THE GROWTH OF RICE AS RELATED TO PROPORTIONS 
OF FERTILIZER SALTS ADDED TO SOIL CULTURES 
By SAM F. TRELEASE 
Of the Department of Plant Physiology, College of Agriculture, Los Banos 
FIVE TEXT FIGURES 
INTRODUCTION 
The essential ‘mineral elements that must enter through the 
plant roots are nitrogen, potassium, phosphorus, magnesium, 
calcium, iron, and sulphur. Soils that support plant growth con- 
tain all of these elements in suitable compounds. Three of 
them—magnesium, sulphur, and iron—are usually present in 
the soil in amounts beyond what the plants need. The elements 
that are likely to be present in insufficient quantities, or that 
usually produce marked improvement in plant growth when 
added to the soil, are phosphorus, nitrogen, potassium, and cal- 
cium.(12) Calcium is most frequently added in fertilizer prac- 
tice as limestone (CaCO,) or as gypsum (CaSO,); and it is 
the indirect effects of these calcium salts upon the soil that are 
commonly beneficial, rather than the added supply of calcium as 
such, 
The present study deals with the growth of rice plants in soil 
cultures to which the three very important elements, phospho- 
rus, nitrogen, and potassium, were added in various proportions. 
The addition of these elements was made by means of the three 
salts, primary calcium phosphate [Ca(H.PO,).], ammonium 
sulphate [(NH,),SO,], and potassium sulphate (K,SO,). These 
three salts are largely used in commercial fertilizers. Primary 
calcium phosphate is commonly used to supply phosphorus, am- 
monium sulphate to supply nitrogen, and potassium sulphate 
to supply potassium. Besides the three elements just mentioned, 
sulphur and calcium also are added when these fertilizer salts 
are used. These three fertilizer salts actually contain all of 
the essential elements for plants except iron and magnesium, 
and in agricultural work a mixture of the three compounds 
would be called a complete fertilizer. 
In the experiments here reported the three salts were added 
to the soil in thirty-six different sets of proportions, including 
all possible sets of proportions with each salt varying in amount, 
171585——_5 603 
