Journal of Agricultural Research 
Vol. XXIV. No. 7 
624 
cated that there was a ^eat tendency to loss of nitrate nitrogen from 
leaching and denitrification in the submerged soil. They also observed 
that plants which were treated with nitrate became pale yellow in the 
^arly period of growth but that they recovered later. This was attributed 
to the physiological effect of poisonous nitrites which were formed by the 
reducing action of certain bacteria. 
Kelley (jj), too, found that rice made a weak yellow growth in pots 
when it was supplied with nitrates as a source of nitrogen, but that the 
plants usually assumed a deep green color as they neared maturity and 
apparently made normal growth thereafter. In one series of sand cul¬ 
tures to which sodium nitrate was added, however, it was observed that 
although repeated plantings were made, the seedlings in every instance 
stood for some days, turned yellow, and died. These results were con¬ 
sidered to indicate that nitrates were unable to nourish the young seedlings 
properly, but Kelley also attributed injury causing the rice plants to 
turn yellow to the action of nitrites in the culture. Perciabosco and 
Rosso (^o), however, showed that nitrites in cultiu’e solution were 
absorbed by rice without evidence of injury. 
More recent work by Trelease and Paulino (25) shows that ammonium 
salts are more efficient sources of nitrogen for rice than are the nitrates. 
The results of Kellner {12) and of Espino (4), however, indicate that, 
while young rice plants require ammonium nitrogen for normal develop¬ 
ment, the older plants utilize the nitrates as well as they do ammonium 
salts. Gile and Carrero {8), on the other hand, have reported results 
obtained by the use of culture solutions in which nitrogen was supplied 
in the form of sodium and potassium nitrates; and while they did not 
claim that theirs was an optimum solution for rice, they stated that when 
the solution was sufficiently acid to insure the availability of enough iron, 
the rice made normal growth and was equal in size to exceptionally large 
field-grown plants. These investigators also observed that the yield of 
plants might be diminished by a deficiency of iron which was not great 
•enough to affect the color of the leaves. 
EXPERIMENTAL DATA 
On account of the effect which the unassimilated residues of the differ¬ 
ent forms of nitrogen have on the reaction of plant culture media and also 
because of the relation existing between the reaction of the medium and 
the appearance of chlorosis, it seemed advisable to reconsider the question 
of the comparative efficiency of nitrates and ammonium salts for rice. 
It was therefore decided to make a study especially to determine the rela¬ 
tionship between the two classes of compounds and the chlorosis due to 
the unavailability of iron for the plant. 
For the earlier investigations the soil chosen was an acid red clay which, 
in a preliminary test, had been found to be very deficient in nitrogen and 
phosphorus. Plants that were grown on this soil were apparently immune 
to chlorosis regardless of the quantity of lime that was added to alter 
the reaction. In the response of plants on this soil to different forms of 
nitrates and ammonium salts no differences attributable to the form of 
nitrogen used were noted. The results, however, were rendered of doubt¬ 
ful value on account of an abnormality which was apparently the straight- 
head disease of rice that is described by Tisdale and Jenkins (24). 
Further tests were made in which there was used an alkaline sandy soil 
from a river bank having the following composition: 
