130 TRANSFORMATION OF NITROGEN BY SOIL MICROBES 



Urea is one of the most important nitrogenous substances in 

 this group. It is excreted by the animal organism in large quanti- 

 ties; a large part of the nitrogen in stable manure is made up of 

 urea; it is formed by various microbes; it is produced in the 

 decomposition of various organic nitrogenous complexes, as in the 

 case of uric acid; it is produced in the transformation of certain 

 synthetic nitrogenous fertihzers, such as cyanamid; finally, it 

 is introduced into the soil as a fertihzer coming from the nitrogen- 

 fixation industry. Urea is decomposed in the soil by various 

 organisms according to the following reactions: 



C0-(NH2)2 + 2H2O = (NH4)2C03 



(NH4)2C03 = CO2 + 2NH3 + HoO 



The transformation of urea into ammonia takes place very rapidly, 

 so much so that in the manure pile there is considerable danger of 

 actual volatilization of this ammonia. There are certain organ- 

 isms known as urea bacteria which are able to effect the hydrolysis 

 of urea by means of an enzyme called urease. The ammonia is 

 produced so rapidly that the reaction becomes quite alkaline and 

 the ammonia itself is readily volatilized in the absence of any neu- 

 trahzing agents. In soil, following the addition of urea, the reac- 

 tion first becomes distinctly alkaline through the formation of 

 ammonia; later the reaction becomes more acid than the original 

 reaction of the soil through the oxidation of the ammonia to nitric 

 acid. 



Chitin is a substance formed in the cells of various micro- 

 organisms. In the tissues of these microbes it plays a role simi- 

 lar to that played by cellulose in the tissues of higher plants. 

 It is a polymer of mono-acetyl-glucoseamine having the formula 

 (Ci4H26N20io)io. On hydrolysis it gives acetic acid and glucose- 

 amine. The decomposition of the glucoseamine finally gives 

 rise to ammonia, carbon dioxide, and water, but its transformation 

 is quite slow compared to the decomposition of most other organic 

 nitrogenous substances. 



Formation of Ammonia by Soil Microbes. — Decomposi- 

 tion of various organic substances containing nitrogen is thus 

 found to give rise to ammonia as an important end product. The 

 organisms which form ammonia from the organic compounds are 



