252 CROP GROWING AND CROP FEEDING 



At the Maryland Station it was found that a complete fertilizer in which 

 nitrate of soda and an organic form of nitrogen was used in connection with 

 acid phosphate and sulphate of potash, gave the best results in the crop, mak- 

 ing several bushels more than the same formula with muriate of potash used 

 in place of the sulphate. 



At the Pennsylvania Station it was found that the use of nitrogen re- 

 sulted in a profit of from $2.17 to $9.56 per acre, according to the combina- 

 tion in which it was used. The use of phosphoric acid resulted in a gain of 

 $7.72 per acre. The use of potash resulted in a gain of $17.39 per acre. The 

 use of phosphoric acid and potash together produced a gain of $52.02 per 

 acre, while a complete fertilizer containing nitrogen, phosphoric acid and 

 potash made a gain of $56.88 per acre. Nitrogen alone made a gain of $2.17 

 per acre, showing a difference in the effect of an incomplete and complete 

 fertilizer of $54.71 per acre. The conclusions arrived at were that on that 

 soil potatoes especially needed potash, and to a somewhat less degree, phos- 

 phoric acid. The effect of nitrogen being shown to be small, it would seem 

 that instead of purchasing costly artificial supplies of nitrogen, if potatoes 

 are to be grown extensively, it would be better policy to secure the needed sup- 

 ply of nitrogen from the air by the cultivation of leguminous crops, either 

 used as green manure or fed to animals, and to confine the purchase of arti- 

 ficial fertilizers to phosphate and potash. It seems altogether probable that 

 such a method of treatment would suffice to keep the supply of nitrogen in 

 the soil up to a point at which purchased mineral fertilizers would yield their 

 best returns. A very important point is the using of phosphoric acid and 

 potash together, for in one experiment, while the phosphoric acid alone gave 

 a gain of $7.72 per acre and potash alone $17.39 per acre, when the two were 

 combined they gave a profit of $51.02 per acre. In some other soils experi- 

 ment has shown that while potash was as important as in these the next im- 

 portant element was nitrogen, and this is usually the case in the early crop of 

 potatoes grown in the South in the early spring. 



The Pennsylvania bulletin further states that it may be interesting to 

 compare the amounts of nitrogen, phosphoric acid and potash applied in these 

 experiments with those contained in the so-called "potato fertilizers 77 so large- 

 ly offered by various fertilizer firms, the average of 47 samples of such fertil- 

 izers analyzed in that State shows the following percentages: Nitrogen, 1.86 

 per cent. ; total phosphoric acid, 11. 16 per cent. ; potash, 5. 55 per cent. Twelve 

 hundred pounds per acre of a fertilizer of this composition would have con- 

 tained the following amounts of these ingredients, as compared with those 

 contained in the 1,200 pounds of mixed chemicals applied in these experi- 

 ments : 



