340 THE PRINCIPLES OF SOIL MANAGEMENT 



is readily soluble in dilute acids. It is now quite gener- 

 ally believed that it furnishes an available supply of 

 phosphorus to the plant. In a statement of fertilizer 

 analyses it is termed "citrate soluble," and this and the 

 "water soluble" are termed "available." 



The degree of fineness to which the material is ground 

 makes a great difference in the availability of the less- 

 soluble phosphate fertilizers, especially in the ground- 

 rock phosphates, and in ground bone. This material 

 should be ground fine enough to pass through a sieve 

 having meshes one-fiftieth of an inch in diameter. 



205. Fertilizers used for their potassium. The pro- 

 duction of potassium fertilizers is largely confined to 

 Germany, where there are extensive beds varying from 

 50 to 150 feet in thickness, lying under a region of 

 country extending from the Harz mountains to the 

 Elbe river, and known as the Stassfurt deposits. De- 

 posits have lately been discovered in other parts of 

 Germany. 



206. Stassfurt salts. The Stassfurt salts contain 

 their potassium either as a chloride or a sulfate. The 

 chloride has the advantage of being more diffusible in 

 the soil, but in most respects the sulfate is preferable. 

 Potassium chloride has an injurious action on certain 

 crops, among which are tobacco, sugar-beets and pota- 

 toes. On cereals, legumes and grasses, the muriate 

 appears to have no injurious effect. 



The mineral produced in largest quantities by the 

 Stassfurt mines is kainit. Chemically it consists of mag- 

 nesium and potassium sulfate, and magnesium chloride, 

 or magnesium sulfate and potassium chloride. Kainit 



