ACTION OF SALTS OR MINERAL MANURES. 107 



living, growing plant in soil, in one year eflfects a greater 

 amount of its decomposition, than all atmospheric influences, 

 in many years, is one of the very highest interest, in a prac- 

 tical view. It is, perhaps, of more value than all the other 

 actions which have been considered. 



142. It is this decomposing action of living plants, on the 

 inorganic elements of soil, which affords a reasonable expla- 

 nation of the action of salts in agriculture. The catalytic 

 power of life dissociates the elements of salts. They enter 

 into new combinations. The base and the acid are separated 

 by the action of the living plant. 



143. On no subject in agriculture are opinions more 

 divided, than on the manner how salts or mineral manures 

 act. Their amount in soil is small. That is soon exhausted. 

 They cannot be artificially supplied, in excess, without induc- 

 ing very serious injury, and, in flict, often produce barren- 

 ness ; yet are often decidedly beneficial. It is not less diffi- 

 cult to account for the good, than for bad effects of salts. 

 Among all the variety of substances acting as salts, a dis- 

 tinct theory is generally framed and adopted for each. If 

 any attempt has been made to arrange all the facts relating 

 to this subject, it has ended in this, that they are stimulants. 

 They are to the plants what condiments are to the food of 

 man. This may do very well as an illustration, and the 

 author has elsewhere said, that *' the soil is the plate, the 

 geine the food, the salt the seasoning." 



144. This leads to no practical result, except it be this, 

 that if salts are seasoning, like the seasoning of our food, 

 they must be used sparingly. Some general law is wanting, 

 which shall at once account for the effects of salts, and while 

 it points out how so very minute a portion as the four-hun- 

 dredth part of one per cent, of the soil produces unquestion- 

 ably good effects, one per cent, will be injurious. Some 



