Ch 2. of Water Movement in Soils, Capillary Barriers and Water Movement
Summary
TLDRThis video script delves into the dynamics of water movement in soil, emphasizing that it's not just gravity but also the soil's solid surfaces that influence water flow. It illustrates how coarse sand layers act as a check valve, retaining water until the overlying soil is saturated, then allowing excess to pass. This principle is pivotal in understanding water retention in soils with mixed textures, such as those in Washington State's Columbia Basin, where the presence of coarse sand and gravel enables the soil to hold more water, making it highly conducive to plant growth.
Takeaways
- 💧 Water movement from an irrigation source is not solely due to gravity but also the attraction to solid surfaces like soil.
- 🌊 As soil becomes wetter, gravity's role in water movement increases, and when saturated, gravitational forces predominate.
- 🏖️ A horizontal layer of coarse sand acts as a barrier to water movement due to the size difference in soil and sand pores.
- 💧 The small pores in soil act like blotting paper, holding water through adhesive and cohesive forces.
- 🚫 Coarse sand's large pores cannot hold water at the same tensions as the smaller pores in the wetter soil above it.
- 💧 Water eventually moves into the sand layer when the soil above becomes very wet, similar to how a blotter would release excess ink.
- 🚰 The sand layer acts like a check valve, holding water back until the soil is very wet before allowing excess to pass.
- 🌱 The presence of coarse sand and gravel in soil can significantly affect the soil's ability to support plant growth.
- 📈 Soils with a layer of coarse sand and gravel can retain more water than those without, doubling the water retention capacity.
- 📍 In Washington State's Columbia Basin, the presence of coarse sand and gravel in the soil composition is beneficial for agriculture.
Q & A
What is the primary force driving water movement from an irrigation pearl?
-The primary force driving water movement from an irrigation pearl is the attraction of solid surfaces, rather than gravitation.
How does the role of gravitation change as the soil becomes wetter?
-As the soil becomes wetter, gravitation plays a stronger role in water movement, eventually predominating when the soil is completely saturated.
Why is the horizontal layer of coarse sand significant in the water movement process?
-The horizontal layer of coarse sand is significant because it acts like a check valve, holding water back until the overlying soil becomes very wet, then allowing excess water to pass through.
What is the comparison between the size of soil pores and sand grains in terms of water retention?
-The pores in the soil are many times smaller than the spaces between sand grains, which is why water is held in the soil by adhesive and cohesive forces rather than readily moving into the sand.
How does the presence of coarse sand and gravel affect the water retention capacity of the soil?
-The presence of coarse sand and gravel allows the overlying soil to retain more than double the amount of water usually held in a fine sandy loam.
What is the principle behind the water movement in soils with a sand layer?
-The principle behind water movement in soils with a sand layer is that the sand acts as a barrier, preventing water from moving into it until the soil above reaches a certain level of wetness.
What is the agricultural significance of soil composition in Washington State's Columbia Basin?
-The soil composition in Washington State's Columbia Basin, which includes a layer of coarse sand and gravel beneath a fine sandy loam, is one of the best for supporting plant growth due to its enhanced water retention capacity.
How does the soil's ability to support plant growth relate to the presence of coarse materials like sand and gravel?
-The presence of coarse materials like sand and gravel in the soil enhances its ability to support plant growth by increasing the soil's water retention capacity, which is crucial for plant health.
Why is the soil in Washington State's Columbia Basin considered one of the best for agriculture?
-The soil in Washington State's Columbia Basin is considered one of the best for agriculture because of the presence of coarse sand and gravel layers that allow the overlying soil to retain more water, thus supporting better plant growth.
What is the role of adhesive and cohesive forces in water movement within the soil?
-Adhesive and cohesive forces hold water within the small pores of the soil, preventing it from moving into larger pores in the sand until the soil is sufficiently wet.
How does the script describe the behavior of water in soil compared to a blotting paper?
-The script compares the pores in the soil to the pores in a blotting paper, explaining that water is held in the small soil pores by adhesive and cohesive forces, similar to how a blotting paper soaks up ink.
Outlines
💧 Water Movement and Soil Interaction
This paragraph explains the complex dynamics of water movement in soil, particularly highlighting the role of soil composition in influencing this process. It begins by observing how water spreads from an irrigation source, noting that the lateral movement is as significant as the downward movement. The text emphasizes that initial water movement is primarily due to the attraction to solid surfaces rather than gravity. However, as the soil becomes saturated, gravity takes over. The example of coarse sand is used to illustrate how soil pores, much smaller than sand grains, hold water through adhesive and cohesive forces, acting like blotting paper. The sand layer's inability to hold water at lower tensions creates a check valve effect, allowing water to pass through only when the soil above is excessively wet. This principle is crucial for understanding water behavior in layered soils, which is common in agricultural lands like those in Washington State's Columbia Basin, where a layer of coarse sand and gravel beneath a fine sandy loam allows the soil to retain more water, making it highly fertile.
Mindmap
Keywords
💡Irrigation
💡Water Movement
💡Gravitation
💡Soil Saturation
💡Coarse Sand
💡Unsaturated Flow
💡Adhesive and Cohesive Forces
💡Blotting Paper
💡Check Valve
💡Columbia Basin
💡Water Retention
Highlights
Water movement in irrigation is not primarily due to gravity but is influenced by the attraction of solid surfaces.
As soil becomes saturated, gravity plays a more significant role in water movement.
The horizontal layer of coarse sand demonstrates an important principle of unsaturated flow.
Small soil pores hold water through adhesive and cohesive forces, unlike the larger pores in sand.
Soil pores function similarly to blotting paper, absorbing water until they reach capacity.
Coarse sand acts as a check valve, holding water back until the soil above is very wet.
The presence of sand and gravel in soil can significantly affect the soil's ability to support plant growth.
Soils with coarse sand and gravel layers can retain more than double the water of a fine sandy loam.
The Columbia Basin in Washington State has a quarter of a million acres of soil with a unique composition of fine sandy loam over coarse sand and gravel.
The soil composition in the Columbia Basin is one of the best for supporting plant growth due to the presence of coarse materials.
The attraction of solid surfaces plays a crucial role in the initial stages of water movement in unsaturated soil.
The transition from unsaturated to saturated flow is marked by a shift in the dominance of gravitational forces.
The behavior of water in soil with a sand layer is analogous to water movement in filled soils with varying material compositions.
The presence of coarse sand and gravel in agricultural land can enhance the soil's water retention capacity.
The soil's ability to retain water is a critical factor in its agricultural productivity.
The soil composition in the Columbia Basin is an example of how soil structure can impact water retention and plant growth.
The principles observed in this study are applicable to understanding water movement in various soil types and conditions.
Transcripts
watch as the water moves out from an
irrigation pearl
note that the movement awkward is almost
as great as that downward this is added
evident water movement is mainly due not
to gravitation but to the attraction of
solid surfaces 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 coarse sand
one of the important principles of
unsaturated flow is described as you
witness what happens as the wedding
front encounters this layer of 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 at the
tensions which exist in the wetted soil
above so 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 just as ink would
drip from a blotter which is swept
excessively the sand layers us to act
something like a check valve holding the
water back until the soil becomes very
wet and then letting the excess pass
through what happens to water in soil
containing a sand layer is typical in
principle of what happens to water in
filled soils for sands and gravels occur
as layers in finer soil material a great
deal of agricultural land is
in this fashion in Washington State's
Columbia Basin there exists a quarter of
a million acres of soil composed of one
to two feet of a fine sandy loam
overlying coarse sand and gravel the
ability of this soil to support plant
growth is greatly affected by the
presence of course fans and gravel
because of these course materials the
overlying soil can retain more than
double the amount of water usually held
in a fine sandy loam this is one of the
best soils in the Columbia Basin
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