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

Decagon Devices, Inc.

17 Sept 201502:40

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

00:00

💧 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

Irrigation refers to the artificial application of water to land or soil to assist in the growth of crops, trees, and other plants. In the video, irrigation is used to demonstrate how water moves out from an irrigation source and its effects on the soil. The movement of water is critical for understanding how irrigation supports plant growth.

💡Water Movement

Water movement in the context of the video describes the process by which water travels through the soil. It is highlighted that this movement is not solely due to gravity but also the attraction to solid surfaces within the soil. This concept is essential for understanding how water is distributed in the soil and how it reaches plant roots.

💡Gravitation

Gravitation is the force of attraction by the earth that pulls objects towards its center. In the script, it is mentioned that as the soil becomes saturated, gravitation plays a stronger role in water movement. This illustrates the transition from capillary action to gravitational flow as soil moisture increases.

💡Soil Saturation

Soil saturation is a state where all the voids in the soil are filled with water. The video script uses this concept to explain the point at which gravitational forces take over water movement, emphasizing the change in water dynamics within the soil.

💡Coarse Sand

Coarse sand is a type of soil particle that has larger pore spaces between the grains. The script describes how coarse sand acts as a barrier to water movement due to the inability of these large pores to hold water at the same tensions as smaller soil pores. This is a key principle in understanding how different soil types affect water movement.

💡Unsaturated Flow

Unsaturated flow refers to the movement of water through soil when not all the pore spaces are filled with water. The video script explains this concept by showing how water moves through the soil before it becomes saturated, which is crucial for understanding water distribution in agricultural settings.

💡Adhesive and Cohesive Forces

Adhesive forces are the attraction between different types of molecules (like water and soil particles), while cohesive forces are the attraction between similar molecules (like water to water). The script uses these concepts to explain how water is held in the small pores of the soil, illustrating the physical properties that affect water movement.

💡Blotting Paper

Blotting paper is used as an analogy in the script to describe the way soil pores hold water. It is mentioned that the pores in the soil are like those in a blotting paper, which soaks up ink. This analogy helps to visualize how water is held and then released from the soil as it becomes wetter.

💡Check Valve

A check valve is a device that allows fluid to flow in one direction and prevents backflow. The script uses this term to describe the behavior of the sand layer in the soil, which holds water back until the soil above is very wet, then lets the excess pass through, similar to how a check valve operates.

💡Columbia Basin

The Columbia Basin is a region in Washington State mentioned in the script as having a significant amount of agricultural land. The soil composition of this area, with a layer of fine sandy loam over coarse sand and gravel, is used as an example to explain how the presence of coarse materials affects the soil's water retention capacity and, consequently, plant growth.

💡Water Retention

Water retention is the ability of soil to hold water against the force of gravity. The script explains that the presence of coarse sand and gravel in the soil allows it to retain more water than a fine sandy loam would, which is beneficial for plant growth. This concept is central to understanding soil's role in agriculture.

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.