VII. 



SPECIAL MANUEES 



155 



The production of potash salts from the German mines has enor- 

 mously increased. The following table l gives, in metric tons, the totals 

 produced in 1907 and 1908 : 



while the prepared salts marketed were as follows, also in metric tons 

 (2205 lb.). 



In this country, the products employed are mainly kainite, the 

 calcined double sulphate of potash and magnesia and " muriate of 

 potash ". For special horticultural purposes, pure sulphate of potash 

 and nitrate of potash are also employed. 



The important potash manures contain their potassium either as 

 chloride or sulphate. The chloride has the advantage in being more 

 diffusible in the soil ; but in most other respects the sulphate is prefer- 

 able. As in the case of other soluble manures, interaction between 

 the potassium salt and the calcium and other compounds in the soil 

 begins immediately, resulting in the formation of calcium chloride or 

 sulphate. The former has an injurious action upon plants, while the 

 latter is harmless or probably beneficial. Moreover, when potassium 

 chloride is applied in large quantities, the salt as a whole seems to be 

 absorbed by some plants, and in the case of tobacco, for example, the 

 ash left when the dried plant is burnt contains the easily fusible 

 potassium chloride. This acts as a fire-proofing material to some 

 extent and prevents the proper burning of the tobacco; potassium 

 sulphate yields a crop containing no such fusible ash constituent. In 

 the case of clover, corn and grass, however, potassium chloride appears 

 to have little or no harmful effect. 



Potash manures are most needed on light sandy or calcareous soils 

 and are seldom required on clay land. Potatoes, grass land and 

 leguminous crops are particularly benefited by potash manures. When 

 the nitrogenous manure used is sulphate of ammonia, the soil is often 

 benefited by potash manuring, while nitrate of soda on the same land 

 will often render it indifferent to potash manures. This is particularly 



1 Engineering and Mining Journal, May 9, 1908 ; Jour. Soc. Chem. Ind., 1908, 

 574. 



