72 ELEMENTARY AGRICULTURE 



and plowed under to enrich the soil. This manure and 

 these legumes have doubtless kept up the fertility of 

 the soil. The farmer has had an opportunity for four 

 years to manure other pieces of land. At the same 

 time he has been following some plan of rotation on 

 the rest of his farm. Each year he has grown tobacco, 

 he has raised corn and sold his hogs, he has made 

 hay for his cattle, and he has sold peas to the canning 

 factory. He lias been taking in money all the time, but 

 he has not greatly exhausted his soil. 



VARIOUS ROOT SYSTEMS. 



T Tobacco, O Oats, Cl Clover, B Beets, W Wheat, C Com, 

 A Alfalfa. 



Crop Rotation and Length of Roots. There is 

 still another feature of crop rotation worthy of study 

 here. It is the different depths to which the roots of 

 various crops penetrate. In the first place, tobacco is 

 a long-rooted crop, and feeds deep down in the soil. 

 Oats, which follow, are short-rooted and feed near 

 the surface. Then comes clover, whose roots penetrate 

 several feet, bringing food matter to the surface from 



