A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1231 



this table shows that there was less tendency in this region than in the 

 others for growers using the most seed to use also the most manure and 

 fertilizer. The figures are therefore all the more conclusive in showing 

 the marked influence of rate of planting on yield. More seed than the 

 amount indicated by the highest rate of planting here reported might 

 have been used with profit in raising the 1913 crop. The coefficient of 

 correlation, 0.367 =b 0.034 (fig. 143), is altogether significant and is the 

 second largest value found for any of the four regions * surveyed. 



DATE OF PLANTING 



The average date of planting potatoes in any region is determined pri- 

 marily by the average date of the last killing frost in the spring, altho 

 elevation, soil type, and the type of potato grown, are also important 

 questions varying with different localities. Thus it is possible to plant 

 earlier on light soils and at lower elevations, than on heavy soils and at 

 higher elevations. However, because of the higher prices which usually 

 obtain early in the harvest season, the earliest possible planting and 

 harvest of early varieties is desirable. 



Zavitz (1916) reported results from thirty-six tests which consisted of 

 planting two early, two medium, and two late varieties on four dates, 

 two weeks apart, extending from May 31 to July 12. He carried this 

 experiment thru a period of six years. Without exception, in all six 

 varieties, both marketable and total yield increased directly with the 

 earliness of planting. A continuation of this test the following year, 

 with the plantings made on six dates instead of on four, gave the same 

 general results. These tests were conducted on ordinary clay loam soil 

 at the Guelph station. Champlin and Winright (1917) compared for two 

 years the yields from planting at intervals of fifteen days from April 1 

 to July 1. For early digging the April 1 planting, and for late digging 

 the May 15 planting, gave the best average yield for the two years. Such 

 results as these are of value, even locally, only when the tests cover a 

 period of several years. 



Because of the small variation in date of planting within each region 

 surveyed for the one year, and because of the fact that conclusions on the 

 best time to plant cannot be drawn from the yield of only one season, no 

 attempt has been made to correlate the date of planting and the yield. 

 The average date of planting in 1912 and in 1913, and the average date of 

 the last killing frost in the spring, for the four regions, are shown in table 

 63. The dates shown in this table indicate that Long Island is the only 

 region in which the crop is planted before the average date of the last 

 killing spring frost. It is evident that the Long Island growers are willing 

 to risk possible damage to the crop from frost in order to enhance the 

 earliness of harvest. The planting season of this region is shown to be 

 at least six weeks earlier than that of the others. 



