CARBON AND NITROGEN CYCLES IN THE SOIL 185 



The Formation of Ammonia. 



Ammonia is in all probability an intermediate product in 

 the formation of nitrates. It is formed in the soil from the 

 proteins of plant residues or manures, and the process is 

 effected mainly by micro-organisms, but not entirely, for it 

 still continues at a diminished rate in presence of antiseptics. 

 The reaction has not yet been completely elucidated. 



There is evidence of the production of amino acids which 

 subsequently hydrolyse, or oxidise.^ Although amino acids 

 are in general fairly stable, several reactions are known 

 whereby they may be decomposed with production of 

 ammonia : — 



R-CH-NH^-COOH + H2 = R-CH2COOH + NH3. 

 R-CH-NH2-COOH + 02 = RCOOH + CO2 +NH3.2 

 R-CH-NH2COOH + H2O = RCH-OHCOOH + NH3. 

 RCH-NHg-COOH + HgO = RCH2OH + CO2 + NH3.3 



It is not, however, known how they break down in the soil. 



Miyake {202b) has shown that the rate of production of 

 ammonia can be expressed by the equation for autocatalytic 

 reactions, which means that it is much affected by the ac- 

 cumulation of the products. Both Gainey * and Neller ^ have 

 studied the connection between the production of ammonia 

 in soil and the evolution of CO2. 



The investigations by Marchal (190) in 1893 of the method 

 of ammonia production in the soil are so complete that little 

 has since been added to the facts he ascertained. Miintz and 

 Coudon (207) had established the micro-organic nature of 

 the process by showing that it was stopped by sterilisation. 

 Marchal, therefore, made systematic bacteriological and myco- 

 logical analyses of soils, and studied the action of the organ- 

 isms thus obtained on solutions of albumin. Of the dozen 



' See R. H. Robinson and H. V. Tartar, y. Biol. Chem., 1917, 30, 135-144. 

 2 Dakin, Jour. Biolog. Chem., 1908, iv., 63 ; Oxidation and Reduction in the 

 Animal Body (Longmans, 1912). 



^Ehrlich, Zeitsch. Verein. Rilbenzucker Ind., 1905, 539-567. 

 * Gainey, Soil Sci., 1919, 7, 293. 

 . R. Neller, Soil Sci., 1918, 5, 225. 



