24 STATE BOARD OF AGRICULTURE. 



lained much nitrogen which could not satisfactorily be accounted for. 

 A\'ith the discovery of the root tubercles, or nodules, a fresh stimulus 

 was given to the investigation, but no tangible knowledge could be 

 obtained in regard to the assimilation of nitrogen until it was found that 

 these tubercles or nodules contained a mass of bacteria which were able 

 to utilize the free nitrogen of the air and convert it into a form suitable 

 for plant assimilation. 



If grown in sterilized soil these nodules do not form. This indicates 

 that the bacteria are in the soil. Varieties exist, for it has been quite 

 conclusively shown that the variety found on one plant cannot be inocu- 

 lated into another with success. % 



Germs which are capable of abstracting nitrogen from the air are 

 found in crevices of bare rocks. Here they probably convert the nitro- 

 gen into the form of nitric acid, which acts upon the rocks and dissolves 

 thf^m. 



In conclusion, aside from the hygienic consideration, we may assign to 

 the micro-organisms of the soil the following functions: 



1. The fermentation of organic matter, resulting in ammonia com- 

 pounds along with others. 



2. The action of nitrifying bacteria upon the fermentation products. 



3. The liberation of free ammonia, soil fermentations. 



4. The liberation of free nitrogen by means of denitrifying bacteria 

 in their action upon nitrates. 



5. The abstraction of free nitrogen from the air by bacteria and its 

 conversion into a form assimilable by plants. 



6. The abstraction of free nitrogen from the air by bacteria and its 

 conversion into a form in which it may act upon rocks and reduce them 

 to arable soil. 



DISCUSSION. 



Q. Has there been found anything to catch nitrogen? Does land plaster retain 

 nitrogen in fermenting niamire? 



Dr. Marshall : There is a wide difference between lime and plaster in their relation 



to ammonia. Plaster, in the presence of abundant moisture, seems to have the dual 



effect of somewhat retarding fermentation and absorbing ammonia. Lime, on the other 



/hand, by chemical action, drives off ammonia, acting as a caustic. Its action in this 



respect is brief, however, as it soon changes to carbonate. 



Q. Why is plaster not as good as thirty or forty years ago? 



Dr. Kedzie: In the natural order of things, but thirty or forty pounds of plaster 

 can be utilized per acre per year. Plaster was applied at the rate of 200 pounds to 

 the acre, and now the soil has all that it needs. This excess of plaster will not always 

 remain, but it will gradually be washed away. 



Q. Is thirty pounds of plaster to the acre then enough? 



Dr. Kedzie: With thirty inches of rainfall our ordinary soils can use but thirty 

 pounds of plaster per acre per year. Some crops receive benefit from the plaster ; 

 others get none. Legumes usually are benefited by an application of plaster. 



