510 



PRINCIPLES OP SOIL MICROBIOLOGY 



In sufficient time, however, there is a narrowing of the energy-nu- 

 trient ratio in the soil organic matter, and an ultimate liberation of 

 plant food takes place. The death of large numbers of microorganisms 

 with a low energy-nutrient ratio leads to the same end. Succeeding 

 generations of microorganisms have at their disposal the energy ma- 

 terial of the decomposition products from the original organic matter, 

 the dead cells of microorganisms and the original compounds which 

 decompose only very slowly; all of these have a narrower energy-nu- 



Nitrale - nitrogen 

 Mgm. 



Days 



Fig. 31. Influence of cellulose on nitrate accumulation in the soil. 



cellulose; — — — ■ nitrate nitrogen. 8-1 and 10-2 are the experiment numbers 

 (from Anderson). 



trient ratio than the original organic matter added to the soil. A 

 gradual accumulation of plant food takes place, which the microorgan- 

 isms are unable to assimilate and which is left for the use of higher 

 plants. 



Decomposition of organic substances of varying carbon-nitrogen ratio. 

 The nature and composition of the organic matter greatly influence 

 its decomposition. The ratio between the carbon and nitrogen of 

 the material used is of especial importance in this connection. The 

 same is true of the nature of the non-nitrogenous organic materials 

 introduced into the soil in addition to the nitrogenous substances. 



