Properties of the Gray Hydromorphic Soils of the Hawaiian Islands^ 
William R. Gill and G. Donald Sherman^ 
The gray hydromorphic soils of the Ha- 
waiian Islands are dark-colored, poorly 
drained, sticky plastic clays. These soils owe 
their morphology to their hydromorphic 
condition produced by their naturally poor 
drainage. This poor drainage of the soil has 
developed poor aeration, reducing condi- 
tions, and a reduction of the biological activ- 
ity, which has prevented the full influence of 
all soil-forming factors essential to normal 
soil development. 
The gray hydromorphic soils are charac- 
terized by a horizon that is mottled gray, 
brown, and yellow by periodic waterlogged 
conditions. Cline et al. (in press) have di- 
vided this intrazonal soil group into three 
soil families, based on the degree of expres- 
sion of the hydromorphic characteristics. The 
soils belonging to the Honouliuli family are 
the least hydromorphic. They have a grayish- 
brown, clayey B horizon that is mottled be- 
low 18 to 20 inches. The water table is gen- 
erally not near the surface, and the mottling 
appears to be the result of impeded down- 
ward movement of water rather than a water 
table. The' soils belonging to the Kalihi 
family are more strongly hydromorphic. The 
mottling in these soils occurs immediately 
below the Ai horizon. The soils of the Kaloko 
family are the wettest of the group. Mottling 
appears in the Ai horizon, and these soils 
^A part of a reasearch project by the senior author in 
partial fulfillment of the requirements for a Master of 
Science degree at the University of Hawaii. Published 
with the approval of the Director of the University of 
Hawaii Agricultural Experiment Station, Honolulu, 
Hawaii, as Technical Paper No. 245. Manuscript re- 
ceived November 16, 1951. 
^Former graduate student and chairman, respectively. 
Department of Soils and Agricultural Chemistry, 
University of Hawaii. 
have a water table near the surface most of 
the year. 
The gray hydromorphic soils are found on 
the islands of Kauai, Oahu, Molokai, and 
Maui. They have developed on the islands 
which are the oldest geologically. They are 
usually found at the lower elevations on these 
islands and are associated with well-drained 
soils in the advanced stages of weathering — 
the latosols. The gray hydromorphic soils 
have properties which make them similar to 
the paddy soils (water-logged soils) and to 
the dark magnesium clays (tropical black 
soil) of the semi-arid regions. All of these 
soils (gray hydromorphic, paddy, and dark 
magnesium clay) exhibit similar physical 
properties in that they are sticky plastic clays. 
The sticky plastic properties of the gray 
hydromorphic soils make their management 
very difficult. The most probable reasons for 
the extreme sticky and plastic nature of these 
soils are, first, the nature and percentage of 
clay in these soils, and, second, the presence 
of a condition in the soil which would cause 
the soil to exist in a deflocculated condition. 
This latter condition has been noted in many 
locations where the amount of exchangeable 
sodium in the soil has been high. Observa- 
tions (Von Kreybig, 1935) indicate that when 
the amount of exchangeable magnesium in a 
soil is very high, and the sum of the exchange- 
able calcium plus exchangeable magnesium 
approaches 100 per cent saturation of the soil, 
the properties of the soil will be similar to 
those of a "sodium soil." 
Usov (1937) described soils in Russia, 
having more than 30 per cent of their ex- 
change capacity filled with magnesium, which 
are plastic and exhibit other "sodium soil" 
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