SOIL ORGANISMS 323 



the loss of nitrates by leaching from fallowed land is 181.1 pounds 

 per acre, while the cropped land shows an average loss of 15.G 

 pounds, or only one-tenth the amount of the fallowed. 



2. Denitrification. Nitrification is an oxidation process, while 

 denitrification is one of reduction or deoxidation by which nitrates 

 are broken down and free nitrogen given oil". In other cases the 

 change may be such as to form nitrites or ammonia. In the latter 

 the nitrogen may not be lost from the soil by it. It takes place in 

 soils when poor aeration results in a deficiency of oxygen, as in 

 heavy, compact, puddled, or water-logged soils. Manure contains 

 large numbers of denitrifying bacteria and extremely heavy appli- 

 cations of coarse manure may result in some loss through the action 

 of these organisms. 



QUESTIONS 



1. What kinds of organisms are found in the soil? 



2. What are macro-organisms? Micro-organisms? 



3. (iive the effects of rodents on the soil. 



4. (Jive the work of insects in soils. 



5. Where are worms most abundant? 



(i. What work do they perform in soils? 



7. (Jive Darwin's statements of the amount of material brought to the 



surface. 



8. (Jive the effects of plants on soils. 



J). What is the work of micro-organisms in soils? 



10. What part do fungi play? 



11. Tell about the injurious forms. 



12. (Jive the two methods of fixation of nitrogen. 



13. What is nitrification? 



14. Tell about the steps in the process. 



!;">. Where are soil bacteria most abundant? 

 1(5. What about the distribution of bacteria? 



17. How do the number of bacteria vary? 



18. How are they distributed vertically? 



10. What effect do different systems of cropping have? 



20. What two general classes of bacteria '.' 



21. (Jive the characteristics of each. 



22. Of what use is aeration to bacteria? 



23. (Jive the experiment by Hall. 



24. What was " nitre farming" ? 



25. Why should bacterial activity almost cease in soils of extreme moisture 



content? 



20. What temperatures ar nest for the work of bacteria? What are 

 detrimental ? 



27. What are t'-e foods of bacteria? 



28. What part does the reaction >f the soil play in bacterial activity? 

 2!). What conclusion do you reach from tables on page 321? 



30. Why should the physical composition of the soil affect bacterial 



activity? 



31. dive the effect of sunlight on bacteria. 



32. How are nitrates lost from soils? 



