COMPOSITION OF SOILS AND THEIR ACTION. 53 



from decayed vegetable and animal matter, that he 

 must depend for this result. These are the true 

 fertihzing ingredients ; and, though other agents may 

 be useful in exciting them to action, these must be 

 considered as constituting the food of plants, as the 

 cause of growth and nutrition. The application of 

 the exciting mineral manures, such as lime and gyp- 

 sum, is productive of the happiest effects, for the 

 reason assigned above ; yet they are not so abso- 

 lutely essential to the improvement of the soil as 

 those of a vegetable or animal origin. Matter which 

 has once lived, which has already taken the forms 

 of organized existence, more readily assumes again 

 the forms of organic life, and is more easily assimi- 

 lated by the organs of plants than that which has 

 never undergone such a change. It is the office of 

 the vegetable to take the crude atoms of matter as 

 they exist in the soil, and prepare them for the sup- 

 port of vegetable life ; and when this has once been 

 done, though a partial decomposition may have been 

 effected, a renewal of the process is comparatively 

 •easy and certain. 



In connexion with the preparation and application 

 of manures, the next most important step which 

 modern agriculture has taken to prevent a deterio- 

 ration of the soil is rotation in crops. Judiciously 

 conducted, the result is certain ; exhausted lands are 

 restored, and the profits of the agriculturist greatly 

 increased. It Avas formerly the custom to let lands 

 adapted to grass remain for that purpose alone ; 

 while those suitable for the plough were annually 

 subjected to its use until exhaustion forbid. They 

 were then left to the restoring processes of nature. 

 There were, at the beginning of this century, lands 

 in the farming sections of England which it was 

 w^ell known had lain in grass for five hundred years; 

 and there were other tracts which had been as con- 

 stantly submitted to the plough, or, at least, as often 

 as the soil promised to repay the expense of cultiva- 



