CHAPTER XVII 

 SOIL MOISTURE 



WATER is as necessary to the growth of plants as fer- 

 tile soil. All the food taken by plants from the soil 

 must first be dissolved in water. The tiny root-tips suck 

 in this food-laden water which circulates to every part of 

 the plant, producing its growth. 



The amount of \vater required by a growing crop is enor- 

 mous. For every pound of dry matter made by the plant, 

 from three hundred to eight hundred pounds of water must 

 be drawn in by its roots and circulate through it. To pro- 

 duce a ton of dry hay on an acre of ground demands that 

 approximately five hundred tons of water be pumped -by 

 the grass stalks from the soil. When the soil lacks water, 

 plants are cut off from both necessary food and drink. 



1. Forms of Soil Water 



Gravitational water. Soil that is thoroughly satur- 

 ated contains a certain amount of free water that will 

 drain off if there is some outlet. That is, the force of grav- 

 ity pulls it down through the soil ; hence its name, free, or 

 gravitational water. 



To watch how this works, place some soil in a funnel 

 closed with a stopper. Pour water over the soil until it is 

 completely soaked. Then remove the stopper and allow 

 what will of the water to drain off. All the water that thus 

 escapes is free, or gravitational water. 



Plants can not use gravitational water for their supply. 



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