228 NITROGEN, PHOSPHORUS AND POTASSIUM 



9. A land owner grows corn averaging 65 bushels per acre, barley averaging 

 40 bushels per acre, oats yielding 50 bushels, red clover averaging 2 tons, and 

 timothy yielding 2 tons per acre, in a 5-year rotation. ^He manures once in 

 the rotation, for corn, at the rate of 15 tons of average manure per acre. 

 Assuming no loss of fertilizing elements through leaching, can the farmer 

 expect to maintain the fertility of his soil by continuing this practice? Would 

 it be possible if it were a 3-year rotation with oats and timothy left out? 



10. In a test, some horse manure containing 10.2 pounds of nitrogen, 

 1.84 pounds of phosphorus, and 8.8 pounds of potassium per ton, was left 

 exposed to weathering for 6 months during the sunmier. During that time 

 36 per cent of the nitrogen, 50 per cent of the phosphorus and 60 per cent of 

 potassium were lost. Suppose 50 tons were thus exposed, what would have 

 been the total loss of each of the three fertiHzing elements? Their total value 

 at 15 cents, 10 cents and 8 cents per pound, respectively? 



11. In the table, page 222, determine the per cent increase in net returns 

 per ton of manure due to the use of phosphates as reinforcing materials. 



