PHOSPHATE FERTILIZERS FOR HAWAIIAN SOILS, 
AND THEIR AVAILABILITY. 
INTRODUCTION. 
It has been shown in previous publications of this station 1 that 
the local soils are rich in phosphoric acid, but that it is securely 
locked up in insoluble and unavailable combinations with the highly 
basic (and probably also with the silicic) soil constituents. Iron and 
aluminum, which occur in abundance, and lime, which occurs in 
widely varying amounts, are known to be active in this fixation, and 
it is highly probable that titanium, which occurs in large amounts 
in Hawaiian soils, is also an important factor in the fixation. In 
view of these peculiarities of Hawaiian soils and also of the further 
fact that the results of experiments made elsewhere with phosphate 
fertilizers, have been so contradictory that it is impossible to apply 
them to Hawaiian conditions, it was deemed important and desirable 
to make a careful study of the solubility of the phosphoric acid 
naturally occurring in the soils as well as of the behavior of various 
phosphates when applied to them. 
Investigations were therefore undertaken to determine the avail- 
ability of the phosphoric acid in untreated and fertilized typical 
Hawaiian soils as well as the manner in which phosphates are locked 
up in the soil. 2 These investigations included several series of pot 
experiments. One series involved five successive crops and extended 
over a period of two and one-half years. In another three suc- 
cessive crops were raised. In connection with these experiments 
determinations were made of the total phosphoric acid in the soil, 
the percentage of phosphoric acid in the soil and in the various phos- 
phates soluble in different solvents, and the quantities of phos- 
phoric acid absorbed by the crops grown. The principal crops used 
in the experiments were millet, cowpeas, and buckwheat. Such 
experiments were considered necessary in order to be able to recom- 
mend the most economical form of phosphate to use on the peculiar 
soils of Hawaii. 
i Hawaii Sta. Buls. 35 (1914) and 40 (1915). 
* The pot experiments carried on in this work were first undertaken in cooperation with the Basic Slag 
Committee of the Association of the Official Agricultural Chemists, but have been continued and broad- 
ened to obtain information in regard to phosphate fertilizers for Hawaiian soils. 
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