Dec. i, 1920 Permanence of Differences in Experimental Plots 



347 



Of the 12 comparisons possible between the interannual correlations 

 deduced from whole plots and from quarter plots (second entry), 9 show 

 lower correlations for quarter plots as compared with 3 which show 

 higher correlations for the quarter plots. Finally, all 12 of the correla- 

 tions deduced from quarter plots are lower than the correlations deduced 

 from half plots. 



It appears, therefore, that 0.085 an d 0.0425 acre are rather too small 

 to give the highest values of the interannual correlations. On areas 

 of this size other factors than the peculiarities of the plots themselves 

 have too large an influence upon variation of yield to allow the indi- 

 viduality of the plots to express itself fully in its influence upon the yields 

 of successive years. 



In support of the conclusion that the lower value of the correlations 

 for half and quarter plots is due to the greater variability of the yields 

 of these plots we note that the coefficients of variation for subplots are 

 without exception larger than those for the plots of the original size. 

 The coefficients of variation are as follows for the years in which the plots 

 were subdivided. 



Crop. 



1913, alfalfa I 



1913, alfalfa II 



1913, alfalfa I and II 



1914, alfalfa I 



1914, alfalfa II 



1914, alfalfa I and II 



1915, ear corn 



1916, ear corn 



Whole 

 plots. 



12. 52 

 13.60 

 II. II 

 17.94 

 19.81 



17-47 

 7.29 



13-43 



Half plots. 



*5 



Quarter 

 plots. 



21.87 



23.68 

 25.87 

 21.88 



9-23 

 17.68 



It is now desirable to examine the results for the individual crops. 

 In doing this it may be noted that there are two factors to be taken into 

 account. First, there is the possibility of an inherent difference in the 

 plots which is persistent from year to year and is quite independent of 

 the crop grown. Second, it is conceivable that the crop itself may exert 

 an influence upon the soil such that the yields of subsequent crops will 

 be influenced by variations in its growth which are measured in terms of 

 yield. 



The first of these factors would influence all correlations between 

 plots — those between the yields of given years and the yields of both 

 preceding and subsequent seasons. The second would influence only 

 correlations with subsequent years. 



In a series of only 46 plots it will probably be impossible to distinguish 

 between the influences of these two factors. 



We note that the higher yields of beets are followed by lower yields of 

 alfalfa in 191 2, but that there is practically no relationship between the 

 yields of sugar beets in 191 1 and the yield of other crops on the same 



