8 University of Xkw Hampshire fSta. Bull. 324 



There is no doubt that the potato is an exacting crop for plant food 

 and that the use of large amounts of fertilizer is justified. The proper 

 ratio and balance of nutrients might well var}- with different soils and 

 under varying climatic conditions as well as the total amount of plant food. 



Table I indicates the response secured by varying the fertilizer form- 

 ula on the Jackson farm field in northern New Hampshire. A study of 

 the data indicates that the omission of any one of the elements reduces 

 potato yields, the decrease for omitting nitrogen, phosphoric acid, and pot- 

 ash amounting to 26, 100 and 149 bushels, respectively. Increasing the 

 potash to three per cent in the 4-8-3 series, increased the yield over the 

 4-8-0 series by 119 bushels and brought the yield to within 30 bushels of 

 the check plot series. All the decreases are statistically significant except 

 for the plots where the nitrogen was omitted. 



Doubling the nitrogen of the fertilizer (8-8-7) gave an increase of but 

 14 bushels; doubling the phosphoric acid (4-16-7) increased the yield 46 

 bushels, while increasing the potash (4-8-10) resulted in an increase of 

 32 bushels per acre. Among these increases only that for phosphoric 

 acid is significant, although the 32 bushel increase for extra potash just 

 fails in this respect. This indicates that on this soil, and under the con- 

 ditions of this experiment, more phosplioric acid and probably more ])Ot- 

 ash than is found in one ton of a 4-8-7 fertilizer could be used to advan- 

 tage on the potato crop. 



In changing over the Jackson farm experiment in 1934, the plots 

 receiving a 4-8-10 formula during the previous period were scheduled to 

 receive a 4-8-14 fertilizer during the next two courses of the rotation. The 

 treatment for the 4-16-7 plots was unchanged, while the plots which had 

 previously received an 8-8-7 formula received a treatment of 4-16-14 in 

 the new layout, one ton per acre in each case. Yields for the second six- 

 year period are given in 1^d)le II. 



1 Ton 4-8-7 Check 371 ± 6 



4-16-7 397 ± 11 26 ± 13 



4-8-14 373 ±15 2 ±16 



4-K,-l4 420 ±15 49 ± 16 



It will be noted that the check plot-yields fell slightly below those of 

 the previous period. This may be due to climatic conditions, and it may 

 also be associated with a decreasing organic matter supply. 



Increased yields due to additional phosphoric acid (4-16-7) are con- 

 siderably smaller than those reported in Tabic I, yet the data are consistent 

 although the increase is not significant. Plots receiving double potash 

 (4-8-14) registered but a small increase, while those getting both addi- 

 tional phosphoric acid and potash gave a significant increase of 49 bushels 

 per acre. 



With respect to the plots receiving increased phosphoric acid (4- 

 16-7), it may be noted that the results follow farm experience quite close- 



