158 MAINE AGRICULTURAL EXPERIMENT STATION. 



needs of the crop to be grown upon it. While it is true that 

 some plants take up more of some one element than others, the 

 difference is insignificant when compared with the difference 

 in soils. The soils of Maine are extremely variable in character 

 and composition and it is therefore impracticable to make a 

 fertilizer formula for potatoes or any other crop that would 

 be applicable in all cases. Each farmer who uses commercial 

 fertilizers extensively should experiment with unmixed goods 

 enough to determine to what elements his soil most readily and 

 profitably responds. Some marl or limestone soils are quite rich 

 in phosphoric acid and consequently a fertilizer containing a 

 small amount of that element and relatively large amounts of 

 nitrogen and potash would give best results, while some of our 

 granite soils and clay loams are quite rich in potash and respond 

 best to a fertilizer containing relatively large amount of phos- 

 phoric acid. 



A study of the experimental data indicates that the potato 

 plant thrives best in a rich soil which is abundantly supplied with 

 all fertilizing elements. In the early stages of its growth, when 

 the vines are -forming, the demand for nitrogen is particularly 

 large, and for this reason a potato fertilizer should contain quite 

 a part of its nitrogen in a soluble, immediately available form. 

 Later in the season, when the tubers are forming, large amounts 

 of phosphoric acid and potash are required, also a bountiful sup- 

 ply of water to take up the plant food, etc., and transmit it 

 through the vines. 



