No. 7. DEPARTMENT OF AGRICULTURE. 399 



the average yields during the twenty-five years on the series of plats 

 treated with phosphoric acid was fourteen per cent, greater than on 

 the untreated plats during the last five years the increase was thirty- 

 one per cent. 



COMPARATIVE EFFECT OF COMPLETE AND INCOMPDETE FERTILI- 

 ZERS HAVING COMPARED THE INFLUENCE OF SINGLE INGRE- 

 DIENTS. 



Having compared the influence of single ingredients, the next step 

 will be to compare the effect of two ingredients. This table shows 

 the average value of the products from twenty-five four year rota- 

 tions where two ingredients were used, in comparison with the un- 

 treated plats and the plats receiving a complete fertilizer consisting 

 of phosphoric acid 48 pounds, potash 100 pounds and nitrogen 24 

 pounds per acre. 



Two Fertilizer Ingredients. 



Alternate years. Value. 



None, |63 03 



P and K, 84 51 



P and N, 80 40 



N and K 64 31 



P, K and N, 91 11 



Average value of products from twenty-five four years* rotations, 

 Pennsylvania Experiment Station. 



The most striking fact brought out by this table is that the appli- 

 cation of 48 pounds of phosphoric acid and 100 pounds of potash 

 applied in alternate years to a rotation consisting of corn, oats, 

 wheat and mixed hay (timothy and clover), namely, to the corn and 

 wheat has, during twentj'-five years, maintained the crop producing 

 power of the soil. 



There is no evidence thus far to show but what the supply of 

 nitrogen can be indefinitely maintained ou this limestone soil by 

 means of a rotation containing clover, provided phosphoric acid and 

 potash are abundantly supplied. The addition of 24 pounds of nitro- 

 gen to the mineral fertilizers has, however, resulted in a material 

 increase in yield. It will be noted from the table that on plats re- 

 ceiving no fertilizer the average value of products from twenty-five 

 four years' rotations was |G3.03, where phosphoric acid and potash 

 was applied $84.51, and where 24 pounds of nitrogen was added to 

 the mineral fertilizers, $91.11. 



It is interesting to note that when potash was applied alone no 

 increase resulted. When, however, potash was applied with phosr 

 phoric acid a material increnso resulted ovop the application of the 

 phosphoric acid alone. In like manner when nitrogen was applied 

 with phosphoric acid or potash or with both increased yields re- 

 sulted, but in less marked degree, OAving to bacterial agencies sup- 

 plying nitrogen. Although not without exception there has been 

 a slight tendency for the nitrogen when applied with phosphoric 

 acid or with both phosphoric acid and potash to increase the grain 

 at the expense of the straw or forage. 



COMPARATIVE EFFECT OF DIFFERENT FORMS OF NITROGEN. 



Nitrogen was applied to different plats in three different fornis, 

 namely, as dried blood, nitrate of soda and sulpliate of ammonia. 



