LOSS OF MOISTURE AT SURFACE OF THE SOIL 55 



surface of the second can to the depth of one inch. Place 

 the cans on the scale pans or suspend them from the arms 

 of the balance and adjust the amount of soil in the two cans 

 until the system balances and the arms of the balance 

 remain horizontal. 



After allowing the apparatus to stand over night, it 

 will be found that the system is no longer balanced. The 

 soil which was covered with the dust or sand has lost but 

 little moisture, while the unprotected surface of the other 

 soil has lost a much larger amount. The amount of water 

 that must be added to the can with the exposed soil surface 

 to restore the balance represents the moisture that has been 

 saved by the protective covering of dust — the dry earth 

 mulch. Li using the home-made balance the bar should 

 be held in a horizontal position while the water is being 

 added. 



Discussion: Have you ever noticed how moist the soil 

 is under a stone or a board even when the surrounding 

 ground is quite dry? The stone or board has kept the air 

 away from the surface of the soil and prevented evapora- 

 tion. When shallow cultivation is practiced, the thin 

 layer of stirred soil soon becomes very dry, but by keeping 

 the air away it serves to prevent the deeper soil from losing- 

 its moisture by evaporation. This loose blanket or mulch, 

 as it is called, also helps to absorb rainfall and to prevent 

 it from running off the surface. 



