EXPERIMENTS IN FIELD PLOT TECHNIC 7 



conditions are different. The error in applying the results, though of 

 course much less in degree, is similar in kind. And, since the rod-row 

 test has no purpose but to indicate the relative value of the strains 

 tested, for field conditions, any pronounced tendency to favor some 

 varieties at the expense of others is fatal to its object. 



Ordinarily, however, the rod-row test is only the first stage in 

 variety testing, and final recommendations are based upon results of 

 tests under conditions which approach those of field culture more 

 closely. When the elimination of varieties in the rod-row tests is 

 not extremely strict a considerable latitude may be allowed, and under 

 these conditions the rod-row test has served a valuable purpose. It 

 is of course desirable nevertheless to reduce these errors to the greatest 

 possible extent. 



Probably the most important of the errors mentioned is that arising 

 from the competition between different varieties, in the single-row test. 

 Obviously a variety grown in a single row between two different va- 

 rieties may yield considerably more or less than the same variety 

 grown between two rows of its own kind. Various expedients for re- 

 ducing varietal competition have been suggested. Sometimes the order 

 of varieties is changed in each series to bring together different va- 

 rieties and thus tend to equalize the effects of competition; sometimes 

 an attempt is made to grow the varieties in such order as to bring 

 together those of similar habit, and thus to reduce the effects of 

 competition. Probably the most effective method is to grow border 

 rows which may be discarded, and some investigators therefore use 

 three-row or five-row blocks, in which the outer row on each side is 

 discarded. 



The principal objection to the use of border rows in the increased 

 area required to test the same number of strains, and the large pro- 

 portion of the crop which is not harvested for yield. This is par- 

 ticularly true when 3-row blocks are used, since in this case two- 

 thirds of the field is used for border protection. The border rows may 

 be used for seed, but two- thirds of the field is of course much more 

 than is required ordinarily for this purpose. When 5-row blocks are 

 used the proportion of the crop harvested for yield is increased from 

 one-third to three-fifths, though it is an increase in size of plot, with 

 some decrease in replication, so that there may be no gain in accuracy. 

 There is a possibility that the effect of competition on the yield of 5-row 

 blocks may be slight enough to permit the harvesting of all five rows 

 for yield, particularly if the varieties may be effectively arranged for 

 the reduction of competition. At any rate, in such plots the error 

 from competition may be expected to be much less than that in single- 



