ORGANIC MATTER AND NITROGEN 211 



cowpeas in the cowpea country of the South, and to the clovers 

 throughout the Central and Eastern states. Where the special 

 legume has not been grown successfully in the vicinity; or even on 

 fields where the legume has not been grown for many years, and 

 where neither manuring, overflow, nor dust storms have brought 

 the bacteria from other fields, it is worth while to consider inocula- 

 tion. 



The bacteria for clover, cowpea, and vetch are now very widely 

 distributed over the United States (in part because of the par- 

 tridge pea and wild vetches); but for alfalfa (except in alfalfa 

 regions) and for soy beans, the question of inoculation should 

 always be considered. For inoculating alfalfa, either alfalfa soil or 

 sweet-clover soil can be used, care being taken to use only well- 

 infected soil, collected where the plants have been growing for 

 several years, well provided with root tubercles. 



The accumulated practical experience of the past twenty years, 

 and the data thus far reported from many comparative experi- 

 ments, combine to prove that the simplest and surest and most 

 economical method of inoculation is by means of well-infected 

 natural soil, collected where the plants are thrifty and free from 

 noxious weed seeds, although the danger of carrying weed seeds or 

 plant diseases by overflow, by wind storms, and in purchased ma- 

 nures and farm seeds is probably a hundred times greater than by 

 using infected soil for inoculation. The amount of soil used varies 

 from 100 pounds to a wagon load to the acre. It may be applied 

 broadcast with some degree of uniformity, and it should be mixed 

 with the surface soil without delay, as by harrowing or disking, 

 because exposure to the sunlight tends to destroy the bacteria. 



Successful seed inoculation can be performed with fresh, properly 

 prepared artificial cultures, but, as a rule, this method has proved 

 unsatisfactory. Some years ago German promoters undertook to 

 establish the business of selling nitrogen bacteria for seed inocu- 

 lation, and more recently American promoters have widely ad- 

 vertised similar products, but failure is the most common report 

 from their use. 



For large seeds, such as soy beans, a very satisfactory method 

 of inoculation, suggested by the Illinois Experiment Station, is to 

 thoroughly moisten the seed with a 10 per cent solution of glue, 



