OVER-IRRIGATION AND ALKALI 373 



from canals in one day is sometimes equivalent to a depth 

 of 20 feet and is seldom less than 3 inches over the whole 

 canal surface. 



The laterals of canals are subject to similar losses. 

 Every irrigation farmer knows that though the flow into 

 the lateral at the head-gate may be ample, frequently not 

 enough water reaches the farm. Practically, another 

 third of the water taken in at the head-gate is gone 

 before it reaches the farmer. 



223. Loss from excessive irrigation. Water is lost 

 by seepage on the farm itself, for the common practice is 

 to irrigate land too heavily. When more than 5 inches of 

 water are added to the soil in any one irrigation, there is 

 usually a loss by seepage; yet, on a great many farms, 

 twice that much water is applied at one irrigation, pro- 

 viding it is available and the soil can be made to absorb 

 it. Evil follows such excessive irrigations, especially if 

 they succeed each other at short intervals. Farmers who 

 misunderstand the use of water usually apply as much as 

 possible, as frequently as possible, and urge upon the canal 

 managers the necessity of having free access to water. 

 An irrigation applied to the soil before the plant roots 

 have had time to remove the water added in the previous 

 irrigation retards the growth of the crop, and soaks down 

 the soil to increase the standing water table. The loss of 

 water due to excessive use of the water on the farm is 

 often very large. It may safely be estimated that one- 

 half of the water taken in at the head-gate of the canal 

 is lost by percolation from canals, ditches and excessive 

 irrigation. This is an awful waste when the great cost of 

 irrigation structures and the vast areas of arid land are 

 considered. The old idea that irrigation should take the 

 place of tillage must be fought vigorously. 



