ROTATION OF CROPS. 2FI 



" (peas or clover) are capable of exhausting the soil of this impo:- 

 " tant ingredient to such an extent that there is only sufficient 

 " left to enable a crop of oats or of rye to form their seeds. 



'' The number of crops which may be obtained from the soil 

 " depends upon the quantity of the phosphates, of the alkalies, or 

 " of lime, and the salts of magnesia existing in it. 



" The existing provision may suffice for two successive crops 

 " of a potash or of a lime plant, or for three or four more crops of 

 " a silica plant, or it may suffice for five or seven crops of all 

 " taken together ; but after this time all mineral substances re- 

 " moved from the field, in the form of fruits, herbs, or straw, 

 " must again be returned to it ; the equilibrium must be restored, 

 '' if we desire to retain the field in its original state of fertility. 



" This is effected by means of manure." 



Since these views were published, further investigation of the 

 subject has so far modified the opinions of scientific men, that 

 Liebig's statements (concerning silica especially) arc no longer 

 accepted as correct in all their details. His general principles, on 

 the other hand, have only beeh more fully demonstrated to be 

 correct, and the deductions that he drav/s from them, so far as the 

 practice of farming is concerned, bear with undiminished force. 



To continue the quotation from this author's works, I take 

 from his " Modern Agriculture"* the following : — 



" Innumerable facts have taught the practical farmer that, in 

 " many cases, the successful cultivation of an after-crop on a field 

 " depends upon the nature of the preceding crop, and that it is by 

 " no means a matter of indifference in what succession or rotation 

 " he grows his crops. The previous cultivation of some under- 

 *' ground crop, or some plant with extensive root ramifications, 

 " will tend to make the soil more favorable for the subsequent 

 " growth of a cereal. The latter will, in such cases, thrive better, 

 " and it will do so without the use (or with the sparing application) 

 '' of manure, and will yield a more abundant crop. But as re- 

 " gards succeed'mg harvests, there has been in reality no saving of 



* "Modern Agriculture." J. Von Liebig. Munich, 1859. 



