FERTILIZING AGENTS 317 



phate rocks, which are derived from the deposits of 

 bones of prehistoric animals, are abundant in many 

 places and furnish tons of phosphorus compounds for 

 fertilizing. 



Wood ashes enrich soil because they contain potash. 

 Up to the beginning of the recent World War, the great 

 potash beds of Germany supplied most of the potash used 

 in agriculture. After the war started the United States 

 began making efforts to locate potash beds and to produce 

 potassium compounds in various ways. 



In October, 1918, Secretary Lane of the United States De- 

 partment of the Interior announced that within two years 

 the United States would be independent of the German 

 supply. Chemists have discovered practical processes by 

 which to produce potash from the brine and from the de- 

 posits of old salt lakes in certain western states. They have 

 also found ways of extracting potash from seaweeds, which 

 have never before been of direct service to man; from minerals 

 that have heretofore been considered worthless; from the 

 fumes of smelters and from the dust of cement plants, which 

 have hitherto been considered not only useless but even 

 injurious. Thus chemistry turns waste into wealth. 



Fertilizing Agents. Among the most important fer- 

 tilizing agents are the nitrogen-fixing bacteria. These differ 

 from the other kinds of soil bacteria mentioned, in that they 

 are able to take nitrogen directly from the soil air and to 

 combine it into compounds. Farmers know that if a field 

 is sowed to clover or to soy-beans, for example, it becomes 

 more fertile. This is owing to the fact that the nitrogen- 

 fixing bacteria live and multiply in great numbers in knots, 

 or nodules, on the roots of these plants. When the clover 



