EXPERIMENT STATION BULLETINS. 281 



NOTE. 



It is earnestly desired that the farmers and gardeners of the State of Michigan 

 will cooperate with this department in furthering the study of bacterial plant 

 diseases by reporting all diseases of this nature that may come under their notice 

 and also by sending In specimens of suspicious material for examination. 

 Wherever possible the whole plant should be sent, for usually root, stem and 

 leaf are required for a satisfactory diagnosis. Address all of your communica- 

 tions relative to suspected bacterial plant diseases to The Department of Bacteri- 

 ology and Hygiene, Michigan Agricultural College, Agricultural College, Mich. 



SUGGESTIONS CONCERNING LEGUME INOCULATION. 



LAWRENCE T. CLAEK. 



[Bulletin No. 231.] 



The soil of many farms in Michigan, as well as in other states, especially in 

 the older states, is becoming depleted, and among the exhausted elements nitrogen 

 is one of the most difficult to recover. The principal means of recovering nitro- 

 gen to the depleted soils are: First, the application of barnyard manure; second, 

 the use of commercial fertilizers; third, the growing of leguminous crops, which, 

 if infected with nitrogen-fixing bacteria, take nitrogen from the atmosphere and 

 store it within the plant. The supply of barnyard manure is inadequate to make 

 up for the losses of nitrogen occasioned by ordinary cropping; the supply of 

 the mineral salts of nitrogen contained within the commercial fertilizers is rapidly 

 becoming exhausted, hence too expensive to be used with profit; finally, this 

 brings us to the growing legume, the nitrogen-fixing bacteria, and the atmos- 

 phere as a feasible solution of this serious question. 



Since 1884 to 1886, it has been definitely known that legumes, possessing nodules 

 on their roots, have the power to take nitrogen from the atmosphere and make 

 use of it in the actual growth of the plant. Plants possessing these nodules or 

 an internal infection without the formation of nodules, were found to be the 

 only ones capable of this action. The organism or germ present within the nodule 

 and root was found responsible for the formation of such enlargements, and also 

 for collecting and transforming the nitrogen into an available form. 



Owing to the fact that these nodules would form only in soils infected with 

 the nodule producing organism, it is impossible to grow legumes, possessing such 

 nodules, in soils where that particular legume or one closely related, has not 

 been previously grown and the proper organism distributed. However, a com- 

 plete inoculation is made possible by a persistent seeding of one field to the same 

 legume. The nodule-forming bacteria are carried in small numbers on the seed 

 from their respective hosts, consequently, by the application of one kind of seed 

 to the same field year after year a quantity of the germs is distributed, which, 

 together with those which have already developed on the host of the previous 

 season's planting, finally succeed in affecting a uniform inoculation over the 

 entire field. This manner of securing a successful inoculation, although a rather 

 long and expensive one, has proved itself a certain one in several cases that have 

 been called to our attention. 



The effect of a previous successful inoculation, although upon a different 

 species of legume, is coming to be considered beneficial to the succeeding legume. 

 For example, a thoroughly inoculated plot of vetch was ployed under at the 

 College Experiment Station in May, 1904, and the plot sowed with uninoculated 

 alfalfa. In May, 1905, this same plot was again plowed up, exposing the alfalfa 

 roots which were heavily laden with clusters of nodules not unlike the typical 

 vetch nodules. Another interesting feature of this observation was the existence 



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