234 Irrigation and Drainage 



which may be moistened and yet be within the reach 

 of plants. 



THE FREQUENCY OF IRRIGATION 



The data presented in the last two sections are a 

 portion of those required to understand the rationale 

 of this important subject. Viewed from the standpoint 

 of labor involved in distributing water for irrigation, 

 it is evident that the fewer the number of irrigations 

 the smaller may be the labor involved and the lower 

 the cost. Moreover, the less often the surface of the 

 soil is wet, the smaller will be the loss of water by 

 evaporation and by seepage in bringing the water 

 to the fields ; hence, the higher will be the duty of 

 water. 



The most general rule which can be laid down 

 governing the frequency of irrigations and the amount 

 of water to be applied at one time, is to apply as much 

 water to the soil which is available to the crop as the 

 crop will tolerate without suffering in yield or quality, 

 and then husband this water with the most thorough 

 tillage practicable, in order to reduce the number of 

 irrigations to the minimum. 



It has been shown that a crop of maize yielding 

 70 bushels per acre may be brought to maturity in 110 

 days with 11.75 acre-inches of water. It has also been 

 shown that a soil of medium texture may carry in the 

 surface 4 feet 4.5 inches of available water, or, if ex- 

 tremely open, 2.5 inches. Could so high a duty of 

 water as this be attained under field conditions, three 



