CHAPTER VIII 

 LIME AND CALCIUM COMPOUNDS 



THE foregoing discussion has concerned almost entirely 

 materials which actually supply the plant with needed 

 food with one or more of the essential elements of plant- 

 food. Lime, though in a few instances a food, is of value 

 more particularly because its indirect action is important. 

 It is not only one of the oldest of all manures, but it is, 

 also, the most popular and continues to increase in use. 

 In spite of these facts it is still the foundation of consider- 

 able misunderstanding, probably because its action is not 

 restricted to any particular channel. It is known that 

 by some plants it is used as a food and that its greatest 

 asset is its mechanical, chemical and biological activity. 



Lime is contained in most soils in sufficient quantities 

 for the support of abundant plant growth. Yet, there are 

 soils, particularly light, sandy soils, to which the addition 

 of lime directly promotes plant growth. Permanent 

 pastures of long standing which were originally well 

 supplied with lime have through years of leaching become 

 deficient in this element in the surface soil, whereas the 

 same soil, had it been thoroughly cultivated year after 

 year, would contain sufficient lime for plant growth be- 

 cause the cultivation would tend to counteract the down- 

 ward movement of the lime and hold a sufficient quantity 

 in the surface soil. 



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