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United States Department of Agriculture

Agricultural Research Service

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Activity 2
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How Fertile Can You Get?
Activity 2

When farmers need a controlled flow rate, they use specialized pumps. To create a uniform flow rate in a laboratory setting, one may use a device known as a Mariotte siphon. This device is much less expensive than a pump and delivers a constant flow from a system based upon the "head" or height of soil surface. When the pressure remains constant, the fertilizer, etc. will flow at a constant rate. This allows uniform application to a field and less chance of overfertilization.


Purpose:

Materials:

1. To discover flow rate for various soil types.

2qt. wax orange juice carton, 20oz. soda bottle, water, sand, *clay, silt or potting soil, stopwatch or watch with second hand, nail for punching hole

*(If you live in the Coastal Plains of South Carolina, clay will be found as the second layer of soil in most yards after the sandy soil.) 


Procedure:1. Cut the top off of the orange juice carton so that all five exposed sides are symmetrical. 

2. Obtain one sample each of sand, clay, and silt or potting soil. You should have enough to fill the orange juice container to within 2cm from the top.

image of soil in a half of a orange juice carton and a soda bottle of water 
  
  

3. Punch an outlet hole in one corner of the bottom of the carton just large enough for water to escape. 
 

  

4. Make a mark 1cm from the bottom of the plastic bottle. Fill bottle with water.

5. Place the *soil in the orange juice carton leaving approximately 2cm at the top.

6. Cover the 20oz. bottle with your thumb or a quarter and invert it over the soil sample and hold the mouth within 2cm of the top edge of the clay. 

image of an inverted soda bottle of water held over soil in carton with one finger regulating the soda bottle opening

  
7. Remove thumb or quarter and begin pouring water over the soil.

8. Begin timing when the water inside the bottle reaches the mark.

9. Stop timing when you see the flow of water out of the hole. 

10. Repeat for all soil samples.

11. Calculate flow rate for each soil sample.

Q = flow rate = KA * H/L
H/L = 1
Q = KA = (v/t)
K = hydraulic conductivity = 
        volume of container
        per time for water
        to flow through soil
        = lxhxw/s 
      L = area of carton
*Note: You may want to start with the clay sample.


image of a flashing light bulbThink about this:

1. What causes the flow rate to change in the soil samples?

2. What effect would saturation level have on the flow rate?

3. Why is knowledge of soil type and soil hydraulics important to farmers?

4. How would this knowledge help in the application of fertilizers? 


 

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Last Modified: 8/12/2016
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