June. 1940] . Expkriments With Potatoes 9 



ly, since demonstrations on land which had previously been cropped ex- 

 tensively to potatoes and had received large quantities of fertilizer, have 

 not shown as large increases from additional phosphoric acid as land which 

 is less frequently plowed and less heavily fertilized. 



It is quite possible, too, that potatoes grown on high land are more 

 responsive to increased phosphoric acid than potatoes on land at a lower 

 altitude because more leaching has occurred on high lands. These soils 

 at higher altitudes apparently have a stronger fixing power for phosphates 

 and require more phosphoric acid than is found in the ordinary potato fer- 

 tilizer formula. 



A carefully checked test on the R. N. Johnson farm, Walpole, New 

 Hampshire, in which different phosphatic carriers were used, was con- 

 ducted in 1934. The soil of this farm lies at 1400 feet elevation and ac- 

 cording to rapid soil tests exhibited a high aluminum fraction, indicating a 

 strong fixing power for solul)le phosphates. The potato crop was fer- 

 tilized uniformly at the rate of one-half ton of an 8-16-16 formula per acre 

 at planting time, and prior to planting plots were laid out and top-dressed 

 with phosphorus carriers which were then harrowed in. Eight hundred 

 pounds per acre of the three materials indicated in Table III were used 

 on separate plots and the potatoes yielded as follows : 



TABLE III. Johnson farm test of phosphatic fertilizers, 1934. 



Yield per acre bu. Gain bu. 



Check — ^ T. 8-16-16 333.9 



y2 T. 8-16-16 + 800 ft raw rock phosphate 352.2 18.3 



y. T. 8-16-16 + 800 ftj basic slag 362.4 28.5 



y. T. 8-16-16 + 800 ttj W/v super 368.3 34.4 



These data coincide to some extent with the Jackson farm tests, and 

 seem to point to a need for a high phosphorus formula as well as phosphatic 

 fertilizers that are readily available on soils that lie at high altitudes. 



With respect to the behavior of varieties other than Green Mountain 

 to changes in the fertilizer formula, the yields of the White Triumph, 

 grown in 1933, are here reported. 



TABLE IV. Fertilizer effects on White Triumph potatoes 

 on Jackson farm in 1933. 



The interesting thing in the response of this variety is that omission 

 of phosphoric acid caused a greater decrease in yield than omission of pot- 

 ash. Increasing the potash to three per cent (4-8-3), increased the yields 

 around 100 bushels per acre over no potash, but an increase up to ten per 

 cent of potash did not increase yields over the three per cent formula. These 

 facts, and the rather large gain in the series for which the phosphoric acid 



