278 



THE FERTILITY OF THE SOIL 



soil by the activities of these organisms, the nitrates are 

 taken up by green plants and combined with sugars and 

 sulphuric and phosphoric acid compounds, to form amino- 

 acids and proteins. These are used to form living proto- 

 plasm or to repair its wastes. When dead, protoplasm 



Sun 

 Air S 



Green Plants 



Animals 



LcOj+HaO- Sugar 

 which may be 

 changed to starch, 

 cellulose, etc. 



Nitrates+sugar(+ 

 sulphate)-amino- 

 acids 



Amino-acids + 

 other amino-acids 



- Proteins 



Proteins +-H20+ 

 fats, salts, ( phos- 

 phates)-Protoplasm 



fHeat- 



». . u .. Work 

 Metabolisms QQ _ 



ko- 



Protoplasm in 

 basic Metabolism 

 yields N-com- 

 pounds: urea, 

 uric acid, etc. 



Nitrogen 

 of the air 



Putrefaction of 

 Dead bodies of 

 Animals & Plants 



H2O 

 Nitrates-* 

 Sulphates •« 

 Phosphates <♦ 



Nitrogen 

 fixing 

 organisms 



The Soil 



Fig. 64. — A Diagram to show some of the transformations of 

 carlxjn and nitrogen in the course of their utilization by living or- 

 gani.sms. Note that the air constitutes the great source or reservoir 

 from which lK)th carlmn and nitrogen are drawn by the metalwlism 

 of plants. Note further that only green plants can withdraw the 

 carlx)n from the air to manufacture sugar and only certain sorts of 

 bacteria and other low forms of plants can utilize free atmospheric 

 nitrogen. All animals depend on these plants directly or indirectly 

 for their usable compounds of carbon and nitrogen. The sun is the 

 original source of the energy used to synthesize sugar and other 

 organic compounds of carlx)n and nitrogen. In the various trans- 

 formations which these compounds undergo until finally released as 

 carl)on dioxid, water, nitrates, et-c., all the energy which was originally 

 locked up in them is again freed in the form of work or heat. 



and its wastes are both decomposed by putrefaction and 

 yield ammonia, which in its turn is oxidized to nitrate. 

 These may be either used by green plants again or re- 



