468 Introduction to the Study of Science 



Exercise. Have several different kinds of soil such as clay, clay 

 loam, sand, sandy loam, and gravelly soil ; the same number of pieces 

 of glass tubing, each about one inch in diameter and six inches long, 

 or tall lamp chimneys. Cover one end of each piece of tubing or 

 chimney with a piece of cheesecloth and tie securely. Place the 

 covered ends in a large pan and put into each one of the sample soils. 

 Pour about one inch of water into the pan. Observe the rise of water 

 in each, and estimate the rate of rising. 



The amount of water each kind of soil will take up may be deter- 

 mined quite accurately by putting each tube into a separate pan and 

 supplying measured quantities of water until the surface of the soil 

 shows moisture. One should test the rate of capillarity with a soft 

 mulch surface and with a hard smooth surface. These will show the 

 effect of mulching the surface to conserve moisture, and of rolling to 

 increase capillary rise of moisture to the surface. 



Why farmers roll soil. Many farmers, after sowing a field 

 with grain, such as wheat or oats, roll it. As the experiment 

 shows, this causes the water to rise rapidly to the surface. 

 The rolling makes the capillaries or pores in the soil more 

 continuous, with the result that the rapidly rising moisture 

 reaches the grain and insures its germination. After seed 

 begins to grow, the smooth, hard surface may be broken up 

 to form a mulch, which largely prevents the escape of soil 

 water. 



Dry farming. A large area of land in the United States 

 does not receive sufficient rainfall during the season to raise 

 a profitable crop. The rainfall of two seasons may be enough 

 for one crop, or that of three years may suffice for two crops. 

 The rainfall is conserved by dry farming. First the ground 

 is plowed as deeply as is thought necessary to provide a deep 

 reservoir. After a rain which is immediately absorbed by the 

 loose, soft soil, the surface is worked into a mulch three or four 

 inches deep. The mulch is retained through the year -by fre- 

 quent shallow cultivation. Thus the continuity of the cap- 

 illary spaces is destroyed and water is prevented from rising 

 by capillary action to the surface. Evaporation is also greatly 

 reduced or prevented by the fine mulch. At the beginning of 



