PLANT FEEDING. 9 



total nitrogen removed, and suppose the weight of the 

 straw to be 2 l / 2 times that of the grain. 



Solution : 2.4% of the grain is nitrogen, .6% of the straw is 

 nitrogen, and since there is 2 l / 2 times as much straw as grain the 

 nitrogen in the straw amounts to 2 l /> X -6%, or 1.5% of the weight 

 of the grain. The nitrogen in both grain and straw, therefore, 

 amounts to 2.4% -f- 1.5%, or 3.9% of the weight of the grain. The 

 weight of the grain is 36 -=- .039 = 920 pounds, or about 15 

 bushels. 



20. One hundred and forty pounds of nitrogen were 

 taken from a lO-acre field by the removal of cottonseed. 

 What was the yield an acre in pounds of seed ? 



Plant food in the soil. Forty-nine different soils 

 were analyzed. They showed an average of 3,053 pounds 

 of nitrogen, 4,219 pounds of phosphoric acid and 16,317 

 pounds of potash an acre in the upper 8 inches of soil. 



21. How many average crops of wheat (14 bushels of 

 grain and 1,680 pounds of straw) will this nitrogen 

 supply? The phosphoric acid? The potash? 



22. How many crops if only the grain is removed and 

 the straw is returned to the land ? 



23. How many crops of corn (grain 29.4 bushels, 

 stover two tons) ? 



24. How many crops of corn if the stover is returned 

 to the land? 



25. How many crops of cotton (165 pounds lint, 330 

 pounds seed) ? 



26. How many crops of cotton lint, if all of the seed 

 is returned to the land? 



Important truth. Almost all soils contain large 

 quantities of plant food. Any soil will become unpro- 

 ductive and exhausted long before it is depleted of plant 



