EXPERIMENTS IN FIELD PLOT TECHNIC 75 



to varying conditions. In one case, reported in this paper, two stand- 

 ard varieties, used as duplicate checks, and grown side by side in 

 120 distributed sections of a field, showed no significant correlation 

 in relative yield of adjoining plots, and differed so widely in plot varia- 

 bility that the number of replications necessary for a given degree of 

 accuracy was more than twice as great for one check variety as for the 

 other. Further investigation is necessary to determine how generally 

 such cases may occur, but this single case indicates at least a possible 

 source of extreme error in the use of check plots, either for adjust- 

 ment of yield or for the determination of the probable error of the 

 experimental results. 



For this and various other reasons the adjustment of yields by 

 means of check plots is at present of doubtful value as a general prac- 

 tice. In some cases, however, such adjustment accomplishes a great 

 improvement in the precision of an experiment, with a relatively slight 

 increase in expense. The practice is more promising for tests of 

 strains or selections of the same variety than for tests of different 

 types. A thorough study of the use of check plots in variety and strain 

 testing may discover methods of overcoming the disadvantages, and 

 thus make available an economical and effective method of increasing 

 precision. Meanwhile, check plots should be used cautiously. Meth- 

 ods for adjusting yields and for determining the extent of plot varia- 

 bility without the use of check plots are available 17 ' 18 , ' and check 

 plots must demonstrate actual value if they are to continue in use in 

 variety tests. 



SUMMARY 



1. In variety and strain tests of barley, oats, and wheat, in five- 

 row blocks, the competing border rows of adjacent sorts gave relative 

 yields often widely different from those of the interior rows of the 

 same plots. 



2. Such competitive effects were much more extreme between 

 different varieties than between different commercial strains of the 

 same variety. 



3. A considerable error from competition affected tests in rows 

 running north and south, as well as those in rows running east and 

 west. 



4. Although in general the higher yielding varieties were favored 

 in competition, the reverse frequently occurred. In some cases a ma- 

 terial advantage in yield in the interior rows was converted to a 

 material disadvantage in yield in the border rows. 



