50 



MISSOURI AGR. EXP. STA. RESEARCH BULLETIN 49 



figure given is the mean of the average variabilities determined for all 

 of the varieties or strains in the experiment. 



TABLE 24. YIELD AND VARIABILITY OF TEST PLOTS. 

 Three-row and Five-row. 



There is no consistent difference in variability between the 3-row 

 plots and the 5-row plots. In some cases the former are more va- 

 riable; in others the latter; and in no case is the difference in varia- 

 bility great. These results are contrary to the general impression that 

 variability decreases with increase in size of plots. Apparently, in 

 tests of this kind, the 3-row plot is lar'ge enough to give a fair sample 

 and nothing is gained by adding the other two rows. When it is con- 

 sidered that the addition of these two rows undoubtedly introduces 

 systematic error from competition to a greater or less extent, and 

 involves a very considerable increase in the labor of harvesting and 

 threshing, there remains little doubt that the border rows of 5-row 

 plots are best discarded in .experiments of this sort. 



Replication of Plots. It is generally considered that the error 

 from soil variability may be reduced to any desired point by replica- 

 tion in sufficient degree. For any given degree of precision the num- 

 ber of replications required is dependent on the variability of the 

 replicate plots. When every plot in a single-row test is provided with 

 two border rows the area required for the test is tripled, the replicate 

 plots are separated more widely, and variability is usually increased, 

 since the range of soil variability will usually be greater when a larger 

 area is included. 



The removal of border effect from the rows harvested for yield 

 may in some cases reduce variability more than enough to balance this 

 increase, but when the unprotected single rows are grown in the same 

 order in each series, variability will not be much affected by competi- 

 tion, as before stated. Consequently more replications of single-row 



