620 
Philippine Journal of Science 
1920 
ture and practically uninfluenced by the potassium content, then 
this moderately increased average yield with cultures having 
lower proportions of potassium sulphate is to be expected. 
From the evidence of fig. 3, and of graph B of fig. 4, it thus 
appears that the increased proportions of potassium added to the 
soil in the present tests were practically without influence upon 
the yield of grain, or possibly even reduced the yield. This 
experiment, therefore, indicates that a marked increase in yield 
of rice grain is not to be expected when a potassium fertilizer, 
or a fertilizer containing very high proportions of a potassium 
salt, is added to the soil, under conditions similar to those of 
the present experiment. 
An examination of graph C of fig. 4 furnishes conclusions 
regarding primary calcium phosphate that are similar to those 
given regarding potassium sulphate. This graph fluctuates very 
widely and exhibits a general tendency to rise somewhat with 
decreasing amounts of primary calcium phosphate. In a given 
group of cultures having the same content of primary calcium 
phosphate the yields vary from low to high values. This is ap- 
parently explained by the fact that the corresponding propor- 
tions of ammonium sulphate also increase in the same manner. 
The tendency of the average value of each group to increase 
somewhat as the proportion of phosphate decreases is inter- 
preted to be due principally to the fact that the average propor- 
tion of ammonium (nitrogen) increases in a similar way. 
Primary calcium phosphate appeared in the present tests to be 
practically without influence upon the yield of grain, or to exert 
a slight retarding action upon this yield. Consequently, the 
evidence presented by the graphs of fig. 4 indicates that slight 
benefit is to be expected from phosphate fertilizers, under the 
present experimental conditions, when compared with the very 
great benefit resulting from the ammonium (nitrogen) fertilizer. 
Logical thoroughness in the interpretation of these results 
requires that at least mention be made of a point that cannot 
be discussed adequately at the present time. The chemical 
elements — nitrogen, phosphorus, potassium, sulphur, etc. — may 
or may not be the units that are important to the plant. It is 
more probable that the ions— NH4+, P+, K+, SO4", etc.— are 
the units that should be considered. The present tests make it 
logical to conclude that ammonium sulphate [(NHJ 2 SO 4 ] made 
the plants grow better, and that the other salts had little or 
no influence beyond determining the partial concentration of 
the ammonium sulphate. If, however, it is stated that the 
