32 Report of the Acting Director and Chemist of the 



rather wide variations in the amount of plant-food supplied by dif- 

 ferent "specials " suggest that manufacturers are still quite far from 

 agreeing upon an ideal formula for potatoes, if, indeed, such an 

 ideal formula is possible. 



3. The Relation of the Constituents of Potato-Fertilizers 

 TO the Amount of Materia.ls Removed by the Potato Crop. 



How many pounds of nitrogen, phosj)horic acid, and potash are 

 removed from one acre by a crop of potatoes yielding 200 bushels ? 

 According to calculations based on the most available data at hand, 

 a crop of 200 bushels of potatoes would take from one acre of soil 

 from 30 to 35 pounds of nitrogen, from 20 to 25 pounds of phos- 

 phoric acid, and from (50 to 65 pounds of potash. 



Comparing these figures with the amounts of fertilizing con 

 stituents contained in 1,000 pounds of the various fertilizers used, 

 we find that the nitrogen in no cases runs below the amount required 

 for the crop, while in some cases it is somewhat in excess. These 

 fairly large quantities are justified, if we assume that the soil itself 

 furnishes little nitrogen or that all of the nitrogen applied is not 

 completely taken up by the crop. 



Jn the case of phosphoric acid, we find that the amount supplied 

 in 1,000 pounds of the mixed fertilizers used was in every case more 

 than twice as much as that consumed by the crop and in some cases 

 was more than three times as much. While it may be well to apply 

 phosphoric acid considerably in excess of the amount used by the 

 crop, it would appear that too great an excess for economy is often 

 used. This, however, is a question which may well be studied 

 in our future investigations. 



In the case of potash, the amount used by the crop was considera- 

 bly less than that supplied, but the difference was not nearly so great 

 as in the case of phosphoric acid. 



It will thus be seen that when we use as much as 1,000 pounds of 

 a good potato-fertilizer we are supplying plant-food rather more 

 than suflicient to meet the demands of the crop. And it would 

 follow, on theoretical grounds, that amounts applied in excess of 

 this, even on poor soils, would not meet with profitable returns. 



4. The Yield of Potatoes. 

 We will next consider the yield of potatoes in reference to the 

 amount of fertilizers used, and also the proportion of culls and 

 marketable potatoes. 



