CORN IN THE GREAT PLAINS AREA. 
In these investigations seasonal variations in climatic factors have 
been of more importance in crop production than differences in 
methods of tillage. This is shown by the fact that at some stations 
in some years climatic conditions have been such that all methods have 
resulted in practical failures in yields. In other years all methods 
have given fair returns. 
Figure 2 shows the earliest and latest dates of the last killing frost 
in the spring, the earliest and latest dates of the first killing frost in the 
fall, and the average length of the frost-free period at each station. 
The heavy hatched horizontal bars represent the periods between the 
average dates of the last killing frost in the spring and the first killing 
frost in the fall, or the average frost-free period, the actual number of 
days being also shown. The solid-line curve at the left shows the 
earliest date at which the frost-free period has begun. The broken- 
Fig. 2.— Diagram showing the average frost-free periods and the earliest and the latest dates at which 
the last killing frost in the spring and the first killing frost in the fall has occurred at fourteen stations 
in the Great Plains area. 
line curve at the left represents the latest date at which the last killing 
frost of the spring has occurred. The solid-line curve at the right 
represents the earliest date and the broken-line curve at the right the 
latest date at which the first killing frost of the fall has occurred. 
This diagram shows clearly the increase in the length of the frost- 
free period from the north to the south. The shortest average frost- 
free period is 100 days at Hettinger and the longest one 194 days at 
Amarillo. The length of the period free from frost is more important 
in the production of corn than in the production of the small grains. 
Young corn being easily injured by frost, planting must be delayed 
until there is little further danger from this source. Where the 
season is short the crop may be caught by frost in the fall. This 
necessitates the use of short-season varieties in a portion of the Great 
Plains. As a season of average length can not be depended on, the 
