EXPERIMENTS WITH NITROGEN FERTILIZERS 19 



of clover and timothy, the roots and stuV)ble of which had accumuhite(l so much 

 nitrogen that additional nitrogen in fertilizers had no effect. The summer was 

 exceptionally hot and normally moist, which was especially favorable for corn. 



In 1921 the plots without nitrogen were again superior in the production of 

 clover hay, the second year from seeding. This unusual result is explained as 

 follows: The new seeding in 1920 consisted of clover, timothy, and red top. 

 In that season the active nitrogen of sodium nitrate and ammonium sulfate pushed 

 forward the grasses which smothered the clover. Grasses were not encouraged 

 in the absence of nitrogen, and the clover gained its foothold, so that its second 

 year's growth on the plots withoxit nitrogen outstripped the grasses on the plots 

 with nitrogen. 



The economic possibilities of the application of nitrogen are shown by com- 

 paring the average harvest from all plots with nitrogen against the average 

 harvest of all plots without nitrogen. The crops chosen for this comparison were 

 shelled corn, seed oats, potatoes, and hay. These products are standard money 

 crops and have definite market values. The various other crops grown on these 

 plots are important, but are usually consumed on the farm and therefore are 

 difficult to evaluate. 



The average gain per plot as the result of applying nitrogen to oats was 

 small, and ranged from only 5 pounds in 1893 to 50 pounds in 1897. During this 

 period oats alternated with soy beans. The first rotation appeared to make 

 additions of nitrogen of little value, but continuous repetition made it necessary. 

 The average result of five harvests was a gain of barely one bushel of oats to pay 

 for applying 4.5 pounds nitrogen. Since the nitrate was, as a rule, the most effec- 

 tive form and at the present time one of the lowest in price, the added nitrogen 

 for oats may be worth while. It should be mentioned that climatic conditions 

 at this experiment station are not favorable to maximum yields of oats. 



The application of nitrogen to the corn crop in 1911 gave no gain in shelled 

 corn. This corn crop followed clover and grass. The accumulation of nitrogen 

 in the turf was all that the crop required. The largest gain from nitrogen was in 

 1906 when corn followed several successive annual crops, which tended to exhaust 

 rather than increase organic matter in the soil. The gain in this year was 177 

 pounds, or a little more than 3 bushels. Other gains ranged from one bushel to 

 barely two per plot. Corn needs nitrogen when following tilled crops. 



Potatoes in 1900, planted on a clover sod, showed an average gain per plot 

 of 62 pounds or about one bushel. Following soy beans in 1904 and Japanese 

 millet in 1917, there were gains respectively of 361 pounds and 243 pounds. 

 These gains would more than pay for 4.5 pounds of nitrogen. Eight crops of 

 hay showed gains from the use of nitrogen which ranged from nothing when the 

 crop was all clover to 201 pounds when grasses constituted most of the harvest. 



Keeping up the nitrogen of the soil in this field appeared to depend on the 

 choice of crops and rotations, when the records of Plots 4, 7, and 9 are considered. 

 In 1883, the soil was that of a "run out" hay field. Corn was grown without 

 fertilizer of any kind. These three plots gave an average yield at the rate of 29 

 bushels of shelled corn and 3700 pounds of stover. Cropped with corn j^ear 

 after year, these three plots without any nitrogen had dwindled in 1889 to 9.3 

 bushels per acre. Soil nitrogen appeared to be exhausted. These plots in 1899, 

 after ten more crops of various kinds had been grown on them without nitrogen, 

 bore a crop of clover hay averaging 3660 pounds per acre. The next year they 

 produced potatoes at the rate of 209 bushels per acre. After ten more years, 



