s 



BULLETIN 498, TJ. S. DEPARTMENT OF AGRICULTURE. 



the l L-year average, and the average for the growing season in the 



live years is 0.13 inch more than the 11-year average for the same 

 months. 



EVAPORATION. 



Records of evaporation from a free water surface have been kept 

 during the seven months, April to October, inclusive, in the years 

 1911 to 1915, inclusive. The method used is the same as at other 

 stations cooperating with the Biophysical Laboratory of the Bureau 

 of Plant Industry. 1 The evaporation tank at Moro is 2 feet deep 

 and 6 feet in diameter. Table IV gives the monthly evaporation, 

 April to October, inclusive, in the years 1911 to 1914, inclusive. 



Table IV. — Evaporation, in inches, from a free water surface at Moro, Oreg., in the 

 seven months, April to October, inclusive, for five years, 1911 to 1915, inclusive. 



Month. 



1911 



1912 



1913 



1914 



1915 



Average. 





5.92 

 6.13 

 9.61 

 11.57 

 9.28 

 4.16 

 2.34 



4.51 

 6.75 

 7.75 

 7.89 

 6.72 

 4.50 

 2.60 



4.09 

 6.24 

 7.36 

 7.90 

 7.82 

 4. 82 

 3.52 



4.02 

 7.43 

 8.29 

 11. 43 

 9.64 

 4.40 

 2.20 



5.13 

 5.90 

 8.45 

 9.05 

 9.59 

 5.30 

 2.98 



4.73 



May 



6.50 





8.29 



July 



9. 57 





8.61 



September 



4.64 

 2.73 







Total 



49.01 



40.72 



41.75 



47.41 



46.40 



45. 07 







The highest evaporation occurred in 1911, when the evaporation 

 for the seven months was approximately five times greater than the 

 total precipitation for that year. The lowest evaporation was in 

 1912, when the ratio of the evaporation for the seven months to the 

 total precipitation for the year was about 3 to 1 . During the 6-month 

 period from April to September, inclusive, the average evapora- 

 tion at the substation in the years from 1911 to 1915, inclusive, was 

 42.34 inches. This is greater than the evaporation reported by 

 Briggs and Belz 1 during a 6-month period at any station north 

 of the fortieth parallel of latitude (the northern boundary of Kansas). 



Table V shows the evaporation and precipitation and the winter- 

 wheat yields at the Moro substation and two other representative 

 dry-farming stations, one in the Great Basin at Nephi, Utah, at an 

 elevation of nearly 6,000 feet, and one in the northern Great Plains 

 at Moccasin, Mont., at an elevation of 4,300 feet. The wheat yields 

 reported in Table V were produced under the same method, alter- 

 nating wheat with summer fallow, at all the stations. Investiga- 

 tions similar to those conducted at Moro are being carried on at 

 Nephi and at Moccasin. The precipitation and evaporation data are 

 taken from the records of the Biophysical Laboratory and the 

 wheat yields from the records of the Office of Cereal Investigations. 



1 Briggs, I.. J., and Belz, J. O. Dry farming in relation to rainfall and evaporation. 

 Bur. Plant Indus. Bui. 1S8, p. 16-20. 1910. 



U.S.Dept.Agr., 



