The experimental work reported in this paper grew out of a study
of ammonium sulphate [(NH4)2S04] as a possible source of nitrogen for
wheat and soybean plants in nutrient solutions. The status of the
problem regarding the direct utilization of ammonium salts by agricultural
plants is still in a very unsatisfactory condition. While experimental
evidence favors the idea that ammonium salts are good sources
of nitrogen for the higher plants, it also indicates that plants differ in
their ability to utilize ammonium salts. Some plants appear to require
the ammonium ion as well as the nitrate ion for growth at certain stages
of their development. In some recent work Espino (5)1 has shown that
the rice plant during the early stages requires the ammonium ion for
normal growth. From a review of the more important contributions
to the literature on the mineral requirements of the rice plant, this
author summarizes by saying:
There is good reason to suppose that: (i) This plant requires the same chemical
elements as do other higher plants. (2) The young plants are not suited to deriving
their nitrogen from nitrates but thrive very well when ammonium sulphate (or possibly
other ammonium salts, such as cholride, nitrate, etc.) is supplied. (3) Older plants
are able to derive their nitrogen supply from nitrates, but may be able to thrive without
the nitrate ion when the ammonium ion is supplied at a proper rate.
He calls attention to the fact, however, that—
none of these points is at all well established in a quantative way.
The more recent work of Trelease and Paulino (79) and that of Trelease
{20) is of interest in this connection. The results of their studies of the
rice plant in soil cultures indicate that ammonium nitrogen is much more
effective than nitrate nitrogen in increasing the yields of this plant. The
yields obtained per unit of molecular nitrogen were highest when the
nitrogen was applied to the cultures in the form of ammonium sulphate;
they were lower when supplied as ammonium nitrate, and still lower
when supplied in the form of calcium nitrate [Ca(N03)2] or sodium nitrate
(NaNOg).
A review of the literature on the general subject of the utilization of
ammonium as a source of nitrogen for the higher plants can not here be