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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 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
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
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
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
Ch. 2: Learning Objectives • Define soil water/soil wetness • How can we measure soil water? • Examples of soil water dynamics during the season
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.
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)
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
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:
Equivalent of depth (dw) Equivalent Depth
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
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!
Time-Domain reflectrometry • Companies (e.g.): • Soil moisture, Ca. • Easy Test, Poland • Imko, Germany • Theta-Probe, U.K. Measurement of soil wetness
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
TDR – Operating principle From Dirksen 1999
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:
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
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
Pine stand, sandy soil:Spatial variation of soil water contentat the beginning of the vegetation period Greiffenhagen & Wolf 2002
Pine stand, sandy soil:Spatial variation of soil water content at the end of the vegetation period Greiffenhagen & Wolf 2002
Average soil water content at several soil depths and net precipitation during the experiment. Pine stand, sandysoil: Soilwaterdynamics in thefield From Wessolek, 2008
Soil water dynamics in the fieldPine stand, sandy soil – Berlin Grunewald From Greiffenhagen, 2004
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.
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.