CROP ROTATION COMPARED WITH CONTINUOUS CROPPING. 



21 



Rotation No. 7. 



Plat A. Oats on spring-plowed, ground. 

 Plat B. Barley on spring-plowed ground. 

 Plat C. Corn on spring-plowed ground. 



Rotation No. 8. 



Plat A. Oats on summer-tilled land. 



Plat B. Spring wheat on ground plowed early the preceding fall. 

 Plat C. Summer tilled. 



Rotation No. 9. 



Plat A. Oats on spring-plowed ground. 



Plat B. Spring wheat on spring-plowed ground. 



Plat C. Corn on spring-plowed ground. 



The nine 3-year rotations are so planned as to give an oppor- 

 tunity to compare the several rotations considered as units and also 

 to compare the several crops grown in different rotations under 

 systems of soil preparation and following different crops. As each 

 rotation is represented by three plats, each of the crops entering into 

 the rotation is represented every year. This is a very important 

 feature and one that has been neglected in most of the rotation 

 experiments heretofore made. By this system the differences in 

 yield produced by the seasonal peculiarities are eliminated and it 

 may safely be assumed that any difference in yield that occurs in 

 any two crops of the same kind grown the same year in two rotations 

 is due either to the method of soil preparation or to crop sequence. 

 Which of these two factors is the controlling one may usually be 

 determined by an easy method of cross-checking with the same 

 crop in other rotations, whereby one or both factors may be elimi- 

 nated. 



As an example of some of the comparisons that may be made and 

 the conclusions drawn, the following are suggested: 



Rotations Nos. 1, 2, and 3 are identical so far as crops and sequence 

 are concerned, but each differs from the other in soil preparation for the 

 wheat crop. Any difference in the wheat yields in rotations Nos. 1 

 and 3 may safely be attributed to the effects of stubbling in No. 1 

 instead of fall plowing the corn ground as in No. 3, this being the only 

 variable factor. The two rotations thus as units may be safely com- 

 pared to determine the effect of stubbling upon the wheat crop and 

 also upon the two crops which follow, namely, oats and corn. The oat 

 crops in these rotations may be safely compared to see whether the 

 effect of the soil preparation for the corn crop is apparent in the sub- 

 sequent crop of oats. The corn crop in these two rotations being so 

 far removed from the only variable factor should be about equal, and 

 any difference will have to be accounted for in a way not apparent, 



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