DISCUSSION OF RESULTS OF DETERMINATIONS. 



21 



at which nitrates were most actively accumulating at different 

 periods and that other factors than cropping evidently determine 

 the seasonal activity of nitrification. 



THE DISAPPEARANCE OF NITRATES. 



Glancing again at figures 1 and 2 it would naturally be asked what 

 became of the water-soluble nitrates in the individual 6-inch soil 

 layers after accumulation had reached a maximum, and why the 

 seasonal shifting of the maximum amount of nitrates has such a dis- 

 tinct downward movement. It would be expected that the rainfall 

 would tend to wash down the nitrates along with other salts, and 

 such probably did take place to some extent. Selecting the week 

 from May 9 to May 16, in figure 2, there would seem to have been 



Fig. 7. — Diagram showing the time and location of the maximum amount of nitrates in the wheat and 



fallow plats. 



such a movement from the surface layer to the 12-inch layer. The 

 rainfall for that week was 1.25 inches. This is the only instance, 

 however, in the two figures which shows the plausibility of such an 

 explanation of the apparent downward "movement" of the nitrates. 

 Inspecting figure 1, where no growing crop complicates the results, 

 it would even appear that the rainfall had the opposite effect, as, for 

 instance, during the period from May 22 to May 29. The effect seen 

 there could not be explained by the washing down of the nitrates by 

 the rains, as there was an increase in nitrates in all of the soil layers 



173 



