60 



CORN CROPS 



the ability of corn to yield will increase with the length of 

 the growing season up to somewhere near 200 days. 

 Therefore, for a good share of the present corn-belt of 

 the United States, the length of the growing season is an 

 important limiting factor. However, the varieties most 



Fig. 2.3. — Length of growing season as indicated b^^ the average date of 

 last kiUing frost in spring and first killing frost of fall. (Bui. V., U. S. 

 Weather Bureau.) 



commonly grown in the South mature in 160 to 180 days, 

 due to other limiting factors than frost, such as the rainfall 

 not being sufficient for the entire season, poor drainage in 

 early spring, or an unfertile soil. 



The accompanying chart, taken from Bulletin V of the 



