QUESTIONS AND PROBLEMS 



149 



of a 2, 10, 4 fertilizer on fall-sown wheat, work problems a, b, c, d, as 

 ou preceding page, but use half the nitrogen in the form of dried blood. 

 12. In a three-year rotation of corn, wheat and clover at the Ohio 

 Station, eight tons of manure were applied on the corn on certain plots. 

 No manure was used on the wheat or clover. These crops got the bene- 

 fits of the manure that was left in the soil. Stall manure and that from 

 the barnyard were used, and were reinforced with different fertilizers. 

 The following are results on a few plots: 



Notice that each third plot is a check plot, to eliminate differences 

 due to the variations in soil. It is assumed that the change from one 

 check plot to another is gradual. Check plot 1 yielded 38.86 bushels 

 of corn, and check plot 4 yielded 33.04 bushels. The difference is 

 5.82. We assume that the soil is getting poorer as we pass froir plot 1 

 to plot 4. If in the width of three plots it has decreased 5.82, we sup- 

 pose that it would decrease one-third this amount or 1.94 in one plot. 

 If untreated it is, therefore, assumed that plot 2 would have yielded 

 36.92 bushels and plot 3 would have yielded 34.98 bushels. In order 

 to check the work we may subtract the 1.94 again and we should have 

 33.04. But plot 2 did yield 59.85 bushels, hence the treatment must 

 have produced an increase of 22.93 bushels. Similarly fill out the fol- 

 lowing table. It may be easier first to make a table of probable yield? 

 of each plot if not treated. 



