16,5 Espino: Salt Requirements of Young Rice Plants 465 
presented by solution cultures are complex, those presented by 
soil cultures are many times more complex. While field experi- 
mentation with agricultural plants will of course go on in large 
volume, for economic reasons it seems desirable that the simpler 
physiological problems that may be attacked by solution cultures 
should be dealt with whenever opportunity allows. It should 
be repeatedly emphasized that the aim of study of this sort is 
to bring about a better understanding of the nutritional re- 
quirements of the plants considered, not to give information re- 
garding the fertilizer treatment of soils. After the plant itself 
is fairly well understood when growing under the simplest pos- 
sible sets of conditions, then soil experimentation may perhaps 
be planned so as to furnish results directly valuable in field 
culture. The studies here reported deal simply with the rice 
plant as a machine, and the solution-culture method offers the 
simplest form of satisfactory root environment that can be de- 
vised. The problems of the physical and chemical characteristics 
of any soil that might be employed are here avoided altogether. 
GENERAL SURVEY OF THE PRESENT STUDY 
These studies were planned to throw some light on the salt 
relations of young lowland rice plants when grown in solution 
cultures in a greenhouse. It was proposed, first, to find out 
whether any set of salt proportions and total concentrations 
possible with the 3-salt type of solution, studied by Shive, might 
be suitable for good growth of the young rice plants. As was 
already foreshadowed in the results of earlier workers with 
rice, it turned out that it is impossible to obtain good growth 
of this plant (for the first few weeks of its growth from the 
seed) in any one of these 3-salt solutions. 
It was then proposed to supply the plants with the ammonium 
ion, following the suggestions of the literature. This was done 
by employing the single ammonium salt, ammonium sulphate; 
other ammonium salts were not tested. Since ammonium is 
a kation, and since there is no question but that the rice plant 
requires all three of the main kations (potassium, calcium, and 
magnesium) needed by higher plants in general, it logically fol- 
lows that ammonium cannot be directly supplied in a complete, 
nutrient solution unless the latter contains four salts. The sec- 
ond stage of these studies therefore dealt with a 4-salt type 
of solution containing the four kations (potassium, calcium, 
magnesium, and ammonium) as well as the generally requisite 
anions (nitrate, phosphate, and sulphate). Many different sets 
