Water Movement In Soils

Summary

The video, created by WSU Irrigation, provides an in-depth exploration of water movement within soil, emphasizing how water navigates through air-dry soils, often affected more by surface attraction than gravity. Using a series of time-lapse experiments, it demonstrates these principles by showing how water moves horizontally, vertically, and radially through various soil compositions such as silt loam and coarse sands. The experiments highlight concepts like capillarity, adhesive and cohesive forces, and differentiate between unsaturated and saturated flow in soils. Practical applications of these findings are discussed, particularly in the context of agricultural practices and landscape management, such as the construction of golf course greens and the impact of soil layering on water retention and plant growth.

Highlights

• Water can move upward, not just downward, defying gravity thanks to surface attraction forces! 🌊
• Sand layers act like check valves, controlling water until soils get really wet. ☂️
• Capillary action allows water to rise between glass plates due to cohesive forces! 🧪
• The speed of water movement in soil varies, changing natural perceptions of water flow. 🎥
• Soil layers affect root depth, drainage, and water tables, with big implications! 📏

Key Takeaways

• Water doesn't just move downward; it moves upward and sideways too! 🌊
• Gravity isn't always the main player; adhesive forces are crucial in unsaturated soils! 🧲
• Changing soil layers, like sand and clay, affect how water moves and is stored. 🏞️
• Good soil structure makes a big difference in irrigation efficiency! 💦
• Understanding soil water dynamics helps boost agriculture and turf management! 🌾

Overview

Water movement in soil behaves unexpectedly, often with horizontal and upward flows overcoming gravitational pull due to adhesive forces. This can be observed in time-lapse experiments that visually showcase these unique soil-water interactions. Understanding the dynamics of these movements is crucial for efficient water management in soils.

The video illustrates how different layers like sands and clays interact, showing a complex relationship between water, soil, and the earth’s forces. By simulating various soil profiles, including those used in agriculture and turf management, the experiments reveal how soil composition impacts water retention and plant health.

These demonstrations have practical applications, particularly in agriculture and landscaping, such as optimizing irrigation strategies, designing golf course greens, and enhancing soil management practices. By understanding and applying these soil hydrodynamics principles, better soil and water resource management can be achieved.

Chapters

• 00:00 - 02:00: Introduction to Water Movement In the chapter titled 'Introduction to Water Movement,' the transcript describes how water behaves when it comes into contact with dry soil. It explains that water is not significantly influenced by gravity alone and can move in various directions—upward, horizontally, as well as downward. The chapter further illustrates these principles through a time-lapse study using demonstrations where soil is positioned between glass plates to observe the wetting process. These glass plates in the demonstrations are detailed to be one foot high and two feet wide.
• 02:00 - 04:00: Principles of Capillarity The chapter 'Principles of Capillarity' focuses on understanding the behavior of water movement through soil. It examines this process by representing a vertical cross-section of a soil profile. The study uses time-lapse photographic processes to accelerate the observation of water movement, which naturally would take several hours, into a few minutes. Through the use of motion picture cameras, single pictures of the models are taken to visualize this phenomenon.
• 04:00 - 07:00: Water Movement in Different Soil Layers The chapter discusses the movement of water through different soil layers. It highlights the rapid movement of water shortly after application, with time intervals observed from 1 to 22 seconds. The chapter describes a motion picture film used to project these sequences, speeding them up by 24 to 500 times the normal speed to illustrate the process effectively. Observations are aided by a speed factor displayed on a card above the model.
• 07:00 - 10:00: Impact of Sand and Gravel Layers The chapter, titled 'Impact of Sand and Gravel Layers,' explores the varying speed of processes in different layers over time, particularly focusing on soil. Initially, processes are fast but slow down later, which is reflected in changes to the speed factor indicated by an arrow on a time card. The soils discussed are comprised of air dry silt loam, screened finely to allow sands, clays, and aggregates to simulate non-uniformities within the soil profile.
• 10:00 - 15:00: Comparison of Soil Types The chapter 'Comparison of Soil Types' discusses the method of adding water to soil either through a furrow or directly on the surface using a device to control water depth. It also explains the principle of capillarity, which describes how water moves into dry soil, using time-lapse photography demonstrations.
• 15:00 - 20:00: Demonstrations of Water Flow The chapter 'Demonstrations of Water Flow' explains how water moves upward against gravity through a porous ceramic rod due to adhesive and cohesive forces. Adhesion, the attraction between water and solid mineral surfaces, and cohesion, the attraction between water molecules, propel the water upward from a dish, counteracting gravitational pull.
• 20:00 - 25:00: Practical Applications and Summary The second demonstration illustrates water climbing between two closely spaced glass plates. This phenomenon occurs due to adhesive forces between the glass and water, and cohesive forces between the water molecules. Near the air-water interface, cohesive forces create a membranelike surface, resulting in water being pulled upward automatically beneath this surface, affecting the pressure.

Water Movement In Soils Transcription

• 00:00 - 00:30 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
• 00:30 - 01:00 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
• 01:00 - 01:30 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
• 01:30 - 02:00 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
• 02:00 - 02:30 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
• 02:30 - 03:00 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
• 03:00 - 03:30 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
• 03:30 - 04:00 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
• 04:00 - 04:30 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
• 04:30 - 05:00 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
• 05:00 - 05:30 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
• 05:30 - 06:00 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
• 06:00 - 06:30 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
• 06:30 - 07:00 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
• 07:00 - 07:30 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
• 07:30 - 08:00 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
• 08:00 - 08:30 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
• 08:30 - 09:00 could not be filled up as long as the opportunity existed for free drainage into the course material
• 09:00 - 09:30 this model has the sand layer on the
• 09:30 - 10:00 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
• 10:00 - 10:30 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
• 10:30 - 11:00 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
• 11:00 - 11:30 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
• 11:30 - 12:00 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
• 12:00 - 12:30 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
• 12:30 - 13:00 a question frequently is raised what
• 13:00 - 13:30 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
• 13:30 - 14:00 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
• 14:00 - 14:30 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
• 14:30 - 15:00 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
• 15:00 - 15:30 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
• 15:30 - 16:00 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
• 16:00 - 16:30 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
• 16:30 - 17:00 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
• 17:00 - 17:30 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
• 17:30 - 18:00 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
• 18:00 - 18:30 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
• 18:30 - 19:00 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
• 19:00 - 19:30 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
• 19:30 - 20:00 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
• 20:00 - 20:30 surface of a new putting green are evident
• 20:30 - 21:00 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
• 21:00 - 21:30 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
• 21:30 - 22:00 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
• 22:00 - 22:30 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
• 22:30 - 23:00 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
• 23:00 - 23:30 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
• 23:30 - 24:00 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
• 24:00 - 24:30 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
• 24:30 - 25:00 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