A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1271 



From information obtained in the survey of the four regions, it has been 

 possible to determine the status of many factors which, tho not studied as 

 to their influence on yield, have nevertheless a vital relation to production. 

 Among these may be listed the time of plowing, the home-mixing of 

 fertilizer, the analysis of fertilizer, the use of lime, the source of seed, the 

 chemical treatment of seed, the date of planting, the method of planting, 

 the date and method of harvesting, the type of storage, and the length of 

 the storage period. 



Both biometrical and tabulation studies have shown the amount of seed 

 used and the value of manure and fertilizer per acre to be the most influen- 

 tial factors as relating to yield of all the factors studied. Second to these 

 are depth of plowing, frequency of cultivation, and frequency of spraying. 

 The influence of these five factors, expressed biometrically in terms* of r, 

 is summarized for each region in table 94. For obvious reasons, based 



TABLE 94. SUMMARY or COEFFICIENTS OF CORRELATION FOR FIVE FACTORS IN THE 



REGIONS SURVEYED 



chiefly on environmental differences between the four regions, consider- 

 able variation in the value of coefficients is shown in the table. In a single 

 case, that for frequency of cultivation on Long Island, the coefficient is 

 negative. Five coefficients out of the eighteen given are too small to be 

 significant, the probable reasons for this being, in most cases, explained in 

 the foregoing text. In but two cases is the probable error greater than 

 the coefficient, these being the probable errors of the coefficients for depth 

 of plowing in Monroe County and in Franklin and Clinton Counties. 



Probably a more reliable measure of the true influence of these five 

 factors on yield may be obtained from the tabulation studies for each 

 region. In view of the proved importance of these factors, a compari- 

 son of the averages of some of them for the fifty highest- and the fifty 

 lowest-yielding farms in the four regions is given in table 95. In general, 

 the values given in this table confirm the results shown in the discussion 

 of these factors. 



