SSC 100-Fall 2002                                          ID_______________

Homework 5                                        Lab Section____________

Due Monday 4 November 2001

 

Value 15 points

 

1.        Use Darcy’s equation and the final flux data from each Mariotte bottle height in your column experiment in laboratory 4 to calculate the saturated hydraulic conductivity of your soil.  Show all your work and use appropriate units.

 

The students should use the data from their lab exercise and plug it into Darcy's equation.  They have already calculated flux as part of the lab exercise.

 

 

          Or if Q is used = A*K*dH/dx

 

q= flux or Q = flow rate

V= volume

A= cross sectional area

K= hydraulic conductivity

t= time

 

2.        The following table shows the total hydraulic head and gravitational component of head as a function of elevation for a soil.  Assume the reference level is at zero elevation.  Answer the following questions.  Use the figure in question 9 page 106 of the text as a guide.

 

a.       Complete the table.

b.      At what elevation is hydraulic conductivity lowest?

c.       At what elevation is the soil saturated?

d.      What is the predominant direction of water movement?

 

 

 

 

Height above reference

Total head

Gravity component of head

Matric component

of head

(cm)

(cm)

(cm)

(cm)

40

20

40

-20

30

20

30

-10

20

15

20

-5

10

10

10

0

0

0

0

0

 

b.         Hydraulic conductivity is the lowest at 40 cm because the soil is the driest there.

 

c.         The soil is saturated at approximately 10 cm, where the matric potential is 0.

 

d.         Water will flow down from high potential (positive) to lower potential (0).

 

3.  Answer question 7 in Chapter 5 of the text.  Question 7.  Water escapes from plants mainly because the stomata open to let carbon dioxide in.  (a) Does transpiration offer any benefits to plants?  (b) Why does a crop's total transpiration tend to correlate with the crop's biomass production?

 

a. Transpiration might offer no consistent benefit to plants.  It can cool leaves, and the transpiration stream to roots and through xylem can speed the delivery of nutrients.  These effects could be beneficial in special circumstances.  Otherwise transpiration seems to be the accidental consequence of stomata being open in sunlight to let in CO2.

 

b. A crop's total transpiration correlates with biomass production because both depend in similar ways on leaf area and solar energy input.