30 ) 



This important question is even at this day 

 too much neglected, and it is more frequently 

 by chance than otherwise, that the alkaline 

 and earthy salts are found in the manures. 

 It is true, as we before said, that nitrogen is 

 an element of valuable consideration in ma- 

 nure; but it is not all-sufficient, for a soil that 

 receives only a purely nitrogenous nutriment 

 will, though thereby excited to vegetation, be 

 soon exhausted of its mineral elements and 

 rapidly rendered sterile. This view is sup- 

 ported by daily experience. Are we not 

 obliged to rotate our crops, or in other words 

 to cultivate different plants alternately upon 

 the same soil, as a bar to its exhaustion of the 

 same mineral substances? ^Do we not, in 

 some localities, leave the ground fallow from 

 time to time, so that a slow decomposition 

 may re-produce the assimilable salts favourable 

 to vegetation? It is very evident that if we 

 restore to the earth, annually, the substances 

 which have been abstracted by the crops, it 

 can produce the same results indefinitely, pro- 

 vided all things are concomitant in other re- 

 spects. 



In calculating the value of nitrogenous ma- 

 nures by their content of nitrogen, the far- 



