ACTION OF MANURE UPON THE SOIL. 197 



selves, or by reaction upon other substances. For instance, 

 by adding lime to peaty soils or reclaimed swamps, we may 

 neutralize noxious acids, and develop the nitrogen and th- 

 er inert substances which they contain, into available plant 

 food. 



Third; by adding to the soil various substances which 

 afford food for plants. This is done by manuring the soil; 

 although as yet we are not able to determine whether what 

 we add to the soil actually feeds the crops or only prepares 

 food for them. There is however reason to believe that 

 some substances, as lime, potash, soda in various forms, but 

 chiefly as salt, act in both capacities; now feeding the plants 

 and then liberating from the soil and preparing other 

 nutriment which enters into the circulation; at other times 

 or at the same time entering themselves into the substance 

 of the plants. This distinction makes it necessary to class- 

 ify all these substances which either enter into the substance 

 of plants or prepare other substances to do this, or which 

 perform both functions, as manure. 



In this sense we may call these substances either simple 

 manures such as common salt; lime; nitrate of soda; gyp- 

 sum; or as mixed or complete manures, as barn yard man- 

 ure; and the various artificial mixed manures which contain 

 all the elements of barn yard manure, and which are now 

 in common use and are largely sold. 



But in considering specially these various manures which 

 improve the soil or promote the growth of crops in any way, 

 we may take them in the following order, viz: animal man- 

 ures; vegetable manures; and mineral manures. 



ANIMAL MANURES. Animal substances have always 

 been considered as exceedingly valuable manure, because 

 they are highly concentrated and so readily decomposed that 

 their action upon vegetation is both immediate and remark- 

 ably apparent. The various animal manures may be in- 

 cluded in the following list, the solid excrements of farm 

 animals and of human beings, and their urine mixed with 

 litter and various vegetable substances which are used as 

 absorbents; flesh; blood; horn; hair; wool; bones; and guano* 



