338 



Journal of Agricultural Research 



Vol. XX. No. 5 



TABLE I. Interannual correlations for yield of hops 



The most reasonable explanation of the higher correlation of more 

 closely associated years is that both field conditions and the productive 

 ness of the individual vines change more or less as time goes on. The 

 result of such changes would be a lower correlation between the yields 

 of periods more widely separated in time. 



The data for the dry-land experiments in Mysore State have been 

 discussed elsewhere (3) in relation to the problem of field hetero 

 geneity. It was shown there that in two dry years the field showed 

 marked hetereogeneity, but that in one unusually wet season there was 

 marked abnormality of yield with little correlation between the yields of 

 adjacent plots. 



It seems of unusual interest, therefore, to determine to what extent 

 the differences between these plots are permanent from year to year. 

 Correlating between the yields of ragi, we find the following correlation 

 coefficients for the whole series of 105 plots for which data are available. 



The correlations are of very substantial order, and without exception 

 they are clearly significant in comparison with their probable errors. 

 They show that the differences in the plots are to a high degree per 

 sistent during the three years of this experiment. 



For grain, straw, and total yield the correlations between the yield for 

 1905 and 1907 are higher than those for 1905 and 1906 or for 1906 and 

 1907. If there were a progressive change in the field one might have 

 expected that the correlations would be higher between consecutive 

 years. Apparently the influence of the abnormal conditions of 1906 has 

 been to lower the correlations for this year. 



The results show that the capacity for production is to a high degree 

 persistent from year to year, notwithstanding great diversity in 

 meteorological conditions. 



A series of records of unusual interest is provided by Smith (6) for 

 yields of com in three successive years, 1895, 1896, .1897. It has been 



