FERTILIZERS. 91 



as an average, that from eight to nine tenths of the 

 mammal elements of the food of animals exists in the 

 manure. 



As the elements of manure are the same as the ele- 

 ments of plants, it is evident that the manure is suited 

 for the growth of other plants, in turn, provided it is all 

 preserved and returned to the soil without loss or waste, 

 and provided sufficient fertilizing material is added to 

 take the place of the part retained by the animal. 



2. It is less concentrated. A ton of average manure 

 contains only about 25 pounds of plant food. The re- 

 maining 1,975 pounds can be of no direct service as food 

 for crops. This renders it more expensive to handle, 

 which is sometimes a serious objection where it must be 

 conveyed a long distance. 



The bulky nature of manure, however, gives it certain 

 advantages. It is of great benefit to heavy soils, by 

 making them mellow and porous for the admission of 

 air, rendering them drier in a wet season, and at the 

 same time enabling them to retain moisture in a time 

 of drought. 



The lack of some mechanical " divisor," such as is 

 furnished in common manure, is a serious objection to 

 continuous farming with artificial fertilizers alone. It 

 often becomes necessary to plow in a crop of clover, or 

 some other bulky substance, in order to supply this want. 

 Without some treatment of this kind, soils after a time 

 are liable to become solid and compact, and may suffer 

 from the slightest drought. 



3. It yields its supplies of plant food more slowly. A 

 large proportion of the valuable elements of ordinary 

 commercial fertilizers is usually soluble, and immedi- 

 ately available to plants. Probably from one half to 



