What affects water movement in unsaturated soil?

Water movement in unsaturated soil is mainly affected by the attraction of solid surfaces and not gravitation.

What happens when the soil becomes saturated?

When soil becomes saturated, gravitational forces predominate.

Why doesn't water move readily into coarse sand?

Water doesn't move readily into coarse sand because the pores are larger than those in the soil above, which hold water due to greater adhesive and cohesive forces.

How do sand layers act in water movement through soil?

Sand layers act like a check valve, holding back water until the soil becomes very wet, then allowing excess water to pass through.

What is the water holding capacity of soil with coarse sand and gravel layers compared to fine sandy loam?

Soil with coarse sand and gravel layers can retain more than double the amount of water usually held in a fine sandy loam.

Ch 2. of Water Movement in Soils, Capillary Barriers and Water Movement

00:02:40

https://www.youtube.com/watch?v=eBJEP_wQSa8

Summary

TLDRWater movement in soil during irrigation is influenced primarily by the attraction of solid surfaces rather than gravity, especially in unsaturated conditions. As soil becomes saturated, gravity takes a more dominant role. The video demonstrates how water moves horizontally and vertically, highlighting that finer soil pores hold water more effectively than coarser sandy layers due to adhesive and cohesive forces. Such sand layers act like a check valve, eventually allowing water passage as the soil wets up. An example is provided from the Columbia Basin, where fine sandy loam over coarse sand and gravel demonstrates increased water retention, supporting better plant growth.

Takeaways

💧 Water moves due to solid surface attraction.
🏞️ Gravity dominates in saturated soils.
🪨 Sand acts as a water check valve.
🌾 Fine sandy loam retains more water.
📈 Coarse layers improve soil water holding capacity.

Timeline

00:00:00 - 00:02:40
The movement of water from an irrigation source is influenced more by the attraction to solid surfaces than by gravity, though gravity becomes more significant as the soil gets wetter. Water moves less readily into coarse sand layers due to larger pores, acting as a check valve. This principle explains water flow in filled soils, crucial for agricultural land, such as in Washington State's Columbia Basin, where fine sandy loam retains more water due to underlying coarse sand, enhancing plant growth.

Mind Map

Video Q&A

What affects water movement in unsaturated soil?
Water movement in unsaturated soil is mainly affected by the attraction of solid surfaces and not gravitation.
What happens when the soil becomes saturated?
When soil becomes saturated, gravitational forces predominate.
Why doesn't water move readily into coarse sand?
Water doesn't move readily into coarse sand because the pores are larger than those in the soil above, which hold water due to greater adhesive and cohesive forces.
How do sand layers act in water movement through soil?
Sand layers act like a check valve, holding back water until the soil becomes very wet, then allowing excess water to pass through.
What is the water holding capacity of soil with coarse sand and gravel layers compared to fine sandy loam?
Soil with coarse sand and gravel layers can retain more than double the amount of water usually held in a fine sandy loam.

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Subtitles

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00:00:12
watch as the water moves out from an
00:00:15
irrigation pearl
00:00:16
note that the movement awkward is almost
00:00:18
as great as that downward this is added
00:00:21
evident water movement is mainly due not
00:00:24
to gravitation but to the attraction of
00:00:27
solid surfaces as the soil becomes
00:00:30
wetter and wetter however gravitation
00:00:32
plays a stronger role and if the soil
00:00:35
becomes completely saturated then
00:00:38
gravitational forces predominate the
00:00:41
horizontal layer you see is coarse sand
00:00:44
one of the important principles of
00:00:46
unsaturated flow is described as you
00:00:49
witness what happens as the wedding
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front encounters this layer of coarse
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sand the pores in the soil are many
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times smaller than those between sand
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grains water is held in these small
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pores by large adhesive and cohesive
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forces the pores in the soil are like
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the pores in a piece of blotting paper
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used to soak up ink the huge pores in
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the sand cannot hold water at the
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tensions which exist in the wetted soil
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above so water does not move readily
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into the sand
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however as the soil above the sand
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becomes very wet the water eventually
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moves into the sand just as ink would
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drip from a blotter which is swept
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excessively the sand layers us to act
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something like a check valve holding the
00:01:35
water back until the soil becomes very
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wet and then letting the excess pass
00:01:40
through what happens to water in soil
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containing a sand layer is typical in
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principle of what happens to water in
00:01:49
filled soils for sands and gravels occur
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as layers in finer soil material a great
00:01:55
deal of agricultural land is
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in this fashion in Washington State's
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Columbia Basin there exists a quarter of
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a million acres of soil composed of one
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to two feet of a fine sandy loam
00:02:06
overlying coarse sand and gravel the
00:02:10
ability of this soil to support plant
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growth is greatly affected by the
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presence of course fans and gravel
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because of these course materials the
00:02:19
overlying soil can retain more than
00:02:21
double the amount of water usually held
00:02:24
in a fine sandy loam this is one of the
00:02:27
best soils in the Columbia Basin