Understanding Soil Water

5,676 views

Published on

I developed this slide set for my Intro to Soils class in Feb 2012.

Published in: Education, Technology, Business
3 Comments
5 Likes
Statistics
Notes
  • excellent work. well done
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • Thank you for share this slide set. I used this for irrigation training.
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • blessing_11111@yahoo.com

    My name is Blessing
    i am a young lady with a kind and open heart,
    I enjoy my life,but life can't be complete if you don't have a person to share it
    with. blessing_11111@yahoo.com

    Hoping To Hear From You
    Yours Blessing
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
No Downloads
Views
Total views
5,676
On SlideShare
0
From Embeds
0
Number of Embeds
10
Actions
Shares
0
Downloads
370
Comments
3
Likes
5
Embeds 0
No embeds

No notes for slide

Understanding Soil Water

  1. 1. Understanding Soil Water
  2. 2. What is the term for the moisture status of a soil when its pores are 100% full of water? Saturation
  3. 3. Why do large soil pores (aka macropores) normally drain within a few days? Large soil pores are drained by GRAVITY
  4. 4. Why doesn’t gravity drain all the water out of soil pores ? Field capacity Wilting point When water is no longer When plants have extracted drained by gravity as much water as they can Capillarity and surface attraction combine to pull more strongly than gravity on: 1) water in “micropores” and 2) water close to the “soil skin”.
  5. 5. Why doesn’t gravity drain all the water out of soil pores ? Field capacity Wilting point When water is no longer When plants have extracted drained by gravity as much water as they can Some water is held too tightly to be pulled away by roots
  6. 6. Pull of the soil matrix on H2O surface attraction + capillarity cohesion H + Soil Skin O adhesion H H + pull H2O into small ? O H pores H O HHydrogen bonding
  7. 7. Pull of the soil matrix on H2O surface attraction + capillarity cohesion H + Soil Skin O adhesion H H + pull H2O into small ? O Water is pulled into H pores H the micropores and O toward the soil skin H by matric forcesHydrogen bonding
  8. 8. What do I mean by “soil skin”? Brady and Weil (2002) http://www.ccma.csic.es/dpts/suelos/clay minerals humus
  9. 9. Soil circulatory system Unavailable water ~0.2 μm Wilting point available less Plant available water Most available Field Capacity 10-30 μm Gravitational water in drainage poresmodel soil pore Saturation Adapted from Buol (2000)
  10. 10. Soil circulatory system Unavailable water ~0.2 μm Wilting point available less Plant available water Most available Field Capacitymodel soil pore Adapted from Buol (2000)
  11. 11. Soil circulatory system Unavailable water ~0.2 μm Wilting pointmodel soil pore Adapted from Buol (2000)
  12. 12. high energy H2O = molecules bouncing around low energy H2O = molecules moving slowlySoil skin Unavailable water Thickness of water film Low energy H2O high energy H2O
  13. 13. high energy H2O = molecules bouncing around low energy H2O = molecules moving slowlySoil skin Unavailable water Thickness of water film Low energy H2O high energy H2O
  14. 14. high energy H2O = molecules bouncing around low energy H2O = molecules moving slowlySoil skin Unavailable water Thickness of water film Low energy H2O high energy H2O
  15. 15. high energy H2O = molecules bouncing around low energy H2O = molecules moving slowlySoil skin There is still some water in air dry soils! Thickness of water film Low energy H2O high energy H2O
  16. 16. Mars Lander probe finds no water in Martian soilsA conductivity probe on the Mars Lander sensed rising and falling humidity levels in theMartian atmosphere, but when stuck into the ground, the probe found “Martian soil” to be completely and perplexingly dry.On Earth, “if you have water vapor in the air, every surface exposed to that air will have water molecules adhering to it that are somewhat mobile, even at temperatures well below freezing," said Aaron Zent , lead scientist for the Lander’s conductivity probe.
  17. 17. Soil water tension (aka potential) can be visualizedas the suction created by a hanging column of water ~1mField capacity Wilting point Air-dryAll of the following are equivalent: 150 m 1 m of H2O There cm of many are water 10,000 m 100 other methods 75 mm of mercury -10 kPa of expressing -0.01 MPa soil water -0.1 bars -0.0987 atmospheres tension -1.45 PSI -1500 kPa -100,000 kPa -15 bars -1000 bars
  18. 18. Soil water tension (aka potential) can be visualizedas the suction created by a hanging column of water ~1mField capacity Wilting point Air-dryAll of the following are equivalent: 150 m 1 m of H2O There cm of many are water 10,000 m 100 other methods 75 mm of mercury -10 kPa You should be of expressing with -0.01 MPa familiar -0.1 bars these units soil water -0.0987 atmospheres tension -1.45 PSI -1500 kPa -100,000 kPa -15 bars -1000 bars
  19. 19. Saturation Are all of the water molecules in this poreunder the same tension ?
  20. 20. FieldCapacity
  21. 21. -1500 kPaWiltingpoint
  22. 22. -100,000 kPa Air-dry
  23. 23. Understanding soil water tension Ψtotal = Ψ gravitational + Ψmatric + Ψosmotic Pull of gravity Pull by micropores and soil skin ?
  24. 24. Understanding osmotic tension Salt added ?
  25. 25. Understanding osmotic tension Salt added
  26. 26. What causes fertilizer burn?Osmotic tension
  27. 27. The same phenomena that causes “dishwashing hands” Osmotic tension
  28. 28. How do water moleculesget from the soil to the top of a plant?
  29. 29. H20 H20 H20 H20 Continuous H20chains of water H20 The chain molecules H20 moves upward move upward if there is a H20 through the negative energy H20 xylem gradient H20 H20 H20 H20 H20 H20 H20 H20 H20 H20
  30. 30. H20 H20 H20 H20 Continuous H20chains of water Solar energy H20 molecules drives H20 move upward transpiration H20 through the xylem H20 Plants provide H20 the conduit H20 H20 H20 H20 H20 H20 H20 H20 H20
  31. 31. Transpiration = air conditioning for plants~ 4000 gallons H2O per acre on a hot sunny day~ 30 gallons H2Oper corn plant per season
  32. 32. The tallest living tree is a coast redwood that stands 112 meters(367 feet, 6 in.), or ~ five stories higher than the Statue of Liberty. Why don’t trees grow any taller ? Hydrogen bonding is only strong enough to hold together ~ 400’ of water molecules Cohesion theory
  33. 33. Soil water is a switch that activates and deactivates soil biologyWater is biologically available, when soil organisms are able to win the “tug of war” with the soil
  34. 34. Up to this point, we have been discussing water tensionWhat is meant by the term water content?
  35. 35. Determining gravimetric soil moisture contentCollect sample. Weigh moist. Weigh after oven drying. g.m.c. = (moist – dry soil mass) / dry soil mass
  36. 36. Water content can also be expressed volumetricallyv.m.c. = volume of water in soil / total soil volume
  37. 37. Why would you want to do this conversion? Converting from gravimetric to volumetric MC Volumetric Gravimetric moisture moisture Density content content Bulk density of H2O volume mass of H2O mass of dry soil volume of H2O = of H2Omass of dry soil * volume of dry * mass of H2O volume soil of dry soil Gravimetric MC is easier to measure but volumetric MC is more useful inappropriate for expansive soils for managing irrigation
  38. 38. Translating between water tension (aka potential) and water content using a “characteristic curve” A characteristic curve (aka water release curve) describes the relationship between water tension and water content for a specific soil.0
  39. 39. A pressure plate system can be used to bring soil to specific water tensionsWhy areall those boltsneeded? A known positive pressure is applied inside the chamber. Soil water is pushed out through a porous ceramic plate.
  40. 40. Different soils have different characteristic curves Field capacity Wilting point Brady and Weil, 2002
  41. 41. Different soils have different characteristic curves Field capacity Wilting point 0.09 – 0.02 = 7% Brady and Weil, 2002
  42. 42. Different soils have different characteristic curves Field capacity Wilting point 34% - 8% = 26% Brady and Weil, 2002
  43. 43. Different soils have different characteristic curves Field capacity Wilting point 54% - 24% = 30% Brady and Weil, 2002
  44. 44. Use the diagram to interpret how much wateris held in the clay @ saturation, FC and WP.Calculate how many inches of water areneeded to bring a 3’ rooting zone of this soilfrom 50% of FC to FC. The volumetric water content @ FC = 0.54 0.54 * 36” = 19.4” of water @ FC 50% of 19.4” = 9.7”
  45. 45. Real soils rarely hold more than 2.5” ofplant available water per foot… based onthis fact, do you think the characteristiccurve for the clay soil is realistic?The volumetric water content @ FC = 0.54The volumetric water content @ WP = 0.24 PAW = 0.30 0.3* 12” = 3.6” >> 2.5”
  46. 46. So how does compaction impact soil water relationships ?
  47. 47. So how does compaction impact soil water relationships ? Loss of drainage pores Gain in small pores
  48. 48. Which soil texture can hold the most plant available water? Field capacity line ~ 2.5” of plant Plant available water Available (PAW) per foot water Wilting point line Brady and Weil, 2002
  49. 49. How does SOM affect PAW? Adapted from Brady and Weil
  50. 50. How does SOM affect PAW? Adapted from Brady and Weil
  51. 51. Prairie soil Farm field Impressive example of the impact of soil organic matter on water holding capacity
  52. 52. So when should you irrigate a clay soil? Wimpy crops Tough crops
  53. 53. So when should you irrigate a clay soil? loam soil? Wimpy crops Tough crops
  54. 54. Brady and Weil, 2002 So how does one measure soil water tension in the field?A tensiometer is a Tensiometers are water filled tube useful for montioring with a porous tensions betweenceramic tip on one 0 and -85 kPa (-0.85 bars)end and a vacuum a range that includesgauge on the other. about half the water in most soils.Water tension in the tube equilibrates When soils are too dry with the water (> -85 KPa), air is drawntension outside the in through the porous tip porous tip. and the vacuum fails.
  55. 55. Gypsum blockMeasuring soilmoisture as a function of electrical resistance Brady and Weil, 2002
  56. 56. Gypsum blockMeasuring soilmoisture as a function of electrical resistance Resistance drops as gypsum starts toCalibration is dissolve critical !! Brady and Weil, 2002
  57. 57. What is this gizmo?
  58. 58. What is this gizmo?
  59. 59. Time Domain Reflectometry The technique involves determination of the propagation velocity of an electromagnetic pulse sent down a fork-like probe installed in the soil. The velocity is determined by measuring the time taken for the pulse to travel down the probe and be reflected back from its end. The propagation velocity depends on the dielectric constant of the material in contact with the probe (i.e. the soil). Water has a much higher dielectric constant than soil.
  60. 60. Measuring infiltration rate
  61. 61. http://soilquality.org/images/infiltration_photo1.jpg
  62. 62. Why do the wetting fronts have different shapes? Capillarity pulls the water farther in finer textured soils http://www.ext.colostate.edu/mg/gardennotes/images/213-7.jpg
  63. 63. Capillary rise in a sandy soilhttp://www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1087.pdf
  64. 64. Capillary rise in a silt loamhttp://www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1087.pdf
  65. 65. What happens when capillary rise lifts water to the soil surface? http://www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1087.pdf
  66. 66. How fast does water move through soil ? Hydraulic conductivityDarcy’s Law Flow rate = Area*Ksat *pressure/length Brady and Weil, 2002
  67. 67. Hydraulic conductivity = permeability Flow rate ~ pore radius4
  68. 68. How does the presence of a coarse textured layer under a fine textured layer affect percolation ? Fine textured layer Coarse textured layer
  69. 69. Water will not enter the coarse textured layer until the upper layer is near Coarse textured layer saturation After waterenters the coarse textured layer, it will percolate more quickly.http://www.personal.psu.edu/asm4/water/drain.html
  70. 70. Does a layer of sandy soil improveLayer with sandy texture drainage ?NO ! Layer with sandy texture
  71. 71. Soil suitability for septic drainfields
  72. 72. What happens if a septic drainfield does not drain adequately?Can a drainfield drain too well? http://organicearthsolutions.wordpress.com/2012/02/16/
  73. 73. Impact of topography on drainagePoorlydrained Interstream divide Somewhat Moderately poorly LANDSCAPE well drained drained POSITIONS Well drained Poorly drained Shoulder Common in IL Valley floor SOIL Backslope DRAINAGE CLASSES N.C. Agric. Res. Bull. 467
  74. 74. Illinois’ natural drainage classeshttp://www.il.nrcs.usda.gov/technical/soils/Suite_Maps.html
  75. 75. What is a hydric soil?http://www.il.nrcs.usda.gov/technical/soils/Suite_Maps.html A hydric soil is a soil that formed under conditions of saturation, flooding or ponding long enough during the warm season to develop anaerobic conditions in the upper horizons. Soils in which the hydrology has been artificially modified are still considered hydric if the soil, in an unaltered state, was hydric.
  76. 76. Hydric soils are dominated by low chroma colors
  77. 77. http://www.wtamu.edu/~crobinson/soils/clayskn05s.jpg Mottles are indicative of a fluctuating water table.
  78. 78. Some hydric soils in McDonough Cty
  79. 79. Artificial drainage in the United States % of land drainedhttp://www.ars.usda.gov/SP2UserFiles/Place/36251500/TheExtentofFarmDrainageintheUnitedStates.pdf
  80. 80. IL has experienced some very wet springs in recent years ?
  81. 81. Yield mapshave made drainage problems more obvious
  82. 82. Could this story be about your farm? Increasing yield by installing drainage By Mindy Ward, Missouri Farmer Today BOONVILLE --- For more than 100 years, the Hoff family has fought to farm wet areas of their fields. For Eddie Hoff, the fourth generation to farm the creek bottom ground in Cooper County, the loss of yield and added expense of working the ground was ultimately affecting his bottom line. “We were losing 60 to 70 bushels per acre in some spots,” he says. We were working the ground over and over. I just wanted to no-till and save some cost.” So, he decided to drain the soils with pattern tile.
  83. 83. Pattern Tiling in Ontariohttp://www.omafra.gov.on.ca/english/engineer/facts/10-091.htm
  84. 84. http://www.omafra.gov.on.ca/english/engineer/facts/10-091.htm
  85. 85. Installing corrugated plastic tile with a tile plowhttp://www.fastline.com/flimages/internet/032/169/3959312_4.jpg
  86. 86. Why do crops on tiled-drained land tend to be more drought resistant ?Ontario Ministry of Ag and Food
  87. 87. The current guide reflects recent developments in drainage science and technology. Most of these are related to new equipment and materials, widespread use of computers, and? water quality considerations. It includes information not in the previous edition on pipeline crossings, water and sediment control basins, drain fields for septic systems, design of drainage water management systems, and design charts for smooth-walled pipes.
  88. 88. Conservation Drainage Maximum conveyanceCrop productivity Environmental quality Controlled drainage system Bioreactor filled with woodchips http://wrc.umn.edu/prod/groups/cfans/@pub/@cfans/@wrc/documents/asset/cfans_asset_212844.jpg
  89. 89. Artificial drainage has greatly increased the number of days when soils in the Upper Midwest are suitable for field operations and deep root growth but has also contributed Pollution of to somewater resources environmental Loss of SOM problems
  90. 90. Which is worse?? Compaction Saturated soil isprobably extends less compressibleseveral feet deep than wet soil
  91. 91. What is the optimum soil moisture for compacting soil?Soils are most compactiblenear field capacity because the particles are well lubricated and the largepores are empty and most collapsible
  92. 92. Soil resistance to penetration is very related to soil moisture content. Healthy crops tend to use more water which can result in higher penetrometer readings.
  93. 93. Understanding Heat Capacity A heat capacity of water = 1 calorie / gram / degree C BHow much will the temperature of the water increase in cup A if300 calories of thermal energy are added? How about cup B?
  94. 94. Why does soil heat up faster than water ? The heat capacity of water is ~ 5 times higher than the heat capacity of dry soil. As a result, moist soils heat up andcool down more slowly than dry soils.
  95. 95. Water has a high thermal conductivity Air has a low thermal conductivityWhat can be done tomaximize geothermal heat transfer ?

×