetric rather than mass readings
• Is a good relative indicator of soil moisture
throughout the entire spectrum from FC to
the PWP
• Recent innovations have made it affordable
Mineralogy and structure of the
solid phase
Sand and silt
Sand and silt
• Composed mainly of primary minerals
(i.e..
Minerals formed at high temperatures)
• typical particle is inherited unchanged from of
igneous and metamorphic rock
• most abundant mineral in this fraction is
quartz followed by feldspars
• shape of sands may be an important
consideration
Sand shapes
Sand
particle
shapes
Sand color
Clay
• Composed mainly of secondary minerals (i.e..
Minerals formed at low temperatures)
• typically particle is either inherited unchanged
from sedimentary rock or formed over time in
low temperature reactions
• most abundant are the clay minerals, but also
includes various oxides, carbonates, and
sulfates
Carbonates and sulfates
• Calcite is the most abundant
carbonate
• gypsum is the most abundant
sulfate generally more common in
arid or semi arid regions
Oxides
• Typically formed in larger quantities in
soils depleted of silicone by leaching
• usually abundant in highly weathered
soils
• consist of hydrous oxides of Fe, Al, Mn
• structure ranges from crystalline to
amorphous
Clay minerals
• Most abundant component of the
clay fraction
• are tiny layer silicates
• have a tremendous impact on soil
properties
Building blocks of clay minerals
Silicone tetrahedron
Alumina octahedron
Layering of clays
• Although the line drawings make it appear
there is a lot of empty space in the crystal
lattice of clays, in reality the atoms are very
tightly packed.
Examples under scanning
electron microscope
Finely divided mica
kaolinite
dickite
montmorillonite
Why do clays have such high
CEC’s?
• Amount of surface area
• charge obtained through
isomorphic substitution
Clay minerals are differentiated
by
• Number and sequence of silica and
alumina layers
• layer charge
• interlayer bond or cation
• cation in the alumina layer
Comparison of common clay minerals
Example of expanding clay
Other clay particles
• Amorphous clays - “young” clay particles
which have not had sufficient time to form
crystalline structure
• sesquioxide clays - highly weathered clays
-hydrous oxides of iron and aluminum
-low plasticity and stickiness
-may be amorphous or crystalline