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MHSE 18: Soil Water

MHSE 18: Soil Water. Dr. Stefan Julich Georg Richter. Lage. Klima. Standort. Boden. http://boku.forst.tu-dresden.de/index.php?msc_modules_eng. user: mastersc password: coh5ye7A Please treat them confidentially!!!!. Access to study materials:. Wasser- haushalt. Stoff- haushalt.

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MHSE 18: Soil Water

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  1. MHSE 18: Soil Water Dr. Stefan Julich Georg Richter

  2. Lage Klima Standort Boden http://boku.forst.tu-dresden.de/index.php?msc_modules_eng user: mastersc password: coh5ye7A Please treat them confidentially!!!! Access to study materials: Wasser- haushalt Stoff- haushalt

  3. Useful WWW links: • Soil Physical Online Experiments (ETH Zürich) • http://www.soil-physics.ch/index_en.htm • Soil Physics Online Learning Module ILIAS • (Uni Freiburg) • http://bkserv2.forst.uni-freiburg.de/ilias3/login.php • Login: bodenkunde • Password: bodenkunde

  4. Chapter 2: Soil Water Content

  5. Ch. 1: Allready learned about… • basic physical properties of soils • Bulk density dB • Porosity P • Soil texture • Soil structure • that control behaviour of soils with regard to • plant growth • water flow • agricultural management • engineering use

  6. Water-Holding Capacity of Soil: Effect of Soil Texture Coarse Sand Silty Clay Loam Dry Soil Gravitational Water Water Holding Capacity Available Water Unavailable Water

  7. Ch. 2: Learning Objectives • Define soil water/soil wetness • How can we measure soil water? • Examples of soil water dynamics during the season

  8. Soil water reservoir

  9. Soil transforms • ... non-continuous rainfall or snow into a continuous supply of water for plant growth. • ... discontinuous precipitation into continuous discharges, i.e., streams and rivers.

  10. Measurement of soil wetness Gravimetric water content ( ) • Mw = mass of water evaporated, g (24 hours @ 105oC) • Ms = mass of dry soil, g • Volumetric water content (v) • Vw = volume of water (cm³) • Vb = volume of soil sample (cm³)

  11. and v can be related to each other: • dB…bulk density • dW…density of water (assuming: 1g/cm³) • Relative saturation (S) Measurement of soil wetness

  12. Equivalent depth of water dw (mm): Volume of water per surface area Air Area = A Storage of Water D b Water Matric Water storage per layer: Volume fraction of soil water:

  13. Equivalent of depth (dw) Equivalent Depth

  14. v & Equivalent Depth: Typical Values for Agricultural Soils Soil Particles: 50% 0.50 m 1 m Very Large Pores: 15% (Gravitational Water) 0.15 m Total Pore Space: 50% Medium-sized Pores: 20% (Plant Available Water) 0.20 m Very Small Pores: 15% (Unavailable Water) 0.15 m

  15. Sample Problem: • The data in the Table were obtaind before and after irrigation. Calculate w and v and determine the amount of water (in mm) added to each layer and to the profile as a whole!

  16. Time-Domain reflectrometry • Companies (e.g.): • Soil moisture, Ca. • Easy Test, Poland • Imko, Germany • Theta-Probe, U.K. Measurement of soil wetness

  17. Time-domain reflectometry (TDR) • Permittivity: a measure of how an electric field affects, and is affected by, a dielectric medium • water = 81 Soil = 4 to 8 air = 1 • v…propagation velocity • c…velocity o light in vacuum (3*108 m/s) • …permittivity of the medium around

  18. TDR – Operating principle From Dirksen 1999

  19. Time-domain reflectometry (TDR) • The propagation velocity of an electromagnetic pulse travelling along a wave guide is: • L…length of sensor • t…travel time between A and B • Equating this with the electrodynamic pulse velocity:

  20. Wave Form dependent on water content

  21. TDR - Calibration

  22. Site spezific calibration: Organic soil

  23. Terms to know • Dielectric (Is a non-conductor of electricity): • Is a dielectric placed between a capacitor, no net flow of electric charge is allowed but only a displacement of charge • Relative Permittivity (Dielectric number) : • ratio of the capacitance of a capacitor with the given substance as dielectric to the capacitance of the same capacitor with air as a dielectric • water = 81 Soil = 4 to 8 air = 1

  24. Soil water dynamics during the season • Example 1: Terrestric soil • Sandy soil (dune sand) • Pine stand (ca. 100 year old) • Example 2: grundwater influenced soil • Peat soil • Grasland

  25. Pine stand, sandy soil:Spatial variation of soil water contentat the beginning of the vegetation period Greiffenhagen & Wolf 2002

  26. Pine stand, sandy soil:Spatial variation of soil water content at the end of the vegetation period Greiffenhagen & Wolf 2002

  27. Average soil water content at several soil depths and net precipitation during the experiment. Pine stand, sandysoil: Soilwaterdynamics in thefield From Wessolek, 2008

  28. Soil water dynamics in the fieldPine stand, sandy soil – Berlin Grunewald From Greiffenhagen, 2004

  29. Temporal variation of soil water during the vegetation period Peat soil, gras cm below soil surface Water saturated Vegetation period: 1.4. to 30.9.

  30. Take home messages • Soils are able to store water. • Soil water content varies from site to site. • Soil water content of a site may vary enormously in time and space.

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