106 



ELEMENTS OF AGRICULTURE 



Continue for about a week. In which does the water rise highest? 

 Why? Notice that it rises highest between the plates where they were 

 nearest together and rises highest in the soil that has the finest spaces. 

 Compare with the rise of oil in a lamp-wick, ink in a blotter, etc. What 

 is the object of compacting the soil over seeds when planted? In what 

 different ways is this done? 



42. Evaporation from the Soil. (Special Importance in Arid Regions). 



Materials. Spring balance; three tin cans, holes punched in sides 

 and string for a bail, the same as used in No. 39; soil, fine grass or 

 straw. 



Fill each can nearly full of soil. Water each with the same amount of 

 water. Cover the top of one with grass. Weigh. As soon as the surface 

 is dry enough, stir the surface on one about an inch deep. Keep this 

 starred Weigh every school day for about two weeks. 



Which loses weight most rapidly? Why? What is one use of cul- 

 tivation during a dry time? Notice that if we stir the soil when it is 

 moist we hasten the evaporation in the part stirred. In dry weather 

 this loose soil may act as a dust mulch to prevent evaporation. Tillage 

 may, therefore, first hasten and then lessen evaporation. What would 

 its general effect be in a wet season? In a dry season? Why is the 

 soil under a board moist? 



