11 
PHOSPHORIC ACID. 
Phosphoric acid is comparatively abundant, but there is a wide 
range of variation in the percentages present. The upland soils of 
Oahu generally, but not always, contain less phosphoric acid than 
any other extensive body of arable land in the islands. The soils of 
windward Oahu, with the exception of the lowlands devoted to rice, 
also usually contain small percentages of phosphoric acid. The 
Kula soils are rich in phosphoric acid, the Haiku soils intermediate, 
while in the Nahiku section of Maui 'the content is variable. The 
soils of Kohala on Hawaii are unusually rich in phosphoric acid. It 
must not be understood that the above statements apply universally 
to a given section for there is often great variation in comparatively 
short distances. 
Notwithstanding the high percentages of phosphoric acid in many 
Hawaiian soils the availability is, on the whole, rather low, and phos- 
phate fertilization is necessary in most instances except where the 
humus content is high. The low availability of the phosphoric acid 
is probably due to its being chemically combined with iron and 
aluminum in difficultly soluble combinations. Hawaiian soils have 
the power of fixing enormous amounts of soluble phosphates. Experi- 
ments have demonstrated that the red clay type of soil can fix more 
than 4 per cent of its weight of phosphoric acid. There is, therefore, 
very little danger of loss of phosphoric acid by leaching. On the other 
hand, it is also necessary to thoroughly mix phosphate fertilizers 
with the soil in order that the distribution of roots may not be too 
near the surface. Experiments seem to indicate that various phos- 
phates continue to be available for a considerable time after having 
been applied, notwithstanding the fact that the phosphoric acid is 
insoluble in water. Decaying organic matter exercises a very marked 
effect on the availability of phosphates, and even insoluble forms may 
be made available by plowing under green manure. ■ 
NITROGEN. 
As stated above, the humus content is high as compared with 
mainland soils, and consequently the nitrogen is also high, but its 
availability is low, due to poor aeration. The soils of Kula, Nahiku, 
Olaa, and parts of Kohala and Kona on Hawaii are generally very 
rich in nitrogen. Table II shows the percentages of humus and nitro- 
gen in representative samples from these districts. 
On account of there being a high percentage of nitrogen present, 
it is desirable to increase its availability whenever possible. This 
can best be done by increasing the aeration, thereby improving the 
conditions for bacterial action which decomposes the organic nitrogen 
into available forms. It has been found, however, that heating soil 
