202 AGRICULTURE 



current production of farmyard manure. 

 Farms which have been adapted to such 

 conditions of management tend to regain 

 fertility, and if artificial manures can also 

 be applied, such land can be profitably 

 farmed indefinitely. But in many parts of 

 the eastern United States one finds wide 

 areas which, at one time under cultivation, 

 are now reverting to forest, the attractions 

 of the virgin land of the West being too 

 great for the farmers who have taken all 

 they can get out of their eastern holdings. 



In the Middle Ages, and more recently 

 in fact, the system is still met with in certain 

 districts of England large areas of tillage 

 land throughout Europe were managed upon 

 the three-field rotation, or, as the Germans 

 call it, the " Dreifelderwirtschaft," under 

 which the tillage area was equally divided 

 between a winter cereal (wheat or rye), a 

 spring cereal (barley or oats), and bare 

 fallow. It was an improvement on this 

 system to substitute beans for bare fallow, 

 especially if the bean crop was taken ad- 

 vantage of to practise summer cultivation 

 for the suppression of weeds. As the number 

 of crop-species increased it became possible 

 still further to modify the three-field rotation, 

 which might then take the form of 



