1. Soil Physics 2010 Outline Announcements Exam Diffusion

2. Soil Physics 2010 Exam answers were posted Friday Exam grades (the circled number 90 ): Page 2 was the decider Announcements 90 0 1 4 6 8 9 82 2 2 3 5 9 79

3. Elevation (cm) Pressure (cm of water) A B C D E F Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Page 2, question 1 Soil Physics 2010

4. Elevation (cm) Pressure (cm of water) A 12 B 8 C 3 D E 8 F 3 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Page 2, question 1 Soil Physics 2010

5. Elevation (cm) Pressure (cm of water) A 12 0 B 8 C 3 9 D E 8 0 F 3 5 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Page 2, question 1 Soil Physics 2010

6. Elevation (cm) Pressure (cm of water) A 12 0 B 8 9 C 3 9 D -4 E 8 0 F 3 5 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Page 2, question 1 Soil Physics 2010

7. Page 2, question 2 Soil ASoil B Change in potential across (2 pts.): Distance across (1 pt.): 76 Hydraulic conductivity (4 pts.): This soil column has a radius of 3 cm, and the outflow is 11 cm 3 /hr. The values in the diagram are distances in cm. Fill in the blanks: Soil Physics 2010

8. Page 2, question 2 Soil ASoil B Change in potential across (2 pts.): 83 Distance across (1 pt.): 76 Hydraulic conductivity (4 pts.): This soil column has a radius of 3 cm, and the outflow is 11 cm 3 /hr. The values in the diagram are distances in cm. Fill in the blanks: Area =  r 2 = 9  ≈ 28.27, so Soil Physics 2010

9. Page 2, question 2 Soil ASoil B Change in potential across (2 pts.): 83 Distance across (1 pt.): 76 Hydraulic conductivity (4 pts.): 0.340.78 This soil column has a radius of 3 cm, and the outflow is 11 cm 3 /hr. The values in the diagram are distances in cm. Fill in the blanks: Area =  r 2 = 9  ≈ 28.27, so Soil Physics 2010

10. Page 2, question 3 Soil Physics 2010 ElevationPressure Total potential 20 50 82 The system at the right started with dry soil in the column, and it has come to equilibrium. The numbers give elevation in cm, with the bottom of the bottle being the reference height. Complete the table (2 points each).

11. Page 2, question 3 Soil Physics 2010 ElevationPressure Total potential 20 5 50 5 82 5 The system at the right started with dry soil in the column, and it has come to equilibrium. The numbers give elevation in cm, with the bottom of the bottle being the reference height. Complete the table (2 points each). No Flow! Pressure = Total - Elevation

12. Page 2, question 3 Soil Physics 2010 ElevationPressure Total potential 20 -155 50 -455 82 -775 The system at the right started with dry soil in the column, and it has come to equilibrium. The numbers give elevation in cm, with the bottom of the bottle being the reference height. Complete the table (2 points each).

13. Soil Physics 2010 More about diffusion Porosity Tortuosity (Constrictivity) (Continuity) or Both!

14. Soil Physics 2010 Diffusion: porosity Diffusion only takes place in the pores :  < 1 Diffusion only takes place in water :  <  or Nothing about pore size! What’s important is the cross-sectional area available for diffusion (or in air:  <  ) =

15. Soil Physics 2010 Diffusion: tortuosity Diffusion pathway isn’t straight: straight distance l path length Ratio /l is called tortuosity,   ≥ 1! (gottta be) or l

16. Soil Physics 2010 Why is tortuosity squared? Suppose = 3*l Then the distance a molecule diffuses is 3 times longer:  But additionally, the gradient is only 1/3 as strong: another   x  =   2 or l

17. Soil Physics 2010 Diffusion: constrictivity Some cross-sectional area doesn’t contribute much to diffusion Constrictivity isn’t in the equation because we don’t know how to measure it Often  or  is known, and [tortuosity x constrictivity] is fitted or Very important Less important

18. Soil Physics 2010 Diffusion: continuity Some pores don’t go anywhere: they’re dead ends Continuity isn’t in the equation because we don’t know how to measure it Often  or  is known, and [tortuosity x constrictivity x continuity] is fitted or

19. Soil Physics 2010 Diffusion conclusion Porosity:area, not pore size Tortuosity:distance ratio squared (Constrictivity)can’t measure it (Continuity)can’t measure it or Both!