NITRIFICATION 125 



in a moist soil under certain conditions, and then find 

 their way through drain waters into surface wells, and 

 cause the spreading of these diseases. 



145. Products Formed by Soil Organisms. — In 



considering the part which micro-organisms take in 

 plant growth, as well as in all similar processes, there 

 are two phases to be considered : (i) the action of the or- 

 ganism itself, and (2) the chemical action of the product 

 of the organism. In the case of nitrification, the 

 action of the organism brings about a change in the 

 composition of the organic matter, producing nitric 

 acid which is merely a product formed as a result of 

 the action of the organism. The nitric acid then acts 

 upon the soil producing nitrates. In the case of soils 

 rich in organic matter, the fermentation changes 

 which take place during humification result in the 

 production of acid products. This is simply the 

 result of the action of the ferments. The acids then 

 act upon the soil bases and produce humates or organic 

 salts. In many fermentation changes there is first 

 the production of some chemical compound, and then 

 the action of this compound upon other bodies. In 

 rendering plant food available, as in nitrification and 

 humification, it is the final product, and not the first 

 product of the organism, which is of value. 



146. Inocculating Soils with Organisms . — In grow- 

 ing leguminous crops on soils where they have never 

 before been produced, it has been proposed to supply 



