EXPERIMENTS IN FIELD PLOT TECHNIC 31 



four determinations are compared the effect of this variability may be 

 considerable. If a field uniformly seeded to a single strain were har- 

 vested in rod-rows and assumed to be made up of several different 

 varieties each in four distributed plots, doubtless the average border 

 yield would differ materially from the average interior yield in several 

 "varieties." It is not however, likely, that such differences as those 

 cited above would be caused by chance variability. Nevertheless, no 

 final conclusions regarding competition as a source of error should be 

 drawn from such individual cases. The extent of error from compe- 

 tition is better shown in the average differences between border yields 

 and interior yields, and in the mean coefficients of competition for 

 complete tests. They are given in the next section. 



Relation of Competition to Various Characteristics of the Com- 

 peting Varieties. It is essential that competition be eliminated by the 

 use of border rows, or counteracted by some such means as grouping 

 varieties. The latter is decidedly the preferable method, from the 

 standpoint of economy, if satisfactory results may be obtained by its 

 use. But competition cannot be effectively controlled by grouping 

 varieties unless there is a close correlation between competitive value 

 and some character like earliness or height, which may be known in 

 advance. Determinations of the correlation between competitive ef- 

 fects and various characteristics of the varieties have therefore been 

 made for each of the tests. The preliminary determinations were made 

 as follows: 



(1) The average yield in interior rows and the average yield 

 in the border rows on each side for all replicate plots of each variety 

 or strain was determined. The replicate plots thus averaged were 

 grown between the same varieties in each series, and it may be assumed 

 therefore that their border rows were subject to the same competition. 

 In the following discussion of competition each individual case repre- 

 sents the mean of all the replicate plots of the test in question. For 

 example, when it is stated that the correlation between competition 

 and yield is determined in a test in which one hundred cases of compe- 

 tition are involved, each of the hundred cases represents the mean of 

 three or four determinations in replicate plots. In most cases the 

 number of replicate plots was four. In the barley test of 1919 only 

 three series were grown, and in the oats variety test of 1919, though 

 four series were grown, only three could be used because one border 

 row of each variety in the first series was harvested for seed and 

 laboratory material. 



(2) Corresponding average yields were determined for check 

 plots, those adjoining the same variety being averaged together. For 



