8 
BULLETIN 498, U. S. DEPARTMENT OP AGRICULTURE. 
the 11-year average, and the average for the growing season in the 
five 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 
4.51 
4.09 
4.02 
5.13 
4.73 
6.13 
6.75 
6.24 
7.43 
5.90 
6.50 
9.61 
/. 10 
7.36 
8.29 
8.45 
8.29 
11.57 
7.S9 
7.90 
11.43 
9.05 
9.57 
9.28 
6.72 
7.82 
9.64 
9.59 
8.61 
4.16 
4.50 
4.82 
4.40 
5.30 
4.64 
2.34 
2.60 
3.52 
2.20 
2.98 
2.73 
49.01 
40.72 
41.75 
47.41 
46.40 
45. 07 
April 
May 
June 
July 
August 
September . 
October 
Total 
The highest evaporation occurred in 1911, when the evaporation 
for the seven months was approximately ^e 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, L. J., and Belz, J. O. Dry farming in relation to rainfall and evaporation. U. S. Dept. Agr., 
Bur. Plant Indus. Bui. 188, p. 16-20. 1910. 
