PRACTICE XX 



THE POWER OF LOOSE SOILS TO RETAIN CAPILLARY WATER 



Use the five stock soils. 



Place disks of damp cheesecloth in the bottom of the tubes ^ 

 and weigh them. Fill the tubes up to the crease (except peat, 

 two thirds full) 1 inch from the top by pouring the soil in 

 gently through a funnel as the tube is held vertically, being 

 careful not to compact the soil by jarring. Weigh the filled 

 tubes and place in an empty galvanized-iron box. Pour water 

 into the box until on a level with the soil in the tubes, thus 

 allowing it to come up through the soils. 



Note the time required for the soils to become moist on top. 

 When the soils have become thoroughly saturated, remove the 

 tubes, wipe dry, and weigh at once to get the total water capacity. 



Cover the tubes with watch glasses or glass plates and set them 

 out to drain. Weigh when drainage ceases. The difference be- 

 tween this weight and the w^eight of tube and air-dry soil is the 

 capillary water retained. 



Calculate the weight of water-free soil by using the average 

 per cent of hygroscopic water given you from Practice VI. 



Measure depth of settled soils. 



Calculate the per cent of capillary water retained. Using the 

 average apparent specific gravity given you from Practice XI, 

 find the weight of a cubic foot of soil. From this and the per 

 cent of water retained, calculate the w^eight of water retained per 

 cubic foot and the acre inches of water retained. 



Land recently plowed 6 inches deep will absorb how many 

 inches of rain without any run-off ? 



Is there any advantage in deep plowing on rolling or hilly land? 



Why do they plow deep in semiarid regions ? 



What is a saturated soil ? 



References. 



" Soils/' Lyon and Fippin, pp. 136-144 and 154-158. 



"The Soil," Hall, p. 67. 



" Physical Properties of Soil," Warington, pp. 64-85. 



"The Soil," King, pp. 157-162 and 187-189. 



" Soils," Hilgard, pp. 229-230. 



1 Brass, copper, or galvanized-iron tubes 2 inches inside diameter and 12 inches 

 long, with a crease 1 inch from the top. The bottom is perforated with numerous 

 small holes and is about 2 inch from lower end of tube. There are two or three 

 notches or holes in the main tube below the bottom for water to enter. 



42 



