Ways of Influencing Soil Ventilation. 209 



be stronger than any other, on account of the great fre- 

 quency with which the changes recur. 



248. Movements of Water and Soil Ventilation The 



water which enters the soil as rain must displace a volume 

 of air equal to the rainfall which penetrates the soil and 

 then, when this water is again lost by the soil, whether 

 by percolation or by capillary or root action, the same vol- 

 ume of air must again be returned. In a climate where 

 the rainfall, which penetrates the soil, is 24 inches dur- 

 ing the growing season, two cubic feet of air per square, 

 foot of surface enters the soil in consequence. 



WAYS OF INFLUENCING SOIL VENTILATION 1 . 



There are important means and methods of controlling 

 and modifying the rate and extent of soil ventilation, 

 which are under the control of the farmer. 



249, Soil Ventilation Modified by Tillage. Nearly all of 

 the operations of surface tillage modify the rate of entrance 

 or escape of air from the soil. Plowing effects a sudden 

 and complete change of air in the soil to the depth stirred 

 and in the spring, when nitrates are deficient, and the 

 pores largely closed with water, this breaking up of the 

 soil may be very beneficial. 



The thorough preparation of the seedbed before plant- 

 ing, so strenuously insisted upon by the best practical men, 

 has a portion of its rational basis in the need of soil ven- 

 tilation; and deep subsoiling, when done at such a time 

 as not to puddle the soil, must always profoundly affect 

 the relation of air to soil, as well as of moisture. Indeed, 

 all of the operations of soil loosening serve, not only to 

 admit air more freely to the soil stirred, but the undis- 

 turbed portions beneath will also be better ventilated be- 

 cause of the surface loosening. 



