FERTILIZERS 131 



these bacteria and the plants enables the latter to feed in- 

 directly upon the limitless and costless store of free atmo- 

 spheric nitrogen. 



Nitrogen is one of the most costly and important of all 

 plant foods and most crops remove large quantities of it from 

 the soil. This applies with especial force to the wheat crop. 

 The commercial supply is so limited that a "nitrogen famine" 

 had already been predicted, but the discovery of nitrogen- 

 gathering bacteria seems destined to lead to the utilization of 

 air nitrogen at a nominal cost. Plants normally obtain through 

 their roots nitrogen in some highly organized form. All non- 

 leguminous plants placed in soil entirely destitute of nitrogen 

 will wither and die. Bacteria alone have this power of fixing 

 nitrogen. Not only have these bacteria increased the nitrogen 

 content of soils planted with leguminous crops, but it is now 

 claimed that for many centuries they have been continually fix- 

 ing atmospheric nitrogen in certain regions of Chile and Peru, 

 thus creating the extensive deposits of nitrate of soda there 

 found in a natural state. 



Men realized the increasing importance of the nitrogen prob- 

 lem as the supply decreased, and it was but natural for scien- 

 tists to turn to atmospheric nitrogen in an endeavor to replen- 

 ish the stores being so rapidly depleted, especially when they 

 remembered that nearly eight-tenths of the air is nitrogen, and 

 that plants are able to obtain all their carbon from a gas 

 constituting only 0.1 per cent of the air. During the last 

 quarter of a century bacteriologists have made numerous ex- 

 periments which have thrown much light upon the subjects of 

 nitrification, denitrification, and the fixation of free nitrogen 

 in the soils. It has been found that the soil is alive with 

 countless micro-organisms. The activity of some of these fer- 

 ments favors, while that of others retards, plaait growth. One 

 group carries on the process of nitrification, and another that 

 of denitrification. In the latter process the nitrates are broken 

 down, deprived of their oxygen, and reduced to ammonia or 

 nitrogen gas. Nitrates thus lose their availability for plant 

 food. Great losses in manures may often occur from this 

 source. It is the part of scientific agriculture to determine 

 how to minimize the activity of inimical 



