26 FIELD CROP PRODUCTION 



In the four-year rotation at Rothamsted wheat yields 

 were not sustained, although that crop immediately fol- 

 lowed the clover. Barley, occupying a less favorable 

 place in the rotation, declined during 40 years from 38 

 to 14 bushels. The decline in yield of turnips and clover 

 was even more striking. 



In the Illinois experiments the rich virgin soil of the 

 corn belt has under a favorable rotation declined in pro- 

 ductiveness during 29 years from more than 70 bushels 

 of corn per acre to an average of 58. Even during 13 

 years the yields have not been sustained. On the rich 

 prairie soils of Iowa corn yields have noticeably declined 

 during a period of nine years under a similar rotation. 

 At the Ohio station, beginning with a poor, run down soil, 

 a favorable five-year rotation has, during a period of 18 

 years, somewhat improved the yield of wheat and main- 

 tained the production of oats, although the corn crop 

 has declined. However, there is no evidence here that 

 anything like satisfactory crop yields can be maintained 

 by rotation. 



From the Pennsylvania experiment station 25 years of 

 crop yields are reported, the rotation being corn, oats, 

 wheat, and hay (clover and timothy). Comparing the 

 average of the first twelve years with the average of the 

 second twelve, we find that where no fertilizer has been 

 added the yield of corn has declined from 42 bushels per 

 acre for the first period to 28 bushels for the second. 

 Oats in this time has dropped from 37 to 25 bushels. 

 Wheat has given the low yield of about 13 bushels for 

 both periods. Hay has dropped from 1| tons to 1 ton 

 per acre. 



All the above are results from carefully conducted experi- 

 ments and are fair examples of what a good rotation 



