BULLETIN 1260, U. S. DEPARTMENT OF AGRICULTURE. 
Hays, Kans., because the sorghums are of little value in regions that 
do not have approximately four months of rather high summer tem- 
peratures. It has been estimated that the optimum temperature for 
growth in sorghum is about 92° F. and that the sorghums make only 
indifferent growth at temperatures lower than 60° F. (14). The few 
experiments at Redfield, Ardmore, and Newell, S. Dak.; Mandan 
and Dickinson, N. Dak.; and Moccasin and Havre, Mont., have 
indicated rather definitely that sorghum is not likely to be a crop of 
much importance in the northern Great Plains. In South Dakota, 
sorghum may be grown for forage with fair success; but in other 
parts of this section preference should be given to corn and other 
crops, such as the small grains, which will thrive at lower tempera- 
tures than the sorghums. 
Altitude is also a limiting factor in the production of sorghums. 
The upper limit of their successful production varies with the lati- 
tude from about 4,000 feet in Montana to 7,000 feet in southern 
New Mexico. The western limit of the Great Plains area is the 
Fig. 1.— Outline map of the United States, showing the distribution of the sorghum acreage in 1919. 
5,000-foot altitude line east of the Rocky Mountains and the eastern 
boundary is the ninety-eighth meridian. (See fig. 2.) The southern 
half of this area, therefore, is well within the limits of sorghum pro- 
duction. 
CLIMATIC FEATURES. 
In order to understand fully the results obtained at the different 
field stations, it is essential to know something of the local climatic 
conditions. The climate is ordinarily classified as semiarid, and the 
limiting factor in the southern half of the Great Plains is almost 
wholly the rainfall, while in the northern Great Plains the tempera- 
tures effectually limit sorghum production, as indicated by the dis- 
tribution of the acreage in 1919. (See fig. 1.) 
Three-fourths of the annual rainfall in the sorghum belt is received 
during the six summer months, April to September, inclusive, as 
shown in Figure 3. 
The distribution of the rainfall is as important as the amount in 
determining yields. The total annual precipitation varies greatly 
