4 8 



THE ROTATION OF CROPS 



more than the amount removed, even if no manure be 

 applied. Farmers have found it wise to make what is 

 called a " rotation of crops,"- that is, to change the crop 

 raised on a given field from year to year, rather than to 

 raise the same crop year after year. Without rotation, 

 certain fields on the farm would soon become too " poor " 

 to produce good crops, while others would have more 

 plant food than the crop needs. 



Tobacco Raising Makes Land Poor In the pictures 

 shown in this lesson, the amounts of nitrogen, phosphoric 

 acid and potash removed from the soil by 1,000 pounds 



Tobacco 



;pp 



X"- 



J< 



FIG. 2O. Showing the pounds of plant food removed by 1,000 pounds of Vir- 

 ginia leaf tobacco, and by 1,000 pounds of clover. 



each of several different crops, are shown in pounds. 

 Each small square indicates one pound. From Figure 

 20 we learn that tobacco removes large amounts of nitro- 

 gen and potash. More than 8,000 pounds of average 

 barnyard manure would be required to furnish the nitro- 

 gen removed by 1,000 pounds of Virginia leaf tobacco. 

 Tobacco is, therefore, not a profitable crop to raise unless 

 it can be sold for a very high price. 



Corn, Wheat, and Oats Require Nitrogen. From Fig- 

 ure 21 we learn that Indian corn, wheat, and oats remove 



