94 ELEMENTARY AGRICULTURE 



diseases and insects that will get a big start unless 

 other crops are introduced on the field. When in- 

 sects find their favorite crop gone and one growing 

 that they do not like, they are without food and 

 starve to death. But perhaps the most important 

 reason for rotation is to keep up the supply of 

 humus in the soil by growing clover, alfalfa, or cow- 

 peas and plowing them under to restore the vege 

 table mould or humus. 



Rotating in the North. There are different sys- 

 tems or methods of rotating crops. Many good 

 farmers in the Northern states divide their farms 

 into five fields, and on each field they raise corn, 

 followed by oats, then by wheat, then clover, and 

 lastly by timothy. Then they plow the timothy 

 stubble and again start with corn. Try to make 

 five diagrams or maps to show what each field con- 

 tains each of the five years. 



In Potato States. In some potato-raising sections, 

 they have a three-year rotation: a crop of potatoes 

 is followed by one of wheat or oats, and that by a 

 clover crop. Such a farm is divided into three fields. 

 In the Corn Belt a good rotation is corn for two 

 years,, next oats, and then clover and timothy. 



Rotation for Cotton. For cotton plantations a 

 good system is: Cotton the first year, followed the 

 second year by corn with cowpeas planted between 

 the rows or sown broadcast just before the last cul- 

 tivation of the corn; the third year oats are grown, 

 and they are followed by cowpeas the same season. 



