OHIO FIELD EXPERIMENTS 443 



ments at Wooster, Ohio, which are summarized in Table 82. 

 The average yield of wheat on the ten unfertilized plots was 19.3 

 bushels per acre in 1894 and 19.5 bushels in 1908, while i.i bushels 

 was the average yield for 1896, and i.i bushels was also the average 

 yield for 1900. The average was 3.0 bushels in 1895 and 13.9 

 bushels in 1907. 



As a rule, land that has been heavily cropped with almost con- 

 tinuous grain-growing, and with little or no manure, will produce 

 markedly better crops for several years after a good rotation sys- 

 tem is well established, and this fact often leads to a most serious 

 error on the part of the farmer; namely, to the conclusion that 

 crop rotation will maintain the productive power of the land. 

 The rotation helps to avoid the breeding of insects that would 

 prey upon a single crop, and it is beneficial in various other ways, 

 especially when clover or other biennial or perennial crops are 

 introduced which increase somewhat the amount of active organic 

 matter in the soil, the decomposition of which will furnish succeed- 

 ing grain crops with some plant food contained in such crop resi- 

 dues and with additional and often more important amounts liber- 

 ated from the soil by the decaying organic matter. 



Of course this benefit upon the grain crops cannot be secured 

 until after the clover or grass crops have been seeded and grown, 

 and the land again plowed up and used for the grain crops; and, 

 furthermore, on land which has not grown clover for many years, 

 the infection with the clover bacteria is sometimes so imperfect 

 that the first clover crop serves chiefly to increase the bacteria, 

 and thus furnish a perfect infection for the second seeding, which 

 very commonly produces a larger yield than the first seeding; 

 and, if so, it may be followed by correspondingly larger yields of 

 corn or other grains. 



In consequence of these different influences the crop yields may 

 be better the second or third rotation than during the first. With 

 the Pennsylvania experiments we can pass over a preliminary 

 period of three years, and then consider the results of three com- 

 plete rotations followed by three other complete rotations; and, 

 by including in our comparison the four crops grown every year, 

 the results are significant; but as yet no such comparisons are 

 possible with the Ohio investigations. We can, however, note the 



