3i8 



SOIL MICRO-ORGANISMS 



but are capable of using gaseous atmospheric nitrogen in the presence of available 

 energy. Soil algae, fungi (with the possible exception of some mycorrhiza fungi), and 

 actinomyces are unable to fix atmospheric nitrogen. 



True proteins are again synthesized by various soil organisms (including algae, 

 fungi, actinomyces, and bacteria) and by higher plants, all using the nitrogen in the 

 form of ammonia or nitrate ; proteins are also produced by the nitrogen-fixing organ- 

 isms. These proteins may again be transformed when the bacteria, algae, and fungi 

 are used as food by the protozoa and other invertebrate animals. 



The processes of nitrogen transformation can be schematically summarized as 

 follows: 



Proteins 



Heterotrophic 

 organisms 



Amino acids 



Ammonia 



Ammonia 



nous micro-organisms 



Proteins 



Ammonia Ammonia 



Autotropliic 

 algae and 

 bacteria 



Proteins 



Heterotrophic fungi 

 and bacteria in presence 

 of available energy 



Higher plants 



Autotrophic 

 Nilrosonwnas 



Proteins 



Proteins 



Nitrites 



i 



Autotrophic 

 Nitrobacter 



Nitrates 



Various bacteria 

 nd fungi 



Proteins 



Proteins 



Proteins 



Leached out 



Nitrites, ammonia, 

 oxides of nitrogen 

 (N,0, NO, NA). 

 gaseous 

 nitrogen 



Nitrogen-fixing 

 bacteria 



Proteins 



TRANSFORMATION OF MINERALS IN THE SOIL 



Among the various mineral elements which are of importance in the growth of 

 plants and which are acted upon in one form or another by micro-organisms, the fol- 

 lowing may be included: sulphur, phosphorus, potassium, calcium, and iron, and to a 

 less extent, magnesium, zinc, and manganese. 



