t 



THE IMPROVEMENT OF SOILS. 51 



acid, and potash are usually regarded as belonging to the 

 first class ; while lime itself, and materials containing 

 lime, belong more particularly to the second class. Lime 

 is one of the most useful agents of the farmer, and does 

 not, as is commonly believed, have the tendency to ex- 

 haust soils unduly, when its use is properly understood. 

 Lime acts powerfully upon and hastens the decay of 

 organic matter from both vegetable and animal sources, 

 by virtue of which the nitrogen becomes more quickly 

 available to plants, and, as already stated, lime also as- 

 sists in the process of nitrification. Lime further aids 

 in liberating potash from insoluble compounds in the soil, 

 thus increasing the store of active plant-food ingredients ; 

 it also promotes the formation of compounds with alu- 

 mina, which have the power of retaining ammonia and 

 potash. The direct effect of lime, as well as the other 

 materials furnishing plant-food, will be discussed in de- 

 tail in the chapter on manures. 



