PHYSICAL PROPERTIES OF HAWAII SOILS 17 
than the laboratory method on disturbed soil. For this reason the 
pore space calculated in Table 4 is somewhat too high, even though 
the figures are comparative. The average porosity for the soil 1 series 
was 61.5. This figure agrees well with the average of the moisture- 
holding capacity of the series, which was 64.7, in view of the fact 
that when the soil is completely saturated with water all the pore 
space is occupied by water. 
MOISTURE RELATIONSHIPS 
Of all physical constants which are determined on soils, those in- 
volving moisture relationships are the most important and the most 
indicative of the true nature of soil. As a matter of fact, the mois- 
ture coefficient may be said to be regarded as a kind of summation 
index of several physical and chemical characteristics, such as tex- 
ture, apparent specific gravity, chemical composition, humus content, 
and colloidal content. Both from a theoretical and a practical stand- 
point it is important to know the nature and amount of the various 
soil moistures and their relationships to plant nutrition. It is well 
known that the different moisture constants vary between very wide 
limits for different soil types and sometimes vary considerably even 
with soils belonging to the same t3 r pe. This is true especially of 
Hawaii soils which, by virtue of their peculiar chemical composi- 
tion and physical characteristics, show great variation in their mois- 
ture relationships. 
To obtain a more or less true picture of the moisture relationship 
existing in Hawaii soils of different types, a number of soils were 
examined for their moisture-holding and moisture-adsorbing prop- 
erties. The various physical and chemical properties of these soils 
which affect their moisture relations varied between wide limits. 
These data are given in Tables 1, 2, 3, 4, and 5, and in the Appendix. 
The moisture constants determined for these soils were the hygro- 
scopic and capillary moistures, the moisture-holding capacity, and 
the moisture equivalent. It should be stated that notwithstanding 
the use of standard methods and of precautions to secure uniformity 
in conditions surrounding the determinations, the results do not rep- 
resent actual field conditions for obvious reasons. In the first place 
the textural and structural conditions of the soil as they exist in the 
field have been disturbed, and their moisture characteristics have 
thus been altered. This is an unavoidable source of error in most 
determinations, and in order to obviate it attempts are made to sub- 
ject all soils approximately to the same degree of alteration by apply- 
ing uniform preliminary treatment in the laboratory. In the second 
place, in most colloidal soils upon air drying a change seems to take 
place in the colloidal complex which alters the moisture-adsorbing 
power to a considerable degree. This alteration may take place to 
different degrees depending on the nature of the colloidal phase and 
to the extent the soil has been subjected to drying. 
Some soil investigators believe that the moisture properties are 
altered to a certain extent immediately upon the removal of the soil 
from the ground to a container. As an extreme example to illustrate 
this point: Certain soils from the Olaa district, Hawaii, having 
been formed under extreme rainfall and poor drainage conditions 
are almost constantly in a water-saturated condition. As a result, 
52031—31 3 
