MINERAL INDUSTRIES OF THE UNITED STATES FERTILIZERS. 15 
another ; but the balance sheet would not remain even, for the whole 
coal by-product industry would receive a serious if not fatal set- 
back, w T ith far-reaching results, because of its intricate ramifications 
into other industries. 
This completes the list of sources from which we at present obtain 
nitrogen on an organized scale. Peat is a nitrogenous substance 
and is used locally to some extent as a fertilizer. The artificial 
bacterial inoculation of peat to increase its nitrogen content opens up 
interesting possibilities, now in process of experimentation; while 
an even more direct use of nitrogen -fixing bacteria, cultivated in a 
medium of organic waste, “ provides a less visionary project than 
might appear offhand.” On general grounds it seems quite logical 
to expect that, inasmuch as bacterial action is the method followed 
by nature in providing the nitrogen compounds required by plants, 
this process speeded up and controlled by man will furnish the 
ultimate solution of the fertilizer aspect of the nitrogen problem. 
If so, this will serve to illustrate again that no problem in this field 
can be solved at one stroke, but rather requires an evolution of suc- 
cessive solutions, each adapted to the current industrial and economic 
situation. 
Finally, in regard to nitrogen, we have two products, garbage and 
sewage, now to a large extent wasted, although possessing a dis- 
tinct fertilizing value. We may look forward to an increasing num- 
ber of municipal plants employed in rendering these materials suit- 
able for use. But development along this line for proper fruition 
must be coordinated with all related activities. 
/ 
Potassium. 
The third major plant food is potassium, which, however, like 
phosphorus and nitrogen, appears in neither fertilizers nor soils in 
the simple elemental condition, but in the form of various com- 
pounds or salts, of which the most important are potassium carbonate, 
potassium chloride, and potassium sulphate. The term “ potash” 
refers strictly to potassium oxide, used for calculating these com- 
pounds to a common basis; but the term is also employed in a loose 
manner to embrace the potassium salts in general. 
Potassium contributes stalk strength and kernel filling to the grow- 
ing plant. It is present in normal soils partly in the form of a 
soluble compound, potassium carbonate, produced during the course 
of soil formation by the chemical decay of complex silicate minerals 
present in the parent rocks. Where potassium in soluble form is 
lacking, due to special geological conditions of soil formation, or 
where it is withdrawn rapidly by continuous crop production, it 
must be added to the soil from an external source. 
