74 ARID AGRICULTURE. 



continued long enough, at the same time adding 

 nothing in plant food, there are few soils upon 

 which, sooner or later, farming will not become 

 unprofitable. Confining the soil to one crop in- 

 duces the accumulation of insects and plant dis- 

 eases, which are peculiar to that crop, and when 



Plate X. Government Farm, Cheyenne 1908. 



the devastation arrives it hits quick and hard. 

 When grain farming is the principle aim in any 

 region, the best practice in addition to the resting 

 of the soil alternate seasons, is to adopt a system 

 of crop rotation which will add fertility. 



ROTATION OP Rotation of crops is not so necessary where 

 THEORY* 1 * ' ail( ^ * s summer tilled every other year as it is to 

 FARMER keep up soil fertility on lands that produce an- 



nual crops. However, .a regular system of rota- 

 tion will pay on all dry farms. The principle 

 aim in a rotation for arid lands, is to keep up 

 the supply of available nitrogen. This is done 

 by the use of legumes which, through the action 



