A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1163 



were added to the sod each year. In the matter of fertilizers, Hartwell 

 and Damon's experiment is not comparable to farm practice in New York, 

 where little or no commercial fertilizer is ever used, stable manure being 

 generally applied, instead, as a top dressing, during the last year of sod 

 or perhaps just before plowing for corn or potatoes. The average yields 

 per acre of potatoes obtained by Hartwell and Damon, in the rotations 

 including grass for one, two, and three years, were 200, 199, and 223 

 bushels, respectively. It appears that their commercial-fertilizer treat- 

 ments were sufficient to maintain a maximum condition of sod thruout the 

 three years. 



A test on the influence of various fertilizers on potatoes, conducted at 

 the Rothamsted station, is reported by Hall (1905). In this test the crop 

 was grown for twenty-six consecutive years on the same land, and under 

 each treatment the yields declined during the later as compared to the 

 earlier years of the test. Long Island is the only section in New York 

 in which the crop is grown without rotation, and it is only the in- 

 creased use of fertilizers that has maintained yields there. Not only is it 

 difficult to get sufficient stable manure for the potato crop on Long Island, 

 but many growers do not find it economical to haul fertilizer in this form so 

 great a distance as would often be necessary. Consequently, each year 

 more than a third of the growers sow a cover crop of rye after potatoes. 

 Some use the cover crop every year, while others use it only every second 

 or third year, and some not at all. In the consideration of the influence of 

 cover crops on yield, only those fields are included on which a cover crop 

 was grown in the fall and winter preceding the potato crop. In table 6 

 the average yields that are obtained directly after cover crops, are com- 

 pared with those obtained when no previous cover crop had been used. 



TABLE 6. RELATION OF COVER CROP TO YIELD ON 313 LONG ISLAND FARMS IN 1912 



The figures given in table 6 should not be construed to mean that cover 

 crops are not beneficial to the potato crop on Long Island, because the 



