RELATION OF THE SOIL TO WATER 



18. Amount of Water Required by Crops. — Ex- 

 periments have shown that it takes from 275 to 375 

 pounds of water to produce a pound of dry matter in 

 a grain crop. In order to produce an average acre of 

 wheat 350 tons of water are needed. The amount of 

 water required for the production of an average acre 

 of various crops is as follows : " 



Average amount. Minimum amount. 



Tons water. Tons water. 



Clover 400 310 



Potatoes 400 325 



Wheat 350 300 



Oats 375 300 



Peas 375 300 



Corn 300 



Grapes 375 



Sunflowers 6 6000 



The rainfall during the time of growth is frequently 

 less than the amount of water required for the pro- 

 duction of a crop. An average rainfall of 2 inches 

 per month during the three months of crop growth 

 would be equivalent to only 369 tons of water per 

 acre, a variable part of which is lost by evaporation. 

 Hence it is that the rainfall during an average grow- 

 ing season is less than the amount of water required, 

 and in order to produce crops, the water stored up in 

 the soil must be drawn upon to a considerable extent. 

 Inasmuch as the soil's reserve supply of water is such 

 an important factor in crop production, it follows that 



