THE ROLE THAT TILLAGE PLAYS 95 



other particles of a different nature, chemical changes are 

 provoked through the interchanges of the chemical ele- 

 ments of the many soil compounds. The interchange of 

 acids and gases always is taking place in the soil, but it is 

 most active when a disarrangement of soil particles has 

 occurred. 



Since oxygen is such an active element, combining 

 freely with elements in all sorts of substances, it follows 

 that when air is allowed entrance and tillage allowed to 

 rule chemical action and change most actively takes 

 place. 



A sure way to injure the soil is to saturate it with water 

 or by tramping to exclude the air: you lessen the activity 

 of the chemical agents : you retard the making of plant 

 food available. 



Whenever humus decays in the soil, the adjoining 

 particles are affected, and, in a measure, at least, decay or 

 rot. These break into simple compounds: they come 

 nearer to the nature of plant food. Hence, when you 

 incorporate humus in the soil, you add a plant food mat- 

 rial to the soil and supply, at the same time, a forcefully- 

 working agent that makes available stubborn food con- 

 stituents. 



Tillage permits better diffusion of salts and gases, and 

 other changes closely allied thereto, and influences fa- 

 vorably the decomposition of earth and earthy materials. 



The microscopic life of the soil is influenced to a 

 marked degree by tillage and its resulting effect upon the 

 chemical nature of the soil. In connection with the nitro- 

 gen element we have the denitrifying bacteria which lib- 

 erate nitrogen into the air, and the nitrifying bacteria that 

 change nitrogen compounds of the soil into nitrates, the 

 form that plants use most eagerly. The first kind is in- 

 fluenced by tillage in this manner: wherever poor aera- 



