Tillage and Its Purposes 137 



presence of abundant supplies of oxygen. Shut out the 

 oxygen and these bacteria cannot live, but other forms 

 that are engaged in denitrifying the soil in which they 

 live, thrive only in the absence of oxygen, and then get in 

 their harmful work. 



These bacteria which carry on the work 



1 lage jj^ ^1^^ g^.j called nitrification, are among 



Promotes ' ° 



Nitrification the most important aids to the farmer. 



The organic decay or humus in the soil 

 contains nitrogen. But our cultivated plants, as we have 

 shown heretofore, cannot use nitrogen imtil it is in the 

 very soluble form of a nitrate. The nitrifying bacteria 

 in the presence of oxygen and a proper temperature take 

 the ammonia of the organic matter and transform it into 

 nitrites, and then another form feeds on these nitrites, 

 adding more oxygen till nitric acid is the result. Then 

 when nitric acid is present in the soil it at once combines 

 with whatever base may be at hand, either hme or potash 

 usually, and a nitrate is formed which plant roots can use. 

 Hence, one of the most important objects in tillage is to 

 promote the growth of these nitrifying organisms through 

 an abundant supply of oxygen, and at the same time pre- 

 vent the growth of the denitrifying organisms that thrive 

 only where oxygen is lacking. 



^. . ^ The complete pulverization of very re- 



Fining the , ,1.1^ 



Soil Promotes fractory minerals, thus enabhng the water 



the Solution and carbon dioxide to act upon every par- 

 of Plant ^j^ig^ ^jH dissolve from them matters other- 



wise insoluble. Feldspar, for instance, is 

 rich in potash, but is very insoluble. But it has been 

 found that when it is finely pulverized and digested a week 



