44 MISSOURI AGR. EXP. STA. RESEARCH BULLETIN 49 



Montgomery 13 ' 14 with wheat, Kiesselbach 5 with oats, and Day 1 with 

 wheat. 



The general conclusions drawn from these experiments are in 

 harmony, though the specific size and shape of plot and number of 

 replications found most desirable vary rather widely. In general, plot 

 variability was reduced by increasing the size of the individual plot, 

 up to a certain limit, but it was reduced much more effectively by rep- 

 lication of plots. For a given area a large number of small plots was 

 always found more accurate than a small number of large plots. 



But the size of the plot cannot be reduced indefinitely for several 

 reasons. As the plot becomes smaller the proportion subject to "bor- 

 der effect" rapidly becomes greater. This border effect may be due 

 to the modified growth of plants adjoining an alley or to the in- 

 fluence of the competition of different varieties in adjacent rows. If 

 the borders are not discarded an important systematic error is involved ; 

 if they are discarded a considerable portion of the land and labor is 

 lost. In either case the disadvantage is increased as the size of the 

 plot is decreased. When single rod-row plots ar.e used the whole 

 plot is subject to border effect. ,The importance of this error has 

 already been discussed. Another disadvantage of the extremely 

 small plot is that slight differences in stand and small mechanical er- 

 rors have a marked effect on the yields. The increased labor involved 

 in handling a large number of small plots rather than a small number 

 of large plots is also an important disadvantage. 



The length of the so-called rod-row has usually been determined 

 by convenience. Commonly used lengths when the rows are a foot 

 apart are 16 feet for wheat, 20 feet for barley, and 15 feet for oats, 

 since with these lengths yields in grams per row may easily be con- 

 verted to bushels per acre. In other cases the most convenient length 

 is determined by the dimensions of experiment fields. Although in- 

 creasing the length of the row would doubtless reduce variability, a 

 greater gain could be made on the same area by further replication. 

 Ordinarily it is preferable, therefore, to retain the most convenient 

 length and to make any desired increase in size of plot in the width, 

 for widening the plots will rapidly reduce the proportion subject to 

 border effect. 



Experimental Results. Size of Plots. By comparing the stand- 

 ard deviations of single rows and blocks consisting of three and five 

 rows each, in the check plots, it is possible to determine the relative 

 value of plots of the three sizes in counteracting plot variability. In 

 this comparison the single-row and three-row plots correspond respec- 

 tively to 3-row and 5-row plots in which the border rows are dis- 



