MANURE. 205 



Such being the normal constituents of the vine 

 and of its fruit, and the latter being, in almost all 

 cases, removed from the soil in which it was pro- 

 duced, it is obvious that a process of exhaustion must 

 be constantly carried on, which, if not counteracted, 

 must, in a short time, perceptibly reduce the crop. 



The means by which the matter thus removed 

 from the soil is restored, are of three kinds : First, 

 the action of the plants themselves, or of man upon 

 the subsoil ; secondly, rain ; and thirdly, by the direct 

 addition of the requisite elements, through the agency 

 of man and animals. 



Although the soil has, to a certain extent, the 

 power of separating- salts and gases from the water 

 which passes through it, the drainage water still re- 

 tains a certain proportion of valuable matter,* and 

 consequently the subsoil also becomes saturated to a 

 greater or less extent with these same elements. 

 Hence one of the effects of trenching is not only to 

 bring up unexhausted soil to the surface, but to return 

 those matters which had previously been washed out 

 of the upper soil by the rains. Tlie plants themselves 

 occasionally bring up some of this matter, sending 



* A eeries of valuable analyses and experiments upon this point ap- 

 peared lately in the transactions of the Highland (Scottish) Agricul- 

 tural Society, which the reader who desires to pursue this subject 

 would do well to consult. 



