16 SEASONAL NITRIFICATION AS INFLUENCED BY CROPS, ETC. 



between the weekly increase in the dry weight of the wheat crop and 

 the amounts of nitrates present. On the contrary, from June 24 to 

 July 3 there was a general increase in the amounts of nitrates corre- 

 sponding to the greatest weekly increase in the growing crop. 



COMPARISON OF NITRATES IN FALLOW, SPRING-WHEAT, AND CORN 



PLATS. 



Figure 3 shows the amounts of nitrates — averages of the four 6- 

 inch soil layers — found during the season in the wheat plat, the fal- 

 low plat, and the corn plat; also the precipitation curve and the 

 weekly crop-increase curve. It is to be regretted that the same 

 amount of data could not have been obtained from the corn plat as 

 from the wheat plat, but time did not permit. Nothing much can 



Fig. 3. — Diagram showing the average parts per million of water-soluble nitrates in dry soil to a depth 

 of 2 feet in the summer-fallow, spring-wheat, and corn plats; also weekly increase of wheat plants 

 and precipitation curve. 



be said about this curve beyond the statement that the rapid decrease 

 in nitrates corresponds quite closely to the period of most rapid 

 growth of the corn as recorded in the notes at the time. 



The corn plat had evidently accumulated quite large amounts of 

 nitrates before the plants were large enough to materially draw upon 

 these salts, for the corn curve shows that on June 19 the accumula- 

 tion of nitrates in the corn plat had reached about the same point as 

 that in the fallow plat. The direction of the corn-plat curve from 

 June 19 to June 24 also suggests the general drop found in the fallow 

 and wheat plat curves. As the corn was not planted until May 7, the 

 plat was evidently in a state of summer fallow until determinations 

 were begun. During the most active growing period of the corn 

 these plants evidently reduced the amounts of nitrates to as low a 



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