A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1159 



ELEVATION 



Elevation as a factor influencing production has been determined from 

 the figures shown on the topographic sheets of the surveyed areas pub- 

 lished by the United States Geological Survey. As far as possible, the 

 location of the potato fields for which data were taken was indicated on 

 these topographic sheets at the time of taking the data. The chief 

 difficulty in determining the absolute influence of elevation lies in the 

 fact that increase or decrease in elevation is usually accompanied by a 

 difference in soil type. A study of elevation, therefore, really involved 

 also the consideration of both climate and soil. The writer is not aware 

 that any test has ever been made in which either one or the other of these 

 factors was studied with the other factor eliminated. 



Progressive increases in altitude and in latitude are similar in that each 

 is accompanied by a reduction in temperature. The United States 

 Weather Bureau, in computing temperature equivalents, makes use of the 

 principle that every 300 feet rise in altitude is accompanied by a reduc- 

 tion in temperature of one Fahrenheit degree. 



Influence of elevation on Long Island 



Elevation cannot be considered a potent factor in the Long Island area, 

 for its highest point does not greatly exceed 200 feet. Many farms along 

 the south shore of Suffolk County are below sea level, the sand dunes 

 alone keeping out the sea. A typical Long Island potato field is shown 

 in figure 131. The relation of elevation to yield in 1912 is shown in 

 table 2: 



TABLE 2. RELATION OF ELEVATION TO YIELD ON 327 LONG ISLAND FARMS IN 1912 



