A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1189 



fertilizers; (3) the use of organic fertilizers in combination with minerals 

 resulted in higher average yields than resulted from mineral fertilizers 

 alone; and (4) manure and commercial fertilizers produced higher average 

 yields than any other type of fertilizer. Ballou (1910) and Gourley (1910) 

 substantiate these general conclusions in reporting the results of a fifteen- 

 years comparison of nitrate of soda, acid phosphate, and muriate of potash, 

 used both alone and in combination on potatoes. These tests have shown 

 that, altho the cheapest cost of increase per bushel was obtained from the 

 use of acid phosphate alone, the greatest profit per acre resulted from the 

 use of the complete fertilizer. The Rothamsted station, in England 

 (Hall, 1905), experimenting for twenty-six years and using five varieties 

 of potatoes on a series of ten plots, compared the yields from plots receiv- 

 ing ammonium salts alone, nitrate of soda alone, superphosphate alone, 

 and mixed mineral fertilizer. The average yields resulting from these 

 treatments varied in the order listed, ranging from the lowest yields with 

 ammonium salts to the highest yields with mixed mineral fertilizer. Since 

 these plots grew potatoes successively for twenty-six years, and since 

 potatoes yielded less with nitrogenous fertilizers than with mineral 

 salts alone, it was concluded that " the potato finds a difficulty in obtaining 

 ash constituents rather than nitrogen from an impoverished soil." Balen- 

 tine (1894) conducted greenhouse experiments to compare the foraging 

 power of the potato plant for phosphoric acid, with that of other crop plants. 

 He used identical amounts and forms of nitrate and potash fertilizer, 

 but varied the phosphatic form. He compared the results from equivalent 

 amounts of phosphoric acid in mostly insoluble forms with those from the 

 soluble form and with the check in each crop series. The results showed 

 that the potato plant is not able to make use of this element in the insoluble 

 form nearly so well as do wheat, corn, peas, and turnips. 



Because of its importance in stimulating the vigor and yield in the 

 crop and in satisfying the feeding requirements of the plant, potash had 

 occupied the most important place in potato fertilizers up to the time 

 when this survey was made. Rane and Hall (1904) compared the yields 

 from plots containing 5, 10, and 15 per cent of potash, respectively, and 

 those from plots containing no potash at all. They found that at the 

 New Hampshire station, altho the yield was increased up to 15 per cent 

 of potash, the most profitable results came from the 10 per cent of -potash 

 in a complete fertilizer. Several years later T. C. Johnson (1916) com- 

 pared complete fertilizers differing only in that they contained 3, 5, and 

 7 per cent, respectively, of potash. He obtained the best results from the 

 5-per cent fertilizer, since that containing 7 per cent of potash seemed to 

 retard maturity and decrease the yield. Conner (1906), at the Florida 

 station, compared complete fertilizers containing 7, 8, 9, and 10 per cent 

 of potash, respectively. Tho this was but a one-year test, the check 

 plots averaged nearly as high yields as did the plots receiving potash, 



