Bacteria and the Nitrogen Problem. 517 



Witli a power sufficiently cheap and with perfect machinery, there 

 seems good reason to believe that in the near future it will he 

 possible to place upon the market a manufactured nitrate of soda or 

 nitrate of potash that will be superior in quality to the deposits 

 found in South America, and that will also be reasonable enough in 

 price to compete with the natural product. 



Nitrogen-Fixing Bacteria. 



Fortunately, there are still other means by which nitrogen gas 

 may be made available for plant food, and that, too, without requir- 

 ing the introduction of a commercial product, which must always be 

 rather expensive, whatever degree of perfection may be reached in 

 the mechanical operation of the process. Ever since the earliest 

 days of agricultural science it has been noticed that cei'tain land, 

 if allowed to stand fallow for a considerable length of time, would 

 gain in nitrates without any visible addition having been made. 

 It is now known that one of the principal means of this increase in 

 nitrogen content is due to a few forms of soil bacteria which have the 

 power of fixing the free nitrogen from the air and rendering it 

 available for plant food. These organisms have been isolated and 

 cultivated artificially, and great hopes were held at one time that it 

 would be possible to inoculate land with these cultures and thus bring 

 about a large increase in the nitrogenous salts without the aid of any 

 manure or mineral fertilizer. Under certain conditions these 

 bacteria seemed able to do a large amount of work, and there are 

 experiments on record where the crops raised from plots inoculated 

 with nitrogen-fixing organisms were much greater than crops from 

 uninoculated land. Unfortunately, these results were not always 

 constant, and such a large percentage of failures had to be reported 

 that from a practical standpoint the use of such cultures is now con- 

 sidered worthless. A matter of such vast importance to agriculture, 

 however, should not be neglected simply because of first failures. It 

 is quite possible that as we become better acquainted with the habits 

 of these bacteria and learn the conditions which are most favor- 

 able to fixing nitrogen and the causes which prevent this operation 

 from going on at all times, we shall be able to discover some 

 means of using these nitrogen gatherers in practical farming. 



Root Tubercle Bacteria. 



In the meantime there is still one other means at hand wliich can 

 be used and has been used for countless centuries as a most efficient 

 method of conserving the world's nitrogen supply. Kver since the 

 time of Pliny and other early writers upon agricultural topics, it has 

 been known that certain leguminous crops, such as clover, beans, 

 peas, etc., did not require the same amount of fertilizer as other 

 plants, and indeed it seemed as though they actually benefited the 

 soil instead of being a detriment. Various theories have been 

 advanced to account for this effect, perhaps the most widespread 



