SYSTEMS OF CROPPING 275 



hausted, and the numerous evil results that follow such 

 exhaustion will be brought on. The control of weeds, 

 diseases and insects and the maintenance of the humus 

 supply are the most important reasons for rotating crops. 



(3) If crops are rotated, we may have legumes and 

 grass on all the fields occasionally. As we have previously 

 learned, these crops are important in keeping up the pro- 

 ductivity of the land. 



(4) Labor is often saved by crop-rotation. Grasses 

 are sown in small grain, so that the land needs but one 

 fitting for two crops. Oats are often disked in on corn 

 land without the land having to be plowed. In Minnesota 

 and some other states, the disking is better than plowing, 

 both for oats and for the grass seeding in oats. It is often 

 convenient to be able to work land at times when it could 

 not be done if crops were not rotated. 



(5) By crop-rotation the land may be kept occupied 

 more of the time. Grass seeded in oats occupies the land 

 after the oats are cut. If corn follows grass, the land 

 may have the benefit of the grass cover until plowed for 

 corn. Where the season is long enough, it is possible to 

 rotate crops so as to grow more than one crop in a year. 

 One of the best rotations for the South provides five crops 

 in three years. 



(6) Deep- and shallow-rooted crops may be alternated, 

 thus allowing the use of different layers of soil. 



(7) Formerly it was thought that the chief reason 

 for rotation was that plants use the different plant-foods 

 in different proportions, so that when the soil became 

 exhausted for one crop it might contain the kind of food 

 that the other crop required. As a matter of fact, the 



