208 



ROCKS AND SOILS 



bottom of the capillary tubes. Observe what happens. Hold 

 one end of a cube of sugar in the colored water. Suspend 

 one end of a piece of blotting paper in the colored water. 

 Record your observations. 



Water rises in tubes and porous materials by capillary at- 

 traction. 



Obtain five tall lamp chimneys. Tie a layer of cloth over 

 the top of each chimney (see Fig. 335). Set the chimneys in 

 a shallow dish. Pour clay into the first chimney, fine sand 



FIG. 334 



into the second, loam (a mixture of sand and clay) into the 

 third, coarse sand into the fourth, and gravel into the fifth. 

 Fill each chimney about three-fourths full. Pour water into 

 the shallow dish and observe how high the water rises in 

 the various types of soil. In your notebook, record your ob- 

 servations and answer the following questions. Why does 

 water rise in soil? Why does a farmer go through his fields 

 with a cultivator to break up the soil? 



Experiment 131. How rapidly does water sink in soils? 



Use the same lamp chimneys for this experiment as were 

 used in the last experiment. Fill the chimneys with fresh 

 samples of the various soils. Hold each chimney over a 

 quart jar and slowly pour into each a pint of water. How 

 much water passed through each type of soil and how long 

 did it take ? Record your results. List the soils in the order 

 of their ability to hold water. 



Activity 132. How are soils kept fertile? 



Interview some farmers in your locality and find the 

 methods employed for keeping the soil fertile. Also go to 

 stores that sell fertilizers and get the names of the fertilizers 

 sold. Find out what chemical elements are present in these 

 fertilizers. Keep a record of your findings and report them 

 to the class. 



Experiment 133. How do plants of the legume family 

 help fertilize soil? 



Locate a clover, alfalfa, or pea plant. Carefully remove the 

 plant with its roots. Soak the roots in water and carefully 

 wash away the dirt. Notice the little nodules attached to the 

 roots. Explain the work they do and their importance. 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



Living things are dependent upon soil for their 

 existence. Most plants obtain water and minerals 

 directly from the soil. Animals live on plants; there- 

 fore, the food elements which nourish their bodies 

 come originally from the soil. 



For untold ages man was a food gatherer. Human 

 population was small and food was very plentiful. 

 Wild animals, fish, edible plants, seeds, roots, and 

 berries he could easily gather to meet his needs. Even- 

 tually because of the increase in population it became 

 necessary for man to plan for his food supply. This 

 led to the development of agriculture. 



For several thousands of years agriculture has been 

 one of man's basic industries. Agriculture furnishes us 

 our food materials and many raw materials for manu- 

 facturing industries. Our present mode of living would 

 be impossible without the foods produced by farming. 

 Man is constantly occupied with the problems of main- 

 taining fertility of old soil and of finding new fertile 

 soils. 



As we proceed with this topic we shall learn about 

 soil and the factors which must be controlled in order 

 to carry on agriculture successfully. 



How are soils formed? You learned in the previous 

 topic how agencies of weathering and erosion change 

 bed rock into smaller particles. Soil in any particular 



FIG. 335 



locality may be formed in two ways. First, the soil may 

 have been formed by weathering from the rocks be- 

 neath it, in which case it is composed of the same sub- 

 stances as the rocks below. Soils formed in this way 

 are called residual soils. Second, the soil may have been 

 brought there from a distance. Soils formed in this 

 manner are called transported soil. Soils formed of de- 

 posits by streams, glaciers, and wind belong to this 

 class. Transported soils generally are composed of a 

 richer variety of materials and are preferred to residual 

 soils for crop raising. 



Particles of rock alone do not make a fertile soil. 



