38 PRINCIPLES OF FARM PRACTICE 



in the United States to supply most of the potassium needed 

 for our farms. 



Potassium, as a commercial fertilizer, is usually supplied 

 in the form of potassium chloride or muriate of potash, 

 sulfate of potassium, and kainit. The first two contain 

 about fifty per cent of potash; kainit, or mineral potash, 

 contains from twelve to twenty per cent. The word potash 

 is u.sed by chemists to express the amount of potassium in a 

 chemical analysis. 



For certain special crops such as potatoes and tobacco 

 which have large potash requirements, it is a good practice 

 to apply some form of fertilizer containing potash. (The 

 buying and use of commercial fertilizers will be considered in 

 greater detail in the next chapter.) 



CALCIUM 



The supply of calcium. Plants require but little calcium 

 for their growth. The store of calcium in most soils is suf- 

 ficient to supply the actual needs of the plant. The chief 

 value to a soil of substances containing calcium, such as 

 limestone or lime, is an indirect one they neutralize soil 

 acids. There are plants, such as legumes, which will not 

 grow well in acid soils. There are other important effects 

 of calcium (in the form of lime or limestone) on soils which 

 will be discussed in the next chapter. 



