8 MISSOURI AGR. EXP. STA. RESEARCH BULLETIN 49 



row plots, since only two of the five rows are subject to competition 

 with a different variety, and each of these is subject to such compe- 

 tition on only one instead of on both sides. 



Another phase of the question which should not be overlooked 

 is the effect of adding border rows on the error from soil variability. 

 If, for example, each rod-row is to be protected from competition by 

 two border rows, the test will require three times as large a field as 

 the same test without the border rows. This can hardly fail to in- 

 crease materially the variability of the yields of replicate plots, to an 

 extent which will vary with the uniformity of the field concerned. 

 The use of border rows may thus necessitate the use of an even greater 

 number of replications for the same degree of accuracy, as far as 

 plot variability is concerned. It is possible that 3-row plots (whether 

 or not provided with border rows) may require less replications 

 for a given degree of accuracy than single-row plots, on account of 

 their larger size. It is possible also that 5-row plots, because of 

 their size, may have an advantage over 3-row plots in reducing va- 

 riability, great enough to justify in practice harvesting all five rows 

 for yield, rather than harvesting the interior three rows and discarding 

 the border rows. 



The importance of any practice that will reduce the variability of 

 the replicate plots is thus increased when border rows are introduced. 

 A familiar method for this purpose is the adjustment of yields by 

 means of distributed check plots. In following this method the yields 

 of check plots are considered measures of the productivity of the 

 soil, which is usually assumed to vary uniformly between them. The 

 yields of the experimental plots are adjusted on the basis of uniform 

 productivity of the field as a whole. Of late this method has rather 

 lost favor among agronomists. In some cases the adjustment actually 

 increases rather than decreases the variability of the replicate ex- 

 perimental plots. Check plots have not been used extensively in ad- 

 justing yields in rod-row tests, principally because of the great in- 

 crease in computation necessary in adjusting the yields of such a large 

 number of plots. 



