36 



PRACTICE 17 



Power of Loose Soils to Retain Water. 



Fill tubes* with sand, loam, silt, clay and peat soils. (Fill tubes 

 about two-thirds full of peat.) 



Place disks of damp cheese-cloth in the bottom of the tubes and 

 then weigh them. Fill the tubes up to the crease (except peat) one 

 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 in the box till it is on the same level with the soil 

 in the tubes, thus allowing the water to pass up through the soils. 



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

 have become thoroughly saturated, remove the tubes and place them 

 in a pan to drain. Cover to prevent evaporation and weigh when 

 drainage ceases. 



Determine the amount of water-free soil by using the percent of 

 hygroscopic moisture found in Practice 6. 



Measure depth of the settled soils. 



Calculate the percent of waterretained, the weight per cubic foot 

 of soil that this represents using the apparent specific gravity found 

 in Practice 9, and the acre inches of water. 



Land recently plowed 6 inches deep will absorb how many inches 

 of rainfall without any run-off? 



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



What is a saturated soil? 



Why do they plow deep in semi-arid regions? 



♦Galvanized iron or copper tubes two inches inside diameter and twelve inohes long 

 with a crease one inch from the top. The bottom is perforated with numerous small 

 holes and is about one-half inch from lower end of tube. There are two or three holes in 

 main tube below this for water to enter. 



