Water Movement In Soils
Summary
TLDRThis educational video script explores the principles of water movement in soil, emphasizing unsaturated flow and the forces of adhesion and cohesion. It uses time-lapse photography to illustrate how water moves upward, downward, and horizontally in soil profiles, influenced by soil texture and structure. Demonstrations show how water interacts with different soil layers, such as sands and clays, and how these interactions affect plant growth and irrigation practices. The script also discusses the practical implications for agriculture, turf management, and soil construction, highlighting the importance of understanding water movement for effective soil management.
Takeaways
- 💧 Water movement in soil is influenced more by the attraction of solid surfaces and water molecules to each other than by gravity, especially in unsaturated conditions.
- 🌱 Capillary action, driven by adhesion and cohesion, allows water to move against gravity, which is crucial for water uptake in dry soils.
- 📏 The size and type of soil pores play a significant role in water movement, with larger pores in sandy soils allowing faster movement compared to smaller pores in clay soils.
- 🏗️ Soil layers with different textures, such as a layer of coarse sand or gravel, can act as a check valve, holding water until the overlying soil is very wet before allowing water to pass through.
- 🌿 The presence of coarse materials like sand and gravel in soil can increase its water retention capacity, which is beneficial for plant growth and irrigation practices.
- 🚧 Compacted or layered soils can restrict water movement and root penetration, impacting agricultural practices and the construction of soil profiles in areas like golf courses.
- 🌈 Time-lapse photography is used to visualize and accelerate the process of water movement in soil, allowing for the observation of patterns that would otherwise be too slow to see.
- 🌊 Water tables can rise above the land surface during wet seasons if layers like clay pans restrict the downward movement of water, affecting land use.
- 🌱 The uniformity of soil mixtures is important for proper water infiltration and storage, as recognized in specifications for golf course putting greens.
- 🌿 The principles of water movement in soil have practical applications in agriculture and land management, such as the construction of soil profiles and the use of vertical aeration channels to improve water infiltration.
Q & A
What are the primary forces responsible for water movement in dry soil?
-The primary forces responsible for water movement in dry soil are the adhesive forces between the solid mineral surfaces and water, and the cohesive forces between water molecules. These forces are responsible for capillarity, which allows water to move upward against the force of gravity.
How does the glass plate model in the demonstration represent a soil profile?
-The glass plate model represents a vertical cross-section of a soil profile. It is designed to show the movement of water in the soil by allowing visual observation as the soil is wetted. The model is made with glass plates a foot high and 2 ft wide with about 1/2 in of space between for soil.
What is the significance of the time-lapse photography used in the study?
-Time-lapse photography is used to speed up the observation of water movement in the soil. In nature, these movements would take many hours, but with time-lapse photography, these processes are sped up to a few minutes, allowing for easier study and understanding of water movement dynamics.
How does the presence of a sand layer in the soil affect water movement?
-A sand layer in the soil acts like a check valve, holding water back until the soil above becomes very wet. The large pores in the sand cannot hold water against the forces in the smaller pores of the finer soil above, so water does not readily move into the sand. However, when the soil above the sand becomes excessively wet, water eventually moves into the sand.
What is the role of cohesive forces in water movement in soil?
-Cohesive forces between water molecules are responsible for creating a membrane-like surface that pulls water upward beneath it. This force, along with adhesion, allows water to move against gravity and is crucial for capillary action in soil.
Why do water tables often rise above the land surface during wet seasons in soil with a clay pan?
-Water tables often rise above the land surface during wet seasons in soil with a clay pan because the clay layer restricts the downward movement of water. The fine pores in the clay layer are not capable of transmitting water quickly enough, leading to a buildup of water above the clay pan.
How does the presence of a layer of fine clay in soil affect plant rooting depth?
-A layer of fine clay in soil can restrict the rooting depth of plants. The extremely fine pores in the clay layer compared to the overlying soil make it difficult for water to penetrate, thus limiting the downward growth of plant roots.
What is the practical application of understanding water movement in soils for golf course construction?
-Understanding water movement in soils is crucial for golf course construction, especially for putting greens. It helps in designing soil profiles with layers that can retain water effectively and ensure proper water infiltration and drainage, which are essential for maintaining the health and playability of the greens.
How does the presence of organic material affect water infiltration in soil?
-The presence of organic material can improve water infiltration in soil by creating small aggregates that are stabilized and have large pores remaining open to the surface. This allows water to be taken up readily, thus maintaining a high infiltration rate.
What is the significance of the soluble dye used in the demonstration?
-The soluble dye is used to visualize the pattern of water movement behind the wetting front. It helps to demonstrate how water moves in the soil and how soluble materials, like fertilizers, can be transported with the water flow, which is important for understanding nutrient placement in agricultural and turf management.
Outlines
💧 Water Movement in Soil
This paragraph explains the principles governing water movement in soil, particularly in dry conditions. The movement is not solely influenced by gravity but also by the attraction of solid surfaces and the cohesive forces between water molecules. A time-lapse study is described, where soil is held between glass plates to visualize water movement. The study uses different soil types and simulates non-uniformities in soil profiles. Water is added to the soil surface, and the movement is captured through time-lapse photography, with speed factors ranging from 24 to 500 times normal. The paragraph also discusses the role of capillarity in water movement and how it's influenced by adhesion and cohesion.
🌱 Soil Water Interactions and Layered Soils
This section delves into how water interacts with different soil layers, such as sand and clay, and how these interactions affect plant growth and water retention. It describes an experiment where water moves into a sand layer, acting like a check valve, and how water tables are influenced by the presence of coarse materials. The paragraph also discusses the impact of clay layers on water penetration and root development, using examples from agricultural land and golf course construction. It highlights the importance of understanding soil profiles for effective water management in various settings.
🌿 Water Flow Through Aggregates and Soil Textures
This paragraph focuses on how water flows through different soil textures and aggregate layers. It explains that water movement is restricted by the size of the pores in the soil and how the presence of large pores in aggregates can slow down water transmission. The text describes experiments showing water movement in coarse sand and aggregate layers, emphasizing the importance of contact with free water for effective water flow. It also discusses the impact of soil moisture on water infiltration and the differences in water movement patterns in dry versus moist sand.
🌱 Soil Water Retention and Movement Patterns
This section discusses the patterns of water movement in soil and how they are influenced by soil texture and structure. It highlights the differences in water retention and infiltration rates between sandy and clayey soils, and how these properties affect agricultural practices and soil management. The paragraph also addresses the challenges of wetting mounds or hills of soil, the impact of soil compaction on water movement, and the benefits of rolling to improve soil structure. It provides practical applications of these principles in managing soil conditions for optimal water infiltration and plant growth.
💧 Principles of Water Flow in Soil
The final paragraph summarizes the principles of unsaturated water flow in soil, emphasizing the importance of the attraction between solid surfaces and water molecules. It discusses how water movement is influenced by the nature of the soil pores and changes in the porous system. The text also touches on the practical applications of these principles in agricultural land management, particularly in the context of golf course putting greens and turf grass maintenance. It concludes by reiterating the importance of understanding water flow dynamics for effective soil and water management.
Mindmap
Keywords
💡Capillarity
💡Adhesion
💡Cohesion
💡Unsaturated Flow
💡Wetting Front
💡Soil Profile
💡Infiltration
💡Gravitational Forces
💡Sand Layer
💡Clay Pan
💡Irrigation
Highlights
Water movement in soil is influenced by factors other than gravity, including capillary action and adhesion.
Time-lapse photography is used to visualize water movement in soil models, accelerating processes that would take hours in nature.
Adhesive and cohesive forces are key in moving water upward against gravity.
Water moves laterally as well as downward in soil, demonstrating the complexity of water flow.
The soil model represents a vertical cross-section of a soil profile, simulating real-world conditions.
Gravitational forces become more significant as soil saturation increases.
The soil's texture and structure, such as coarse sand layers, affect how water moves and is retained.
Clay layers can restrict water movement and root depth, impacting plant growth and water tables.
Soil with uniform textures transmits and retains water differently than stratified soils.
The presence of coarse materials like sand and gravel can increase a soil's water retention capacity.
Water movement in soil is crucial for plant growth and is influenced by soil preparation and management.
The principles of water movement in soil are applied in the construction of soil profiles in turfed areas.
The USGA's specifications for putting green construction recognize the importance of soil uniformity.
Water movement in soil is affected by the presence of organic materials and their impact on soil structure.
Vertical aeration channels can improve water infiltration in compacted or thatched areas of soil.
The position of water channels relative to the water table is critical for effective drainage in sports fields and golf courses.
The principles of water flow in soil have practical applications in agriculture and turf management, including irrigation strategies.
Observing water movement in soil can provide insights into the effectiveness of soil management practices.
Transcripts
when water moves into air dry soil it is
only slightly affected by gravitation
water moves upward and horizontally as
well as
downward the principles governing water
movement are graphically shown in this
time-lapse study in these demonstrations
soil is held between glass plates so
that you can see what happens as the
soil is wetted the glass plates are a
foot high high and 2 ft wide with about
1/2 in of space between for
soil think of this model as representing
a vertical cross-section of a soil
profile time-lapse photographic
processes used here permit speeding up
the action in nature it would require
many hours for the water movement which
you will observe in the film in only a
few
minutes using a motion picture camera
single pictures are Tak of the models at
Short Time intervals as the water moves
into the soil the time intervals are
from 1 second up to 22 seconds the
completed Motion Picture film is then
projected so that speed up times in
these sequences range from 24 times
normal to as much as 500 times normal
speed the speed Factor will be observed
on a card above the
model because water movement usually is
rapid when water is first applied
and is very slow at later times the
speed up Factor often is changed during
the sequence this is indicated by
changing the arrow on the time card
which points to the appropriate speed
Factor the soil used is an air dry silt
Loom which has been passed through a
fine screen Sands Clays and Aggregates
made from the soil are used to simulate
non uniformities in the soil profile
water will be added in a Furrow or on
the soil surface with a device which
keeps the water level at any desired
depth before you see the sequence using
time-lapse photography here are two
demonstrations that illustrate the
principle of capillarity this principle
is involved when water moves into dry
materials liquid is pulled upward from
free water in the dish into this por
ceramic Rod because of the attraction of
solid mineral surfaces for water called
adhesion and attraction of water
molecules for each other called cohesion
adhesive and cohesive forces then are
responsible for moving water upward
against the downward force of gravity
in the second demonstration water rises
between two closely spaced glass plates
because of the adhesive forces between
glass and water and the cohesive forces
between water molecules cohesive forces
near the airwater interface create a
membranelike surface and water is pulled
upward beneath this surface the pressure
beneath this negatively curved surface
is negative the opposite of the internal
pressure of a raindrop which has a
positive curvature and is positive water
in pores with a negative airwater
interface may be said to be under
tension now to the models and time-lapse
pictures it may be observed here that
water moves outward from an irrigation
Channel almost as rapidly as downward
this this is evidence that the forces
responsible for this type of water
movement are mainly due not to
gravitation but to the attraction of
solid surfaces for
water as the soil becomes wetter and
wetter however gravitation plays a
stronger role and if the soil becomes
completely saturated then gravitational
forces
predominate the horizontal layer you see
is course sand one of the important
principles of UN saturated flow of water
is Illustrated here as the wedding front
encounters the coarse sand the pores in
the soil are many times smaller than
those between sand grains water is held
in these small pores by large adhesive
and cohesive forces the pores in the
soil are like the pores in a piece of
blotting paper used to soak up ink the
huge pores in the sand cannot hold water
against the forces in the smaller pores
above hence the water does not move
readily into the sand
however as the soil above the sand
becomes very wet the water eventually
moves into the sand in the same way as
ink would drip from blotting paper which
was excessively wet the sand layer thus
acts something like a check valve
holding the water back until the soil
becomes very wet and then letting the
excess water pass
through what happens to water in soil
containing a sand layer is typical in
principle to what happens to water in
soil situations where Sands and gravels
occur as layers in fine soil material
much agricultural land as well as land
in Turf and other vegetation is layered
in this fashion in Washington State's
Columbia Basin there exists a quarter
million Acres of soil composed of 1 to 2
feet of fine Sandy LOM overlying coar
Sands and
gravels the ability of this soil to
support plant growth is greatly affected
by the presence of coar Sands and
gravels
because of these coarse materials the
overlying soil can retain more than
double the amount of water usually held
in a fine Sandy LOM this soil is one of
the best in the
Basin these principles are usefully
employed in the construction of soil
profiles in turfed areas such as plane
fields and particularly on golf courses
recognition of this principle is evident
in the specifications for putting green
construction adopted by the green
section of the United States Golf
Association now in this sequence you see
a layer of fine clay in an otherwise
uniform soil this clay layer is similar
to a clay pan or any type of layer in
which the pores are extremely fine
compared to the pores in the overlying
soil these layers often restrict rooting
depth of plants and are particularly
known for the trouble they cause in
preventing downward penetration of water
when excess water is added to the soil
water tables often are buil up over such
layers if they occur at shallow depths
water tables often rise above the land
surface during wet Seasons imposing
serious limitations on the use of the
land despite the fact that a clay pan
hinders downward movement of water it
does absorb water readily as the soil
above is wetted observe the wetting
front as it moves into the clay Pan the
pores in the clay are much finer than
than those in the overlining soil so
that they can pull water from the soil
water tables are not built up over clay
pans because of inability of water to
enter them instead water tables result
from slow transmission of water through
them the resistance to water movement in
the extremely fine pores of layers like
these is sufficiently great that even
over periods of weeks and months little
water is transmitted through them into
the soil below where a soil profile may
be artificially created as in Golf
Course putting greens uniformity of soil
mixtures is an important consideration
as is recognized in USGA putting green
specifications the extent to which
downward movement is restricted and
water storage is altered depends on the
finess of the pores and the thickness of
the restricting layer this is in
contrast to what was shown earlier in
soil overlying coar sand layers there
downward movement of water was
temporarily checked but water tables
could not be filled up as long as the
opportunity existed for free drainage
into the course material
this model has the sand layer on the
left and the layer of course Aggregates
on the right these Aggregates are about
the same size as the sand grains but are
made up of soil particles like those of
surrounding soil the large pores between
Aggregates are about the size of the
large pores between sand grains water
movement in so materials which wet
readily depends upon procity each
individual aggregate contains numerous
fine pores of a size similar to the
pores in the surrounding soil
note that the small Aggregates in the
aggregate layer will wet up as soon as
the wetting front reaches them however
pores between Aggregates are too large
to pull water from the soil pores in the
finer soil hence the large pores remain
empty all of the water passing through
the layer must first move through the
fine pores of the Aggregates and then
across the contact points between
Aggregates the small number of contacts
between Aggregates therefore restricts
the rate at which water can move through
the aggregate
layer if free water is supplied directly
to a layer of coarse sand water rushes
in rapidly filling all of the pores
these are conditions of saturated flow
the moving force is due to positive
pressure from the water in the channel
under saturated conditions large pores
can transmit water readily but the rate
of transmission depends upon the
hydrostatic pressure of the water supply
the positive pressure is dissipated
rapidly over a very short distance in
the fine pores giving way to absorptive
forces in the drier soil thus water
moves out into the soil from a sand
layer under unsaturated conditions it is
pulled into and through the soil because
of the attraction for water of the
mineral surfaces making up the fine
pores of the soil the sand in the layer
at the left is the same kind of sand
through which water is Flowing at the
right here however the layer is not in
contact with free water or water under
positive pressure hence the surrounding
soil is wetted under unsaturated
conditions where the water is present
only under negative pressure
the sand layer cannot wet until the
water pressure in the films of the
adjoining soil becomes nearly positive
which means that the soil becomes very
wet as this happens the layer takes
water porous materials with very large
pores Aid in movement only under
conditions where they contact free water
that is water under zero or positive
pressure where water exists only under
negative pressure such material stops or
materially retards water flow for
a question frequently is raised what
differences in flow might be expected if
underlying Sands were moist rather than
air
dry here you're looking at dry soil
overlying dry sand on the left and moist
sand on the right since water movement
has so far been detected by observing
color change a different technique is
needed to help you see water entering
sand which already is moist a chemical
substance has been added to a white sand
which when contacted by added water
containing another chemical will turn
pink the water content of the sand on
the right is about the quantity which
would be present in a sand just barely
wet enough to support plant growth the
presence of some water in the sand
should make a difference in the tension
when added water enters the
sand it may be seen here that water
enters the dry sand at nearly the same
time as it enters the
moist there is a difference in the rate
and pattern of water penetration into
the sand in the two cases but in both
the water retained above the sand is
about the
same a fingering pattern develops in the
moist sand because it already is wet and
a few of the smaller channels can
readily transmit a little water thus
reducing the buildup of water above and
flow in ad joining larger channels under
many conditions in nature including
situations where irrigation is practiced
Sands and gravels lying below finer soil
materials are naturally
moist it is important to illustrate
differences among uniform soils with
respect to their ability to transmit and
retain water apart from problems of
stratification note that the depth of
penetration at any given time is
greatest for the Sandy LOM which has the
largest pores and at least for the clay
LOM which has the finest pores the finer
the pores the more the rate of water
flow is
restricted but after the water source is
removed the forces causing continued
water movement are greatest in the clay
LOM which has the finest pores and least
in the Sandy LOM with the larger pores
despite this however the net useful
storage is greatest in the clay LOM and
least in the Sandy
Loom although a Sandy LOM retains less
useful water than does the clay LOM it
is nevertheless a good soil in an
irrigated area where lack of water
holding capacity can be compensated by
irrigation the infiltration properties
are generally good Clay loms on the
other hand often are difficult to
irrigate because of low infiltration
rates in dry climates with no irrigation
a Sandy LOM would not hold enough water
to carry most plants through the growing
season a clay loone by contrast would
retain more water over a long period of
time the principles Illustrated here
have important application to situations
where control of soil materials and
profiles is possible as in a golf course
putting green such as that specified by
the
USGA Sandy soils are favored because
they resist compaction and their use is
permitted because frequent irrigation is
practical also the presence of coar sand
and gravel layers in deeper soil
increases is the water storage capacity
of such a
soil in the demonstration so far your
attention has been mostly focused on the
movement of the wedding front now with
the aid of a soluble dieye the pattern
of water movement back of the wedding
front appears any water soluble material
which is not strongly absorbed by the
clay particle will have the net movement
you see here
the die traces are not streamlines the
reason for this is that geometry of the
absorptive force field responsible for
water movement is changing the die
traces include the effect of any change
in direction of water flow due to the
development of a non-uniform
field such a non-uniform field is
produced as the two wedding fronts
join in the beginning the Dy moves
radially away from the Water Source this
continues as long as the movement of the
wedding front remains radial and uniform
soluble fertilizer material such as
nitrates moving with the water will
Trace out patterns like these the die
traces show the importance of proper
fertilizer placement with respect to the
position of the wedding stream in an
irrigation
fural now consider what will happen to
the the dice spots midway between the
two furrows when the two wedding fronts
come together note particularly the
middle dice spot at the same level as
the water in the furrows when the
wedding fronts join there is a radical
change in the pattern of water movement
water continues to move upward into the
dry Hill above and downward into dry
soil below that D Spot in the middle
shows little movement because water flow
Above This level is upward and below it
is downward and after the soil in the
hill is entirely wetted only evaporation
will cause further upward flow such
upward flow is of much practical
importance for example soluble
fertilizers and salts in the upward
moving stream will tend to accumulate in
the surface out of wrench of plant roots
such phenomena have been observed in
numerous placement
studies a further illustration of how
water moves in soil may be seen in this
cross-section through an 18in Mound or
Hill simulated an irrigation fur in
agriculture are numerous planting
situations as with soil preparation for
Turf loose soil thrown up into a mound
like this can be difficult to wet
because of the presence of excessively
large por spaces excessive elevation
differences Complicated by increasing
procity from the bottom of a mound to
the top can lead to poor wedding at the
upper level in potato culture loose soil
in Hills has been observed to to remain
dry during an entire growing season with
important reductions in yield quantity
and
quality compacting the mound with a
roller at planting time as you see it on
the left can help in two ways first the
elevation is greatly reduced second the
reduced prosity will help to increase
the rate of upward water movement
applied to soil conditions on a much
smaller scale the advantages of rolling
are firming a newly planted seed bed or
for that matter ly settling of an entire
surface of a new putting green are
evident
a practical application of principles of
water flow is shown here water moves
rapidly into soil with good tilt
propertiy practices on the soil in the
center have produced numerous small
Aggregates which have been stabilized by
decomposing organic material the
resulting large pores which remain open
all the way to the surface take water
readily thus the infiltration rate
remains High the same amount of organic
material when turned under in a layer
does little to improve soil tilt and if
anything makes conditions worse the
straw layer like a sand layer checks
downward flow of water in this case not
only does less rainfall penetrate into
the root Zone but more water remains on
the surface making it vulnerable to
damage from foot and vehicle traffic and
the impact of falling
rain on the right an irregular Channel
filled with coarse sand simulates an
open Channel left by mechanical aeration
or perhaps a channel left by decayed
roots or burrowing insects or worms such
channels or cracks do not assist in
water movement when they are not open to
a source of free water they aid water
flow only when they connect with free
water at the surface the principle
involved also applies to tile drains
water can move into such drains only if
positive water pressure exists in the
surrounding soil hence tile placed in
wet soil for drainage must be located
below the water table if they are to be
effective on athletic fields or on Golf
Course putting greens where a soil
profile is artificially created with a
gravel layer and tile lines for drainage
tiles must be located below the gravel
layer
water moves rapidly into the soil
through a vertical ation Channel filled
with sand or coarse organic materials
but this is true only if the channel
extends all of the way to the surface
use of such vertical aration channels
has particular application on Golf
Course putting greens or tea surfaces it
is of great benefit on compacted or
thatched areas where infiltration rates
at the surface are extremely limited a
vertical channel is cut into the soil
with an aerifier a top dressing sand of
a desirable particle size is then worked
into the open ation holes until they are
filled to the surface this makes rapid
infiltration possible permitting water
to quickly reachen and move into the
underlying dry soil thus reducing
surface
runoff since the water in the
surrounding soil is under negative
pressure none has entered the channel on
the right this important point to
remember here is that the channel or air
fire hole must remain in contact with
free water or water under positive
pressure to do any good and if the top
of the channel is covered over or
becomes plugged for instance by the
application of a fine silt top dressing
material water flow into the channel is
restricted even though the soil might be
saturated
these demonstrations amplify the
principles of water flow under
unsaturated conditions conditions under
which crops are grown on agricultural
land and particularly where grass is
grown and managed especially on golf
courses each demonstration has its
counterpart in
nature except possibly this last
one in nature the demonstrations may be
less dramatic but the principles hold
and can be seen in operation if one
observes carefully in summary then
unsaturated flow of water in soil and
other porest materials takes place
because of the attraction of solid
surfaces for water and of water
molecules for each other how the water
moves depends upon the nature of the
pores and changes in the porous system
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