LIME AS A SOIL AMENDMENT 351 



tion analysis, is not present in very fertile soils of any 

 region, according to Loew. If injury from magnesium 

 is suspected, the obvious means of correction is to 

 increase the proportion of calcium by its addition in 

 some form. 



The use of limestone, ground or burned, that contains 

 a large percentage of magnesium may be injurious to 

 some soils, as may also those Stassfurt salts containing 

 magnesium. 



The presence of soluble calcium, with its effects 

 upon the soil, retards the development of certain plant 

 diseases, like the "finger and toe" disease of the cruci- 

 ferae. On the other hand, it may promote some diseases, 

 as, for instance, the potato "scab." 



221. Forms of calcium. Calcium is used on the 

 soil in the form of calcium oxide, or quicklime (CaO), 

 water-slaked lime (Ca(OH) 2 ), air-slaked lime (CaC0 3 ), 

 ground limestone (also a carbonate), and calcium sulfate, 

 or gypsum (CaS0 4 , 2H 2 0). The application of any of 

 these is usually called liming the soil, although gypsum 

 does not serve exactly the same purpose as do the other 

 forms. Owing to differences in the molecular weights 

 of these compounds of calcium, it requires more of some 

 forms than of others to furnish the same amount of 

 calcium. Approximately equivalent quantities of some 

 of the common forms when fairly pure are: 



Quicklime 56 pounds 



Water-slaked lime 74 pounds 



Air-slaked lime, marl and ground limestone .... 100 pounds 



Caustic lime, or the hydrate, when added to the soil, 

 eventually assume some of the more insoluble forms of 



