And of course a supply of water for supplementary irriga- 

 tion may be obtained by pumping from the ground, especially 

 where electric energy is cheap. 



With low-cost electric energy available for pumping, a 

 matter considered in more detail later, there would be under 

 proper conditions opportunity for the use of the same water 

 several times before it would escape to the rivers. Pumped 

 from the groundwater store and applied to supplementary 

 irrigation, such part of the water as is not evaporated and 

 transpired would infiltrate back into the groundwater 

 reservoir and become available for reuse. If extensive use 

 of pumped water existed over large areas, even some of that 

 which is evaporated and transpired might be returned 

 somewhere in the form of rain. 



The value of supplementary irrigation, especially appli- 

 cations of water at critical periods of the growing season, 

 even in climates where the average annual rainfall is adequate, 

 is not yet fully appreciated. The stage of experiment has 

 been passed, and the following has been adequately demon- 

 strated. The annual rainfall may be adequate, but not 

 distributed with regularity from year to year or throughout 

 any year. Availability of water permits calculated regu- 

 larity of application. Also each crop has a critical period 

 of growth when, if enough water is available, the yield will 

 be much greater than it would be otherwise, even if an 

 equivalent amount of water were available earlier or later. 

 Sometimes rain provides sufficient water during the critical 

 period, but frequently does not; and often, if adequate at 

 the critical period of one crop it may not be for the critical 

 period of another. But if a farmer has a small individual 

 reservoir or other impounded water, or wells, and cheap 

 energy for pumping, he can be more certain that each crop 

 will receive the proper amount of water during its critical 

 period and at other times if Nature fails. In addition, 

 within limits, every application of water will increase yield, 

 the rate of increase and the limit varying with different 

 crops. Supplementary irrigation is a form of crop insurance. 



We are accustomed to think of irrigation as important 



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