346 MAINE AGRICULTURAL EXPERIMENT STATION. I916. 



But, aside from the extra labor and expense involved, the 

 results from check plots have been far from satisfactory in 



In the present paper a method is proposed for use in cor- 

 recting for differences in the soil of different plots. The 

 method in its present form is adapted for use only when the 

 plots are arranged in rectangular blocks. The method of 

 obtaining this correction factor is as follows : In the first 

 place the probable yield of each plot is obtained by the con- 

 tingency method. This "calculated" yield represents the most 

 probable yield of each plot on the supposition that they have 

 all been planted with a hypothetical variety whose mean yield 

 is the same as the observed means of the field. 



This "calculated" yield may then be used as a basis for 

 determining a correction factor. If the calculated yield of a 

 given plot is above the mean of the field it must be taken that 

 the soil of this plot is better than the average of the field and 

 a corresponding amount must be deducted from the observed 

 yield. Likewise, if the calculated yield is below the average, 

 a proportional amount must be added to the observed yield in 

 order to make the plots comparable. 



Still more comparable results will be obtained if the correc- 

 tion factors are based upon the percentage of the mean rather 

 than upon the absolute figures. 



Tests of the efficiency of this method by means of the meas- 

 ure of soil heterogeneity proposed by Harris show in all cases 

 a very marked reduction in the amount- of heterogeneity when 

 the corrected figures are used. When tested on our own experi- 

 mental plots, this method leads to results which from other 

 evidence, we have reason to believe, more nearly represent the 

 truth than do the uncorrected yields. 



It is realized that this method is not ideal and does not 

 obviate all the difficulties connected with soil differences in 

 plot experiments. It is hoped that this method may prove use- 

 ful in certain kinds of plot experiments and that it may lead 

 to further study of this problem. 



