8 BULLETIN 1039, U. S. DEPARTMENT OE AGRICULTURE. 
both 1911 and 1912. The 1913 crojp was probably benefited by the 
abundant late rains in 1912. 
EVAPORATION. 
The seasonal evaporation probably ranks next in importance to 
seasonal precipitation among the factors which influence the growth 
of crops at Xewell. The daily evaporation has been recorded at the 
Belle Fourche Experiment Farm, and the total depth in inches by 
months from April to September is shown in Table II. The record 
of evaporation was not kept for the month of March, but at Xewell 
crops ordinarily make little growth during that month and hence 
this omission is not of importance. The evaporation is determined 
from a free water surface, the method being that employed at all 
of the stations where the Biophysical Laboratory of the Bureau of 
Plant Industry has been cooperating. 7 
Table II. — Jifonthlu evaporation from a free vater surface at the Belle Fourche 
Experiment Farm from April to September of each uear. 1908 to 1919. in- 
^.7,,.-. ;,-„ 
elusive 
[Evaporation and precipitation data in inches.] 
Precipitation. 
Year. 
Apr. 
May. 
June. 
July. 
Aug. 
Sepr. 
Total. 
April 
to Sep- 
tember, 
inclu- 
sive. 
Ratio 
to 
evapo- 
ration. 
lQOx 
. 5. 535 
5.917 
6.413 
6. 521 
5. S59 
8.081 
7. 598 
7.S66 
S.243 
6. 745 
5.001 
40. 965 
36. >7i 
^.95 
14.37 
1-4.6 
1909 
3. 657 
1:2.6 
1910 
5. 40S 
5.306 
S.975 
10.429 
7.295 
4.302 
41. 715 
9.71 
1:4.3 
1911 
4. 649 
8. 302 
10.241 
10. 714 
6.6S2 
6.113 
46.701 
4.70 
1:9.9 
1912 
4.^49 
6.423 
S. 175 
7.9^0 
6.604 
3.713 
37.744 
14.36 
1:2.6 
1913 
4. 705 
4.302 
7.046 
S.235 
8.144 
4.707 
37. 139 
8.32 
1:4.5 
1914 
3.369 
5.133 
6.712 
S.737 
6.966 
4.194 
35. Ill 
8.21 
1:4.3 
1915 
. .' 4. 454 
3.970 
4.612 
5. 352 
5.113 
3.956 
27.457 
17.08 
1:1.6 
1916 
3.6^9 
5.269 
5.13S 
7.519 
5.43S 
5.429 
32. 4S2 
10.23 
1:3.2 
1917 
2.01S 
4.704 
6.271 
9.-536 
6.9^ 
5.307 
34. S19 
10.01 
1:3.5 
1918 
3. 27S 
5.171 
6.555 
6.4>-2 
7.129 
3.951 
32.566 
14.65 
1:2.2 
1919 
3. 519 
6.769 
8.904 
9.-564 
S. 224 
5. 122 
42.102 
^.44 
1:5.0 
Average 
4. 094 
5.640 
7.109 
S. 361 
7.0S7 
4. ^7S 
37. 139 
10.76 
1:3.5 
The average evaporation for the six months from April to Sep- 
tember, inclusive, for the 12 years from 1908 to 1919 was 37.139 
inches. The lowest total evaporation. 27.457 inches, was recorded in 
1915. the year of the greatest rainfall during the same months. The 
highest total evaporation. 46.701 inches, was recorded in 1911, the 
year of the lowest seasonal rainfall. Thus the evaporation usually 
varies inversely with the precipitation, though this is not always 
the case. 
7 Brings. L. J., and Belz, J. O. Dry farming: in relation to rainfall and evaporation. 
U. S. L^pt. Agr., Bur. Plant Indus. Bui. 1SS. p. 16-20. 1911. 
