EXERCISES WITH SOILS 117 



The reason for the effect of color is explaiued hy the fact 

 that black absorbs heat rays and white reflects them. 



8. Effect of a Dust Mulch. — Nearly fill two cans with garden 

 soil of the same kind. Moisten them and pack them alike. This 

 packing should be done by striking the cans on a table or the floor 

 to draw the soil particles together. On the top of one spread a, half- 

 inch layer of loose, dry soil to form a " dust mulch." The top of the 

 soil in the other can should be pressed with a smooth surface, as the 

 bottom of a bottle, giving the effect of a field roller on a field surface. 

 Now, with the scales used in a preceding exercise, weigh each of the 

 cans of soil and record their weights. Allow them to stand either 

 in the room or dry, open air for about two days. Weigh each again. 

 Which has lost more moisture? If the experiment has been carefully 

 done, and the soil has not cracked or shrunken away from the sides 

 of the can, the loss will be greater from the " rolled " soil. The 

 dust mulch checks loss of moisture. 



In garden work, a dust mulch may be maintained among 

 the plants between the rows by the use of a common garden 

 rake or with small shovel cultivators. Moisture which is 

 abundant in the soil in early spring will be held by the use of 

 a dust mulch until it is needed by the plants during the dry 

 weather of summer. The maintenance of a dust mulch 

 throughout the growing season is best for most garden crops 

 (Fig. 65). 



g. Carpet or Hay Mulch. — In warm, dry weather, place a piece 

 of carpet or a layer of hay a few inches thick over about one square 

 yard of bare soil, leaving other- bare soil near it for a comparison. 

 After a few days of dry weather remove the carpet, or hay mulch 

 and notice the difference between the soil .just uncovered and the rest. 



A mulch of any kind on soil prevents much of the evapora- 

 tion of moisture from it. This is because there is no contin- 

 uous solid matter through which the moisture may climb by 

 capillary action. It is by capillary action that oil climbs in 

 the wick of a lamp, and it is by the same process that moisture 

 climbs in the soils of the field. A mulch on top of dust or 

 fine soil made with a harrow, or of other material, breaks the 



