UTILIZATION OF NITROGEN 30 1 



chiefly present in an organic state. Culture solutions should 

 therefore be seeded with samples of the soil under examination 

 and the beginning and rapidity of the nitrification carefully noted. 

 In conjunction with this the nitrogen present in the soil in a nitric 

 or ammoniacal form should be accurately determined. 



The quantities of Chile saltpeter which should be applied per 

 acre vary with so many conditions as to make any definite state- 

 ment impossible. On account of the great solubility of this salt, 

 no more should be used than is necessary for the nutrition of the 

 crop. For each 100 pounds used, from 14 to 15 pounds of nitro- 

 gen will be added to the soil. Field crops, as a rule, will require 

 less of the salt than garden crops. There is an economic limit 

 to the application which should not be passed. As a rule, 250 

 pounds per acre is a maximum dressing for field crops. The 

 character of the crop must also be considered. Different amounts 

 are required for sugar beets, tobacco, wheat, and other standard 

 crops. It is rarely the case that a crop demands a dressing of 

 Chile saltpeter alone. It will give the best effects, as a rule, when 

 applied with phosphoric acid or potash. But this is a branch of 

 the subject which cannot be entered into at greater length in 

 this manual. The reader is referred to Weitz's work on Chile 

 saltpeter for further information. 62 



265. The Utilization of Nitrogen in fhe Air as a Fertilizing 

 Material. The only form of plant which has developed these tu- 

 bercles to any extent is the legumes. It is, therefore, commonly 

 understood that the nitrifying organisms of symbiotic forms are 

 confined to leguminous plants. At the same time, mention is made 

 in Volume I of the possible direct nitrifying of atmospheric nitro- 

 gen without the intervention either of any organic form thereof, 

 or the activity of other symbiotic nitrifying activity. Some of 

 the results of earlier workers in this field seem to indicate the 

 existence of organisms which are capable of directly nitrifying 

 atmospheric nitrogen and making it available as a fertilizing 

 material. These earlier ideas which are mentioned in Volume I, 

 have of late years received further investigation, with the result 

 of establishing more firmly the belief that nitrification, indepen- 



62 Der Chilisalpeter als Diingemittel, 1905. 



