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Water & Transpiration or Water, water everywhere and all the boards did shrink. Water, water everywhere and not a drop to drink. J.G. Mexal A/H 100
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Soil Properties Water Holding Capacity Water Holding Capacity (WHC): amount a water held by a soil; a function of texture. Field Capacity (FC): amount of water held against the force of gravity after irrigation. Permanent Wilting Point (PWP): amount a water at which the plant wilts permanently. (Does not hold well for trees & shrubs) Available Water Content (AWC): FC - PWP = AWC Maximum Allowable Depletion (MAD): ~50% AWC
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Water & Transpiration Important Definitions Field Capacity~0.03 MPa –amount of water held against the force of gravity; usually measured 24 h after irrigation Permanent Wilting Point ~1.5 MPa –amount of water resulting in wilting from which plant will not recover; developed for agronomic crops
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Water & Transpiration Colligative Properties of Water Conversions MPa = mega Pascal 1000 kPa 10 bar 1000 g/cm 2 ~ 1 atm (14.7 lb/in 2 ) ~760 mm Hg
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Water & Transpiration Relative Humidity Comparison
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Soil Properties Soil-Water Path
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Irrigation Scheduling- nonstressed Soil Type Available Water (in/ft)MAD (%)
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Soil Properties Water Holding Capacity
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Water Holding Capacity F.C.P.W.P.
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Water & Transpiration Factors Influencing Transpiration RoT Water moves from Hi to Lo Concentration Water moves through the Soil-Plant- Atmosphere-Continuum in response to this concentration gradient.
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Water & Transpiration Factors Influencing Transpiration Plant species R.H. Stomata (number, size, and aperture) Leaf morphology Wind Temperature (air & soil) Soil moisture availability
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Water & Transpiration Factors Influencing Transpiration Component –Soil –Root System –Xylem –Leaf Mesophyll –Substomatal Cavity –Stomata –Boundary layer –Atmosphere Water Potential (MPa) –> -0.1 –~ -0.3 –~ -0.7 –~ -1.2 –~ -2.0 –< -2.0 –< -3.0 –< -10.0
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Water & Transpiration Factors Influencing Transpiration/Soil Water Time (days) Soil Wilting Plant Soil at soil-root interface Field Capacity
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Water & Transpiration Factors Influencing Transpiration < -3.0 MPa ~ -1.2 MPa ~ -2.0 MPa
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Water & Transpiration Factors Influencing Transpiration/Soil Temp Collards Cotton Watermelon
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Water & Transpiration Factors Influencing Transpiration Stomata Frequency & Location
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Water & Transpiration Water Potential vs. Ps and Growth Corn Ps Sunflower Corn Growth
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Water & Transpiration Factors Influencing Transpiration/ Wind Wind Speed = 0.5 cm/sec = 1 mph Wind Speed = 10 cm/sec = 22 mph
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Irrigation Requirements/ Harris et al. 1999 June December
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Water & Transpiration Water Use Efficiency (WUE) Species –Alfalfa C 3 –Cotton C 3 –Corn C 4 –Sorghum C 4 g H 2 O/g D.W. –864 –538 –366 –365
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Things to Know Colligative properties Hydrologic cycle Irrigation Solvent Solute Field Capacity Permanent Wilting Point Water Use Efficiency Potential Evapotranspiration Transpiration Turgor Wilting MAD RH AWC Water Potential Xeriscaping
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