214 FIELD CROPS FOR THE COTTON-BELT 



261. Influence of rainfall. Seasonal rainfall and its 

 distribution is the most important climatic factor in corn 

 production. While corn requires less water to produce 

 one pound of dry matter than many other crops, the large 

 total weight of dry substance to the acre produced by this 

 crop makes necessary large quantities of water. It is es- 

 timated that 14 to 20 tons of water must be -transpired to 

 produce one bushel of corn. This equals 7 to 10 acre- 

 inches for a yield of 50 bushels to the acre. When it is 

 remembered that this water requirement does not include 

 the loss from run-off, drainage, and evaporation, the im- 

 portance of an abundant rainfall in corn production is at 

 once appreciated. 



In the cotton-belt the May, June, July, and August 

 rainfall is most important in producing corn. The distri- 

 bution of the rainfall during this season is of utmost im- 

 portance in determining the character of growth and total 

 yield. Excessive rains in the early part of the growing 

 season favor the development of a shallow root-system 

 which unfits the crop to withstand the frequent dry 

 weather of July and August. Comparatively heavy rains 

 at considerable intervals throughout the entire growing 

 season, with sunshiny weather in the meantime is the 

 condition most favorable to the normal growth of the corn 

 plant. Frequent light showers permit the excessive loss 

 of moisture by evaporation. 



262. Influence of sunshine. The relation of sun- 

 light to the normal growth of the corn plant was discussed 

 in the chapter on the physiology of the corn plant. The 

 effect of sunshine will be in proportion to the number of 

 sunshiny days and the intensity of the sunlight. Corn, 

 being a semi-tropical plant, requires considerable sunshine 

 for its normal growth. Except where extreme cloudiness 



