EXPERIMENTS IN FIELD PLOT TECHNIC 49 



reason for the harvesting of these rows. They are not wasted because 

 they are not harvested, for they serve a valuable purpose; the waste 

 would be involved rather in harvesting them, for the added labor and 

 expense would contribute nothing to the accuracy of the experiment. 



Although protected 3-row plots are less variable than protected 

 single-row plots, they are not necessarily preferable. Three protected 

 3-row plots require the same area as five protected single-row plots, 

 and the harvesting of almost twice as large a crop (nine rows in the 

 first case for every five in the second). If the mean yield of five 

 single rows has as low a probable error as the mean yield of three 

 3-row plots, the protected single-row plot will ordinarily be pre- 

 ferable, because of the reduction of labor in harvesting and thresh- 

 ing. When the standard deviation of the check plot yields is known, 

 the probable error of the mean of any number of replicate plots can 

 be computed and the number of replications for any given degree of 

 accuracy determined. If single-row plots were 29 per cent more 

 variable than 3-row plots, the probable errors of the mean of three 

 3-row plots and of five single-row plots would be equal, since the prob- 

 able error of the mean is equal to the probable error of a single deter- 

 mination divided by the square root of the number of determinations, 

 and since the square root of 5 is 29 per cent greater than the square 

 root of 3. In the cases herein cited the advantage of the 3-row plots 

 was considerably less than 29 per cent in every case, and we may con- 

 fidently expect therefore that protected single-row plots repeated five 

 times will be less variable than protected three-row plots repeated three 

 times, which would require the same area and more labor. 



Some further evidence on the relative variability of the protected 

 3-row plot and the unprotected 5-row plot, or, in other words, of 

 5-row plots, harvested with and without their border rows, may be ob- 

 tained from the yields of the tested varieties and strains. Since the 

 number of replications of each strain is small, average deviations are 

 given instead of standard deviations. The inclusion of border rows in 

 the 5-row plots should not increase variability, since the adjacent va- 

 rieties are the same in each series, and the competitive effect should be 

 no more variable than would be that of the same variety. A clear-cut 

 comparison of 5-row and 3-row plots is therfore available in this case. 

 In the case of the check plots this comparison was somewhat obscured 

 by the competitive effect of different varieties on the border rows, which 

 might be expected to increase variability and thus to conceal a possible 

 advantage of the 5-row plot. 



The average variability of 3-row and 5-row plots in the strains 

 tested in these experiments is shown in Table 24. In each case the 



