186 SOIL ORGANISMS IN RELATION TO SOIL FERTILITY 



14. What is meant by nitrogen fixation in soils? How else is nitrogen fix- 



ation accomplished? 



15. What are the main differences between legumes and non-legumes? 



16. From what sources do legumes get their nitrogen? 



17. How much nitrogen may be added to the soil by the free nitrogen- 



fixing organisms? 



18. Tell how the nodule bacteria work. 



19. How much nitrogen may be added to the soil on a farm in growing clover? 



In growing alfalfa? 



20. Explain why, under like conditions, corn should yield better on clover 



sod than on timothy. 



21. Discuss the relation of crop failure to a lack of nodule bacteria. Why is it 



necessary that legumes should have these nodule bacteria? 



22. What is the meaning of soil inoculation? Cross inoculation? Illustrate. 



23. Suppose a field is to be inoculated for alfalfa; explain how it should be done. 



24. If, after growing alfalfa, soybeans are to be grown, would inoculation be 



necessary for soybeans? Why? 



25. How often should inoculation for the same legume be made? 



26. Have you ever seen legumes that probably needed inoculation? 



27. What are the soil conditions favorable to the growth and activity of the 



helpful soil organisms? 



28. For an outline summary of this chapter, see table of contents. 



