34 



MOISTURE IN THE SOIL 



4. What are the sources of soil water ? 



5. What is irrigation ? 



PRACTICAL EXERCISES 



1. Place two or three cubes of sugar, one upon the other, in a 

 saucer, and pour in a small quantity of red ink. This shows the 

 upward movement of film moisture by the force of capillarity. 

 Tie pieces of cloth over the ends of three tall lamp chimneys. 

 Place these in a pan or a large flat dish. Fill one lamp chim- 

 ney with dry sand,, another with dry loam, and the other 

 with dry clay. Now pour water into the pan or dish to a 

 depth of about an inch. In which soil does the moisture move 

 upward most rapidly ? 



2. Repeat the above exercise, using chimneys of the same size, 

 and equal volumes of sand, loam, and clay. Place each chimney 

 in a separate saucer or other small dish. Measure the water 

 added to each to determine which soil can hold the largest 

 amount of film moisture. Be sure that the depth of water 

 remaining in the bottom of each saucer is the same when you 

 compare the amounts of water absorbed by the three soils. 



In these two exercises it is necessary to place a small wedge, a 

 bit of cardboard or match, under each lamp chimney so that it 

 may not rest so close to the bottom of the dish as to prevent the 

 entrance of water. 



If long glass tubes could be used instead of lamp chimneys, 

 it would be possible to show that film water will rise higher in a 

 soil of fine texture than in one of coarse texture. 



