282 MICROBIOLOGY OF SOIL. 



Inoculation with Legume-Earth. The use of soil as inoculating mate- 

 rial was tried by various experiment stations of the United States, with 

 results not varying widely from those secured in the pioneer experimental 

 work at Bremen. It was found in general that the commonly grown 

 crops, such as the common clovers, peas and beans, made little or no 

 increase as a result of inoculation with old legume-soil. With new crops, 

 however, such as alfalfa and soy beans when they were first introduced, 

 it was found impossible in many places to secure a successful stand until 

 the fields on which these crops were to be grown had received a top-dress- 

 ing of soil from land that had already grown the crop in question; and it 

 became a common practice to inoculate soil in this manner before seeding 

 with these new crops. It was early observed, however, that this method 

 of soil transfer for inoculation purposes was not an unmixed benefit. 

 Aside from the expense and difficulty of handling and transportation of 

 soil, fungus and bacterial diseases, not only of legumes but of other crops, 

 as well as the seeds, of noxious weeds, were transmitted from one field to 

 another and even from one section of country to another. It was to avoid 

 this difficulty that the preparation of pure cultures was introduced. 



Inoculation with Pure Cultures. Nitragin. The first pure culture 

 method was launched in 1896 by Nobbe and Hiltner, German investigators 

 who prepared cultures of the legume bacteria on nutrient gelatin and 

 arranged with a firm of manufacturing chemists to place them on the 

 market under the trade name of Nitragin. 



Nitragin met with an enthusiastic reception on the part of experi- 

 menters and farmers. The results of its use, however, were so 

 varying and uncertain that the product fell into disrepute and its manu- 

 facture was discontinued. Improvements have been made by Hiltner 

 and his associates, and a new Nitragin which has been placed on the 

 market within the past four years has given results much more positive 

 and uniform than were obtained with the old preparation. 



Dried Cultures. In the United States the matter of pure cultures 

 was first taken up by the Department of Agriculture about 1902. 

 Cultures of the nodule-forming bacteria were cultivated in nitrogen- 

 free culture media, dried on cotton and distributed to farmers with a 

 small package of salts from which a culture solution was to be made 

 by the farmer and applied to the seed. This method gave poor results, 

 chiefly because the bacteria could not withstand the drying on cotton. 

 Afterwards the cultures were sent in a liquid condition with somewhat 



