EXERCISES WITH SOILS 



121 



When garden soils are rolled, the soil is packed and the 

 moisture from below is brought toward the surface rapidly. 

 This is done when small seeds are planted, for the purpose of 

 bringing moisture to them to cause germination. Unless a 

 dust mulch is produced soon afterward, the water will escape 

 and be lost in the air. When soils are rolled, the roller should 

 be followed with a harrow or weeder to break up the very top 

 layer of soil. Eollers with a rough surface are used by some 

 farmers for the purpose of 

 bringing moisture close to the 

 top and then checking its 

 evaporation. 



15. Absorbing Power. — 

 With several bottles and cups or 

 glasses, arrange an apparatus as 

 shown in figure 71. Use several 

 kinds of soil. Perhaps only two 

 or three different kinds will be 

 available. Pour water over each 

 soil, keeping it covered. Note 

 the time required in each ease for 

 the water to begin dripping 

 through below. 



This shows which kind of soil will take in rainfall most 

 rapidly. Those with close texture retard the flow of water, 

 and much of the rainfall on such compact soils will run away 

 during heavy rain. 



16. Water-holding Power. — Arrange the apparatus as in the 

 preceding exercise (Fig. 71). After the different dry soils are placed 

 in the bottles, a definite amount of water is poured on each soil. 

 Care is taken to carefully measure the water used on each soil. When 

 some runs through below, no more is poured on that soil. After each 

 is through draining, the water in the lower cups is poured back into 

 the measuring cup. The amount of water each soil keeps is easily 

 determined. 



Some trials show that soils full of humus hold many 

 times the amount of water held by sand. One trial showed 



Fig. 70. — Fine-grained soil (clay) conducts 

 water upward farther than sand. 



