THE STUDY OF MICROORGANISMS IN THE SOIL 



A. Suggested Arrangement of Class Exercises in Soil Micro- 

 biology for Course of Five Credits for one Semester 

 of 18 Weeks 



Because of the time required for the incubation of the different 

 groups of microorganisms, it is suggested that the exercises be 

 given in the order listed below. 

 Introduction 



General Characteristics of the Soil Population: 



1. Bacteria. 



2. Fungi. 



3. Algse. 



4. Protozoa. 



5. Invertebrate population of soil, non-protozoan in nature. 



6. Approximate number of microorganisms in soil. 



A. Microscopic examination of microorganisms: 



1. Examination of living microorganisms in hanging drops. 



2. Examination of bacteria in Congo red or Nigrosin preparations; of 

 yeast and yeast spores in Erythrosin or Rose Bengal preparations. 



B. Methods for counting numbers of microorganisms : 



3. Number of algae in soil according to dilution method. 



4. Number of protozoa according to the dilution method. 



5. Number of fungi according to the plate method. 



6. Number of bacteria according to the plate method (aerobic). 



7. Number of anaerobic bacteria in the soil. 



8. Number of spore-forming bacteria in the soil. 



9. Number of thermophilic bacteria. 



10. Effect of season of the year on number of microorganisms. 



11. Effect of plant roots on number Of microorganisms. 



12. Effect of depth of soil on number of microorganisms. 



13. Effect of manures on number of microorganisms. 



14. Dilution method for determining the number of specific physiological 

 groups of bacteria. 



15. Direct microscopic examination of soil. 



16. Winogradsky's method of microscopic analysis of soil. 



17. Determination of numbers of nematodes (and other worms) and 

 insects in soil. 



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