EXPERIMENTS IN FIELD PLOT TECHNIC 63 



of yield. A possible explanation is the extremely low variability of the 

 actual yields, indicating that the field, which was quite small, was re- 

 latively uniform. Any gain in uniformity from a check adjustment 

 of yields would of course be expected to be greater in highly variable 

 than in more uniform fields. The relative uniformity of this field 

 is indicated not only by the low mean deviation of the test plots, but 

 also by the low standard deviation of the check plots, which was only 

 11.68 per cent, as compared with a standard deviation of 22.59 per 

 cent in the check plots of the adjoining oats variety test. 



The effect of adjusting yields on the variability of 3-row and 

 5-row plots in the wheat variety test of 1920 is shown in Table 34. 

 In this test the check variety, Fultz, was grown in every seventh plot. 

 There were four series of the ninety-six varieties. 



The reduction in variability was very marked, being 37 per cent 

 for 3-row plots and 42 per cent for 5-row plots. The variability of 

 almost every variety was reduced, and the reliability of the results 

 was undoubtedly much increased. 



The wheat variety test of 1921, occupying an equal area on a 

 neighboring field, and with similar varieties and the same planting 

 plan, gave decidedly different results. In this field the check va- 

 riety was Poole. Several check plots on the border were abnormal, 

 and the computations are therefore given both for three series and for 

 four, the series affected by the abnormal check yields being dis- 

 carded in the former case. The relative variability of actual and ad- 

 justed yields is shown in Table 35. 



Although the check yields are somewhat less variable for three 

 series than for four, the adjustment was not effective in either case in 

 reducing variability. The adjusted yields are 10 per cent more va- 

 riable than the actual yields for the three series and 34 per cent higher 

 for the four. 



Similar results were obtained in the wheat mixture test of the 

 same season, in which several of the same varieties were included, 

 and the same check variety was used. In this test the check variety 

 was in every sixth plot, and four replications were used. The results 

 of adjusting yields are shown in Table 36. Variability was increased 

 from 9.84 per cent to 13.81 per cent, an increase of 40 per cent. Thus 

 the results of adjusting yields of wheat varieties in 1921 are directly 

 contrary to the results of the same practice in 1920. 



Difference in Results Obtained by Adjustment with Different 

 Check Varieties. In the oats variety and strain tests of 1921, two 

 check varieties, Kherson and Red Rustproof, were grown. In these 

 tests 96 strains were included, 32 of Kherson, 32 of Red Rustproof, and 



