DISCUSSION OF RESULTS OF DETERMINATIONS. 



17 



content as did the wheat plants in the wheat plat. Apparently the 

 corn plants were as fond of the nitrates as were the wheat plants. 

 The general field observation that a corn crop renders the ground 

 more productive for grain than a previous grain crop is apparently 

 not due to the leaving of greater amounts of nitrates in the soil. 



WITHDRAWAL OF NITRATES BY CORN ROOTS. 



As already mentioned, the general decrease in the amounts of 

 water-soluble nitrates in both the fallow and the wheat plats masked 

 the effect of any progressive withdrawal of the nitrates by the wheat- 

 plant roots in the successive soil layers. In the case of the corn plat, 

 however, there was the advantage of the fact that the nitrates had 

 already been accumulated, and so the corn offered an opportunity for 

 observing the removal of nitrates from the various soil layers as the 



Fig. 4.— Diagram showing the parts per million of water-soluble nitrates in dry soil in each G-inch soil 

 « layer in the corn plat to a depth of 2 feet. 



season progressed. Figure 4 shows the probable effect of the feed- 

 ing of the corn roots and indicates that the surface 6-inch layer early 

 lost considerable amounts of nitrates and that very shortly there- 

 after the 12-inch layer was drawn upon most heavily. From July 3 

 to July 17 the corn plants made their most rapid growth, and the 

 curves also show that at this period the nitrates were most heavily 

 drawn upon. The 18-inch layer contained most nitrates and lost 

 most. All of the layers to a depth of 2 feet were probably reduced 

 to the limit of the powers of the corn roots to withdraw nitrates from 

 this heavy soil. 



The curves in figure 4 also show variations in the activity of 

 nitrification, especially an increase from June 24 to July 3, but the 



1T3 



