212 INTRODUCTION TO GENERAL SCIENCE 



h. 1608 : 50-51. Drainage and Ventilation. 



t. 1610 : 42-43. Drainage and Irrigation. 



j. 1611:49-53. Irrigation. 



k. 1612 : 152-153. Draining the Land. 



151. SOIL AIR 



Air is necessary for plant growth, as well as for animals. 

 The plants need it themselves, and the soil bacteria require 

 it, and must use it in the formation of the nitrates. Then, 

 also, oxygen is needed to carry on some chemical changes of 

 decomposition, as well as to prevent the loss of the nitrate- 

 forming material. If the soil is too wet, the air is excluded, 

 and for that reason, drainage is necessary. Drainage, either 

 natural or artificial, is necessary for plant growth. 



The soil is ventilated by natural means, due to the changes 

 of temperature, causing expansion or contraction of the air 

 in the soil; by changes of barometric pressure; and by the 

 changing of the level of the water table. Man can accomplish 

 much in the direction of soil ventilation by underdrainage. 



References : 



1. 1601 : 239-244. Needs of Soil Ventilation. 



2. 1601 : 244-248. Natural Process of Soil Ventilation. 



3. 1601 : 248-251. Ways of Influencing Soil Ventilation. 



4. 1605 : 94-95. Importance of Soil Air. 



5. Farmers' Bulletin No. 245 : 7. Soil Air. 



6. Farmers' Bulletin No. 408 : 37-38. Air Necessary for Plant 



Growth. 



7. Bureau of Soils, Bulletin No. 73 : 25-30. Oxidation in Soil. 



a. 1207 : 330-331. The Atmospheric Circulation of the Soil. 



b. 1602 : 34. The Air and Water in Soil. 



c. 1607 : 125-127. Movement of Air Through Soil. 



d. 1608 : 52-54. Soil Ventilation and its Effects. .. 



e. 1611:6. Soil Air. 



/. 1612 : 36. Air Circulation in Soils. 



