Calcareous Concretions and Sheets in Soils 
Near South Point, Hawaii 1 
G . Donald Sherman and H aruyoshi Ikawa 2 
White calcareous concretions and sheets 
are found in the soils of the Pakini series of 
the Reddish Brown great soil group in the 
South Point area of the Kau section on the 
island of Hawaii. These soils have developed 
on a series of wind-deposited volcanic ash as 
described by Palmer (1931) and Wentworth 
(1938). The calcareous concretions found in 
these soils have been formed by biogenetic 
processes in that the carbonates have been 
precipitated around the roots of plants, espe- 
cially the deep-rooted plants. These rhizo- 
concretions occur only in the subsoil, B hori- 
zon, of the soil profile. The calcareous sheets 
occur as layers in the parent material of this 
soil which is the aeolian silt and sand. The 
character of the effervescence of these cal- 
careous depositions indicates the presence of 
appreciable quantities of dolomite in the car- 
bonate fraction of these materials. Wentworth 
(1938) has reported the occurrence of both 
calcareous stem casts and calcareous sheets in 
overlying, looser aeolian ash of this area. The 
occurrence of calcareous rhizo-concretions 
has been mentioned by Bryan (1952) in his 
report on soil nodules. The occurrence of 
dolomite in soil concretions has not been 
described; however, the occurrence of dolo- 
mitization in soils has been described by 
Sherman et al. (1947). 
This study was initiated to determine the 
nature of the composition of these calcareous 
rhizo-concretions and sheets. In order to do 
] Published with the approval of the Director of the 
Hawaii Agricultural Experiment Station, University of 
Hawaii, as Technical Paper No. 395. Manuscript 
received May 14, 1957. 
2 Department of Agronomy and Soil Science, Uni- 
versity of Hawaii, Honolulu, Hawaii. 
this, samples of these materials were collected 
and analyzed by methods designed to de- 
termine the composition of carbonates in 
soils as described by Sherman (1937). 
The samples were collected from an area of 
soils which had been classified by Cline et al. 
(1955) as the Pakini very fine sandy loam — a 
soil which has developed from the moderate 
weathering of a series of layers of volcanic 
ash. The surface horizon of about 5 to 6 inches 
is dark-brown very fine sandy loam (An) over 
a slightly lighter colored very fine sandy loam 
(Ai 2 ) of varying thickness. The total thickness 
of the combined Ai horizon does not exceed 
15 inches. The material below the A horizon 
is a B horizon of yellowish -red silty material 
containing sand and gravel. In places a weak 
blocky structure has developed in contrast to 
the crumb structure of the A horizon. This 
material gradually grades into a reddish-yellow 
silt loam in which continuous white layers 
(sheets) of carbonates occur as bands about 
half an inch in thickness. The carbonate- 
coated decayed roots of plants of the previous 
original vegetation of the area occurred in 
this layer and in the B horizon immediately 
above it and at a depth of 36 to 58 inches be- 
low the surface. The original vegetation has 
been removed and replaced by grasses suit- 
able for grazing. 
The rhizo-concretions of carbonates are 
shown in Figure 1. They retain the general 
shape of the root. The concretions in the cen- 
ter row of the illustration show a deposition 
layer on the outer surface of the root and a 
mixture of carbonates and decomposed or- 
ganic material in place of the root in the center 
of the concretion (inner portion). The outer 
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