312 Journal of Agricultural Research voi. xix.no. 7 



Their mangolds — 



looked a uniform ajid fairly heavy crop for the season and soil, 



while in their wheat field — 

 a very uniform area was selected. 

 The data of Larsen were drawn from an experiment — 



auf einer dem Auge sehr gleichmassig erscheinenden, 3 Jahre alten Timotheegraswiese. 



Montgomery's data were secured from a plot of land only yj by 88 

 feet in size, which had been sown continuously to Turkey wheat for 

 three years — 

 and was of about average uniformity and fertility. 



Coombs and Grantham selected a field on which — 

 the crop was extremely regular as judged before the cutting and it had not been 

 subjected to any attack of borer or any devastation of rats or birds. 



Lyon's potato field was selected from — 

 a piece of apparently uniform land. 



Mr. C. S. Scofield kindly informs us that the Huntley tract was 

 selected for apparent uniformity and that prior to the calculation of the 

 constants presented in this paper there was no reason, from general 

 observation, to suspect irregularities in the field. Batchelor and Reed 

 have assured me that their orchards are to all appearances uncommonly 

 uniform. Kiesselbach emphasizes the apparent uniformity of his oat 

 field. 



Nothing could more emphasize the need of a scientific criterion for 

 substratum homogeneity than the fact that correlations between the 

 yields of adjacent plots ranging from r= +0.020 to r= +0.830 can be 

 deduced from the data of fields which have passed the trained eyes of 

 agricultural experimenters as satisfactorily uniform. 



A second phase of this investigation has been to ascertain whether 

 the physical or chemical requisites for plant growth are so distributed 

 over experimental fields that they may be reasonably looked upon as 

 the source of the demonstrated heterogeneity in yield. 



The heterogeneity coefficients for percentage of water content for the 

 upper 6 feet on the Experimental Farm of the Office of Western Irrigation 

 Agriculture at San Antonio, Tex., range from +0.32 to +0.70 and are 

 statistically significant for each of the 6 upper feet of soil. Hetero- 

 geneity is least at the surface and greatest at a depth of 4 feet. The 

 surface layer of soil might, therefore, be apparently uniform in water 

 content while underlying layers might differ greatly from one part of the 

 field to another. This may be the explanation of the correlation between 

 the yields of adjacent trees in groves planted in an apparently uniform 

 locality. 



Analysis of the data of Waynick and Sharp shows that there is a 

 correlation of from +0.23 to +0.50 between adjacent borings for so 

 important soil constituents as nitrogen and carbon. The correlation 



