5G THE CHEMISTRY OF THE FARM. 



of assimilating certain of the silicates contained in the 

 soil ; other crops exhibit no such capacity. In such a 

 case it is easy to imagine that an alternation of cereals 

 with crops of a different description may be for the benefit 

 of both, each drawing to some extent upon distinct sup- 

 plies of food. Again, leguminous crops are clearly able 

 to assimilate nitrogen to a far greater extent than cereals, 

 and probably in some measure from a different source. If 

 crops of winter beans and winter wheat are grown on 

 similar unmanured land, the bean crop will generally 

 contain twice as much nitrogen as the wheat. The land 

 is not however impoverished for wheat by the growth of 

 beans, for wheat after beans will be a far better crop than 

 wheat after wheat, thus affording a striking example of 

 the advantages of rotation. 



The quantities of plant food required by different crops 

 are given in the table printed on page 38 ; these also 

 furnish reasons for the alternation of crops. It will be 

 seen, for instance, that the cereals require but little potash 

 and lime, while root crops, beans, and clover, demand a 

 large supply ; it is obvious, therefore, that the resources 

 of the soil are husbanded by growing these two classes of 

 crops in alternation, the greater demand for potash and 

 lime thus falling every alternate year. 



The nett result of a judicious alternation of crops, in 

 which the special characteristics of each are turned to 

 good account, is the production of a maximum total yield 

 of produce with a minimum amount of manure. 



Losses to the Land during Rotation. — The table show- 

 ing the composition of ordinary farm crops will supply the 

 requisite information as to the loss which a farm may 



