66 
Journal of Agricultural Research 
Yok XXIII, No. x 
ammonium-nitrate plots in series A and the ammonia plots in both 
series. There would seem to be a tendency toward a greater depression 
in the plots of the first application. This tendency shows itself more 
clearly in series B. 
On the other hand, results obtained on the Arlington Farm, in an ex¬ 
periment carried out on lines similar to these, again failed to disclose any 
correlation between the application of nitrogen and the phosphoric-acid 
content (Table VII). 
It would seem, therefore, that there are conditions under which the 
application of nitrogen causes a depression in the phosphoric-acid content 
of the crop and that under other conditions the application of this element 
has no effect on the phosphoric acid content. What factors are involved 
in these seemingly contradictory tendencies ? 
Of the four cases cited here it happens that the two (Colorado and 
Nebraska), which show a correlation between the application of nitrogen 
and the phosphoric-acid content, deal with hard winter wheats and the 
other two (Kentucky and Arlington Farm), which show no such correla¬ 
tion, deal with soft winter wheats. This would suggest the possibility 
that these two groups react differently toward an abundance of available 
nitrogen. The underlying principle then would be, in the case of the 
hard winter wheats, some interchange between phosphorus and nitrogen, 
based on the similarity of their functions. The depressed phosphoric-acid 
content would be directly correlated with the high protein content. 
This assumption, however, does not seem to be borne out by the results 
in Table V. In those cases where the third application of nitrogen 
resulted in a high protein content, especially in series A, no depression in 
the phosphoric-acid content can be observed. 
Another possible factor accounting for the different effects of applied 
nitrogen on the phosphoric-acid content is the supply of available phos¬ 
phoric acid in the soil. It may be assumed, then, that when the supply 
of available phosphorus is limited the stimulation of growth, caused by 
the application of nitrogen, creates a physiological scarcity of this element. 
This assumption would seem to be borne out, in a general way, by the 
results here obtained. The application of nitrogen at the first two 
stages which resulted in increased yields also caused a depression in the 
phosphoric-acid content. There is also an apparent tendency toward a 
greater depression resulting from the first application, which produced 
the highest yields. This assumption, however, would not seem to be 
borne out by Headden’s results. In his experiments the application of 
sodium nitrate did not cause an appreciable increase in yield, if any. 
Nevertheless, it produced consistent depressions in the phosphoric-acid 
content. 
It is clear that under certain conditions the presence of nitrogen inter¬ 
feres with the assimilation of phosphoric acid by the plant. It is not 
unlikely that this interference is indirect. Under certain conditions the 
nitrogen may be instrumental, through its action on the soil flora, in 
transforming the available phosphoric acid into less available forms. 
The phosphoric acid in the straw follows the same tendency as that in 
the grain (Table VI). 
The ash and potash contents of the grain were also determined, but as 
the results failed to disclose any consistent tendencies they are not given. 
