ORGANIC MATTER AND* NITROGEN 197 



process until the solution contains about .7 per cent of free lactic 

 acid, beyond which they become inactive; but, if the free lactic 

 acid is neutralized by the addition of some base, the bacteria again 

 become active. 



In the process of nitrification there is required, not only the 

 presence of calcium or some other alkaline element or group, in 

 suitable form (as in carbonates) , but also a good supply of the ele- 

 ment oxygen; for calcium nitrate contains but one atom of calcium 

 (Ca) with two atoms of nitrogen (N) 2 , and six atoms of oxygen 

 (O 3 ) 2 , in each molecule, as indicated in the formula Ca(NO 3 ) 2 . 

 Magnesium nitrate, Mg(NO 3 ) 2 , potassium nitrate, KNO 3 , and all 

 other nitrates also contain oxygen. The supply of oxygen for the 

 formation of nitrates in the process of nitrification comes from the 

 air, and, aside from the killing of weeds, one of the most important 

 effects of cultivation, or tillage, is that it permits the air more 

 freely to enter the soil, and thus promotes nitrification. 



Another absolute requirement for the process of nitrification is 

 the presence of phosphorus and probably of other mineral food 

 supplies necessary to the growth and multiplication of the bacteria 

 themselves. It is known that without phosphorus there can be 

 neither growth nor life. These minute forms of plant life do not 

 utilize the carbon dioxid of the air by means of the sun's energy; 

 but they derive energy from the oxidation of the nitrogen com- 

 pounds, and by means of this energy they are able even to decom- 

 pose carbonates, if necessary, and to derive their supply of carbon 

 from this source for the formation of their own organic bodies; 

 but for all of this the mineral plant food must be supplied. (As a 

 rule, the carbohydrates furnish the necessary carbon for bacterial 

 growth.) 



An important consideration in this general connection is the 

 fact that in the conversion of sufficient organic nitrogen into nitrate 

 nitrogen for a hundred-bushel crop of corn, the nitric acid, if 

 formed, would be alone sufficient to convert seven times as much 

 insoluble tricalcium phosphate into soluble monocalcium phosphate 

 as would be required to supply the phosphorus for the same crop. 

 While this specific reaction could not occur in quantity, because 

 the acid monocalcium phosphate would prevent nitrification, the 

 suggestion is of interest in that it affords a quantitative comparison 



