28 
utilize this phosphate, although it was present in amounts 23 times 
the largest application and 90 times the smallest. The plants were 
low and the heads very small. 
In Experiment II, in which another application of phosphate was 
made after harvesting the second crop, the results indicated that the 
effectiveness was to a slight extent proportional to the amount of 
phosphate added. The lowest yield was from theP^ pots, while the 
highest was from the P x t j 2 pots. The results as a whole prove the 
unavailable condition of the phosphate naturally occurring in the 
red-clay soil, and show further that the addition of any type of 
phosphate to the soil either assists in the assimilation of that already 
present, or itself acts as a source of phosphate to the plants. 
The fate of soluble phosphates when added to the red-clay soils and 
their influences upon the physical condition have been quite thor- 
oughly dealt with in previous bulletins of this station. 1 The fixing 
power of this soil for phosphoric acid has been shown to be so very 
high and rapid that a loss of phosphate by drainage, through over- 
application, is impossible. The fixation of the calcium phosphate is 
greater and more rapid than that of the sodium phosphate, but the 
sodium of the latter acts as a strong deflocculating agent and would be 
more completely distributed throughout the soil. This probably 
explains its greater effectiveness as compared with acid phosphate, 
which tends to flocculate the soil particles. 
Lime was added throughout the experiments on the assumption 
that it would cause a reversion of the soluble phosphate and thus 
delay its ultimate, combination with the trivalent oxids. From 
the results obtained, the conclusion is obvious that a normal applica- 
tion of lime is not capable of holding the phosphate in reserve in a 
form available for the plant and, furthermore, that the benefit de- 
rived from the application of the lime, while it may be due in part 
to its chemical activities, is primarily physical. The action is only 
temporary, and its influence is exerted to the greatest extent in the 
first crop. The nature of its action is a flocculation of the clay 
particles which temporarily disturb the colloidal condition in which 
the iron and aluminum oxids and hydroxids exist. These compounds, 
together with some silica, combine to form the clay present in this 
type of soil. The most important function of this flocculation is to 
hinder or perhaps only delay the occlusion of the phosphoric acid by 
the colloids. That the soil does finally return to such a state in due 
time following the application of lime is indicated by the physical 
condition of the soil in the pots after the third crop of millet in 
Experiment II, and the further fact that it had reached a state of 
apparent acidity, as determined with litmus paper. At the same 
i Hawaii Sta. Buls. 35 (1914) and 40 (1915). 
