440 
PACIFIC SCIENCE, VoL VII, October, 1953 
BARREN SOIL 
GRASS AND SHRUB 
VEGETATION 
% VOLATILE 
MATTER 
% VOLATILE 
MATTER 
^///A FERRUGINOUS CRUST \////A HARDENED SOIL ^ 
FRIABLE SOIL 
Fig. 1. The location and relationship of the hardened crust and vegetative cover of two adjacent profiles from 
Waimea Canyon, Kauai. 
files as shown in Figure 1 and in a like manner 
from Other similar areas, including the crust 
developed on an irrigation ditch bank. The 
bulk density, particle density, differential 
thermal analysis, cation exchange capacity, 
and content of the major oxides were deter- 
mined for each soil sample. The bulk density 
of the soil was determined by two methods. 
The first was by removing the soil from a 
given space and determining its dry weight. 
The volume of soil was determined by fitting 
a plastic bag to the space occupied by the 
soil and ascertaining the amount of water 
required to fill the hole. The second method 
was similar except that the soil was taken by 
a sharp-edged cylinder of a known volume. 
The particle density of the soil was deter- 
mined by the pycnometer (Wright, 1934). 
The cation exchange capacity and the oxide 
analysis were made by methods described by 
Piper (1944). Differential thermal analysis was 
made according to the procedure proposed 
by Norton (1939). 
EXPERIMENTAL RESULTS 
Bulk Density and Particle Density: The most 
striking characteristics of the laterite crust are 
the high apparent and true specific gravity. 
Fujimoto etal. (1948) have described a laterite 
crust in which the surface horizon contains 
more than 50 per cent heavy minerals. In the 
profile there is a tremendous difference be- 
tween the indurate surface horizon and the 
friable layer in their bulk density and soil 
particle density. This same difference was 
present in the surface layer of the barren pro- 
file but was not apparent in the profile with 
a vegetative cover. In Table 1 the bulk densi- 
ties and particle densities of the soils taken 
from a profile without vegetative cover and 
a profile with vegetative cover are given. The 
bulk density of the soil samples from the 
well- developed laterite crusts was 1.9 or great- 
er, and their particle density was higher than 
3.8. The bulk density of the soils from the 
profile with a vegetative cover was 1.0 or 
lower and the particle density ranged from 
2.7 to 3.3. The highest bulk<*density and par- 
ticle density, 2.5 and 4.1, respectively, were 
found in a fragment of the crust from an 
irrigation ditch bank wall. The data clearly 
demonstrate the obvious difference between 
the soils of the barren areas and those with 
a vegetative cover. The observations indicate 
that the vegetative cover does protect the soil 
from hardening to an indurate horizon. The 
differences are more clearly demonstrated in 
Table 2, which presents the averages of the 
different types of soil profiles in Table 1. 
