14 
Nebraska Experiment fetation Research Bulletin 19 
NORMAL LENGTH OF FROST-FREE GROWING SEASON 
The length of the frost-free period between the last killing 
frost in the spring and the first killing frost in autumn, (Figures 
5 and 6), is expressive of the relative length of the growing 
season available to corn in various parts of the State. The mean 
duration of the frost-free period in the extreme southeast is ap- 
proximately 171 days, as compared to 121 days in the north- 
west. The lines of equal frost dates tend to run in a north- 
easterly direction. 
CkT.ll 
Fig. 6 — Average dates of first killing frost in autumn. 
Sept21 
REGIONAL MOISTURE VARIATIONS WITHIN THE STATE 
The principal moisture considerations comprise: (1) total 
annual precipitation together with its character and distribution 
thruout the year; (2) evaporating power of the atmosphere 
