CHAPTER XXXIX 



Rotation of Crops (continued) 



When we say that the ground is worn out 

 and needs rest, we mean that it has been ex- 

 hausted by the crops already produced. The 

 crops deprive the ground of a large amount of 

 the materials necessary to plant life, and 

 when there are not enough of these left the 

 ground will no longer produce and is ex- 

 hausted. To restore the former fertility 

 would entail great expense in manure ; so it 

 is often more profitable to proceed by one or 

 other of the following methods. 



Sometimes the land is left to lie fallow ; 

 which means that it is left without any 

 attention for several years. The weeds grow 

 freely, while the water, air and frost act on 

 the soil, break it up, lighten it, and promote 

 the formation of certain substances that are 

 necessary to vegetation. The weeds are con- 

 verted into humus and after a time of rest the 

 ground is able to produce a fresh crop. This 



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