Dec. i, 1920 Permanence of Differences in Experimental Plots 349 



Tablb IX. — Comparison of correlations between different yields of alfalfa with correla- 

 tions between yields of alfalfa and yields of other crops 



Cuttings of alfalfa. 



1912, single cutting 



1913, first cutting 



1913, second cutting 



19 13, first and second cuttings , 



1914, first cutting , 



1914, second cutting 



19 14, first and second cuttings 



1914, third cutting 



19 1 4, first, second, and third cuttings 



With other With 

 cuttings of yields of 

 alfalfa. other crops. 



+0. 331 

 + .611 

 + -604 

 + • 7 2 ° 

 + .666 

 + .629 

 + -699 

 + .5 2 4 

 + -7°6 



+0. 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



+ 



Difference. 



160 



424 



322 



446 

 371 



385 



409 



221 



390 



It is clear, therefore, that either stand or specific adaptation of the 

 individual plots to alfalfa influences to an unusual degree the closeness 

 of correlation between the yields of the plots of alfalfa in the different 

 years. 



In the first crop of ear corn (191 5) we find higher yields of ear corn in 

 1916, a negligible difference in the yield of oat grain and straw and total 

 yield in 1917, higher yield of silage corn in 1918, and slightly but not 

 significantly higher yield of barley grain, straw, and total yield in 1919 

 following higher yield of corn in 191 5. 



Turning to the constants for ear corn in 191 6, we note that higher 

 yields of grain in this year are followed by higher yields of oat straw 

 and grain in 191 7 and of silage corn in 191 8, and by slightly higher 

 yields of barley grain and straw in 191 9. 



The average value of the correlation between the yield of ear corn 

 in 1 91 5 and the yield of other crops during the eight years is +0.167, 

 whereas that for ear corn in 191 6 and other crops is +0.486. These 

 averages include the correlations for alfalfa, which are, as shown by 

 Table VIII, high for the crop of 191 6. 



Considering the correlations for- oat straw, grain, and total crop on 

 the several -plots in 191 7 and the yields of silage corn in 191 8, we find 

 that higher values of each of these measures of capacity for oat produc- 

 tion are on the average followed by slightly, but perhaps not signifi- 

 cantly, higher yields of silage corn in 191 8 and generally by higher 

 barley yields in 191 9. 



For the oat yields the average correlations with other crops are: for 

 straw, +0.202; for grain, +0.289; and for total yield, +0.293. 



The correlations of the yields of silage corn with the yields of the 

 preceding crops are, with one exception, positive in sign. The average 

 value for the eight years is +0.226. 



The averages of the correlations between barley yields and the yields 

 of other crops on the same plots during the eight years of the experiment 

 are +0.141 for grain, +0.086 for straw, and +0.126 for total yield. 



