EXERCISE 18 



THE MOVEMENT OF FILM, OR CAPILLARY, WATER IN THE SOIL 



Statement. Film, or capillary, water is capable of moving through the soil. Its movement is always 

 toward the driest part of the soil. If the subsoil is driest, the movement is downward ; if the surface 

 soil is driest, the movement is upward. Large quantities of moisture are stored in the subsoil at depths 

 which the plant roots cannot conveniently reach, but by means of capillary action the moisture is 

 brought within reach of the plants. Soils vary in the ease and rapidity with which films of water may 



pass through them and in the depth from which 

 moisture may be raised. This is called the capillary 

 power of a soil. 



& y ■ || II 1| ffu Object. To study the capillary power of dif- 



*\, . = a i i i - ij..i = $\ ferent types of soils. 



Materials. Sand; light sandy loam; silt loam; 

 clay; four strong glass tubes (i£ to 2 inches in 

 diameter and 2 or 3 feet long) or four lamp chim- 

 neys ; percolation rack ; four shallow pans ; cheese- 

 cloth; string. 



Directions. Tie cheesecloth over the bottoms 

 of the four glass tubes or lamp chimneys and place 

 them in the percolation rack. Fill each tube with a 

 different type of soil and jar it to settle the soil. 

 Let the bottom of each tube rest in a shallow pan 

 and pour water.into the pans. Keep the water level, 

 the same in all the pans, and observe the rapidity 

 with which the water rises through the soil. Meas- 

 ure the height to which the water rises every fifteen 



Fig. 23. 



Rack and tubes for testing the movement of 

 capillary water in the soil 



minutes for an hour. If glass tubing is used, measure the height to which the water rises in five hours 



in each soil ; in one day. Record the amount of water taken up by each soil in one hour ; in one 



day ; in one week. 



Apply the results obtained and explain their bearing upon the value of the different types of soil 



of the neighborhood. Also explain what factors affect the capillary power of soils and how this 



power may be influenced by the way in which the soil is managed. 



Questions. In which soil did the water rise with the greatest rapidity ? In which did it move most 

 slowly? If the long tubes are used, in which soil did the moisture reach the greatest height? How 

 may the capillary power of a soil be increased ? How may the soil in which water rises rapidly for a 

 short distance and then stops be treated so as to cause water to rise to a greater height ? Write state- 

 ments describing capillary (and film) water and free (or gravitational) water and the value of each 

 to growing plants. When the surface of the soil is loose and open, as when cultivated, does the 

 moisture rise to the surface? Why? What means are used to prevent capillary moisture from 

 reaching the surface, and what is the practical effect? How does such practice affect the power of 

 crops to resist drought? What is the effect of rolling upon the capillary rise of water in the surface 

 soil ? Why does the farmer usually roll the land after sowing small seed like millet in dry ground ? 



References. Waters, H. J. Essentials of Agriculture, pp. 64-66. Ginn and Company. Mosier and 

 Gtjstafson. Soil Physics and Management, pp. 206-208. J. B. Lippincott Company. Lyon, Fippin, Buck- 

 man. Soils, their Properties and Management, pp. 221-243. The Macmillan Company. 



[36] 



