SOIL WATER AND SOIL AIR 



the roots may then be deep enough to receive plenty of water 

 from below through capillary action. Hence, we have the 

 apparent paradox of supplying more water to plants by 

 removing part of it. 



Soil management. Proper soil management with refer- 

 ence to water supply and control is difficult at best. It can 

 be accomplished only by making intelligent use of the facts 

 concerning soil water 

 that have been pre- 

 sented in this chapter. 

 Further details of soil 

 management will be 

 considered in a chapter 

 devoted to the subject. 



AIR IN THE SOIL 



What soil air is. 

 Atmospheric air con- 

 tains nearly 21 per cent 

 of oxygen, 79 per cent 

 of nitrogen, and .04 per deeper. 

 cent of carbon dioxide. 

 Soil air differs from 

 the free air above, in the respect that it has less oxygen and 

 from 5 to 75 times as much carbon dioxide. Plant roots and 

 decaying organic matter produce" enough carbon dioxide to 

 account for this difference. 



How air is held in the soil. The soil spaces which are 

 not occupied by water are filled with air. The presence of 

 air in the soil may be shown by pouring water into a vessel 

 containing soil. When the water enters, bubbles of air will 



Diagram of section of drained soil. 



A. Early in season. Free water removed 

 upper level permitting roots to grow 



B. Late in season. Feeding area of roots 

 within region of capillary water. 



