Unsolved Problems Related to the Inoculation of Legumes

Almost forty years have passed since Hellriegel and Wilfarth solved the nitrogen problem in soil fertility, by giving a comprehensive explanation of how legumes, with the aid of bacteria living in the nodules on their roots, could grow in a medium devoid of any combined nitrogen. During this time considerable advancement has been made in our knowledge of the subject of soil bacteriology, particularly with reference to inoculation, but, all soil bacteriologists will agree that there yet remain many unsolved problems related to the inoculation of legumes. The purpose of this paper is to call attention very briefly to some of these important problems that await solution

The numbers of microorganisms in Carrington loam as influenced by different soil treatments

This bulletin presents the results of studies made on the soils from a number of field plots which are located on Carrington loam and have been under definite soil treatments and cropping systems for a period of 12 years. The following conclusions seem justified: 1. The highest numbers of bacteria were found in the soils in March, 1926. In 1925 the highest numbers of bacteria were found in July and November. Great fluctuations in numbers of bacteria occurred from one sampling to another. 2. The greatest number of fungi was found in the soils in November, 1924. The numbers gradually decreased during the winter months and reached a minimum in June, 1925. Another maximum was reached in January, 1926. This increase was followed by a decrease in numbers which reached a low point in April. From then on great fluctuations occurred which can not be explained from the data secured. 3. The numbers of actinomycetes varied with the number of bacteria. An increase in bacteria was followed by an increase in numbers of actinomycetes. The relative proportion of these two groups of organisms was between 1 to 10 and 1 to 20. 4. No correlation existed between the numbers of microorganisms and the nitrate accumulation in the soils. 5. The amount of moisture varied in the soils at the different samplings, but this factor did not have any appreciable influence on the numbers of microorganisms. 6. Applications of manure alone, or of manure and lime, did not affect the numbers of fungi in this soil. 7. Superphosphate and rock phosphate, when added with lime and manure, caused a slight increase in the numbers of fungi present. 8. All of the soil treatments studied increased the numbers of bacteria in this soil. Manure and lime increased the number more than did the manure alone; manure, lime and rock phosphate increased the number more than did the manure and lime; and manure, lime and superphosphate brought about the greatest increase in numbers of bacteria. 9. The various soil treatments did not seem to affect the number of actinomycetes in this soil. 10. All of the soil treatments increased the crop yields. There was a direct correlation between the number of bacteria in the different plots and crop yields. Where superphosphate or rock phosphate was used a correlation was noted between numbers of fungi and actinomycetes and crop yields. 11. The data were not complete enough to permit of definite conclusions regarding the effect of crop rotations on the numbers of microorganisms in this soil. Studies along this line must be carried on over a long period of years

Comparison of Aerated and Non Aerated Cultures for Nitrogen Fixation Studies by Soils

In any good system of soil management the farmer has two natural ways of maintaining the nitrogen supply in the soil; (1) by the proper growth and use of inoculated legumes; and (2) by encouraging the development of the non-symbiotic nitrogen fixing microorganisms in the soil. Altho the first method is probably the more important especially in those regions where legumes are commonly grown, undoubtedly many farmers have unconsciously practised the second method. It has been definitely shown that even where legumes are not grown the nitrogen balance in the soil is automatically cared for, to some extent at least, by microorganisms which are capable of fixing large amounts of nitrogen from the air without the aid of a host plant. The exact relation of this process of non-symbiotic nitrogen fixation to soil fertility is an interesting problem of both practical and scientific importance. It has attracted the attention of many soil bacteriologists, but in spite of much accumulated information on the subject, there are many questions still to be answered before it will be known just how much nitrogen is fixed annually per acre of soil by this process

The Significance of the Hydrogen-Ion Concentration in Soil Nitrification Studies

Although considerable work has been reported in the literature which shows some correlation between nitrification and the crop-producing power of soils, very little attention has been given to the significance of the soil reaction in nitrification studies. The object of this paper is to consider this problem and data are presented which show the relation of the reaction of the soil or its hydrogen-ion concentration to its nitrifying capacity

Studies on nitrification and its relation to crop production on Carrington loam under different treatment

In the summer of 1926 certain plots on the Agronomy Farm of the Iowa Agricultural Experiment Station were sampled four times and studies made on the amount of nitrates, moisture, and the reaction of the soils at the time of sampling and the nitrifying power of the soils as determined by three methods, (a) nitrification of the soils\u27 own nitrogen, (b) nitrification of ammonium sulfate and (c) nitrification of ammonium sulfate in the presence of calcium carbonate. The reaction of the soils was also determined after the 30 days of incubation. The following conclusions seem to be justified from this study: 1. The amount of moisture was not affected by the crop rotations used nor by the various soil treatments. Neither did the variations in moisture content which occurred in these soils have any appreciable effect on the crop yields or on their nitrifying power. 2. The crop rotations on the Carrington loam did not seem to affect appreciably the nitrifying power of the soils from plots which were left untreated for 12 years nor those which were manured, manured and limed, or treated with crop residues and lime. 3. The application of manure alone did not increase the nitrifying power of the Carrington loam. 4. The soils from the three-year rotation corn plots showed the largest amount of nitrates present at the various times of sampling and the highest nitrifying power when this was measured by the nitrification of the soils\u27 own nitrogen. 5. Definite correlations were obtained between the crop yields, the nitrifying power and the reaction of the soils after incubation, when the nitrifying power of the soil was tested by measuring the nitrification of ammonium sulfate. The reaction of the soils at the time of sampling also correlated with the nitrifying power of the soils as determined by this method. 6. Perfect correlations were not obtained between the nitrifying power of the soils and crop yields\u27 when the test was made by measuring the nitrification of ammonium sulfate in the presence of CaCO3, altho the soils all showed a high nitrifying power in all cases where the crop yields were high. 7. The nitrifying power of all of the soils was shown to be greater when calcium carbonate was used with the ammonium sulfate in the nitrification test. 8. The soils from plots which had been limed in the field showed the highest nitrifying power, and hence there seemed to be a definite correlation between the reaction of the soils and their nitrifying powers

Soybean inoculation studies

The results of the soybean inoculation studies reported in this bulletin were obtained under field conditions, and the experiments extended over a period of three years. These studies included the testing of different ways of applying inoculated soil to soybean seeds as well as to the soil, and also the testing of a number of commercial cultures, secured from different sources, on the inoculation of soybeans. Data have also been reported which show the relative efficiencies of soil from different sources, pure cultures of soybean bacteria, and different commercial cultures on the inoculation of different varieties of soybeans. The effects of inoculation, lime and lime and superphosphate, on the percentage of nitrogen in soybean plants have also been noted. In some cases the experiments were repeated for two or three years, and the results obtained each year agreed remarkably well

Preliminary Note on the Sterilization of Seeds of the Leguminosae with Hydrogen Peroxide

In the scientific study of many bacteriological problems it is necessary to deal with pure cultures of the organism with which the worker is interested. This has been true in our studies on the nodule producing organisms of leguminous plants. Before any morphological or physiological studies are made on these organisms they should be tested on the host plant for their inoculating ability, and in order to do this all possible chances for contamination by other organisms must be eliminated. If, in testing out a certain culture for its inoculating ability on the host plant, the plants were grown under conditions that were not sterile, and certain results were obtained, we would have no right to say that these results were due to the culture used, because they may have been due to contamination from the air, from the soil used, or from using seeds that were not sterile. In our studies on these organisms we have attempted to overcome these difficulties and sources of error, and it is the purpose of this paper to present the results of some preliminary work on the sterilization of seeds of the Leguminosae

Occurrence of the Various Groups of Legume Bacteria in Iowa Soils

For a long time it has been known that the root-nodule bacteria of the Leguminosae differ considerably in their ability to inoculate plants. An outstanding example of this fact was brought to the attention of the early investigators when it was found that soybeans failed to produce nodules in European soils, while many other species of legumes were naturally inoculated. Kirchner (4), the first investigator to inoculate soybeans in Germany, found that it was necessary to use soil from Japan where the soybean was native and naturally inoculated. Since that time many such examples have been recorded. Just recently Gangulee (3), at the Rothamsted Experiment Station, England, has reported that the legume, Crotalaria juncea, was not naturally inoculated in British soils, and could not even be inoculated artificially until soil from India, where the plant is native, was used for that purpose

Significance of Residual Organisms in Foods after Substerilizing Doses of Gamma Radiation: A Review

The nature of the flora surviving substerilizing irradiation of foods is dependent on the dose applied and the conditions of applications as well as the microenvi¬ronment of the food. At a dose level low enough to preserve acceptable sensory properties of fresh food, few if any of the common contaminants of public health significance survive irradiation. Survivors are weakened and present no unique problem of acquired resistance through recycling. Those bacteria surviving a low dose treatment of a relatively contaminated product like ground beef can grow under normal storage conditions and cause obvious sensory spoilage. Thus, low dose irradiation extends the shelf-life of fresh foods and reduces public health hazards, but foods so treated require normal care in production and distribution