MAINTAINING SOIL FERTILITY 89 



growing a legume comes from turning under the crop as a green 

 manure. It is, however, not often profitable to plow under one 

 of the regular legume crops as a manure, for the reason that 

 legumes are too valuable as food for live stock. 



We have at last learned that there is no soil of inexhaustive 

 fertility ; that all soils, if carelessly or unintelligently managed, 

 sooner or later need to be rested and repaired. When a soil's 

 productiveness has been materially decreased, it is no easy matter 

 to build up that soil again and make a living from it at the 

 same time. Therefore it is much better to keep lands produc- 

 tive than to allow them to become depleted and then attempt 

 to build them up. It is the duty of the younger generation of 

 farmers so to inform themselves regarding methods of soil man- 

 agement that they will be able to maintain the productiveness 

 of their land. 



QUESTIONS AND PROBLEMS 



1. Why is an old cultivated field less favorable to plant growth than a 

 new field ? 



2. Suggest methods by which a farmer may prevent his land from 

 becoming an unfavorable place for plant growth. 



3. If the Mississippi River carries a deposit each year that would cover 

 72 sections of land to a depth of 4 feet, how many farms of 160 acres each 

 would this cover with a surface soil 8 inches deep ? 



4. The average farm is supporting three families one on the land 

 and two in town. Allowing five people to each family, and supposing each 

 farm to include 1 60 acres, how many people could be supported by the land 

 washed away each year in the Mississippi basin ? 



5. How may this great waste of erosion be retarded? 



6. It is sometimes stated that one third of the fertility of the soil in 

 the corn belt has been exhausted in two generations. If this is true, what 

 are some of the reasons for a change in farming methods ? 



7. What are the best reasons for crop rotation ? 



8. Based upon the experiments made by the Illinois and Missouri ex- 

 periment stations in crop rotation in mind, explain why the different yields 

 of corn were secured. 



9. In what ways do green manures affect soils? What crops make the 

 most valuable green manure? 



