462 NATURE AND PROPERTIES OF SOILS 



soil rich in organic matter it may be added to advantage. It 

 is especially useful in reinforcing farm manure, seemingly be- 

 ing about as effective under such conditions as is acid phos- 

 phate. Its higher phosphorus content and lower cost a ton 

 gives it an added advantage. The figures from Ohio, 1 cover- 

 ing a period of fourteen years in a rotation of maize, wheat, 

 and hay may be taken as evidence regarding these points. 

 The manure, reinforced to the ton with 40 pounds of acid 

 phosphate and raw rock phosphate, respectively, was applied 

 to the corn at the rate of eight tons to the acre. 



Table XCVI 



A COMPARISON OF ACID PHOSPHATE AND RAW ROCK IN EQUAL 

 WEIGHTS WHEN ADDED TO THE SOIL WITH MANURE. 



FERTILIZERS USED FOR THEIR POTASSIUM 



The production of potassium fertilizers is largely confined 

 to Germany, where there are extensive beds varying from 

 50 to 150 feet in thickness, lying under an area extending 

 from the Harz Mountains to the Elbe River and known as 

 the Stassfurt deposits. Large deposits of crude potash salts 

 occur in other sections of Germany, and also in France. 

 While small deposits occur in other parts of the world the 

 French and German mines are at present the only ones of 

 any great commercial importance. The World War stimu- 

 lated considerable investigation regarding possible sources of 



1 Thome, C. E., et al., Plans and Summary Tables of the Experiments 

 at the Central Farm; Ohio. Agr. Exp. Sta., Circ. 120, p. 112, 1912. 



