68 PLANTS GROWN ON THE FARM 



and keep up its fertility, the general farmer practices 

 rotation of crops. Instead of raising the same crop on 

 the same land each year, he follows one crop with a 

 crop of another kind. This is called rotation of crops. 

 One crop may improve the soil for another kind 

 of crop. The legume plants often enrich the soil by 

 adding nitrogen which is taken from the air by the 

 bacteria which form nodules or tubercles on the roots 

 of these plants. A rotation of crops is usually planned 

 to have the land in clover, alfalfa, or some other 

 legume crop for one or more years; then a cultivated 

 crop like corn or potatoes is grown for one or two 

 years ; and then a grain crop for one or two years, 

 after which the land is again seeded to another legume 

 crop. Each crop is called a course, so if three crops 

 are used, the plan is a three-course rotation. If a 

 farmer plows under a clover sod for corn, then follows 

 with wheat, and again with clover, he is using a three- 

 course rotation. 



QUESTIONS 



1 . What crops are raised to produce food for man ? 



2. Make a list of food products for man that are grown in 

 your vicinity. In what form do they appear as food ? 



3. What are the most important fiber plants of the world ? 

 What is the most important fiber crop of the United States ? 



4. What are the most useful timber trees ? 



5. What crops are raised mainly v to furnish food for animals? 



6. What are cereal crops ? 



