NITROGEN FIXATION LOF 



NEED FOR FERTILIZERS 



205 



The fertility of the soil would thus remain practically unchanged 

 if all the ingredients removed in the various farm products were 

 returned to the land where they come from. This is to some extent 

 accomplished by feeding the crops grown on the farm to animals, 

 carefully saving the manure and returning it to the soil. A care- 

 ful study of the present conditions of farming indicates, however, 

 that as a rule the manure produced on the farm is far from suffi- 

 cient to maintain its 



fertility, and artifi- |g»a*B# ««i»!»ftw i »g»fcfift8 l . l »N.»!»»,.Kl 



eial fertilizers must 

 be resorted to. 



It has been esti- 

 mated that the 

 yearly loss of nitro- 

 gen from soils under 

 cultivation in this 

 country by grain 

 crops alone amounts 

 to over 2,000,000 tons 

 per year. Of this, 

 not over 3 per cent 

 is at present being 

 supplied from organic fertilizer sources, such as tankage, cottonseed, 

 etc., and this supply is constantly diminishing. The remainder must, 

 therefore, come from inorganic materials. It would, of course, not 

 pay to fertilize to the above extent immediately, but it merely indi- 

 cates the extent to which nitrogen is needed for fertilizer purposes. 



With our constantly increasing population, an increased food sup- 

 ply must be provided, and this can only be assured by increased 

 cultivation and fertilization of the soil. How far behind we lag in 

 this respect as compared with certain European countries, which of 

 necessity have been forced to an intensive use of fertilizer, is shown 

 by the following table : 



Fig. 2. — Inorganic nitrogen consumption in United States 

 as given by Nitrate Division of the United States Ord- 

 nance Department. Black portions represent inorganic 

 nitrogen used in agriculture. White portions represent 

 nitrogen used in industries and for explosives 



