40 HUMUS IN THE SOIL 



QUESTIONS AND EXERCISES. 



1. What is humus? In what ways does humus improve 

 the soil? 



2. What is the color of a soil that is rich in humus? 



3. How can humus be added to the soil? What is the 

 best source of humus? 



4. Why does a soil that has an abundance of humus 

 absorb more heat from the sun than a soil low in humus? 



5. Under what conditions might it be profitable to plow 

 under a crop of rye as a green manure? 



