CEREALS ON THE BELLE F0URCHE EXPERIMENT FARM. 
9 
The ratio of precipitation to evaporation, also given in Table II, 
shows the evaporation for the 12 years to be 3.5 times the precipi- 
tation. In 1915 the ratio was the narrowest, the evaporation for that 
year being only 1.6 times the precipitation. In 1911 the ratio was the 
widest, the evaporation being 9.9 times the precipitation. The ratio 
of precipitation to evaporation is a fair indication of the seasonal 
moisture conditions as related to crop yields. 
WIND. 
The record of wind measurement has been taken at the Belle 
Fourche Experiment Farm during the growing season since May, 
1909. The anemometer stands near the evaporation tank at a height 
of about 2 feet from the surface of the ground. The average wind 
velocities in miles per hour during the six months from April to Sep- 
tember for the years 1908 to 1919, inclusive, are presented, in 
Table III. 
Table III. — Average wind velocity at the Belle Fourche Experiment Farm for 
the six months from April to September, during the 12-year period from 1908 
to 1919, inclusive. 
[Data in miles per hour.] 
Month. 
1908 
1909 
1910 
1911 
1912 
1913 
1914 
1915 
1916 
1917 
1918 
1919 
Aver- 
age. 
9.1 
10.1 
6.2 
6.0 
5.6 
5.7 
9.2 
8.2 
9.3 
7.7 
6.6 
6.2 
9.2 
11.6 
9.1 
7.9 
7.3 
7.9 
9.5 
11.1 
7.6 
6.0 
6.9 
7.6 
6.2 
5.9 
6.8 
5.8 
5.1 
4.5 
8.2 
7.7 
6.7 
5.0 
5.0 
6.2 
6.6 
7.4 
6.2 
5.0 
4.1 
5.9 
7.8 
8.7 
7.3 
5.1 
4.4 
6.2 
7.8 
5.7 
6.3 
5.3 
4.2 
5.1 
9.2 
6.6 
4.5 
4.2 
2.8 
2.2 
7.4 
7.3 
7.7 
6.7 
5 8 
5.5 
8.2 
May 
June 
July 
August 
September 
8.3 
7.2 
5.0 
6.8 
6.5 
8.2 
7.1 
5.8 
5.4 
5.8 
Average 
6.8 
7.1 
7.9 
8.8 
8.1 
5.7 
6.5 
5.9 
6.6 
5.7 
4.9 
6.7 
6.8 
The average wind velocity during this period was 6.8 miles per 
hour. The highest average wind velocity, 8.8 miles per hour, was 
recorded in 1911, while the lowest, 4.9 miles per hour, was observed 
in 1918. The velocity during April, May, and June was consider- 
ably higher than in July, August, and September. The velocity of 
the wind has a decided influence upon the crops. The evaporation 
from the surface of the soil or plant is greatly increased by wind. 
Hot winds, such as occurred in 1914 and 1917, caused the cereal 
plants to be prematurely ripened or deadened before the grain was 
fully developed. Winter wheat was injured somewhat nearly every 
spring by the blowing of the soil before the spring rains had mois- 
tened it. In 1916 some of the spring grains had to be resown be- 
cause of being blown out after emergence. Owing to the high wind 
velocity in the early spring, together with the tendency of the soil 
to blow at that time, it was necessary practically to discontinue sum- 
mer fallowing as a preparation for grain crops. 
77754 °— 22 2 
