126 SOILS 



compounds that remain in the soil? That we shall at- 

 tempt to answer now. 



Just after decay nitrogen compounds are not ready for 

 plants. When nitrogen compounds are reduced from 

 their complex forms plant or animal tissue by decom- 

 position bacteria, they are unavailable plant food, still. 

 They must be made to combine with more oxygen : they 

 must be oxidized. Scientific men call this process nitrifi- 

 cation. Organic compounds of nitrogen, when applied to 

 the soil and decomposed, eventually oxidize to a nitrate, 

 and then become usable plant food. 



The chemical process. In this disorganization of the 

 higher and complex compounds, nitrogen compounds, 

 like those of other elements, are reduced to more simple 

 ones, reaching, finally, a point where nitric acid is formed. 

 This acid now unites with bases or metals, producing 

 compounds now known as nitrates. The common ni-^ 

 trates are: potassium nitrate (KNCX), sodium nitrate 

 (NaNO 8 ), calcium nitrate (Ca(NO 3 ) 2 ), and ammonia 

 nitrate (NH 4 NO 3 ). 



Nitrification is a biological process. Nitrification, at 

 first, was thought to be a chemical process. The chemist 

 had learned that he could do this same work in his labo- 

 ratory : he could oxidize, under certain conditions, nitrous 

 bodies into nitric acid bodies : he could oxidize unavail- 

 able plant food into available nitrogen plant food. But, 

 in recent days, many things have been discovered about 

 soil bacteria. Further study has revealed the fact, that 

 some of these many busy bodies of the soil are back of 

 this oxidization process : some of them cause nitrification : 

 some of them change unavailable nitrogen into the desired 

 form. 



One way of proving this theory is this : secure a sam- 

 ple of soil which when mixed, divide into two parts. One 



