EXPERIMENTS IN FIELD PLOT TECHNIC 73 



CONCLUDING REMARKS 



The best method for preliminary variety testing is one which will 

 permit the accurate determination of the relative value of the va- 

 rieties under field conditions, with the use of a small area of land for 

 each variety. Some precision must be sacrificed to save land, and in 

 so far as the errors involved are of such nature that their extent can 

 be approximately determined, and conclusions drawn accordingly, this 

 sacrifice of precision is permissible. In many cases it is advisable, for 

 example, to reduce the number of replications and to increase the least 

 difference in yield regarded significant to a sufficient degree to com- 

 pensate for the decrease in precision. 



But these considerations do not apply to systematic errors, which, 

 since they affect the yields of replicate plots similarly, and consequently 

 have little effect on plot variability, cannot be accurately measured. 

 Typical systematic errors commonly involved in preliminary testing 

 are (1) modification of growing conditions favoring some varieties 

 more than others, such as hand planting or wide spacing between rows, 

 and (2) competition between varieties of different type, resulting from 

 the use of single-row plots. The relative value of varieties under 

 such conditions may be vastly different from their relative value un- 

 der typical field conditions. Even should measurable experimental 

 error be reduced to the absolute minimum, such a variety test might 

 give results entirely misleading. The error cannot be counteracted, 

 as can non-systematic errors, by increasing the least difference con- 

 sidered significant, nor can the extent of error of this sort be measured 

 or estimated by a study of the experimental results. 



Systematic error must therefore be reduced by every practicable 

 means. Growing conditions in the preliminary test should be made as 

 similar to ordinary field conditions as possible. The effect of varietal 

 competition must be reduced to the minimum. If this can be ac- 

 complished without increasing the size of plots, it is desirable to do 

 so. On the other hand, if larger plots are necessary for the control 

 of competition, larger plots should be used. If the area to be used 

 for preliminary testing cannot be correspondingly increased, the num- 

 ber of replications can be reduced sufficiently to permit the use of 

 the larger plots required on the area available. This will necessitate 

 a decrease in the degree of precision of the test, and will reduce the 

 rapidity of elimination of the less valuable varieties. But is it not 

 better to eliminate the undesirable varieties slowly than to risk the 

 elimination of desirable ones by a more rapid analysis? 



