THE ROTATION OF CROPS 



49 



nitrogen chiefly, but that they require far less of this 

 than does an equal weight of tobacco. We observe also 

 that Indian corn reduces the soil fertility less rapidly than 

 oats or wheat. One thousand pounds of average barn- 



Indian Corn 



W^eal 



Oats 





FIG. 21. Showing the amounts of the three important plant foods removed from 

 the soil by 1,000 pounds each of the grain of Indian corn, wheat, and oats. 



yard manure contain about five pounds of nitrogen. 

 This enables us to compute the number of tons of barn- 

 yard manure required to furnish the nitrogen for 1,000 

 pounds of each of the grains named. 



M;lk 



Otrawberries 



R 2 



FIG. 22. Showing the amounts of nitrogen, phosphoric acid, and potash removed 

 from the soil when 1,000 pounds each of beef, milk, butter, and strawberries 

 are sold. 



Dairying Removes Little Fertility From Figure 22 



we learn that beef removes about as much nitrogen, pound 

 for pound, as wheat, and more phosphoric acid. But 

 beef is worth two or three times as much per pound as 



G. & M. Ag. 4. 



