Cultivation and Drainage 



a dirt mulch of fine clods. 

 A mulch tends to prevent 

 capillary water from 

 passing through from 

 the soil below, and thus, 

 very largely, stops evap- 

 oration at the surface 

 (Fig. 32 and Exp. i). 

 Whenever the mulch be- 

 comes packed, as it may 

 after a rain, it should 

 be restored to its former 

 condition by proper cul- 

 tivation (Fig. 33 and 

 Exp. 2). 



(4) It ventilates the 

 soil. The roots as well 

 as the green portion of 

 any plant must be sup- 

 plied with oxygen, and 



they get it from the air that is found among soil 

 particles. (Exp. 3.) If the surface of the earth is 

 allowed to bake, air is excluded and the crop suffers. 

 A plant, while growing rapidly, consumes about its own 

 volume of oxygen daily, and a seed uses about a thousand 

 times its volume of oxygen in the process of germination. 

 The necessity for soil ventilation is very great, and the 

 ventilating is done chiefly by cultivation. 



In the last chapter we considered the bacteria that 

 add to the store of available nitrogen in the soil. These 

 helpful bacteria cannot work without plenty of soil air. 



W. T. SkUting 



FIG. 32. The effect of a mulch. In a few 

 seconds water rose from the glass vessel 

 to the top of the loaf sugar, but it could 

 not go up through the powdered sugar. 



Keeping 

 mulch 



The need 

 for air 



Effect of 

 air on 

 helpful soil 

 bacteria 



