CARBON AND NITROGEN CYCLES IN THE SOIL 85 



The reactions involved in all these changes are obviously complex, 

 but they have been partially disentangled, and we can now pass on to 

 a more detailed consideration of the separate changes. 



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 

 studied, but there is some evidence of the production of amino acids 

 which subsequently hydrolyse, or oxidise. Although amino acids are 

 in general fairly stable, several reactions are now known whereby they 

 may be decomposed with production of ammonia : — 



R-CH-NH^COOH + O^ = RCOOH + CO^ + NH3.2 

 RCH-NHa-COOH + H^O = RCH-OHCOOH + NH3. 

 RCH-NHaCOOH + H2O = RCH3OH + CO^ + NHj.^ 



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



The investigations by Marchal (193) 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 (206, 207) 

 had established the micro-organic nature of the process by showing 

 that it was stopped by sterilisation. Marchal, therefore, made sys- 

 tematic bacteriological and mycological analyses of soils, and studied 

 the action of the organisms thus obtained on solutions of albumin. 

 Of the dozen or so varieties that invariably occurred, practically all 

 decomposed the albumin and formed ammonia. B. mycoides proved 

 very vigorous and was studied in some detail. The process was con- 

 sidered to be a simple oxidation necessary to the life of the organism ; 

 oxygen was absorbed and carbon dioxide evolved, the ratio NH : CO2 



' Containing less than lo per cent, of organic matter. 



^Dakin, jfourn. Biolog. Chem., 1908, iv., 63. 



* Ehrlich, Zeitsch. Verein. Rubenzucker Ind., 1905, 539-67. 



