l88 SOILS AND FERTILIZERS 



Mangels, 10 tons 150 



Meadow hay, 1 ton 45 



Clover hay, 2 tons . 66 



Potatoes, 150 bushels 75 



230. Amount of Potash in Soils. — In ordinary- 

 soils there are from 3,500 to 12,000 pounds of potash 

 per acre to the depth of one foot. Many soils with 

 apparently a good stock of total potash give excellent 

 results when a light dressing of potash salts is applied. 

 The amount of available potash in the soil is more 

 difficult to estimate than the available phosphoric 

 acid. There is also a great difference in crops as to 

 their power of obtaining potash. Some require 

 greater help in procuring this element than others. A 

 lack of available potash is sometimes indirectly due to 

 a deficiency of other alkaline matter in the soil, which 

 prevents the necessary changes taking place in order 

 that the potash ma}' be liberated as plant food. 



231. Sources of Potash in Soils. — The main 

 source of the soil potash is feldspar, which, after dis- 

 integration, is broken up into kaolin and potash com- 

 pounds. Mica and granite also, in some localities, 

 contribute liberal amounts. The most valuable forms 

 of potash are the zeolitic silicates. The amount of 

 water-soluble potash, except in alkaline soils, is ex- 

 tremelv small. Bv the action of many fertilizers the 

 potash compounds undergo changes in composition. 

 For example, the gypsum which is always present in 



