BXJIjTjETUST 



OF THE 



DEPARTMENT OF AGRICULTURE, 



NEW '• 



JAMA.IO.A. 



GAtD! 



Vol. VI. FEB. & MAR., 1908. Parts 2 & 3. 



THE PRESENT STATUS OF THE NITROGEN 



PROBLEM*. 



By A. F. WOODS. 



Pathologist and Physiologist and Assistant Chief of the Bureau of 

 Plant Industry, U. S. Dept. of Agri. 



Introduction. 



One of the greatest problems in the maintenance of soil 

 fertility for the maximum production of crops is how to secure 

 and keep a sufficient supply of available nitrogen of the least cost. 

 For most of our arable land it is now prettj well agreed that 

 this is a problem of bacteriology, with the soil as a culture me- 

 dium. As in most other great problems, nature and practical 

 experience have pointed the way to its solution. Many of the 

 standard practices of cultivation, crop rotation, etc., which have 

 developed from experience have very important relations to bac- 

 terial action in the soil. In fact, the true relation of many of 

 these practices can be understood only from the standpoint of 

 bacterial activity. It remains for science to explain, systematize, 

 and improve practice, placing conditions more accurately under 



our control. 



The sources of nitrogen supply are, first, the nitrogen already 



' contained in soils ; second, that supplied to the soil by the decay 



^ of organic matter ; and third, the fixation of atmospheric nitrogen. 



THE DIRECTLY AVAILABLE NITROGEN CONTENT OF SOILS. 



The nitrogen in soils is of two types : (i) The ammonia, nitrites, 



and nitrates, in which forms it is available to crops ; and (2) the 



nitrogen locked up in organic matter and not directly available. 



*From the Yearbook of the U. S. Department of Agriculture, 1906. 



