A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1157 



of the present study have borne out that conclusion. Therefore, in con- 

 sidering the influence of a given factor on yield, an effort has been made 

 to eliminate as far as possible, or at least to give due credit to, other con- 

 tributing factors. 



Since the study of each region concerns but a single year, too definite 

 conclusions must not be drawn in interpreting the data presented. De- 

 pending upon the normality of the season in which the crop was grown, 

 the degree of influence of a given factor may or may not be maintained 

 under average conditions. Tho cultural practices are not usually varied 

 radically from one year to another, differences in the length of the grow- 

 ing season, in the average growing-season temperature, and in rainfall, 

 tend to affect the influence of those practices. Therefore it will not be 

 possible to answer, in any appreciable degree, many of the questions 

 that will be raised. The consideration of experimental results is there- 

 fore of value in furnishing background for the study of each factor. As 

 stated by Warren (1914), there are questions that can be answered only 

 by a study of the results obtained on farms, and other questions that can 

 be answered only by the results of experiments. 



Little attempt has been made to discuss any potato literature except 

 that pertaining to seed, fertilizers, and planting, these being obviously 

 the most influential factors under the grower's control. In reviewing the 

 literature, one is impressed by the large quantity available and by the 

 meagerness and unreliability of the data given to substantiate the state- 

 ments. 



THE STUDY OF FACTORS 

 CLIMATE 



A brief review of climatic conditions in each of the surveyed areas has 

 been given, not because of any definite influence on the crop under con- 

 sideration, but to make clearer the normal conditions to which the crop 

 is subject. Facilities for taking weather data in each of these regions 

 are not yet sufficient to allow of any attempt at the correlation of rainfall 

 and temperature with yield for a given year. 



In general, the average growing-season temperature to which the crop 

 is subject has a marked influence on- the vitality of that crop as used for 

 seed. Briefly, high temperatures tend to produce devitalization. Long 

 Island growers obtain average yields ranging from 150 to 250 bushels per 

 acre from new Maine seed, but the use of the same stock for seed a second 

 year results in greatly inferior yields, as is indicated in figure 131. The 

 same principle is demonstrated in the rather common practice of introduc- 

 ing seed from northerly latitudes, a practice which is justified on the basis 

 of better yields, as is shown in the tests cited under the caption Source 

 of seed. 



