92 The Potato 



head irrigation in humid sections. One of the greatest 

 needs of potato-growers everywhere is a new variety 

 possessing the table quahty, yield and appearance of 

 those now in use together with the heat-resistance of the 

 McCormick. 



W^d£rjre^uirements 



Lack of sufficient water is often a limiting factor on 

 the yield of potatoes. Many experiments indicate that 

 about 400 tons of water are used by the potato plant for 

 each ton of dry matter produced, or over three tons for 

 ^achjbiishel. This equals 3 inches of rainfall for each 

 100 bushels to the acre. Study of Weather Bureau 

 records of rainfall shows that the average amount in the 

 entire growing seasons in most potato-growing secti ons 

 is only 10 to 18 inches. The losses from run-off and 

 from evaporation are so heavy that this factor must 

 be provided for if exceptional yields are to be raised. 

 IMethods of conserving the soil water left by winter rains, 

 for the use of the crop, are of great value. The use^ 

 of ordinary surface irrigation in the West and of over-^ 

 head irrigation in the East produces much heavier 3'ields 

 ^han when rainfall is the wKole dependence. With these 

 Ihethods, yields of over 500 bushels to the acre are common. 

 Surface tillage to prevent evaporation and the incor- 

 poration of organic matter with the soil are the principal^ 

 means of conserving moisture. Plants on rich soil or 

 when manures or fertilizers are used^, are able to secure' 

 their plant-food from the soil by the use of less water 

 than when grown on poor soil. Any means of extend- 

 ing the growth of roots makes more water available. 

 The great need of water for the potato crop comes at the 

 time when the tubers are forming. It is a matter of 



