EXPERIMENTS WITH NITROGEN FERTILIZERS 21 



These results of the application of lime are due primarily to the chemical 

 reaction between the lime and the acids of the soil. Lessening the acidity favors 

 the growth of the bacteria that change the nitrogen of organic matter and am- 

 monia into nitrates, which are the most available of nitrogen fertilizers. 



Another important effect is produced by the reaction of lime with the ammo- 

 nium sulfate, which forms calcium sulfate, a substance sometimes found to be 

 beneficial and always harmless; while if lime is absent, ammonium sulfate forms 

 other sulfates with the soil minerals, that are often injurious, particularly to 

 clover, timothy, and corn. Several bulletins of this experiment station describe 

 this behavior of ammonium sulfate. 



Lime was not applied in uniform quantities every year like the superphos- 

 phate and potash but at infrequent intervals in amounts of 2000 pounds or more 

 per acre. Calcium carbonate dissolves very slowly in the soil water, yet the rain- 

 fall will gradually carry it down below the surface soil. Calcium sulfate is more 

 soluble than the carbonate, from which it is formed by ammonium sulfate; 

 therefore plots fertilized with ammonium sulfate will lose the benefits of liming 

 most quickly. To show how the effects of liming wore away, a comparison is 

 made year by year between the average yields of the sodium nitrate plots, 1 and 

 2, and the averages of the ammonium sulfate plots, 5, 6, and 8. 



The comparison is graphical in form, with the yields on the nitrate plots 

 set always at 100, while the ammonium sulfate yields are proportional. It is 

 begun with the crop of 1897, though Plot 8 had been limed in 1894. The effect 

 on this had nearly disappeared but its results led to the application of lime to 

 all plots in 1898, and in subsequent applications all plots were treated alike. 



The use of different kinds of crops in the experiment was partly responsible 

 for the fluctuations in production on the two sets of plots; but it should be noted 

 that the deepest depressions occurred from three to five years after an applica- 

 tion of lime. A positive rise from the depression took place with the application 

 of lime, except in 1919, when it occurred in the following year. 



Because agricultural lime in its different forms is a low-priced commodity 

 in comparison with nitrogen fertilizers, it has been customary to apply it at the 

 rate of one ton or more per acre at intervals of several years. The graph indicates 

 that greater efficiency of ammonium sulfate as a nitrogen fertilizer may be se- 

 cured by more frequent applications of a smaller quantity of lime at a time. 



SUMMARY AND CONCLUSIONS 



Field A was laid out in 1883 on "run out" hay land and included eleven plots 

 of one-tenth acre each. 



Seven successive crops of corn were grown from 1883 to 1889, to study the 

 effects of different forms and kinds of plant food. The earlier harvests showed 

 potash to be the most needed fertilizer; the later ones indicated that a complete 

 fertilizer had become necessary. 



Four standard types of nitrogen fertilizers — nitrate of soda, sulfate of am- 

 monia, dried blood or fish or cyanamid, and stable manure — were compared in 

 1889, and the comparison was continued with minor changes until 1921. 



A variety of crops was grown, and tables show results obtained with oats, 

 soy beans, potatoes, hay, corn, and miscellaneous crops. 



When Field A was planned, the use of nitrogen from the air by plants was 

 considered to be doubtful. By 1889, it had been shown that leguminous plants 



