134 TRANSFORMATION OF NITROGEN BY SOIL MICROBES 



determining the amount of ammonia liberated in a given period 

 of time. The larger the relative nitrogen content the greater is 

 the relative amount of nitrogen liberated as ammonia in a given 

 period of time. If one gram of cottonseed-meal containing only 

 5 per cent of nitrogen and 1 gram of dried blood containing 10 per 

 cent of nitrogen are added to a given quantity of soil, more ammo- 

 nia will be produced from the dried blood in a period of 10 to 30 

 days. Even when 2 grams of the cottonseed-meal are added to a 

 certain quantity of soil and 1 gram of dried blood is added to 

 another similar quantity of soil, more nitrogen will still be pro- 

 duced from the dried blood than from the cottonseed-meal. The 

 above considerations readily explain the reasons for this difference. 

 The 2 grams of the cottonseed meal contain three to four times as 

 much non-nitrogenous energy-yielding substance as the dried 

 blood. Even assuming that both organic substances decompose 

 with the same degree of rapidity, still the microorganisms decom- 

 posing the meal, which offers a greater amount of available energy, 

 will reassimilate and store a greater amount of the nitrogen which 

 would have otherwise been liberated as ammonia. 



The amount of nitrogen liberated as ammonia will also be 

 affected by the nature of the flora bringing about the decomposi- 

 tion. In the case of acid forest soils, for example, fungi are largely 

 concerned in the decomposition processes. In the arid alkaline 

 soils, bacteria and actinomyces are more active. Fungi synthesize 

 larger amounts of cell substance as mycelium, and will, therefore, 

 liberate less ammonia for the same amount oforganic matter de- 

 composed. Actually the fungi may be more active than many bac- 

 teria and, if a short incubation period is used, they may liberate 

 more ammonia; if a sufficiently long period is employed, the 

 reverse may be true. The reaction of the soil, nature of the inor- 

 ganic material, soil aeration, and presence of mineral nutrients all 

 influence the type of active flora and, therefore, the nature of 

 decomposition brought about by this flora. 



So many different organisms can produce ammonia from 

 organic materials that comparatively small differences are appa- 

 rent in ammonia formation from soils varying greatly in chemical 

 and physical conditions and in general fertility. Since anaerobic 

 bacteria of many kinds are able to spUt off ammonia quite readily, 

 there may be large amounts of ammonia formed even where oxygen 

 is excluded. Further, while ammonia may become oxidized to 



