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Hon. W. R. Boyd, President, Cedar Rapids.

Hon. Thos. Lambert, Sabula.

Hon. D. A. Emery, Secretary, Ottumwa.

AGRICULTURAL EXPERIMENT STATION STAFF

E. W. Stanton, M. S., LL. D., Acting President.

C. F. Curtiss, M. S. A., D. S., Director.

W. J. Kennedy, B. S. A., Vice Director.

J. B. Davidson, B. S. A., Chief in Agricultural Engineering.

M. L. King, B. M. E., Assistant Chief in Agricultural Engineering.

W. H. Stevenson, A. B., B. S. A., Chief in Agronomy.

H. D. Hughes, M. S., Chief in Farm Crops.

A. W. Dox, B. S., A. M., Ph. D., Chief in Chemistry.

L. C. Burnett, M. S. A., Assistant Chief in Cereal Breeding.

S. L. Jodidi, B. S., Ph. D., Assistant Chief in Soil Chemistry.

P. E. Brown, B. S., A. M., Assistant Chief in Soil Bacteriology.

John Buchanan, B. S. A., Superintendent of Cooperative Experiments.

H. C. Cosgriff, Field Superintendent.

H. B. Kinney, Assistant in Soil Chemistry.

E. H. Kellogg, Assistant in Soils.

Robt. Snyder, Assistant in Soils.

W. J. Kennedy, B. S. A., Chief in Animal Husbandry.

H. H. Kildee, B. S. A., Assistant Chief in Dairy Husbandry.

J. M. Evvard, M. S., Assistant Chief in Animal Husbandry.

F. N. Marcellus, B. S., Assistant Chief in Poultry Husbandry.

E. J. Strausbaugh, Herdsman.

R. E. Buchanan, M. S., Ph. D., Chief in Bacteriology; Associate in Dairy and Soil Bacteriology.

L. H. Pammel, B. Agr., M. S., Ph. D., Chief in Botany.

Charlotte M. King, Assistant in Botany.
Harriette Kellogg, Assistant in Botany.

R. E. Neidig, B. S., Assistant in Chemistry.

W. G. Gaessler, B. S., Assistant in Chemistry.

S. C. Guernsey, B. S., Assistant in Chemistry.

M. Mortensen, B. S. A., Chief in Dairying.

B. W. Hammer, B. S. A., Assistant Chief in Dairy Bacteriology.

H. E. Summers, B. S., Chief in Entomology.

R. L. Webster, A. B., Assistant in Entomology.

S. A. Beach, M. S. A., Chief in Horticulture and Forestry.

L. Greene, B. S., M. S. A., Assistant Chief in Horticulture.

G. B. MacDonald, B. S. F., Assistant Chief in Forestry.

J. H. Allison, Assistant in Plant Introduction.

T. J. Maney, Assistant in Horticulture.

C. H. Stange, D. V. M., Chief in Veterinary Medicine.

F. W. Beckman, Ph. B., Bulletin Editor.

F. C. Colburn, Photographer.

SUMMARY

1. Applications of limestone up to three tons per acre increased the total number of soil bacteria which develop on "modified synthetic" agar plates.

2. These increases probably occurred in species more resistant to drought.

3. The three ton application gave a proportionately greater increase in numbers than the two tons.

4. Application of limestone up to three tons per acre increased the ammonifying, the nitrifying, and the nitrogen fixing powers of the soil.

5. The ammonification of dried blood and cottonseed meal did not run parallel in tests of field soils subjected to continued drought."

6. The three ton applications of lime gave proportionately greater increases in the ammonifying, nitrifying, and nitrogen fixing powers of the soil than the two tons.

7. Continued drought reduced the nitrifying power of the soil, less reduction occurring in the limed than in the unlimed soils.

8. Continued drought followed by wet weather led to increased nitrogen fixing power.

9. Notwithstanding extreme, irregular moisture and climatic conditions, applications of lime up to three tons per acre increased the crop yield of corn.

10. Increased bacterial activities as indicated by the methods employed were accompanied by increased crop production.

BACTERIOLOGICAL STUDIES OF

FIELD SOILS. I.

BY PERCY EDGAR BROWN.

INTRODUCTION.

Soil fertility has been defined as the "crop producing power of a soil under given climatic conditions," and it is now generally recognized that this crop producing power of any soil depends on three factors: i. e. the chemical, the physical, and the bacteriological character of the soil.

The chemical and the physical composition of a soil may be determined with a fair degree of accuracy by the methods which are at present available, but without some knowledge of the bacterial conditions such determinations are of practically no value in ascertaining the fertility of the soil, for it is through the agency of microorganisms that the insoluble, unavailable plant food is transformed to forms readily available for plant nourishment.

It is the aim, therefore, of all soil bacteriological investigations to determine the extent and character of the bacterial activities in the particular soil studied and, by correlating such results with the results of chemical and physical analyses, to throw some light on the crop producing power of the soil.

It is not the intention of the writer to discuss here the history of soil bacteriology, to tell of the difficulties which have been encountered in the past and partially overcome, nor to dwell upon the limitations which the unsatisfactory methods at present available put upon the interpretation of all results, for these are fully discussed in other publications.

The purpose with which this series of experiments was begun was to determine the effects of different treatments on certain bacterial activities in soils under field conditions. Eventually it is hoped that it will be possible to ascertain whether there can be said to exist any relationship between these bacterial activities and the crop producing power or fertility of the soil. The various plots now in experiments under the direction of the agronomy section offer unexcelled opportunity for the prosecution of this work and will be freely used in the future. These plots are managed with the greatest possible care with respect to application of materials, preparation of seed beds, seeding, cultivation, harvesting, etc. While they are thus protected against many difficulties which would be encountered in ordinary field experiments, these plots present typical field conditions under control.

The method employed in the work of testing certain bacteriological activities in the soil was that known as the "beaker" method. This was used because it is the best method which has yet been devised for this purpose. It is clearly recognized, however, that there are certain objections to it which it is hoped may be overcome in the future and it is understood, also, that there are distinct limitations to its usefulness. In other words, while the beaker method is absolutely inapplicable to certain problems it seems to be well adapted to others. It is the purpose of the writer to discuss fully in a future publication the objections to, and the limitations and the value of the method, so further space will not be devoted to it here.

It should be stated here also that owing to the character of field conditions, it is clearly understood that changes in bac terial activities apparently produced by special treatment may be due to other circumstances connected with the particular work and too great care can not be observed in interpreting results. If the effects of special treatments predominate any local peculiarities which may be observed, then conclusions are, of course, permissible.

All these things should be kept continually in mind and great care observed in avoiding too great generalization in interpreting the results. While, therefore, any conclusions which are drawn from these investigations need not be applicable to any other soil and climatic conditions, it is deemed that they are of sufficient interest to warrant the attention which has been accorded the work. It remains for further study under different conditions to show the local or general application of the results, and it is hoped that apart from determining the effect of certain treatments on bacterial activities in field soils, some relations between such activities and crop production may be established.

1.

I. THE EFFECTS OF LIME.

The fourfold action of lime on soil has been discussed in a previous publication1 and a resume of the work which has been done in the past along this line may also be found in the bulletin mentioned so that neither of these need be included here. Suffice it to say that in most cases lime has been shown to exert a remarkable influence on the activities of bacteria in the soil. The work of the writer, already cited, which was carried out under greenhouse conditions, showed very clearly the beneficial action of lime on certain groups of bacteria in a typical Wisconsin drift soil. While the value of greenhouse experiments

1Research Bulletin 2. Iowa Experiment Station.

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