ARID AGRICULTURE. 197 



thorough soaking up of the ground, running the 

 water between each of the rows, but do not let it 

 stand too long. Water should never come in 

 contact with the crowns of the plants. If a large 

 crop is the principal consideration, the potatoes 

 should be irrigated once in a week or ten or 

 twelve days through the season after starting, as 

 indicated above. They must not be allowed to 

 get dry enough to check their growth. After 

 the growth becomes checked once, new irrigation 

 will start second growth, which produces large 

 vines, new setting of tubers or knotty, ill-shaped 

 potatoes. If it can be avoided, irrigation should 

 not be done when the weather is hot and sultry. 



ROTATION IN * Farmers who make a business of potato rais- 

 ing follow a regular system of rotation in which 

 alfalfa is the crop used to bring back the soil fer- 

 tility. Potatoes do well on sod land and one or 

 two crops may be raised. This should be fol- 

 lowed with a crop of grain, and if the soil condi- 

 tions are favorable, alfalfa may be sown with the 

 grain. The alfalfa is left in the ground two or 

 three years. It is then plowed late in spring after 

 the alfalfa plants have started. This plowing is 

 difficult and must be thoroughly done. The deep 

 cultivation immediately after plowing will pull 

 out the principal roots and prevent their inter- 

 fering with future cultivations or ditching for 

 irrigation. Such alfalfa ground may be kept in 

 potatoes two years if disease does not appear, 



