284 NATURE STUDY AND AGRICULTURE 



Vary this experiment by filling one chimney with clay, 

 and another with the same kind of clay mixed with an 

 equal amount of humus. Pour the water in as before. 

 What is the effect of humus on the porosity of the soil? 

 It will take several days to complete these experiments. 

 In the meantime, cover the chimneys to prevent evapora- 

 tion of moisture from the soils. 



What kind of water dripped from the soils ? This was, 

 of course, the free water that in a field could be removed 

 by under drainage. The most common method of under 

 drainage is by tiles made for this purpose. Later we shall 

 see that drainage benefits the soil in many ways. From 

 your experiments, which do you think stands more in need 

 of under drainage, a field with a sandy subsoil or one with 

 a heavy clay? 



Is there any water left in the soil after the free water 

 has all dripped out? What becomes of this capillary 

 water ? 



Fill a tumbler with moist soil. Over it invert another 

 tumbler the same size. Set it aside. Examine after 

 twenty-four hours. What do you find on the inverted 

 tumbler? Where did the moisture come from? What 

 may be done to prevent the evaporation of water from the 

 soil ? Again place moist soil in the tumbler. Put on top 

 a layer of very dry, fine soil, one inch deep. Invert a 

 tumbler over this . as before, and note whether or not any 

 evaporation takes place. If the moisture in the top layer 

 of soil evaporates, does this in any way affect the moisture 

 farther down in the soil ? There is a movement of capil- 

 lary water through the soil which we can best understand 

 by some experiments. 



