TRANSFORMATION OF ORGANIC MATTER 705 



nitrogen and energy and on the organisms concerned. If the organic 

 matter added to the soil is of a narrow carbon-nitrogen ratio, the same 

 processes will take place, with a tendency for the ratio to become wider. A 

 part of the nitrogen, depending on its original concentration, is liberated as 

 ammonia. When the carbon-nitrogen ratio of the soil is wider than 

 normal, the soil is not in a condition to support active plant growth and 

 nitrogen starvation will be observed as long as the excess of carbon 

 lasts, since the microorganisms using the carbon as a source of energy will 

 assimilate every trace of available nitrogen that would otherwise be 

 utilized by the higher plants. In the case of a soil with a constant 

 carbon-nitrogen ratio, the activities of the microorganisms are in a con- 

 dition of a more or less unstable microbiological equilibrium: only small 

 amounts of energy are utilized, resulting in the liberation of correspond- 

 ing amounts of ammonia, which are later transformed into nitrates. 

 The amount of ammonia (and nitrate) liberated in a soil under normal 

 conditions depends on the amount and kind of organic matter in the soil 

 as well as on the environmental conditions. However, the addition of 

 fresh organic matter with aC:N ratio of 10:1 will also stimulate the 

 activities of microorganisms, which bring about a liberation of C0 2 and 

 a parallel formation of ammonia. 



The inhibitive effect of a wide C :N ratio is not exerted upon legumes, 

 which do not rely upon fixed nitrogen for their requirements of this ele- 

 ment, as shown elsewhere. 



It is known that growing plants like maize and wheat have a depres- 

 sive influence upon the nitrate accumulation in the soil. It was sug- 

 gested" that the roots of the growing plants liberate organic matter 

 much of which is non-nitrogenous; this favors the development of 

 nitrate-consuming organisms in the soil, with the subsequent trans- 

 formation of the nitrates into other nitrogenous substances. The com- 

 position of the organic matter liberated (or made available) by the living 

 and decomposing plant roots has a potent influence upon the activity of 

 the nitrate consuming organisms. The amounts of nitrate nitrogen 

 recovered by leaching, when different roots and dried blood are added 

 to the soil, were found to vary directly with the percentage of nitrogen 

 in these substances (by comparing the decomposition of organic matter 

 added, in quantities sufficient to contain 0.6 gram of nitrogen, to 28 

 pounds of soil and incubating three months) . There was about the same 



99 Lyon, T. L., Bizzell, J. A., and Wilson, B. D. Depressive influence of 

 certain higher plants on the accumulation of nitrates in soil. Jour. Amer. Soc. 

 Agron., 15: 457-^66. 1923. 



