140 MASS. EXPERIMENT STATION BULLETIN 162. 



many years for comparison of different phosphates, and those for the 

 comparison of different potash salts, make it possible to compare the 

 effects of phosphoric acid and of potash. In each case the average in- 

 crease of all the plots receiving in the one case phosphoric acid, and in 

 the other potash, is compared with the average of the no-phosphoric 

 acid or the no-potash plots. There are 3 no-phosphate plots and 10 

 receiving phosphate in the one experiment; and in the other there are 5 

 plots which receive no potash and 35 which do receive it. The table 

 shows the results : — 



Potatoes — Relative Effects, Phosphoric Acid and Potash. ' 



Fourteenth Year {1910)."- 

 No-phosphate plots, 



Phosphate plots, 



Tenth Year (1907).^ 

 No-potash plots, 



Potash plots, .... 



Sixteenth Year (1913).* 

 No-potash plots. 



Potash plots 



A verage 

 Yield per 



Acre 

 (Bushels). 



248.4 

 256.1 



197.96 

 255.17 



41.20 

 90.67 



I^"CRBASE. 



Per Acre 

 (Bushels). 



7.7 



Per Cent. 



3.09 



29.39 



120.55 



The station has carried out a few co-operative soil tests with potatoes 

 as the crop. The results of four of these, located respectively in Marble- 

 head, Hadley, Concord and Amherst, have been averaged, and in so far 

 as they serve to indicate the relative need for phosphoric acid and potash 

 for this crop the averages are here presented. * As is customary in soil 

 test work ^ each plant-food element is used by itself, in combination with 

 each of 'the others and in combination with both of the others. Averages 

 will be presented showing the results of the two elements under com- 

 parison when used alone, as well as when each is used in connection with 

 both the others. The latter figures, as will be understood, are the more 

 significant, as each element may more fully show its effect and importance 

 when all others are present in sufficient amounts. 



1 The number of the years as given indicates length of time the fertilizer experiment had con- 

 tinued. Crops have always been rotated. 



2 For details see twenty-third annual report. Part I., pp. 42-44. 



3 For full details see twentieth annual report. Part I., pp. 39-42. 



* From unpublished results. The very small yield in this year was due chiefly to seasonal 

 peculiarities. 



' For details see Bulletin No. IS, Hatch Experiment Station. 



8 The plan followed in this soil test work, as well as in all the other similar work referred to in 

 this bulletin, is given in Bulletin No. 9 of the Hatch Experiment Station. 



