16,5 Espino: Salt Requirements of Young Rice Plants 521 
SUMMARY 
The studies here reported deal with the mineral nutrition of 
lowland rice plants in solution cultures, for the phase of their 
development represented by the three-week period following 
germination. They involve experimental data on the growth 
of the plants in three different types of solutions: 3-salt solution 
type I comprising, besides a trace of ferric phosphate, the three 
salts monopotassium phosphate, calcium nitrate, and magnesium 
sulphate; 4-salt solution type A comprising, besides a trace of 
ferric phosphate, the three salts just mentioned together with 
ammonium sulphate; and 4-salt solution type B comprising, 
besides a trace of ferric phosphate, the four salts monopotassiurn 
phosphate, monocalcium phosphate, magnesium sulphate, and 
ammonium sulphate. Each type was studied with reference to 
a large number of different sets of salt proportions and several 
different total salt concentrations. The experiments were car- 
ried out in the spring and summer in a greenhouse in Baltimor(j, 
and the results are to be considered as applicable to the climatic 
conditions prevailing there. 
For each solution type the various sets of salt proportions 
were arranged on the basis of molecular proportions, instead of 
on osmotic proportions, as was done in several previous studies 
dealing with salt proportions and physiological balance in nu- 
trient media. With this improvement in the method of planning 
and preparing the numerous solutions to be tested it is possible 
to make up a single, somewhat highly concentrated stock solution 
for any given set of molecular salt proportions and, by simple 
dilution of portions of this stock solution, to obtain solutions with 
the same set of salt proportions but with lower concentrations. 
The following are the main generalizations derived from the 
experimental data: 
1. No set of salt proportions of 3-salt type I gave even fair 
growth. 
2. Excellent growth was obtained with proper sets of salt 
proportions of 4-salt solution type A. This suggests that these 
plants require the ammonium ion, thus apparently differing from 
many other plant forms. 
3. It appears highly improbable that young rice plants could 
thrive with any 3-salt type of solution; there is no doubt that 
rice requires the kations potassium, calcium, and magnesium (as 
well as a little ferrum) like other plants, and the ammonium-ion 
cannot be introduced into a 3-salt solution without its being the 
