POTASH FERTILIZERS 21 5 



of available potash is sometimes indirectly due to a 

 deficiency of lime or other alkaline matter in the soil, 

 which prevents the necessary chemical changes taking 

 place in order that the potash may be liberated as plant 

 food. 



246. Sources of Potash in Soils. The main source 

 of the soil's potash is feldspar, which, after disintegra- 

 tion, is broken up into kaolin and potash compounds. 

 Mica and granite also, in some localities, contribute lib- 

 eral amounts, and the zeolitic silicates are a valuable 

 source of potash. There is but little water-soluble pot- 

 ash except in alkaline soil. By the action of many fer- 

 tilizers the potash compounds undergo changes in com- 

 position. For example, the gypsum which is always 

 present in acid phosphates liberates some potash. The 

 potash compounds of the soil are in various degrees of 

 complexity from forms soluble in dilute acids to insoluble 

 minerals as feldspar. 



247. Commercial Forms of Potash. Prior to the in- 

 troduction of the Stassfurt salts, wood ashes were the main 

 source of potash. Since the discovery and development 

 of the Stassfurt mines, the natural products, as kainit, 

 and muriate and sulphate of potash, have been exten- 

 sively used for fertilizing purposes. A small amount of 

 potash is obtained also from waste products, as tobacco 

 stems, cottonseed hulls, and the refuse from beet-sugar 

 factories. 



