Tillage, Fertilizing and Rotation 103 



form. It seems that a combination of chlorin exerts 

 an undesirable influence on the quality of the crop. 

 This behavior is perhaps more noticeable -with Irish 

 potatoes than with sweets. The supply of potash is 

 obtained largely from the potash mines of northern 

 Germany. Sulfate and murate of potash, kainit, 

 sylvinit, high-grade sulfate of potash and double sulfate 

 of potash are the most common forms. As with murate 

 of potash, kainit also contains large amounts of chlorin, 

 although in reality the potash is in the form of a 

 sulfate. 



For sweet potatoes, potash is best applied in the form 

 of sulfate. It gives largest returns on light sandy 

 soils and on lands with a high humus-content. . Clay 

 soils are usually well supplied with potash, With a 

 good clay subsoil, when the surface is sandy, sweet 

 potato crops do not respond noticeably to applications 

 of potash, especially when the sand is not deep and 

 plowing has brought some of the clay to the surface. 



Potash is sometimes applied in the form of hard- 

 wood ashes, which in the unleached state contains about 

 5 per cent potash. This, however, is usually an expen- 

 sive medium and is seldom used except when the lime 

 contained is decidedly unleached, when it contains in 

 addition to 4 to 6 per cent potash, about 30 per cent 

 lime and from 1 to 2 per cent phosphorio acid. 



Commercial fertilizers. 



Commercial fertilizers differ from farm and green- 

 manures in that they exist in a form readily exchanged 

 and handled in commerce. The following table * gives 



1 Farmers' Bull. 44. 



