1 16 BACTERIA AND SOIL FERTILITY 



soil decreases the ammonia in it. This is probably due to two 

 factors: (i) The decay organisms turn to the carbohydrates for 

 their energy and leave the protein intact. (2) Large quantities 

 of carbohydrates in a soil favor the growth of microorganisms 



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Fig. 26. — ^IHustrating- the relationship between bacterial activities in 

 a soil and crop yield. 



which feed upon ammonia and transpose it into a protein. Hence, 

 we may have in a soil to which carbohydrates have been added 

 the bacteria competing with the higher plants for the limited sup- 

 ply of food. This at times results in a decreased yield. 



Importance of Process.— We have seen that ammoniii cation 

 is a process by which the complex compounds are changed into 

 simple. Now, higher plants cannot feed on fish, meat, or manure, 

 but when these are changed into nitrates they become excellent 



