1. 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

2. 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

3. 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

4. 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

5. Water & Transpiration Relative Humidity Comparison

6. Soil Properties Soil-Water Path

7. Irrigation Scheduling- nonstressed Soil Type Available Water (in/ft)MAD (%)

8. Soil Properties Water Holding Capacity

9. Water Holding Capacity F.C.P.W.P.

11. 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.

12. Water & Transpiration Factors Influencing Transpiration Plant species R.H. Stomata (number, size, and aperture) Leaf morphology Wind Temperature (air & soil) Soil moisture availability

13. 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

14. Water & Transpiration Factors Influencing Transpiration/Soil Water Time (days) Soil  Wilting  Plant  Soil  at soil-root interface Field Capacity 

15. Water & Transpiration Factors Influencing Transpiration  < -3.0 MPa  ~ -1.2 MPa  ~ -2.0 MPa

16. Water & Transpiration Factors Influencing Transpiration/Soil Temp Collards Cotton Watermelon

17. Water & Transpiration Factors Influencing Transpiration Stomata Frequency & Location

18. Water & Transpiration Water Potential vs. Ps and Growth Corn Ps Sunflower Corn Growth

19. Water & Transpiration Factors Influencing Transpiration/ Wind Wind Speed = 0.5 cm/sec = 1 mph Wind Speed = 10 cm/sec = 22 mph

20. Irrigation Requirements/ Harris et al. 1999 June December

21. 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

22. 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