EXPERIMENTS IN FIELD PLOT TECHNIC 55 



adjusted. The reduction of variability of the adjusted plot yields is 

 the measure of the efficiency of the method. 



Morgan 15 reports an experiment of this sort, in which 63 plots, 

 planted first to wheat and then to fodder corn, in the same season, 

 were used. The variability of the plot yields was steadily reduced as 

 the number of check plots was increased. 



In a similar experiment reported by Lyon 11 , in which 37 replicate 

 1/100 acre plots of corn were harvested, the use of checks in every 

 second or third plot was found to reduce variability, but they were of 

 little value when farther apart. 



Montgomery" states that alternating check plots with test plots 

 gives a high degree of accuracy, but the total number of plots required 

 when this method is used is greater than when the same degree of ac- 

 curacy is attained by the use of replication. 



Kiesselbach 5 reports a comprehensive trial of three methods of 

 adjusting yields by means of check plots in a uniform field of 207 

 1/30-acre plots of Kherson oats. The effect on plot variability is shown 

 in Table 29. 



TABLE 29. EFFECT ON PLOT VARIABILITY OF ADJUSTING YIELDS BY CHECK 

 PLOTS (KIESSELBACH). 



Coefficient 



Method of of variability 



adjustment Actual Adjusted 



yields yields 



Alternate check plots. 

 Correction based on 

 average of two ad- 

 jacent checks 7.85 7.01 



Checks every third plot. 

 Correction based on one 

 adjacent check plot 7.79 7.35 



Checks every third plot. 

 Correction by progres- 

 sive method, based on 

 two nearest checks 7.87 6.57 



From these results Kiesselbach concludes "The yield of system- 

 atically distributed check plats cannot be regarded as a reliable meas- 

 ure for correcting and establishing correct theoretical or normal 

 yields for the intervening plats." 



It should be noted at this point that even if adjustment by check 

 yields were found invariably effective in experiments of this sort, 



