308 



Journal of Agricultural Research 



Vol. XIX. No. 7 



fairly well suited to the testing of shallow-rooted crops. Below this it 

 might show a higher degree of heterogeneity. Possibly this heterogeneity 

 of lower-lying strata is the explanation of the large correlations obtained 

 for the yields of neighboring trees in groves planted on apparently 

 uniform soil. 



TABLE IV. Differences and criteria of trustworthiness of differences in the correlation 

 of adjacent plots in soil moisture determinations at various levels 



We can pursue this question of the relationship between the water 

 content of the plots somewhat further. If the factors which determine 

 the similarity in the moisture contents of the combination plots affect 

 more than a single layer, we should expect a correlation between the 

 contents of the first and second foot, and so on, in the same boring. 

 The possible correlations have been worked out for the first foot and the 

 remaining layers and are as follows : 



There is a statistically significant and even high correlation between 

 the water content of succcessive levels in the same boring. 



When we turn to the problem of chemical heterogeneity, we find that 

 while a number of soil chemists have noted the desirability of consider 

 ing the variability of the soil in taking samples, the available data suit 

 able for testing the degree of heterogeneity of experimental fields are 

 not extensive. 



