Summary 



FERTILIZER studies with potatoes reported in this bulletin have been 

 conducted by producing potatoes with a 4-8-7 fertilizer, one ton per 

 acre, and comparing with this standard treatment a fertilizer in which 

 each of the elements was omitted, reduced or increased with the other two 

 elements constant. 



Evidence obtained warrants the conclusion that in omitting an element, 

 potash causes the greatest reduction in yield, with phosphoric acid second 

 and nitrogen third. This was true both for the Jackson farm lying at a 

 high elevation in northern New Hampshire, and for Lane farm lying at a 

 lower elevation in south central New Hampshire. 



Phosphoric acid caused a greater increase in yield than either of the 

 others when this element was doubled on the Jackson farm, with potash and 

 nitrogen ranking in that order, while on Lane, stimulation from extra 

 phosphoric acid and potash were nearly equal, nitrogen again ranking 

 last. 



Tests during the second six-year period on Jackson farm ascribe con- 

 siderably more stimulation to a fertilizer with a high phosphorus level than 

 with high potash, with however, a significant increase for a fertilizer in 

 which phosphoric acid and potash were both doubled. 



Need for Phosphorus 



Because of the apparent need for more phosphoric acid than is found 

 in the normal potato fertilizer, especially on land at higher elevations or 

 northern latitudes and since there is already a tendency toward higher 

 potassium formuke, it seems that it will often be advantageous to increase 

 both elements from the 1-2-2 or 2-4-5 to a 2-5-5, or perhaps a 1-3-3 ratio 

 at least. 



Evidence is presented indicating that the potato variety may have an 

 influence upon the choice of the fertilizer ratio, some varieties being more 

 sensitive to phosphoric acid variations than others. In the main, the tests 

 reported were witli the Green Mountain, a variety that is less sensitive 

 than either the White Triumph or Chippewa, although these varieties were 

 grown but one year each. 



Different levels of fertilizer of 4-8-7 grade on Jackson farm gave an 

 increase of 68 bushels for a ton over the one-half ton application, and a 

 further increase of 45 bushels for another half ton in addition to the ton 

 amount. The increase for the additional one-half ton in the latter case 

 was appr<jximalely equal to that for extra j^hosphorus in the 4-16-7 form- 

 ula. In the Lane test one ton of fertilizer increased the actual yield 69 

 bushels per acre over no fertilizer, although the average size of the potatoes 

 produced with no fertilizer was so small that this procedure is not to be 

 recommended. 



The use of lime in conjunction with a fertilizer carrying no potash had 

 a depressing effect upon yields, indicating that lime ties up potash that 

 would otherwise be available to the potato crop. 



