Relations of Higher Plants to the Formation of Nitrates 43 



in the unplanted soil during the latter part of July. The nitrate content 

 of the planted soil was slightly higher than that of the unplanted soil 

 before the crop was seeded, and nitrates continued to develop more rapidly 

 under the maize up to the latter part of July. From that time until 

 the maize was mature in September the nitrates under the crop decreased 

 as compared with those in the unplanted soil, in the usual manner; the 

 analysis of October 17, however, shows a greater relative increase in the 

 planted soil, which is contrary to the hypothesis that has been advanced. 

 It is possible that the very feeble growth of the crop may account for 

 this. 



Potatoes, which yielded a normal crop, gave results similar to those 

 obtained from normal yields of maize. The difference in the nitrate 

 content of the potato plats and of the contiguous maize plats on October 

 17 is very marked. Although the vines were dead at this time, the 

 nitrates were lower under the plants than at any period during their 

 growth, while nitrate formation had again gone forward in the unplanted 

 soil. 



Nitrates under the planted and the unplanted sections of the oat plats 

 were of the same relation as in previous years. On the planted sections 

 the nitrates continued to decrease after harvest, as shown by the analysis 

 of September 9 — one month after harvest. A slight increase is shown 

 by the analysis of October 17, but it will be noted that, while nitrates 

 in the planted soil increased 15 parts per million between harvest and 

 October 17, the unplanted soil shows an increase of 57 parts per mil- 

 lion in its nitrate content. The course of the nitrates in the planted and 

 the unplanted soil is shown in Diagram V. 



Nitrates at different depths. — In order to ascertain what effect the 

 upward and downward movement of nitrates may have on the apparent 

 connection between the plant and the nitrate content of the surface soil, 

 samples were taken on the north ends and on the middles of each plat to 

 a depth of four feet, each foot being analyzed separately. The results 

 of these analyses are shown in Table 15. 



The analyses show that nitrates are found to a depth of four feet, but 

 that the changes in nitrate content of the soil are not great beneath the 

 first foot. When changes occur in the second foot, they usually accompany 

 corresponding changes in the surface foot. An increase in the nitrates 

 in the surface foot is seldom accompanied by a decrease in the second 



