511 



discussed ia a very interesting paper by M. Gaetan Cantoui, Director 

 of the Eoyal Superior School of Agriculture at Milan, Italy, pub- 

 lished in a late number of Journal d^ Agriculture Pratique. The discus- 

 sion is based upon the opinion that the best system of rotation is not 

 that of a succession of crops according to their different chemical 

 necessities, nor that which takes from the soil the smallest quantity 

 of mineral i^lant-food, but rather that which, though it takes from 

 the soil more of fertilizing materials, also returns a larger quantity 

 in the residual matter which remains after harvesting the crop. Fields 

 may preserve an undiminished rate of production without manuring 

 for a year or two. Thus, after crops of clover or lucerne, either of which 

 make large demands upon the soil, the land with an application of fer- 

 tilizers entirelyi nsufficient to supply the deficiency caused by the de- 

 mand already made upon it, may be devoted to other crops to advan- 

 tage, and the profit of subsequent crops will be proportionate to the 

 time during which the land has been in clover or lucerne. The same 

 experiment after a single crop of wheat or barley would furnish small 

 results, yet the amount of valuable constituents of plant-food removed 

 by these crops is by no means as large as that removed by the two 

 crops of clover or lucerne. In evidence of the latter fact the following 

 table was prepared, showing a comj)arison of the total quantities of val- 

 uable fertilizing materials removed by a number of crops of clover or 

 luzerne and a single crop of wheat. 



Matter extracted. 



Dry matter in normal condition produced 



Nitrogen 



Pliosphoric acid 



Potassa 



Lime 



Clover, 

 two crops. 



Pounds per 

 hectare. 

 44, 095 



882 

 308 

 448 

 545 



Lucerne, 

 five crops. 



Pounds per 



hectare. 



165, 255 



3,805 



842 



2,513 



4,763 



Wheat, 

 one crop. 



Pounds per 

 hectare. 

 11,023 

 97 

 46 

 57 

 22 



The amount of fresh manure necessary to restore these elements of 

 plant-food are exhibited below. 



This shows that the exhaustion of the soil by crops of clover and 

 lucerne must be much greater than in the case of wheat. 



The leguminous crops are considered ameliorating, because they seem 

 capable of absorbing and assimilating atmospheric nitrogen, but they 

 cannot obtain from the atmosphere the mineral matter they contain. 

 The favorable action must therefore be sought in some other cause. 

 According to M. Cantoni, this cause may be found in the modifications 

 occasioned by different crops in the soil, among which may be enumer- 

 ated the mechanical treatment necessary for certain crops ; abundant 

 fertilizing, with a view to the production of surplus leaves ; and, finally, 



