386 



THE IRRIGATION AGE. 



THE DUTY OF WATER AND THE BEST METHODS 



OF APPLYING IT, 



BY A. McPHERSON, Superintendent of Agriculture, Tw.n Falls Tr ct. 



In discussing this question, it is necessary to take 

 into consideration the character and depth of the soil, 

 the cultural methods, the lay of the land, precipitation, 

 etc. It is also necessary to , consider whether the land 

 had ever been irrigated or not. 



These conditions vary considerably in the arid, dis- 

 tricts, ,and this being true, I think it best to .confine 

 my remarks to the Twin Falls tract, where I am, now 

 located. 



The soil of the Twin Falls tract is commonly con- 

 sidered to be of volcanic origin, varying, from two feet 

 to an unknown depth, consisting of very fine particles. 

 , When we began work on the Twin Falls Experi- 

 mental Farm in 1905, we dug prospect holes from 

 seven to ten feet in depth in order to determine the 

 character of the soil, and the amount of moisture 

 present. The only difference we observed in the soil 

 was that the first foot was somewhat darker in color. 

 With regard to moisture, the first eighteen inches con- 

 tained some moisture, but below, it was perfectly dry, 

 consequently we irrigated before planting. It required 

 twenty-four to thirty-six hours to saturate to a depth 

 varying from seven to ten feet. 



No effort was made to determine the quantity of 

 water used during the season after that. 



This year (1906) it was determined to measure 

 the amount of water used on the farm, and the amount 

 running off as waste, as well as the evaporation, with a 

 view to determining the quantity of water necessary 

 to keep the soil in proper condition. 



The miners' inch was used in measuring half a 

 cubic foot per second for the farm, and a device was 

 employed in connection to obviate any fluctuation in 

 the head. A weir with an automatic register attached 

 was used as a check on the miners' inch measurement 

 in order that we might be sure that just the amount of 

 water desired was supplied. 



At the lower end of the farm, a weir and register 

 was installed for measuring the waste. Elias Nelson, 

 of the Bureau of Irrigation and Drainage Investigation, 

 added an evaporating tank. 



We began irrigating May 2, with the amount of 

 water allowed under the contract between the settlers 

 and the Twin Falls Land & Water Company that is, 

 one-eightieth of a cubic foot per second per acre, con- 

 tinuous flow. 



The amount of water applied during each month 

 up to the first of September, 1906, is given below, as 

 well as the waste and evaporation: 



Applied. Precipitation. Total Am't. 



In May 6.99 in. 



Waste 

 .209 



Evaporation 

 4.99 



Difference 



(or water retained 



by the soil) 



3.37 



1.58 in. 8.57 in. 



Percentage 



3% 

 Percentage 



58.2% 

 Percentage 



39.3% 



Applied. 



In June .... 7.74 in. 

 Waste 

 .309 

 Evaporation 



6.81 



Difference 



' (or water retained 



by the soil) 



3.34 



Applied. 



In July ..... 10.09 in. 

 Waste 

 .98 in. 

 Evaporation 



9.02 



Difference 



(or water retained 



by the soil) 



.18 in. 



Applied. 



In August . . 6.79 in. 

 Waste 



.84 

 Evaporation 



7.24 



Difference 



(or water retained 



by the soil) 



1.19 loss 



Precipitation. Total Am't. 

 2.72 in. 10.46 in. 



Percentage 



4% 

 Percentage 



65.1% 

 Percentage 



31.9% 

 Precipitation. Total Am't. 



.09 in. 



10.18 in. 



Percentage 



.9.7% 

 , Percentage 



88.6% 

 Percentage 



1.7% 

 Precipitation. Total Am't. 



.1 in. 



6.89 in. 



Percentage 



12.4% 



Percentage 



105.07% 



Percentage 



17.2 loss 



Total amount applied 36.10 in. 



Total percentage, 100% 



Total amount precipitation 4.49 in. 



Total percentage, 12.4% 



Total amount wasted 2.34 in. 



Total percentage, 7.4% 



Total amount evaporated 28.06 in. 



Total percentage, 77.7% 



Total per cent wasted 7.4 in. 



Total per cent evaporated 77.7 in. 



Total difference (or water retained by the 



soil) 5.694 in. 



Total percentage, 15.82% 



It will be noticed that the waste during the month 

 of July was greater than any other month. This oc- 

 curred while we were irrigating the lower tier of plats, 

 and no opportunity was afforded whereby we could 

 again use the waste. 



The farm consists of forty acres, and being an 

 experimental farm, there are a great many different 

 crops grown, requiring water at different times and 

 in varying quantities. 



It will also be noticed that the evaporation almost 

 equaled the amount of water applied during this 

 month, less the waste and evaporation as shown by the 

 evaporating tank. 



Assuming that the evaporation from the water- 

 free surface in the tank was equal to the amount evapo- 

 rated from the ground, plus the amount used by the 



