PHOSPHATES IN MASSACHUSETTS AGRICULTURE. 139 



' From Van Slyke, "Fertilizers and Crops." 



- Most published analyses are higher for this constituent. 



The totals for phosphoric acid and potash in the surface 8 inches of 

 the average Massachusetts soil (as determined by analyses which have 

 been made here), and showTi in this table, may be compared with the 

 requirements of large crops, also shown in the table. This comparison, 

 made by dividing the totals in the soil by the totals in the crops, shows 

 that there is phosphoric acid enough in the soil for from 92 to 800 crops. 

 The potash is sufficient for from 42 to 290 crops. It is, of course, not the 

 writer's belief that without manure or fertilizer profitable crops can be 

 grown for the number of years which this method of calculation shows; 

 for long before the supply of phosphoric acid or potash should become 

 exhausted the yield would fall below the limit of profitable production; 

 indeed, on many of the soils included in arriving at the averages presented, 

 profitable production without the addition of both phosphoric acid 

 and potash in manures or fertilizers is already impossible. Plants can- 

 not "lick the platter clean." 



It is generally known that the root sj'stem is by no means confined 

 to the surface soil. Where the water table allows, most crops feed to 

 some extent to the depth of several feet. The relation of total phos- 

 phoric acid and potash in surface soil to the amount in crops is never- 

 theless of interest in connection with our consideration of the applicability 

 of the Hopkins theory of farm fertility under our conditions. The facts 

 cited strengthen the writer's contention that potash rather than phos- 

 phoric acid is the key to profitable agriculture in most cases in Massa- 

 chusetts. 



RELATIVE NEED OF PHOSPHORIC ACID AND POTASH. 



Experimental Results. 



Full details will not be given in this paper. They will be brought 

 together for publication in a bulletin on "Potash Requirements in Mas- 

 sachusetts Agriculture." Detailed reports on results from year to year 

 in most of the experiments to which reference will here be made have 

 appeared in bulletins and annual reports of the station. 



The Potato. — The experiments which have been in progress for so 



