640 SOILS: PBOPURTIES ANB MANAGEMENT 



nitrogen. Some soils respond more rapidly to quicklime 

 or water-slaked lime than to carbonate of lime, Copecially 

 when the carbonate is in the form of marl or ground lime- 

 stone, these substances never being in such a finely pul- 

 verized condition as is caustic lime. The use of the 

 caustic forms of lime has been said to result in the loss 

 of nitrogen by the too rapid decomposition of organic 

 compounds. 



On clays the granulating effect of caustic lime is more 

 marked than that of the carbonate, and for this reason 

 the former has a distinct advantage for use on heavy clay. 

 For the same reason an occasional moderate dressing is 

 better than a heavy dressing given less frequently. 



461. Carbonate of lime. — Air-slaked lime has the 

 advantage of being in a finely divided condition, and 

 does not produce the injurious action on organic matter 

 that is sometimes attributed to caustic lime. Its effect 

 on the granulation of clay soils is probably less pro- 

 nounced than that of caustic lime. 



Marl (par. 27) differs from air-slaked lime principally 

 in its property of being in a less finely pulverized condi- 

 tion. It acts less quickly than does caustic lime. Owing 

 to the fact that marl deposits differ greatly in the com- 

 position of their products, it is well to know the quality 

 of the material before buying it. The carbonate of lime 

 in marl may vary from 5 or 10 to 90 or 95 per cent in 

 different samples. 



Ground limestone has been used extensively in recent 

 years. It is very important that it be finely ground, as 

 on the comminution of the material much of its efficiency 

 depends. However, it is doubtful whether there is any 

 advantage in making it finer than is required to pass 

 through a sieve with 50 meshes to the inch. 



