156 MAIXE AGRICULTURAL EXPERIMENT STATION. 



potato manure should be, but even these earn- much more phos- 

 phoric acid in proportion to the nitrogen and potash they con- 

 tain than is found in the plants or in farmj'ard manure. 



It is possible that in using commercial fertilizers, more phos- 

 phoric acid is applied than is needed in many cases, yet there is 

 not much evidence at hand in the form of accurate experimental 

 data to prove this assertion. Many experiments have been made 

 both in this country and Europe in growing potatoes with com- 

 mercial fertilizers and chemicals, but very few experimenters 

 have made a study of the relative proportions of the fertilizing 

 dements that can be most profitably used. 



L. Hecke* in his quite extensive experiments with chemicals 

 on the potato plant found that it needed, throughout its entire 

 period of growth, Hberal supplies of all fertilizing elements. The 

 demand for nitrogen was especially strong in the first half, and 

 for potash in the last half of the season. The application of 

 potash had a marked influence on the production of tubers and 

 starch. Phosphoric acid had less effect, probably because the 

 soil was quite rich in phosphates. 



Experiments are reported by the New York Experiment Sta- 

 tion„f in which the primary object was to determine the profit- 

 able amount of fertilizer to apply. Two formulas were used, 

 one of which carried approximately nitrogen 4%, phosphoric 

 acid 8.2%, potash lo^c ; the other, nitrogen 6.5^c, phosphoric 

 acid 4.8%, potash 10%. The quantities applied were the same 

 for each formula, being 500, i,oco, 1,500 and 2,000 pounds per 

 acre. One thousand pounds per acre of either kind yielded the 

 largest profit, but the one carr^^ing the most phosphoric acid 

 gave the largest yields in everj^ case; the greatest difference 

 occurring when but 500 pounds were used, and least when 2,000 

 pounds were applied per acre. As the mixture high in phos- 

 phoric acid cost several dollars per ton less, on account of con- 

 taining less nitrogen, it was more profitable than the other. 



Experiments were made at the Kentucky Experiment Stationi 

 on a limestone soil quite rich in phosphoric acid, in groAving 

 potatoes with chemicals. The best yield was obtained when the 

 three elements, nitrogen, phosphoric acid, and potash were used. 



* Jonr. Land'w. 43 (IsSS) p. 283. 

 t Bulletin 1-37, 189". 

 { BnUet1n,55. 



