Water in the Soil 73 



106. Amount of Water Re quired to Mature a Crop. For 



every pound of dry matter made by growing corn, cotton, 

 oats, etc., it has been estimated from many experiments 

 that from two hundred to four hundred pounds of water 

 are required. This includes the entire plant above 

 ground, regardless of that which is harvested. Accepting 

 these figures as nearly correct, let us estimate how much 

 of the rainfall is consumed in maturing a good crop of 

 corn, cotton, oats, etc. In a field of corn making fifty 

 bushels per acre the figures would be roughly as follows: 



50 bushels corn (72 pounds to bushel). . .3,600 pounds 

 Stalks and leaves 3,600 " 



Plant substance 7,200 " 



Approximate quantity of water required 



for each pound of plant substance. . . 300 " 



Water used by crop 2,160,000 " 



A cubic foot of water weighs 62.3 pounds. A rain-fall 

 of one inch would be 5.19 pounds per square foot of 

 soil, or 43,560X5.19=226,176.40 pounds on an acre. 

 Dividing 2,160,000 by 226,176.40, we find that less than 

 ten inches of rainfall would be used by the plants in 

 making fifty bushels of corn per acre. This does not 

 include the water that would evaporate from the soil 

 or be lost by the surface run-ofT. 



106a. At Kansas City, Mo., the average annual rainfall is about 

 38 inches. What per cent of this would be required to make 50 

 bushels of corn per acre? What is the average rainfall in your 

 county? See Appendix H. 



107. Soil Drainage. There are many places in low 

 bottom lands on which water accumulates to an injuri- 

 ous extent, either from seepage from the hills or from 

 the lack of an outlet for the surplus water in very wet 

 spePs. Again, there are low "sweeps," "swags," "runs," 



