572 PRINCIPLES OF SOIL MICROBIOLOGY 



coccum was found 45 to secrete soluble nitrogen compounds only after 

 death; Az. agile&nd Az. vinelandii, however, readily secrete soluble nitrog- 

 enous compounds during active growth. 



The nitrogen synthesized by Azotobacter is utilized by higher plants. 

 This is accomplished either by the secretion of a substance which has a 

 favorable influence upon plant growth, 46 or through the autolysis of 

 the dead Azotobacter cells. The proteins of the Azotobacter cells are 

 not completely broken down by the soil bacteria and are not readily 

 acted upon by proteolytic enzymes. 47 Remy, 48 however, considered the 

 microbial proteins readily available for plant growth. 



Chemistry of process of non-symbiotic nitrogen-fixation. Due to its 

 position in the periodic system, nitrogen shows a strong affinity for the 

 electropositive elements and only a slight affinity for the electronegative 

 elements. The combination of nitrogen and hydrogen is exothermic so 

 that 



N 2 + 3H 2 ^2NH 3 + 24.0 Cal. 



At ordinary temperatures, 90 per cent of the nitrogen is found as NH 3 . 

 With increasing temperatures, the ammonia breaks up more and more. 

 The combination of nitrogen with oxygen is endothermic: 



N 2 + 2 = 2NO - 43.2 Cal. 



The oxidation of nitrogen, therefore, requires large quantities of energy 

 and must be carried out at a high temperature so as to obtain the 

 necessary reaction velocity and favorable equilibrium between N2 

 -\- 2 <=* 2NO, which amounts to 5 per cent at 3200° and 10 per cent at 

 4200°. With an increase in temperature the molecular nitrogen changes 

 to atomic (N 2 <=^ 2N) and brings about an increase of contact between 

 the reacting molecules. In the presence of catalyzers, the reactions are 

 brought about at lower temperatures. The bacteria depend primarily 

 on catalyzers. Winogradsky 49 believed that, in the case of the anaerobic 

 Clostridium, the bacterial plasma produces ammonia out of the nitrogen 



46 Moler, T. Ein Beitrag zur Kenntnis der Entbindung des durch Azotobakte 

 fixierten Stickstoffes. Botan. Notiser, 4: 163-178. 1915; (Centrbl. Bakt. II 

 47: 635. 1917). 



46 Kayser, E. Influence de la matiere azotee elaboree par l'Azotobacter sur le 

 ferment alcoolique. Compt. Bend. Acad. Sci., 172: 1539-1541. 1921. 



47 Bonazzi, 1924 (p. 560). 

 48 B.emy, 1909 (p. 569). 



49 Winogradsky, 1893-1895 (p. 107). 



