56 



BULLETIN 1026, U. S. DEPAETMENT OF AGRICULTURE. 



conditions are different and when water is plentiful the safe opera- 

 tion of the canal requires that the user take his supply of water 

 from the canal day and night until he orders it cut off by the ditch 

 rider. ^^Taen water is scarce the user takes it eagerly, day or night. 

 It is necessity in these forms, rather than any virtue in its practice 

 in the Cache la Poudre Valley, which is responsible for night irri- 

 gation there. Row crops are not often irrigated at night and mat- 

 ters are usually so arranged that the supply may be turned for the 

 night on alfalfa or pasture land where a small excess of water will 

 do no harm. 





; 



\PRIL 

 20 



MAY 

 10 20 





JUNE 

 20 



1 



JULY 

 20 





AUGUST 

 10 20 



SEPTEMBER 

 10 20 











































19 



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PiG. 8.- 



-Irrigation of potatoes. Water requirements of 157 acres In 1916 

 and 285 acres in 1917. 



It is seldom possible to apply enough water to a field for a 

 uniform, thorough irrigation without having a certain run-off at the 

 lower end. The amount of this run-off was determined for a num- 

 ber of fields of alfalfa and grain and was found to range from 2 to 

 18 per cent, with an average slightly under 6 per cent. In the 

 majority of cases this can be called waste only with reference to the 

 particular field from which it comes as the general practice is to 

 collect it in ditches and use it on lower fields. 



In figure 4 the relation between the head used and the area irri- 

 gated per 24-hour day is shown by curves for both flood and furrow 

 irrigation. The curve for flood irrigation is based on 284 irriga- 

 tions of fields of alialf a and grain, while the curve for furrow ii ri- 



