1. Soil Water Movement and Retention

2. Medium for plant growth Regulator of water supplies Recycler of raw materials Habitat for soil organisms Engineering medium Functions of Soil

3. Medium for plant growth Physical Support Gas exchange Water Temperature Nutrient source

4. Functions of Soil Regulator of water supplies Infiltration Run-off Storage/Movement Distribution Purification Integral to hydrologic cycle

5. Water Movement

7. Two Forces Responsible for Water Movement in Soils Gravity Capillarity

8. Gravity

9. Spontaneous movement of water into and through pore spaces in soil without the aid of gravity.

10. Adhesion and Cohesion

11. Cohesion

12. Adhesion and Cohesion oxygen H H SURFACESURFACE adhesion oxygen H H cohesion

13. Adhesion and Cohesion adhesion Cohesion (H-bonding) Surface droplet

14. Adhesion and Cohesion Strong adhesion Weak adhesion

15. Weak Adhesion

16. Adhesion to Soil Particles Strong Adhesive Forces

17. Soil Pores Adhesion and Cohesion Adhesion to the tube or pore wall Cohesion between water molecules capillarity

18. Capillarity Tube/Pore wall } Force down h = 0.15 r adhesion cohesion

19. Capillarity h = 0.15 r h Small pores

21. Capillarity

22. Soil Pores and Pore Size Distribution Texture Density Structure

23. Particle Size Large/coarseMedium Fine/Small Sand Loamy Sand Sandy Loam Silt Sandy clay Loam Silty clay Loam Silt Loam Loam Clay Loam Sandy Clay Silty Clay Clay Pore Size Large/Macro Meso/MediumMicro/Small CapillarityWeakModerate Strong Texture

24. Soil Pores Sandy Silty Clayey

25. Gravity Dominated Capillarity Dominated

26. Density Depth in Profile Arrangement of Particles Compaction

27. Structure Micropores Macropores

28. Examples

29. Sand Clay Water

30. Sand Clay Initial Saturation

31. Uncompacted Compacted Initial Saturation Sandy Loam

32. Aggregates

33. Wet Moist Same Texture and Density

34. water Relevance transpiration

35. Quantification: Soil Water Energy

36. Potential Energy Energy waiting to be used or exploited

37. High potential Energy Low potential Energy Water moves in response to differences in potential energy, from high potential energy to low potential energy. Gravitational Potential Energy The greater the difference in height The greater the difference in Gravitational potential energy.

38. Gravitational Potential Ψ g = mgh The greater the height, the greater the potential energy. The potential energy of a unit quantity of water. Unit quantities:volume mass weight ψgψg = mg Ψ g = h (cm) mg

39. Gravitational Potential Reference level Ψ g = 0 Height (cm) 100 50 a b ψ ga = 100 cm ψ gb = 40 cm 40 soil Difference in energy determines movement Independent of soil properties

40. Gravitational Potential Reference level (Ψ g = 0) Height (cm) 100 a b Ψ ga = 60 cm Ψ gb = 0 cm Ψ ga – Ψ gb 60 - 0 = 60 cm 40 0

41. Gravitational Potential 1. Gravitational potential energy is due only to the height of an object (water) above some reference point. 2. Gravitational potential energy is independent of soil properties.

42. Capillary Potential Energy (Matric Potential Energy)

43. Matric Potential “suction” potential - capillarity Narrow capillary tube – high capillary rise h = 0.15 - strong force r - compared to free water Small particles, small pores Applies to unsaturated soils

44. Primary Factors in Matric Potential Texture, Density, Aggregation Pore Size Distribution Moisture Content Which Pores are Filled

45. Capillarity and Soil Texture Small pores Strong suction Strong capillarity Large pores Weak suction Weak capillarity

46. Capillary Potential Energy water Dry soil Suction potential energy Matric potential energy

47. Porous block Suction (capillarity) Capillary Potential 100 cm Dry soil Ψm = -100 cm (suction) Vertical distance between the surface of the water and the porous cup.

48. suction Soil Texture 1000 cm Dry soil ψ m = -1000cm (suction) Vertical distance between the surface of the water and the porous cup. Sandy Soil Porous block

49. suction Soil Texture 10,000 cm Dry soil Ψ m = -10,000 cm (suction) Vertical distance between the surface of the water and the porous cup. Fine-textured soil

50. suction ClaySand Soil Texture Unsaturated soils have negative matric potential energy

51. Submergence Potential

52. Submergence Potential (ψ s ) Equal to the distance below a free water surface Water Table 10 cm

53. Units of Potential Centimeters of water Bars Pascals 1 bar = 1020 cm water (4 o C) 1 KPa = 10 cm water 1 bar = 100 kPa

54. Total Potential Energy is the sum of the gravitational, submergence, and matric potential energies. Ψ g + ψ m + ψ s = ψ T

55. Gravitational Potential + Matric Potential = Total Potential Reference level Ψ g = 0 Height (cm) 50 20 a 10 Ψm = -65 cm Ψg = 50 cm Ψ T = -15 cm

56. Gravitational Potential + Matric Potential = Total Potential Reference level Ψ g = 0 Height (cm) 50 20 a b 10 Ψm = -65 cm Ψm = -5 cmΨg = 10 cm Ψg = 50 cm Ψ T = -15 cm Ψ T = 5 cm

57. Reference level Ψ g = 0 Height (cm) 50 20 a b 10 Ψ Ta = -15 cm Ψ Tb = 5 cm Ψ Ta – Ψ Tb = (-15cm) - 5cm = -20 cm Energy Differences

58. Reference level Ψ g = 0 Height (cm) 50 20 a b 10 Ψ Ta = -15 cm Ψ Tb = 5 cm Ψ Ta – Ψ Tb = (-15cm) - 5cm = -20 cm Which way will water move?

59. Determining the Direction of Water Flow 4. Point A – Point B 5. Water moves from high to low energy PositivePoint A to Point B NegativePoint B to Point A 1.Sum the individual potentials at each point 2.Determine if there is a difference in potential 3. Water will move from the higher to the lower energy

60. Next: Characterizing Water Status