16,6 
Espino: Salt Requirements of Young Rice Plants 459 
Lehmann based these conclusions would not now be considered 
as convincing in itself, yet his general conclusions still appear 
to stand. Of course the modern problem of the nitrogen re- 
quirements of plants involves not only nitrates and ammonium 
salts, but also nitrites and many other compounds containing 
nitrogen, and must take account of such topics as nitrification, 
denitrification, and the assimilation of elemental nitrogen. The 
question regarding the direct utilization of ammonium salts by 
specific agricultural plants bids fair to maintain an important 
position in agronomic discussions for a long time to come. It 
will of course be necessary that each important kind of plant be 
made the subject of special and rather elaborate experimenta- 
tion. 
Without here attempting to summarize the literature of this 
broad subject, attention may be directed to Hutchinson and Mil- 
ler’s ® experiments and to their discussion. They grew wheat 
and peas in solution culture and also in sand culture. They 
conclude that — 
* * * agricultural plants of various kinds can produce normal growth 
when supplied with nitrogen in the form of ammonium salts under con- 
ditions which exclude the possibility of nitrification. Some plants grow 
equally well with ammonium salts or nitrates as source of nitrogen. Other 
plants, while assimilating ammoniacal nitrogen in the absence of nitrates, 
appear to prefer nitrates. It is less certain whether ammonium salts can 
ever produce better final results than nitrates although we have indications 
that this may be the case. 
In connection with the doubt expressed by Hutchinson and 
Miller, “whether ammonium salts can ever produce better final 
results than nitrates,” the studies on rice by Nagaoka, Kelley, 
and others, which will be mentioned later, are of interest. 
Turning to the rice plant in particular, the problem of its 
salt nutrition has been touched upon from almost all angles, 
but in a rather hit-and-miss way. Kellner^ conducted perhaps 
the first solution-culture experiments on lowland rice, with the 
aim of determining whether this plant thrives best with one or 
another form of nitrogen-bearing salt. He grew his plants in 
nutrient solutions supplying all the essential chemical elements 
for normal growth of ordinary higher plants. In one solution 
nitrogen was supplied as potassium nitrate, and in another as 
ammonium sulphate, and his experiments were repeated several 
® Hutchinson, H. B., and Miller, N. H. J., Direct assimilation of ammo- 
nium salts by plants, Joum. Agr. Sci. 3 (1909) 179-194. 
’ Kellner, 0., Agriculturchemische Studien fiber die Reiscultur, Landw. 
Versuchsst. 30 (1884) 18-32. 
