14 Diseases of Truck Crops 



in the soil two definite processes take place, all 

 thanks to the work of certain soil bacteria. 



1. AMMONIFICATION. In this process, the soil 

 bacteria attack the complex proteids and convert 

 them into ammonia. The odor of ammonia from 

 decomposed urea, manure, or any other organic 

 matter is always an indication that ammonification 

 takes place. According to Sackett 1 and others the 

 ability to bring about this change is attributed to the 

 following soil bacteria: Bacillus mycoides. Bacillus 

 proteus vulgaris, Bacillus mesentericus vulgatus, Bacil- 

 lus subtilis, Bacillus janthinus, Bacillus coli-communis, 

 Bacillus megatherium, Bacillus fluorescens liquefaciens, 

 Bacillus fluorescens putridus, and Sarcina lutea. 



2. NITRIFICATION. Both ammonia and ammonia 

 compounds are forms of nitrogen that are not yet 

 readily available to plants. They must be changed 

 further into simpler compounds or, as the process is 

 known, must undergo nitrification. The ammonia 

 is first oxidized into nitrous acid and nitrates. This 

 is accomplished by two species of soil bacteria, 

 Nitrosomonas and Nitrosococcus. The nitrates are 

 then oxidized into nitric acid and nitrates, through 

 the work of the bacterium Nitrobacter. The nitrates 

 are the only forms of nitrogen which plants can use. 



C. ACTION OF SOIL FLORA ON MINERAL SUBSTANCES 



We have already pointed out that the inert mineral 

 substances in the soil are not in a form in which 



Sackett, W, G., Colorado Agr. Expt. Sta. Bui. 196 : 3-39, 1916. 



