Research Bulletin (Iowa Agriculture and Home Economics Experiment Station)


These experiments were undertaken to determine the effects of liming on certain groups of soil bacteria in a typical Wisconsin drift soil. They justified the following general conclusions:

1. Applications of lime up to three tons per acre lead to an increase in the numbers of bacteria developing on "modified synthetic" agar. They also produce an increase in ammonification, nitrification, and in nitrogen fixation when these processes are tested by the beaker method. These increases are in all cases almost proportionate to the amount of lime applied.

2. Natural increases in numbers of bacteria tend to obscure the effects of applications of lime, while natural decreases make them more pronounced.

3. Peptone solutions do not permit of the determining of the largest number of bacteria which will destroy humus with the production of ammonia.

4. The beaker method, with dried blood or cottonseed meal for ammonification, with ammonium sulfate or dried blood for nitrification, and with mannite for nitrogen fixation, is eminently satisfactory.

5. The ammonification of dried blood or of cottonseed meal runs parallel with the numbers of bacteria while there is very little relation between the ammonification of peptone solutions and numbers.

6. Increased nitrification leads to slight accumulations of nitrates in the soil.

7. Natural accumulations of nitrates in the soil tend to obscure the differences due to the lime treatment.

8. The solution method for nitrogen fixation is quite unreliable.

9. Applications of lime increase the yield of oats; one-half and one ton per acre very slightly, but two and three tons to quite a large extent.

10. Applications of lime up to three tons per acre increase the nitrogen content of the oats crop more rapidly than the yield itself.



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