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BULLETIN 339, U. S. DEPARTMENT OF AGEICULTUEE. 



because there have sometimes been great variations in the yields 

 produced by the same quantity of water on the same crop upon 

 adjoining farms. These variations have made it very evident that 

 dependable results can be secured from agricultural experiments 

 only by basing conclusions upon the average of results from a large 

 number of experiments. 



WEATHER CONDITIONS IN IDAHO DURING THE INVESTIGATION. 



It has not been considered practicable, although it would have 

 been desirable, to install a rain gage in connection with each tract 



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Fig. 1.— Comparison of average annual precipitation with that occurring during the growing season. 



experimented upon. The United States Weather Bureau has a 

 large number of cooperative observers' stations scattered quite 

 uniformly throughout the territory involved in the investigation, 

 and the precipitation recorded at the station nearest each tract 

 has been used. This may be slightly inaccurate, but the errors 

 are compensating and small at the most. 



The normal annual precipitation in the districts of southern 

 Idaho which have been -investigated ranges from slightly less than 

 10 inches per annum at Oakley to 17.75 inches at Hailey. Hailey 

 is situated at a comparatively high altitude, and the precipitation 

 in this place is consequently above the average for irrigated southern 

 Idaho. The average precipitation in the typical irrigated districts 



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