CHAPTER XI 



THE FORMS OF SOIL WATER AND THEIR 



MOVEMENT 



Under all normal conditions the soil bears a certain 

 amount of moisture, which must be reckoned with in 

 any study whether of a practical or of a theoretical na- 

 ture. Moreover, the amount of water varies in its char- 

 acteristics according to its position. It also has move- 

 ment, which goes far in determining its usefulness to plants. 

 Before a discussion of the different forms of water, their 

 movement, and their availability to plants, may be entered 

 into, however, some way of quantitatively stating the 

 amounts present must be determined upon. 



131. Methods of expressing soil moisture. — During 

 the many years of soil investigation, especially where the 

 problems had to deal either directly or indirectly with 

 moisture, five methods of water expression have been 

 evolved, their use depending on the nature of the work 

 and on the points to be expressed. These may be listed 

 under two general heads : — 



A. Percentage expression 



1. Percentage on a wet basis 



2. Percentage on a dry basis 



B. Volume expression 



1. Cubic inches to the cubic foot of soil 



2. Percentage by volume 



3. Surface inches 



198 



