Aeration & Soil Microorganisms Bacteria

Information on the Aeration of Soil and the Growth of Soil Bacterial Cultures

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Exercise Experiment - An Illustration of the Effect of Soil Aeration and the Activity of Microorganisms Present

The Effect of Aeration of Soils and Bacteria

Apparatus Needed

Coarse, medium, and fine sand; magnesium oxide; dilute HC1; N/10 NH 4 OH; N/10 HC1; indicator; sterile 1 c.c. pipette; ten sterile 250 c.c. Erlenmeyer flasks; condenser; sterile 1% peptone solution.

Culture

B. mycoides, broth culture.

Method or Protocol

1. Prepare the sand for use by first heating it with dilute HC1; then wash it several times, first with tap water then with distilled water and dry at 110 C.

2. Place 50 gms. Of coarse sand in each of three flasks; do the same with the medium and the fine sand.

3. Sterilize the flasks in the autoclav at 120 C. for thirty minutes.

4. Place 50 c.c. of the 1% peptone solution in the remain ing flask.

5. Add sufficient peptone solution to the other flasks to make 10%, 20% and 30% moisture content according to the following table :

Soil.

Moisture.

After twenty days.

Coarse sand \

(

10% 20% 30%

Medium sand -\

10%

20%

30%

Fine sand !

10%

20%

1% peptone solution

30% 99%

6. Inoculate each flask with 1 c.c. from a broth culture of B. mycoides and shake to distribute the organisms evenly.

7. Make ammonia determinations after twenty days.

Note. Ammonia determinations from the above are made by the following procedure: Remove the cotton plugs, add 200 c.c. of water, 10 gms. MgO and a small piece of paraffin. Distill off the ammonia present, collecting it in N/10 HC1 and titrating against N/10 NH 4 OH, using methyl orange as indicator.

8. Record your results in the form given above.

9. How does aeration affect bacterial activity? Size of sand grains?

What interrelation have grain-size and moisture con tent of soil?

How do microorganisms obtain their food in soil that is not wet?

What influence does humus have on aeration? On bacterial activity?

10. Draw any conclusions warranted by your results and point out any practical applications.

References for Soil Aeration & Microorganisms

RAHN, O.: Tech. Bui. No. 6, Mich. Agr'l Expt. Sta.