THE NATURE OF ARGILUC HORIZON
IN HAWAIIAN ULTISOLS
A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULRLLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
IN SOIL SCIENCE
JANUARY 1969
By
Cherm Sangtian
Thesis Committee:
Haruyoshi Ikawa, Chairman Yoshinori Kanehiro Pow-Foong Fan Wa cartify ttiat wa hava read this thasts and that in our opinion it is satisfactory in scopa and qucdity as a thasis for tha degree of Master of Science in Soil Science.
THESIS COMMITTEE
Chairman
TT------ACKNOWLEDGMENT
The author would like to express his sincere thanks to
t Dr. L . D. SwindeUe and D r. G. Uehara for their advice. The
author also is thankful to the assistance of Annie K. S . Chang,
Bernardino G . Cagauan, and Sandra Y . H. Yee. The kind
ness and the friendliness of the staff members and the fellow
students is highly appreciated.
Special thanks and gratitude is made to the Institute for
Student Intercheuige, East-West Center, for providing a grant to the author. Without the grant this thesis would not be possible.
1* ti
TABLE OF CONTENTS
ACKNOWLEDGMENT ...... |
UST OF TABLES ...... iv
UST OF FIGURES ...... v
INTRODUCTION ...... 1
General Statement of the Problem ...... 1
Definition of Terms to be U s e d ...... 1
REVIEW OF ^LITERATURE ...... 4
Conditions Relating to the Formedion of Illuviation Clay M in erals...... 4
Factors Affecting Clay Orientation...... 7
Environments of Soils Containing Illuviation Clay Mineral ...... 9
Criteria for Recognizing the Argillic Horizon . . . 11
MATERIALS AND METHODS ...... 13
The Soils ...... 13
Methods of A n a ly s i s ...... 30
RESULTS AND DISCUSSION ...... 33
Particle Size Distribution...... 33
Differential Thermal Analysis ( D T A ) ...... 38
X-Ray Diffraction A n a ly s is ...... 46
I Cation Exchange Capacity, Exchangeable Bases, and Base Saturation...... 51
Soil Acidity ( p H ) ...... S3 iii
TABLE OF CONTENTS (CONTINUED)
Fage
^2^3* ^(^2^^2^3 * * ...... Thin Section Study...... 60
Comparison ol the Argillio H orizons...... 79
Field Relationships of Hawaiian Ult is o ls ...... 61
SUMMARY AND CONCLUSION ...... 83
UTERATURE CITED ...... 84
"■tv.
'i' V. iv
UST OF TABLES
T abla Page
1 Genetic Factors of the S o i l ...... 14
2 P article Size Distribution in the Leilehua and Paaloa S o ils...... 34
3 Particle Size Distribution in the Olelo Silty Clay Loam and Olelo Silty C lay...... 37
4 Some Chemical Properties of the Leilehua and Paaloa Soils ...... 52
5 Some Chemical Properties of the Olelo Soils . . . 54
6 SIO2, R2O3, end Si02/R 2^3 Retio of the Leilehua and Paaloa Soils" . . 56
7 SIO2, R2O3, and S102/R 203 Ratio of the Olelo Soils . . . . .» . . . . . « . . . . 59
8 Some Characteristics of the ArgilHc Horizons of Four Soils ^ ...... 80
. . V
UST OF FIGURES
Figure Page
1 Map of Maui Showing Sample Sites of Olelo S o i l s ...... 15
2 Map of Oahu Showing Sample Sites of Leilehua and Paaloa S o ils...... 16
3 Relationship Between Clay Movement and D ef^ of P r o file ...... 39
4 Differential Thermal Curves of Whole Soil in the Profile of LeilehuaSoil ...... 40
5 Differential Thermal Curves of Whole Soil in the Profile of Paaloa So il...... 41
6 Differential Thermal Curves of Whole Soil in the Profile of Olelo Silty Clay Loam ...... 43
7 Differential Thermal Cuiwes of Whole Soil in the Profile of Olelo Silty C lay...... 44
8 X-R ay Diffraction Patterns of K-Saturated Clay Fractions from the Surface Horizon to B23t Horizon (1-4) of Paaloa S o i l ...... 47
9 X-R ay Diffraction Patterns of K-Saturated Clay Fraction from the Surface Horizon to C Horizon (1 -6 ) of Olelo Silty Clay Loam..... 49
10 X-Ray Diffraction Patterns Showing the Mineralogy of the Cutan In Olelo Silty Clay and of the Clay Fractions of Olelo Silty Clay Loam, Olelo Silty Clay, Leilehua, and Paaloa Soils . . . 50
11 Relationship Between SIO2/R 2O3 Ratio and Depth of Profile ...... 58
12 Photomicrographs of Stress Cutans in the 62 ]^ Horizon of the .Leilehua S o i l ...... 61
13 Photomicrographs of Comiidex Cutans in the B22 Horizon of the Leilehua Soil ...... 62 vi
UST OF FIGURES (CONTINUED) ♦ Figure Page
14 Photomiorogrephs of lUuvieHon Cutans in the B23t Horizon of the Leilehua Soil ......
15 Photomicrographs of llluviation Cutans in the B2lt Horizon of the Paedoa S o il...... 66
16 Photomicrographs of Illuviidion Cutans in the B22t Horizon of the Paaloa S o il......
17 Photomicrographs of llluviation Cutans in the B22t Horizon of the Paaloa S o il...... 70
18 Photomicrographs of llluviation Cutans in die ^22t of the Clelo Silty Clay Locun . . 72
19 Photomicrographs of llluviation Cutans in the ^22t Olelo.Silty Clay Loam . . 73
20 Photomicrographs of llluviation Cutans in the ^22t Olelo Silty Clay Locun . . 74
21 Photomicrographs of llluviation Cutans in the ^22t Fiorizon of the Olelo Silty Clay Loam . . 75
22 F hotomiorographs of llluviation Cutans in the B22t Horizon of the Ol^o SUty C lay......
23 Photomicrographs of llluviation Cutans in the ®22t Horizon of the Olelo SUty C lay...... 78 INTRODUCTION
Qyaeral Statement of the Problem
In the new Comprehensive Classilioation System of the
United States, soils are classified according to diagnostic horizons
€u»d natural properties (Soil Survey Staff, I960). The horizon
differentiation is the most importemt criterion, because the develop
ment of a diagnostic horizon is a result of the interaction of
various factors which influence the properties of soils.
This manuscript presents the study of one of the diagnostic
horizons, the argillic horizon, in Hawaiian Ultisols. Although the
3. argillio horizon has been investigated in soils of the Temperate * ■ I regions, similar studies in soils of the Tropical regions are rare. ■■A. . The objectives of this investigation are: ■i 1. To determine some of the chemical, physical, and
ir - mineralogical properties of the argillic horizon.
2. To determine the nature of the illuviation cutans.
3. To understand the field relationship of Hawaiian Ultisols.
Definition of Terms to be Used
Terms which are used in describing and discussing the
argillic horizons will be included in this section. Less frequently
used terms may be found in "Fabric and . Mineral Analysis of
Soils," (Brewer, 1964). 2
Arqillio Horizon
The argilllc horizon, as defined by the Soil Survey Staff
(I9 6 0 ), is an illuvial horizon in which layer-lattioe silicate clays have accumulated by illuviation to a significant extent. It is a hori zon formed below the surface of the mineral soil, though it may be exposed at the surface by erosion.
Clay Skin
Clay skin is a tern> used by many investigators to mean either a coating of clay on the surface of peds or the wall of voids or an assemblage of optically oriented clay.
Cutan
Cutan is a miodification of the texture, structure, o r fabric on the natural surfaces of soil materials due to the concentration of particular components or it is an in situ modification of the plasma.
Brewer (1964) classified cutans based on the process of formation. Illuviation cutans are true coating formed by the move ment of cutanic material in solution or suspension and subsequent deposition. Diffusion cutans are cutans coating on the natural
surface of soil njaterial and formed by diffusion. They may coat o r concentrate within the soil material and may reach a maximum
at the surface. Stress cutans are in situ modifications of the
plasn.a due to differential forces such as shearing. They are not true coatings. Complex cutans are those formed by a combination of tnore^than one of the above proceases.
Cutana may be desoribed In several ways but the following may be most suitable: (1) kind of surfaces associated with cutans; ( 2 ) kind of outans; (3) kind of outanio materials; (4) orientation pattern; (5) sharpness of boundary; and (6) degree of separation.
S~matrix
This is a term used to define the soil material within peds in which pedological features occur. ‘ REVIEW OF LITERATURE
Conditions Relating to the Formation of llluviation Clay Minerals
The argillio hoHzon is formed by the process of eluviation
and illuviation. There is movement of clay minerals as well as
free oxides of iron, aluminum, or titanium, and organic matter
from the surface or upper horizons to the lower horizons where
they accumulate as cutans on the surface of grains and peds and
along the wall of channels and voids. At the present time, the
mechanism governing die movement of clay minerals is not clearly
understood. Similarity of clay minerals in the eluvial and illuvial
horizons have led the Soil Survey Staff (I960), Frei et aJ.
(1949), and Thorp et al. (1959) to believe that the clay minerals
are carried down by water. Brewer ^ (1957) supported this idea and further showed that clay illuviation can also take
(Jace by the upward movement of partioles in suspension.
Hallswerth (1963) showed that water percolating through artificial
soils can also move clays.
The amount, kind, and proportion of clay minerals in the
soil material are some of the factors which determine the extent of clay mobility. Brewer (1956) stated that clay illuviation is not
determined by clay type.
Particle size of soil material also influences the movement of
clay. The movement is restricted when the m«dor portion of the 5 total pore space is occupied by sirall, non-coiloidai particles.
The movement is enhanced if the mejor part of soil material con sists of particles of large size (Hallsworth, 1963).
Sodium ions and organic matter are believed to be responsi ble directly or indirectly in the movement of clay (Soil Survey
Staff, 1960).
The nature and concentration of ions are responsible for the quantity of clay movement (Hallsworth; 1963). Brewer and . :k; -r ■ 2 ^ Haldane (1957) found that the form.ation of cutans is independent of salt concentration and other factors but diat it is dependent on the removal of water.
Soil pH is still another factor involving the n^ovement of clay.
Swindale (1966) note;d that clay m Tlie evidence of clay migration may be indicated by segre gation of soil materials, color modification, orientation of clay . r. mineral, and alteration of refractive index (Hendricks et ^ . , 1962; Soil Survey Stcdf, i960). The appearance of some thin elongated voids filled with pale brown oriented clay in peds may also be used to identify clay movement. Frei ^ (1949) proposed that the layering and optical continuity of the clayey bodies are the evidence of clay material deposited by water. They also suggested that the aggregates and voids between the aggre gates contained localized clay concentration. Stephen (1967) did 7 not consider the clay content which increased with depth as proof of illuviation. He considered the presence of homogeneous clay deposits on ped surfaces and in channels, cracks or pore spaces to be indications of clay movement. In the field, the presence of small ripple-like markings are suggestive of olay migration. The other important evidences of clay illuviation are described by the Soil Survey Staff (I960; 1967). Factors Affecting Clay Orientation McCaleb (1954) described that surface tension due to depositing olay,oolloidal^suspension affects clay orientation. The olay particles with associated iron oxides were oriented with their c-axis perpendicular to ^the pore walls. Brewer and Haldane (1957) proposed that the proportion of clay to sand, the freedom of movement of the individual clay particles, the drying force 76 • exerted by the contraction film of water or clay suspension around the sand grains, and the shape of olay size particles as factors which influence the orientation of olay. Minashina (1958) stated that the orientation of olay is favored by the flaky habit of the -individual particle, the ability to cohere to each other when dry, the suHace tension of >water, mechanioal pressure and other factors. Van Olphen (1951) concluded that oriented clay skins are not likely to form by flocculation but rather through dehydra tion of dispersed olay. He also suggested that the cessation of 8 water moveinent in the soil and removal of water by roots may be the most important factors. Brewer (1956) reported that pore size and total pore space have different effects on the orientation of clay. Small pore sizes and low total pore spaces formed weakly orieitfed clay, while larger pore size and greater pore spaces formed strongly oriented clay. He also found that the size of the clay material influenced the pattern of orientation. The finest size clay was strongly oriented, while the coarser clay was particdly orieided. The silt sized particles were unoriented. Stephen (1967) considered that the amount of soluble salt in the soil affected the degree of orientation. If soluble salt were not in ex cessive amount, tfie clay was strongly oriented. In the presence of high amount of soluble salt, however, the clay was only weakly or>iented. Platy shc^e or micaceous habit is considered to be aiother important factor influencing clay or*ientation. Most of the clay minerals except halloysite possess this proper*ty. If the clay sus pension is allowed to sediment, the ornentation of the 001 hkl plane will be parallel to the sur*faoe of deposition. The Soil Surwey Staff (1960), Stephen (1967), Williamson (1947), and Frei et (1949) have shown that the clay pcuHioles in clay skins are strongly ornented. Fry (1933) mentioned that aggregates of soil colloids may or may not show double refraction under crossed niools. Double refraction, however, was more common, and the 9 absence of double refraction was associated with high iron content. Clay orientation may be determined by means of the petro- graiphio microscope. There will be alternating brightness and extinction of the transmitted light when the thin section is examined by rotating the microscope stage with the niools crossed. In jjv addition,^ the layers of oriented clay associcded with peds and pores often can be distinguished from clays that have not moved. The boundary between clay coatings and the matrix is usually sharp, and the coating is nearly free of sand and silt inclusion J (Soil Survey Staff, I960). McCaleb (1954) reported that the continuity of optic properties is a good evidence of orientation. Uehara ^ al. (1962) noted that the development of structure in Hawaiian latosols is in part related to the degree of clay orientation as measured by the degree of anisotropy. • ... - Environments ci Qwitaining llluviation Clay Mineral Cutans are found in many ^ ils including the Brunizem, Solonetz, Brown Fodzolic, Gray-Brown Podzolic, Humic-Gray, Flanosol, Latosols, Red-Yellow Podzolic, Low Humio Latosol, and several other great soil groups (Buol and Hole, 1961). Cutans can develop from many different parent materials and under various conditions, but wetting and drying is the most important process that can produce cutans (Soil Survey Staff, 10 1960; Buol and Hole, 1961; Brewer and Haldane, 1957; and Minashina, 1958). Thorp (1959) studied the genesis of the Miami Silt Loam in Richmond, Indiana. These soils are developed from medium textured, highly o^careous glacial till with silty overlay. The present average’ annual ridnfall Is 40 inches, and the average winter and summer temperatures are 28.5* F and 71.5* F , respectively. The native vegetation, before the settlement of white men, was dense deciduous forest, mostly oak. These soils are well drained and well developed. The soil clay minerals are vermiculite and kaolinite in the upper horizon and montmoriilonite in the deeper horizons. Thin section studies showed that oriented clay was found in the B21 and B22 horizons. "Flake" and "chips" of clay, probably formed m place from die parent material, were found more commonly in the A and C horizons. The soil pH ranged between 4.8 to 7 .7 . The surface horizon was 6.6 while that of the C horizon was 7 .7 . In the B horizon the soil reaction was very strongly acidic to lightly acidic. Brewer (1956) studied the Tenningerie soil series of the Riverine Plain Area, Murrumbidgee Irrigation eur*ea, Australia. These soils, derived from wind-blown sandy material, was dominated by red- brown earth on coarse-grained parent material. The landscape was composed of broad low drained soil. The climate was semi-arid with an average annual 11 rainfall of 15 Inchas. Clay minerals were illite and kaolinite. 0 f' These were twice as much when compared with kaolinite. Quartz was present in all horizons. Thin section studies of samples from the B21 horizon showed oHeiUed clay coatings on primary grains and in pore s(>aoes. Total pore space was large. In Hawaii, Swindale (1966) reported the occurrence of strongly developed V5 argillic horizon in the Lolekaa soil. It is a dark brown, acidic soil formed from old alluvium and fans. Criteria for Recognizing the Argillio Horizon Soil horizons which contain illuviation clays or cutans are not necessarily argillio horizons. The diagnostic characteristics of the argillic horizon are described in detail by die Soil Survey staff, (1967): — 1. If an eluvial horizon remains, and there is no lithologio discontinuity between it and the argillic horizon, the argillio horizon contains more total and more fine clay than the eluvial horizon, as follows: a. If any part of the eluvial horizon has less than 15 percent total clay in the fine earth (less than 2 mm.) fraction, die argillio horizon must contain at least 3 percent more clay. (13 percent versus 10 percent, for example.) b. If the eluvial horizon has more them 15 percent and less than 40 percent total clay in the fine earth fraction, the ratio of the clay in the argillio horizon to that in the eluvial horizon must be 1.2 or more. .’1^ c. If the eluvial horizon has more than 40 percent total clay in the fine earth fraoHon, the argillic horizon must contain at least 8 percent more clay. (50 percent versus 42 percent, for example.) 12 2. An argtUio horizon should be at least one-tenth the thickness of the sum of all overlying hoHzons, or more than 15 cm. (6 inches) thick if the eluvial and illuvial horizons are thicker than 1.5m. (60 inches). The clay increases required under item 1 eure reached within a vertical distance of 30 cm. (12 inches) or less. 3. In massive soils the argillio horizon should have oriented clays bridging the sand grains and in some pores. 4. If peds are present, an argillic horizon either (1) shows clay skins on some of both the vertical and horizontal ped surfaces and in the fine pores, or shows oriented clays in 1 percent or more of the cross section; or (2) meets requirements 1 and 2 above and has a broken or irreg ular upper boundary accompanied by some clay skins in the lowest part of the horizon; or (3) if the horizon is clayey with kaolinitic clay and the surface horizon has more than 40 percent clay, there are some clay skins on peds and in pores in the lower part of that horizon having blocky or prismatic structure; or (4) if the illuvial horizon is clayey with 2 to 1 lattice clays, clay skins may be lacking, provided there are evidences of pressure caused by swelling; the evidences of pressure may be occasional slickensides or wavy horizon bound aries in the illuvial horizon, accompanied by unooated sand or silt grains in the overlying horizon. 5. if a soil shows a lithologic discontinuity between the eluvicU horizon and the argillic hori^n, or if only a plow layer overlies the argillic horizon, the argillic horizon need show only clay skins in some part, either in some fine pores, or if pads exist, on some vertical and horizontal ped surfaces. Thin sections should show that some part of the horizon has about 1 percent or more of oriented clay bodies. MATERIALS AND METHODS The Soils Location of Sampling Sites ■ i;-'- The Olelo silty clay loam (sicl) and Olelo silty clay (sic) are located on the plateau of Mt. Eke, Wailuku, West Maui, at elevations ranging from 3,000 to 3,600 feet. The approximate location of Olelo silty clay loam is at 156* 33' 12" E . long, and 20* 49' 38" N. lat., and that of Olelo silty clay is at 156* 33' 32" E . long, and 20 * 50' 3" N. lat. Figure 1 shows the approximate locations of the sample sites. ■■ 4^,4^ - . ^ The Leilehua soil is located in a pineapple field at Waipio, Oahu, at elevations ranging from 900 to 1,200 feet. The approx imate location is at 157* 59' 35" E . long, and 21* 28* 6 " N. lat. The Faaloa soil is located on the uplands of Waialua, Oahu, at elevations ranging from 1,000 to 1,700 feet. The approximate samfJe site is at 158* 1' 42" E . long, and 21* 36' 4" N. lat. Figure 2 shows the approximate locations of the two sample sites. Environment of the Soils Table 1 shows tiie genetic factors and general informistion of '1=.. the four soils. The Olelo silty, clay loam and Olelo silty clay occur on the plateau of steep and deeply dissected mountains. Tha climate is dry and sunny at the lower elevations and wet and frequently Table 1. Genetic Factors of the Soils Genetic Factors Olelo sic* Olelo sicl* Paaloa** Leilehua** Classifioation moxic Humoxio Humoxic Humoxic 3pohumults T ropohumults Tropohumults T ropohumults Vegetation ses & shrubs: Grasses: Rattail, Sugarcane, pasture Pineapple, sugarcane >hia, Fukeawe; Hilogr asses Ohia, koa, guava, Natural vegetation: ?ns: Amaumau; Herbs: Horsetail, fern, and California unimportant. isses: Sedge, Lantana, grass Hilograss, Sedge Rattail; -bs: Plantain, Horsetail, Dandelion Parent Material ,alt Basalt Alluvium & basic Basalt igneous rocks Elevation 00 feet 3,025 feet 1,000-1,700 feet 900-1,200 feet Slope 856 2- 12% 2- 12% Eromon ip gullies without Surface soil Slow-medium runoff Slow-medium runoff dening Drainage 1-drained Well-drained Well-drained Well-drained Rainfall 5" 4711 70-90" 60-80" Soil Temperature F 64*F 70 *F 70* F ♦Stoop (1967) ♦♦SCS, USDA 155 4 0 35 3 0 25 20 0 5 155 0 0 Fig. 1. Map of Maui showing sample sites of Olelo soils. cn 25 21 20 Fig. 2, Map of Oahu showing sample sites of Leilehua and Paaloa soils, 17 oloudy at the higher elevations. At 2,800 to 3,000 feet elevation, the land is utilized for pasture. Below this elevation, die vege- tation is sparse grassland, whereas at the higher elevaHon, the vegetation is forest. The annual rainfall ranges from about 50 to 60 inches as the elevation increases. Tlie aspect of the area occupied by these two soil series is south-southeast, and the topography is genUy rolling. Soil temperature of both soils measured at 50 inches is 64* F. The Leilehua soil occurs on gendy to strongly sloping up lands. The elevation is about 900 to 1,200 feet. The annual rainfall is 60 to 80 inches, and the mean annual air temperature is 74* F . The Paaloa soil occurs on the uplands immediately below the steep sloping and deeply dissected area. The uplands are ✓ separated by deep and steep canyons. Tlie slope of soil ranges from 2 to 12% similar to that of the Leilehua soil and is nearly always convex except at the too which is concave. Annual rain fall is 70 to 90 inches. Annual air temperature is about 70* F . Sunlight is deficient because of cloudiness. Soil temperature of both soils at 50 inches is approximately 70* F . Description of the Soils Samples of the Olelo silty clay loam (sicl) and the Olelo 18 silty clay (sic) used for ohemical and physical ancdyses are those described and collected by Stoop (1967). Samples used for petrographic study were collected by tiie author and others from the same sample sites. Samples of the Leilehua and the Paaloa were collected by the author and others from sites previously described by the Soil Conservation Service (S C S ) personnel, USDA In 1966. These four soils are classified as Ultisols. According to Swindale (1966), the Ultisols are soils of the wet climate. The difference between the mean summer and mean winter temperature is less than 9 * F . The upper portion of argillio horizon contains at least 15% humus. These soils have a base saturation of less than 35% in the lower portion of the argillio horizon and a cation exchange capacity of less than 20 meq/100 g of soil. The clay content in the argillio horizon is greater than that of the surface horizon. The profile descriptions (Stoop, 1967; and S C S , U SD A, 1966) are as follows: Olelo Silty Clay Loam Horizon Dep^ Description cm Aj^ 0-25 Dark reddish brown (5YR 3/3) silty clay loam, and dark reddish brown (SYR 3 /3 ) when dry; weak very fine granular 19 Horizon Depth Description cm structure; loose, very friable; slightly sticky fluid slightly plastic; many roots; many pores; cleflu* smooth boundcu*y. A J 25-43 Dusky rad (2.5YR 3/2) clay, and wecdc red (2.5Y R 4 /2 ) when dry; mflussive to weak, fine and medium subanguleur blocky structure; slightly hflu*d, frifldile, very sticky and very plflistic; many roots; many very fine and fine pores; many shiny specks; moderate high bulk density; clear smooth bound B21 43-61 Dusky red (2.5Y R 3 /2 ) clay, with red dish brown clay skins flurtd with pockets of black heavy oxides; moderate fine and medium subangular blocky structure; * ' * V • * friable; very sticky and very (Mastic; many roots; many very fine and fine pores; abrupt smooth boundeu*y. ®22t 61-99 E>usky (lOYR 3 /4 ) silty clay, with pockets of black heavy oxides; strong, very fine, fine and medium subangular blocky struc ture with a tendency to plflity; frifldile. 20 Horizon Depth Description cm very sticky and very plastic; few roots, many very fine and fine pores, almost continuous clay skins; gradual smooth boundary. ®23t 99-117 Dark red (lOYR 3 /6 ) silty clay, mod erate to strong fine and medium sub- angular blooky structure; friable, very sticky and very plastic; few roots; many very fine and fine pores; almost con tinuous clay skins; occasional fragments of weathered rook; gradual wavy boundary. 117-140 Dark grayish brown and dark brown soft weathered rock with soil material with same color as B22t! weathered rook with soil material equal to B22t. Olelo Silty Clay Horizon Depth Description cm 0-10 Dark gray (lOYR 4 /1 ) silty clay, and gray (10YR 5/1) when dry; maeeive struc ture and the upper 2" (5cm ) granular; 21 Horizon Depth Deecription cm slightly hard, friable, sticky and plastic; many roots; many pores; many shiny specks; moderate high bulk density; clear smooth boundary. 10-25 Dark gray (lOYR 4/1) silty clay, and gray (lOYR 5 /1 ) when dry; massive structure; slightly hard, friable, sticky and plastic; common roots; many pores; high bulk density; clear smooth boundary. B21 25-38 Dark brown (7.5YR 3/2) silty clay; weak fine and medium subangular blooky structure; slightly hard, friable, very sticky and very plastic; few roots; many fine and very fine tubular pores; common clay skins In pores; moderate high bulk density; clear smooth boundary. ®22t 38-51 Variegated brown to dark brown (7 .5 YR 4 /4 ) and reddish brown (SYR 4 /4 ) silty clay; weak to moderate fine and medium subangular blooky structure; friable, very sticky and very plastic; few roots; many fine and medium pores; many clay skins 22 Horizon Depth Deecription om on pads and in pores; gradual wavy boundary. ®23t 51-99 Dark reddish brown (2.5Y R 3 /4 ) with coatings of dark reddish brown (SYR 3 /4 ) silty day; strong medium and coarse (4aty structure; friable, very sticky and very plastic; few roots; many very fine pores; many clay skins on pad faces and in pores; many hard earthy lumps; gradual wavy boundary. 99-140+ Yellowish red (SYR 4 /6 ) silty clay; moderate fine and medium subangular blocky structure; friable, very sticky and very plastic; many fine and medium pkores; many clay skins on peds and in pores. Leilehua Soil Horizon Depth Description cm Ap 0-31 Dark reddish brown (SYR 3 /3 ) silty clay, reddish brown (SYR 4/3) dry; moderate fine, medium and coarse 23 Horizon Dep^h Description cm granular structure; very hard, firm, v.i . ^ ' *' '--r. sticky and very plastic; plentiiul roots; common very fine and many fine inter stitial pores; many veiry fine glistening specks; common fine particles of gray (SYR S/1) material mixed by tillage irom a lower horizon; decomposing pine apple trash throughout horizon; bottom ol horizon has 1-inoh layer of pineapple trash; extremely acid (pH 4 .1 ) ; abrupt smooth boundary. 6 to 12 inches (15- 30 cm) thick. B21 31-44 Dark reddish brown (215YR 3 /4 ) moist and dry silty clay; weak medium and coarse subangular blooky structure; hard, firm, sticky and plastic; plentiful roots; common very fine and fine tubular pores; few fragments and pockets of dusky red (lOYR 3 /3 ) material mixed by tillage; many very fine glistening specks; com mon fine gray ( SYR 5 /1 ) whan moist material; compacted by tillage; extremely 24 Horizon Depth Description cm acid (pH 4 .0 ) ; abrupt smooth boundary. 5 to 7 inches (13-18 cm) thick. B 22 44-56 Same color and texture as above; weak coarse subangular blooky breaking to : moderate very fine and line subangular blocky structure; hard, firm, sticky and plastic; low fine roots;7many very fine glistening specks; common fine fragments of gray (5YR 5 /1 ) material; numerous L very firm earthy lumps; extremely acid (pH 4 .1 ) ; abrupt smooth boundary. 5 to 7 inches (13-18 cm) thick. , "J •'*- . ^ ®23t 56-80 Dusky red (lOYR 3/3 ) silty clay, dusky red (lOYR 3/4) dry; weak coarse and m.edium moderate subangular blocky structure with few pockets of moderate very fine subangular blocky structure; hard, fricd>le, sticky and very plastic; very few roots; many very fine and fine and common medium tubular pores; thin patchy clay films and weak pressure cutans on pads; extremely acid (pH 4 .5 ) ; 25 -■s.: Horizon Depth Deecription cm clear smooth boundary. 9 to 12 inches (23-30 cm) thick. ®24t 80-105 Dark reddish brown (2.5Y R 3 /4 , 3/3 •s: crushed) clay, reddish brown ( 2 .SYR 4 /4 ) dry; weak coarse subangular blooky breaking to moderate very fins and fine subangular blooky structure; hard, firm, * sticky and very plastic; many very fine and fine tubular pores; nearly continuous pressure cutans on ped faces; many thin patchy clay films; com.mon vary firm earthy lumps; extremely acid (pH 4 .3 ) ; abrupt wavy boundary. 9 to 13 inches (23-33 cm) thick. ®25t 105-123 Dark reddish brown ( 2 .SYR 3 /4 , 3/3 crushed) heavy silty clay, reddish brown (2.SYR 4/4) dry; moderate very fine subangular blooky structure; hard, firm sticky and plastic; many very fine and fine tubular pores; many fine distinct dark reddish brown (2. SYR 3 /4 ) coating on ped faces; continuous pressure cutans 26 Horizon Depth Deecription on ped faces; many thin patchy clay films; many very firm earthy lumps; peds have a brittle feel; common iron segre gations; few pockets of highly weathered gravel; extremely acid (pH 4 .1 ) ; clear wavy boundary. 7 to 10 inches (18-25 cm) thick. C j 123-159 Dark reddish brown (2.5Y R 3 /3 ) clay, dark reddish brown (2.5Y R 3 /4 ) dry; moderate very fine, fine and medium subangular blocky structure; very hard, J firm, sticky and very plastic; many very fine and fine tubular pores; dark reddish brown (2.5Y R 3 /4 ) coating on ped faces: continuous pressure cutans on ped faces; sonie appear to be clay films; many very firm earthy lumps; few highly weathered gravels; extremely acid (pH 4 .2 ) gradual wavy boundary. 14 to 16 inches (36-41 cmj thick. C2 159-192 Dark reddish brown (5YR 3/4) clay, reddish brown (5YR 4 /4 ) dry; moderate 27 Horizon Depth Description cm very fine, fine and medium subangular blocky structure; hard, firm, sticky and plastic; many very fine and tubular pores; stringy dark reddish brown ( 2 .SYR 3/4) patchy clay films on ped faces; pressure cutans on ped faces; many weathered gravels; extremely add (pH 4 .3 ) . Paaloa Soil Horizon Depth Description cm Ap 0-44 Mixture of about 50 percent of dark brown ( 7 .SYR 3 /2 ) and dark reddish brown (2 .SYR 3 /3 ) silty day, dark brown (7-SYR 4/4) and dark reddish brown ( 2 .SYR 3/4 ) dry; strong fine and very fine subangular blocky structure; hard, firm, sticky, and plastic; abundant roots; few fine and very fine tubular and ' t' interstitial pores; strongly acid (pH 5 .4 ); abrupt smoodi boundary. 15 to 17 inches (38-43 cm.) thick. 28 Horizon Depth Description cm ®21t reddish brown ( 2 .SYR 3 /4 ) silty clay, dark red (2.SYR 3/6) dry; mod erate fine and very fine subangular blooky structure; hard, friable, sticky and plastic; few roots; root map caps this horizon; common fine tubular pores; dusky red (lOR 3/4 moist) clay films in pores and moderately thick nearly continuous clay film on ped faces; strongly acid (pH 5 .1 ); clear wavy boundary. 6 to 9 inches (15-23 cm) thick. ®22t 64-92 Dark reddish brown ( 2 .SYR 3 /4 ) moist and dry silty clay; moderate fine and very fine subangular blooky structure; hard, friable, sticky and plastic; few very fine roots; many fine and medium tubular pores; thin nearly continuous dark red (lOYR 3 /6 ) moist clay films in ^ , pores and thin patchy films on ped faces; 30 to 50 percent of this horizon consists of dark'reddish brown (5YR 3 /3 ) moist saprolite gravels coated with clay films Av • - A' 29 Horizon Depth Description cm as above; very strongly acid (pH 4 .7 ) ; clear wavy boundary. 10 to 12 inches '-V ^ (25-30 cm) thick. ^A;AA *23t 92-115 Dark raddish brown ( 2 .SYR 3 /4 ) clay, #■: dark red ( 2 .SYR 3 /6 ) dry; moderate, AfyfA: ■•'. medium fine and very fine subangular ::S 'C -A: :^.vv''u4: ■ - ■■ blocky structure; hiu*d, firm, sticky and - ‘ , V ; ' ■ ■ ■ very plastic; few very fine roots; few ■ ‘ - '•■Af-' . ■' very fine and fine tubular pores; thin S&.- continuous dark red (lOR 3/6 moist) clay films in pores, and thin patchy films on pad faces; very strongly acid (pH •T U'-;" 4 .8 ) ; clear smooth boundary. 9 to 11 :»A\ inches (23-26 cm) thick. B24J 115-154+ Dark reddish brown ( 2 .SYR 3 /4 ) silty ■ clay, dark red (2.SYR 3/6) when dry; :'^^A’X"'.v..-'-- / > ;■ v A ‘ . moderate fine and very fine subangviiar blocky structure; hard, friable, sticky • Zf'^y A •••■?..-, . •;• and very plastic; few very fine roots; common tubular pores; thin continuous dark red^^Ol^ 3 /6 ) moist clay films in {X>res and thin patchy clay films on ped 30 Horizon Depth Description tsi. cm iaces; very strongly acid (pH 4 .7 ) . Methods of Analysis Particle Size Distribution Particle size distribution was determined according to the procedure described by Kilmer and Alexander (1949) and Day (1965) using Calgon (sodium hexametaphosphate) as a dispersing agent. The fine to coarse clay ratio (0.2u /2.0u ) was determined by the method described by Jackson (1956). Differential Thermal Analysis (D TA) The Stone Automatic DTA unit was used to determine the amount of kaolin and gibbsite and/or hydrous oxide of iron. A 0.1 g sample of 100-mesh whole sample, which was previously equilibrated at 57% relative humidity, was analyzed. Ignited alumina was used as a standard reference, and the sample was heated at an average rate of 1 0 * 0 /minute. Nitrogen gas was used to suppress the oxidation of organic matter. X-Ray Diffraction Analysis The Tem -Fres X-ray diffractometer was used to determine the mineral composition of the olay fractions by the procedure of Jackson (1956). Powdered sand fractions of selected horizons were also analyzed. 31 Ea Cation exchange capacity of the whole soil was determined after saturation with and distillation of the NH3 from NaCl extract according to the procedure described by Peech et al. (1947). The ammonium acetate (pH 7) extractant used in the above determination was analyzed for exchangeable bases. The Perkin- Elmer, Model 303, Atomic Absorption unit was used to determine Ca emd Mg, while the Beckman DU Flame Spectrophotometer was used to determine Na and K . The base saturation was calculated by dividing the sum of the exchangeable bases.by the cation exchange capacity. Son Acidity (pH) - Glass electrodes, using soil-water ratios of 1:1 and 1:5 and " soil-1 ^ KCl solution ratio of 1:1 was used to determine the pH of the samples. f Si02, ^2^3* Si02/R2Q3 ,.r ; The samples were fused with lithium tetraborate and dissolved in dilute nitric acid according to the procedure outlined by Suhr and Ingamells (1966). The Si02 as well as the F 2O3 were determined oolorimetrically. For the purpose of this investigation, -V • ♦. 'r-, r R2O3 includes AI2O3, Fe203, and Ti0 2 . Thin Section Study Thin sections of sam.|:Jes from the argillic horizon were 32 prepared by the standard procedure using Caedax as an impregnating medium. The petrographic microsTOpe was used to describe the cutans and the mineral fabric. Photomicrographs of selected areas were also taken. >p-.;V • t - ■V' RESULTS AND DISCUSSION Particle Size Distribution Leilehua and Paaloa Soils Table 2 shows the particle size distribution of the Leilehua and Padoa soils. TTie Leilehua soil is a fine textured clayey soil. The clay fraction, as determined by the pipette method using Calgon as a dispersing agent, ranged from 89% in the A horizon to 95% in the B21 horizon, followed by a gradual decrease in the lower B and C horizons. The ratio of the clay content in the B21 horizon over the A horizon was 1.07. The ratio in the B22 horizon over the Ap horizon was 1.02, and the proportion of the fine to coarse clay (0.2u/2u) in the B22 horizon was 2 .4 . The increase in clay content between the Ap and B2X hori zons or between Ap and B22 horizons is not quite 8% as proposed by the Soil Survey Staff (1967). The B21 horizon is distinctly finer in texture than the rest of the horizons. However, the Ap horizon is also fine in texture. Therefore, in a soil like the Leilehua soil, where the cutans a r e observed and where the argillio horizon may be in the initial stage of formation, the clay increase in the illuvial horizon need itot necessarily be 8%. Although the ratio of the fine to ooarse olay of the other horizons was not determined, that of t h e 22 was 2.4. It may 34 Table 2. Particle Size^DiatHbution in the Leilehua and Paaloa Soils Depth Horizon Sand Silt Clay Fine/Coarse cm % % % Clay Ratio Leilehua Soil 0-31 Ap 1.7 9.0 89.3 31-44 ®21 1.1 4.0 94.9 44-64 1.4 7.9 90.7 2.353 , ®22 ■: 64-79 ®23t 3.7 14.5 81.8 79-117 C 6.5 26.1 67.4 Paaloa Soil # 0-41 Ap 4.9 32.0 63.1 1.317 41-59 B21t 17.0 — 83.0 1.599 59-92 ®22t 9 .2 3^.9 86.9 0.975 "’_V^ ^ 92-115 ®23t 19.2 7.4 73.4 0.028 35 not be unreasonable, tfierefore, to classify this horizon and the 831 horizon which has the finest texture in the profile as argillio horizons. However, based on field observation and for ease of discussion, only the 832 horizon will bo treated as an argillic horizon in this investigation. ■i? The clay content of the Paaloa soil ranged from 63% in the Ap horizon to 83yS in the 82 ]^! horizon and 87% in the 8331 horizon. It decreased to 73% in the B23( horizon. The propor tion of clay fraction in the horizon to that in the A horizon was 1.3, while that of the B22t horizon over the B2j[j horizon was 1.05. The^ proportion of the fine to coarse clay in the ^ 2 1 t horizon was 1. 6, while th^ in the 8331 0.9 8 . Although the increase in clay content between the Ap and ^ 21t over 20%, it is not so between the 83 ^^^ and 822t horizons. The ratio of fine clay to coarse clay in the B3;j^^ suggests that this horizon may be the argillio horizon. However, the presence of cutans in edl of the subsurface horizon collected for this study may qualify all of them to be argillic horizons. A s in the case of the Leilehua soil, based on field observation and for ease of discussion, only the B2]^^ horizon will be treated as an argillio horizon. The location of the horizon with the greatest clay content in a profile (the "clay bulge") appears to be related to the amount of rainfall of an area. The Paaloa soil is located in a higher 36 rainfall area than the Leilehua soil, and it seems reasonable to assume,that the depth of the "clay bulge" will be deeper in the former. -V The data suggest that the olay has moved down from the A to the B horizons. However, the amount of movenent, as repre sented by the difference, is small. This small amoutU may be due to the high olay content which can reduce soil porosity (Hallsworth, 1963). A s the texture of a soil becomes finer, clay movement to die lower horizons becomes more limited. Hallsworth reported that the amount and kind of olay in the soil material are factors which determine clay movemeid. The movement appeared to be restricted if^ the proportion of the olay increased over 40% for kaolinite and over 20% for montmorillonite. Small amount of clay movement may also be due to compaction of the soil by heavy farm, machinery. ^ On the other hand, the small difference in the olay content between the,A and B horizons may be due to mixing; for example, by plowing. Distribution of the silt and sand fractions in the Leilehua soil differs from that observed in the Paaloa soil. The reason k>r such differences is unknown. Olelo Silty Clay Loam i»d O l^ , Silty Clay Table 3 shows that the olay fraction of the Olelo silty olay loam and the Olelo silty olay are much lower than those of the Leilehua and Paaloa soils. These differences may be attributed 37 Table 3. Partlole Size Distribution in the Olelo Silty Clay Loam and Olelo Silty Clay Depth Horizon Sand Silt Clay Ffawr/ Coarse om % % % Clay Ratio Olelo Silty Clay Loam 0-25 ^1 1.0 61.3 37.7 25-43 1.8 55.6 42.7 43-61 ®21 5.2 58.0 36.8 61-99 ® 22t 26.3 38.5 35.3 5.429 99-117 ®23t 58.3 14.9 26.8 ^ 117-140 C 51.2 28.4 20.4 ■,e .:■■ Olelo Silty Clay 0-10 A l 4 .6 58.1 37.3 0,489 10-25 A3 8 .5 52.4 39.0 0.262 25-38 B21 22.9 38.5 38.6 0.596 38-51 ®22t7 26.3 29.1 44.6 0.548 ■V -ft t J 51-99 ®23t 59.2 6.6 34.3 1.389 > 99-140+ C 81.8 7.9 10.4 1.556 38 to the varying influence of one or more soil forming factors on Oahu and Maui. In the Olelo silty clay loam, the clay content is highest in the A 3 horizon. The gradual decrease is then noted with depth. In the Olelo silty clay, however, the clay content is highest in the ®22t horizon. The "clay bulge" at a greater depth in the latter soil may be due to higher rainfall in the sample site. The relatk>nship between the amount of clay movement and depth of profile for the four soils is shown in Fig. 3. Based on the presence of cutans, the ^ 22^ horizons of both soils will be treated as the argillic horizons. A" : Both of the Olelo soils show a decrease in the silt fraction ' i and an increase in the sand fraction with depth. Although the V. A r. problem, of dispersion of certain Hawaiian soils is well known (Hawaii Agricultural Experiment Station Soils Department Staff, personal communication, 1968), it is difficult to exp4aln the distri bution patterns of these two fractions. DiitorwAli TheriBal Aiialysis (DTA) - 5. ^ ■ it' ' ' Leilehua €uid FatJoa Soils Figures 4 and 5 show the DTA curves of the Leilehua and ? i * Faaloa soils. 5 . The curves of the Leilehua soil indicate the presence of both -i- kaolin and gibbsite and/or hydrous oxides of iron. These curves indicate further that the mineralogy is rather constant throughout PERCENT Fig, 3, Relationship between clay movement and depth of profile. Co VO 40 TEMP. (“C ) Fig. 4. Differential thermal curves of whole soil in the profile of Leilehua soil. 41 25 200 400 600 800 1000 TEMP. Cc ) Fig. 5. Differential thermal curves of whole soil in the profile of Paaloa soil. 42 the profile. The exception is the occurrence of a well-defined exothermic peak at eipproximately 930 *C in the curves of samples from horizons 4 and 5. An exothermic peak, which is not clearly defined, occurs at approximately 800*C in the curves of samples from the upper horizons. The curves of the Paaloa soil also indicate the presence of both kaolin and gibbsite and/or hydrous oxides of iron. However, there is a slight increase of these minerals going down the profile. The well-defined high temperature exothermic peak is also observed in the lower horizons of the Paaloa soil. Such changes in a profile are quite common in other Haweuian soils and may indicate a morphological difference in the kaolin clay within a profile. The wide exothermic band at approximately 700*C in horizon 2 may be due to the presence of an iron oxide. Every horizon of both profiles shows a cuz*ve with a low temperature endotherm v^ich is associated with adsorbed water. This endotherm which is located at approximately 150*C is some- tinies attributed to the presence of allophane (Fieldes, 1966). Based on the DTA results, it is not possible to distinguish the mineralogical differences within a profile to locate the argillic horizons. Olelo Silty Clay Loam and Olelo Silty Clay The DTA curves of Olelo silty clay loam and Olelo silty clay are shown in Figs. 6 and 7. 43 TEMP. (C) Fig. 6. Differential thermal curves of whole soil in the profile of Olelo silty clay loam. 44 TEMP. (C) Fig. 7. Differential thermal curves of whole soil in the profile of Olelo silty clay. 45 The curves of the Oleio silty olay loam Indicate the presence of small amounts of kaolin in horizon 1. Very small amoui^s of the same mineral is also observed in horizon 5 and increases with depth in horizon 6. Small amounts of gibbsite and/or hydz*ous oxide of iron are found in the upper three horizons. These mineral(s) increase with depth in horizons 4 and 5 but decrease slightly in horizon 6 . The latter is the parent material and the presence of less gibbsite and/or hydrous oxide of iron and more kaolin in this than in .i.-- horizon 5 suggests that weathering has not progressed to a con siderable extent at this depth. The peak attributed to the presence of adsorbed water is found in all horizons of toe Olelo silty clay loam. This peak decreases from horizon 1 to 2, but ^thereafter, it increases with depth. The mineralogy of horizon 1 is different from that of the lower four horizons. T h o curves of the Olelo silty olay show that gibbsite and/or the hydrous oxide of iron and adsorbed water increased with depth. In contrast to the Leilehua and Faaloa soils, the Olelo soils contain predominantly large amounts of adsorbed water and small to moderate amounts of gibbsite and/or hydrous oxide of iron. The hydration and mineralogy suggest that the Olelo soil may have been derived from volcanic ash or at least may have been 46 influenced by volcanic ash. Loganathan (1967) showed similar DTA curves of samples derived from voloaido ash. A s in the case of the Leilehua and Paaloa soils, it is diffi cult to distinguish the mineralogical differences within a profile to locate the argiUic horizon. X-Ray Diffraction Analysis Paaloa Soil Figure 8 shows the X-ray diffraction patterns of K-saturated, preferentially oriented olay slides of the Paaloa soil. Tlie patterns indicate the presence of mica (1 0 .0 , 3 .3 A ) , kaolin (7 .1 , 3. 5 A), gibbsite (4 .9 A ) , and quartz (4 .3 , 3.3 A ) . The mica decreases with depth. The kaolin and gibbsite, on the other hand, increase in the subsurface horizons. The presence of a weak 02 hk dif fraction band (4.3 A ) in die lower horizons suggests that meta- halloysite or a disordered kaolin may be present in addition to kaoliidte. Mica and quartz have been detected in the upper horizons of Hawaiian soils (Gardiner, 1967; Loganathan, 1967). The occurrence and genesis of these minerals have been proposed by Swindale and Uehara (1966) and Juang and Uehara (1968). If these two minerals are not considered, kaolin and gibbsite repre- sent the dominant minerals in this soil. Tlie lack of crystalline mineral in horizon 1 also suggests the presence of X-ray PAALOA DIFFRACTION ANGLE (DEGREE 26) Fig, 8 . X -r a y diffraction patterns of K-saturated clay fractions from the surface horizon to 6 2 3 ^ horizon (1-4) of Paaloa soil. -J ' 48 amorphous malarial. Hie amounts of kaolin and gibbsite are greater in horizons 2 through 4 than in horizon 1. If the peak ■4 size of the minerals (Fig. 8 ) is related to clay content (Table 2 ), - and if the latter is an indcation of clay movement, then kaolin and gibbsite are the minerals which have moved in this soil. Olelo Silty Clay Figure 9 shows the X-ray diffraction patterns of K-saturated, preferentially oriented clay slides of the Olelo silty clay. The dominant mineral is mica (1 0 .0 , 3.3 A ) . The asymmetrical out line of the 10 A peak suggests that perhaps the mica may be a mixed-layer mineral. There was a slight expansion in the Mg- saturated, glyoolated clay. The other minereds a r e kaolin and gibbsite which occur in smedl amounts. If the clay content (Table 3) and peak size of the minerals (Fig. 9) are related to clay movement, then the mixed-layer mica appears to be the dominant mineral which has moved in this soil. Others Figure 10 shows the X-ray diffraction patterns of the argillic horizons of the four soils used in this investigation. These patterns indicette that the clay minereds in the eu?gillic horizon can 'v' be kaolin, gibbsite, mica, and/or quartz. Although based on the •a: result of only one sample of Olelo silty clay, the mineralogy of the cutan and the clay fraction appears to be similar. OLELO SILTY CLAY 100 7.1 33 10 2 0 30 40 50 DIFFRACTION ANGLE (DEGREE 26) Fig, 9. X -r a y diffraction patterns of K-saturated clay fraction from the surface horizon to the C horizon (1-6) of Olelo silty clay. VO 10.0 7.1 3.5 3.3 CLAY IN SOIL (OLELO SILTY CLAY) CUTAN (OLELO SILTY CLAY) CLAY IN SOIL (OLELO SILTY CLAY LOAM) V CLAY IN SOIL (PAALOA) CLAY IN SOIL (LEILEHUA) J I I J 1 I 1 I L J L 10 20 30 40 50 DIFFRACTION ANGLE (DEGREE 29) Fig, 10. X -r a y diffraction patterns showing the mineralogy of the cutan in Olelo silty clay Cn and of the clay fractions of Olelo silty clay loam, Olelo silty clay, Leilehua and Paaloa O soils. 51 The occurrence of the mixed-layer mica and quartz in the Olelo soils is interesting. Mica has been mentioned previously as occurring in the upper horizons of soils of the higher rainfall areas (Gardiner, 1967; Loganathan, 1967). If the mica in the J* Olelo soils has indeed moved from the upper to the lower hori zons, it may be desirable to investigate these soils still further to understand the role of mica not only in clay movement phenomenon but also in the genesis of such soils. If this mineral does move downward In a profile, it must be very fine-grained. On the other hand, there may have been the downward movement of kaolin and gibbsite, and then resilication to form a mica-type . -.-V mineral. Cation Exchange Capacity, Exchangeable Bases. Leilehua and Paaloa Soils The chemical properties of the Leilehua and Paaloa soils are shown in Table 4. The cation exchange capacity of both soils is low. The ex change capacity of the Leilehua soil solum ranges from 15 to 16 meq/100 g of soil, while that of the Paaloa soil solum ranges from 15 to 22 meq/100 g of «>il. The average values meet the requirement to classify these soils as Ultisols. The content of exchangeable bases and base saturation are also very low. V '■ht' y.. Table 4. Some Chemical Properties of the Leilehua and Paaloa Soils Depth CEC , Exohangeatte > Cations, Base cm meq/100 g Sat. pH pH pH TT % l:lHoO IrlKCl *- 'W'"' •!* Lmlehua Soil 0-31 16.43 0.38 0.19 0.07 0.22 5.2 4.63 4.32 4.21 31-44 11.52 0.39 0.12 0.07 0.14 6.2 4.52 4.25 4.20 44-64 11.70 0.34 0.08 0.10 0.18 5.9 4.41 4.26 4.22 64-79 15.06 0.42 0,38 0.07 0.12 6 .5 4.47 4.30 4.25 79-117 4.47 0.36 0.16 0.10 0.12 16.6 4.90 4 .62 4.43 Faaloa Soil 0-41 21.84 0.29 0.31 0.16 0.17 4.2 4.42 4.45 4.23 41-59 21.45 0.03 0.12 0.11 0.07 1.5 4.85 4.85 4.55 59-92 15.29 0.04 0.19 0.09 0.07 2.5 5.05 4.90 4.50 92-115 15.96 0.17 0.24 0.12 0.07 3.7 4.95 5.00 4.40 Cn to 53 These results do not appear to indicate which of the horizons may be classified as argillic horizons. Olelo Silty Clay Loam and Olelo Silty Clay Table 5 also shows the ohemical properties of the Olelo soils. Although based on the results of only two profiles, the argillic horizons in the Olelo soils are characterized by an in crease in the cation exchange capacity and a decrease in the base saturation when compared with the horizon just above it. The content of exchangeable bases is almost similar in both toe epxpe- don and the argillio horizons. Soil Acidity (pH) Leilehua and Faaloa Soils In the Leilehua soil, the pH (1:1 H2O) is lightly higher than the pH (1 :5 H2O ). Generally, the former is lower than the latter because of the dilution effect of water. The higher pH reading of 1:1 H2O when compared with 1:1 KCl indicates the clays are negatively charged. This soil is strongly cusidic. In the Faaloa soil, the pH (1:1 H2O) and pH (1 :5 H2O) are similar. The results also indicate that this soil has clays which are negatively charged. > This ..soil is strongly acidic. In the Leilehua and Paaloa soils, there does not seem to be any relationship between soil pH and the occurrence of the ft argillic horizon. .-A''/':---• ' - ■ i> ,• ■ V: ■/' " 4.. Table 5. Some Chemical Properties of the Olelo Soils Dep4h CEC Exchangeable Cations, Base cm meq/100 g meg/100 g» _ Sat.* pH pH pH Ca % 1:1KC1 A Olelo Silty Clay Lioam 0-25 29.70 3.3 1;4 6^1 0.3 17.2 5.68 5.96 5.20 25-43 11.40 1.5 0.8 0.1 0.2 22.8 5.89 6.33 5.33 43-61 9.60 1.3 0 .5 < 0.1 0.1 19.7 5.88 6.40 5.40 61-99 15.40 0.8 0 .3 0.1 <0.1 8.6 5.68 5.75 4.74 99-117 20.70 0 .7 0 .4 0.1 <0.1 6.3 4.85 5.45 4.58 117-140 24.20 0 .4 0 .4 0^*2 0.1 4 .5 4.95 5.12 4.13 Olelo Silty Clay 0-10 16.50 0.6 0 .7 0.1 0.3 10.3 5.15 5.73 4.45 10-25 11.20 0.2 0.3 0.1 0.1 6.2 5.08 5.78 4.33 25-38 21.50 0 .3 0 .4 0.1 0.1 3.7 4.80 5.65 4.24 38-51 24.40 0.3 0 .4 0.1 0.1 3 .3 4.88 5.67 4.15 51-99 23.10 0.2 0 .3 0.1 0.1 3.0 4.84 5.28 4.25 99-140 20.60 0.1 0.2 0.1 0.1 1.9 4.78 4.90 4.63 ♦Stoop (1967) Cn 4^ 55 Olelo Silty Clay Ijom xn and Olelo SU|y In the Olelo soils, the pH (1:1 H2O) is lower than the pH (1 :5 H2O ). The clays are negatively charged and the soil is moderately to strongly acidic. A s in the case of the Leilehua and Paaloa soils, it is difficult to see any relationship between soil pH and the occurrence of the argillic horizon. Sj02, Si02/R2^3 Leilehua and Paaloa Soils Table 6 shows the Si0 2 , R203(Sum of AI2O3, Fe203, and Ti0 2 ), and S 102/R 203 ratio data. Both soils show a slight decrease in the Si02 and the S102/R 203 ratio with depth. The exception is the S i0 2 /R 2 03 ratio of the C horizon of the Leilehua soil. In general, with a decrease of S 102, there is a corresponding increase or concen tration of the R2O3 . The S i0 2 /R 2 0 3 ratio of the Paaloa is slightly lower than that of the Leilehua soil. This may be due to the effect of rainfall. The higher rainfall on the Paaloa soil may contribute to greater leaching of the Si0 2 > According to the Soil Survey Staff (1967), the Si02/R203 ratio is closely associated with the clay content. The clay frac- H'-. Hon has a lower S i0 2 /R 2 ^ 3 redio than the silt and sand fractions • Therefore, as the clay fraction increases, there should be a decrease in the SiC2/R 203 raHo. However, when the results 56 Table 6. SIC2, ^2*^3* SIO2/R 2O3 Ratio of the Leilehua and^ Paaloa Soils Depdi Si02 R2O3 (%) S102/R 203 om % AI2O3 F s203 TIO2 Ratio Leilehua Soil 0-31 26.60 16.15 23.33 4.97 0.598 31-44 25.26 17.66 24.62 4.92 0.535 44-64 24.02 17.82 24.72 5.05 0.505 64-79 20.09 18.50 31.10 6.71 0.357 79-117 19.87 16.82 27.11 4.51 0.410 Paaloa Soil 0-41 24.28 9.75 29.88 9.35 0.496 41-59 21.42 15.02 30.52 5.52 0.470 59-92 21.93 17.71 27.22 5.49 0.435 92-115 21.24 17.93 27.30 5.84 0.416 57 of the particle size distribution are compared with the Si02/R 203 ratio, the latter is not,necessarily associated with the clay content. The lack of association may be related to the lack of weatherable minereds in the coarser fractions which are primarily aggregates of the same clay minerals found in the clay fraction. Although the S i0 2 /R 2 ^ 3 ratio decreases with depth in both soils, it does not appear to be a strong indicator of the argillic horizon ( Fig. 11). Olelo Silty Clay Loam and Olelo Silty Clay Except for the C horizon in the Olelo silty clay loam, the Si02 and the S 102/R 203 ratio also decreases with depth in the Olelo soils (Table 7 ). The decrease in these variables, accom panied by a corresponding increase in the R2^ 3* more pro nounced in the Olelo soils than in either the Leilehua or the Paaloa soils. This characteristic may be attributed to the mature age of the Olelo soils. These restilts suggest, therefore, that in a mature Ultisol, a low and decreasing Si02 and Si02 /R 2^3 ratio may indicate the general position of the argillic horizon. When the results of the four soils are considered, the Si02/R 2^3 ratio also indicates the processes of chemical weath ering. Kaolinization is the dominant process in the Leilehua and Paaloa soils, while kaolin decomposition is the dominant process in the Olelo soils. Sherman (1949) described that the aluminum o X \- Cl LJ Q 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 RATIO Fig. 11. Relationship between S i 0 2 /R 2 0 3 r'at'O and depth of profile Oi CD 59 T •?• fable 7. S ip 2, R2O3, and SIO2/R 2O3 Ratio ol the Olelo Soils -'T-' . ^ Depth R aO l (%) ®i? 2 ^ S 102/R 203 cm .AI2O3 F # ^ i TIO2 Ratio S' ■ Olelo Silty Clay Loam 0-25 17.28 , 4.31 40.68 *10.89 0.309 ■ 25-43 17.90 3.65 47.30 13.90 0.276 43-61 10.11 2.46 63.15 16.62 0.123 8.00 . , ■•• .y'-/-'v 61-99 2.65 59.17 14.96 0.104 99-117 5.82 6.50 52.66 7.74 0.087 ^ 117-140 15.42 10.59 41.03 6.67 0.264 Olelo Silty Clay ’i- -‘i*.■ . , • - 0-10 18.08 3.30 41.24 18.58 0.286 '3;>' 10-25 16.26 2.82 46.31 19.00 0.239 25-38 13.45 3.19 50.63 11.50 0.206 . . - 38-51 10.62 4.09 50.07 9.23 0.168 «1- ■' 51-99 4.58 3.71 57.88 8.17 0.066 99-140 4.75 4.20 63.52 8.88 0.062 60 content (bauxite) as well as oxides of iron and titaruum of certain Humic Ferruginous Latosols increased with clay mineral forma tion and decreased with clay mineral decomposition. TTiin Section Study Leilehua Soil S 21 horizon— A study of the thin sections of the B2I hori zon showed the presence of stress cutans. Figure 12 shows r - v A photomicrographs of these stress cutans. Under crossed niools, the cutans, which were light yellow'^ weakly to moderately oriented, had striated patterns. They occurred randomly in the s-matrix and were not confined to any pores or channel walls. It was not possible to distinguish between the boundary between the cutans and the s-matrix. Except for the presence of many sm.ail black opaque grains believed to be magnetite or titano- magnetite, the texture of the s-matrix was a fine and uniform dense day. The amount of pores in the B 2 1 horizon was low. However, channels, probably cracks in the s-matrix were some what common. Other voids were elongated suggesting that they were being compressed by some pressure. There were no indication of clay movement. B22 horizon— Figure 13 shows the presence of complex cutans, a oombination oi stress and illuviation outans, in the ^22 horizon. Tlie stress outans were similar to those observed in T- ; - - ¥■' - Fig. 12. Fhotomicrographs of stress cutans in the B2I horizon of the Leilehua soil. 160x. Crossed niools and plain light, respectively. I-:•■‘r-- ' ■■ r • .. -r ‘ L F ‘ - i . 61 Fig. 13. Photomicrographs of complex cutans In the B22 horizon of the Leilehua soil. 160x. Crossed nicols ^and plain light, respectively. Stress cutans occur in the s-matrix, while Illuviation cutans occur along walls « of a channel. 62 63 the B21 horizon, biU the former showed more concentration near voids. The illuviation cutans were observed as thick coatings on the walls of pores and channels. The degree of orientation of the illuviflUion cutans was sh?ongly continuous as indicated by the presence of isogyres when observed under crossed niools of the microscope. There were some remnants of cutans in the s - matrix near the voids. They showed high birefringence and strong orientation and appeared to be displaced illuviation cutans. The amount of stress cutans greatiy exceeded the amount of illuviation cutans. Although the boundary between the stress cutans and the s-matrix was diffuse, th«d of the illuviation cutans as well as of the remnant cutans and die s-matrix was rather - ■* sharp. The s-matrix in the B22 horizon was similar to that observed in the section of the B2^ horizon, but the pores were more numerous, larger in size and more spherical in shape. Small grains of black opaque grains believed to be magnetite or titanomagnetite were common, in addition, although not seen In the F^otomiorographs, occasioned large grains of gibbsite were observed. B23t horizon—.Figure 14 shows photomicrographs of a section of the B23t horizon. Illuviation cutans domineded this horizon. They were moderately oHented and were observed as coatings on channel walls. The boundary between these cutans and the s-matrix was sharp. A s in the case of the upper S's' Fig. 14. Photomicrographs of illuviation outans in the B23t horizon of the Leilehua soil. 160x. Crossed nicols and plain light, respectively. The illuviation outans coat the walls of the channels.' 64 65 horizons, the s-matrix was fine-taxtured olay. Pores were numerous and spherical. C horizon—“No photomicrographs of the C horizon are shown. Observation of the thin sections,, however, showed that illuviation ■'*'* -V cutans also dominated this horizon as in the B23( horizon. The texture of the s-matrix was coarser than that In the upper hori zons indicating a decrease in the clay content. Fores were even more numerous and larger than in the B23^ horizon and some of them, were filled with fine textured materials which included gibbsite. The other materials appeared waxy and were light in color under reflected light. Paaloa Soil B2it horizon— Figure 15 shows illuviation cutans in the B2it horizon of the Paaloa soil. Tbese outans eu*e associated with walls of large channels and pores and surfaces of peds. They had moderate to high birefringence and were moderedely to strongly oriented. The boundary b^ween the cutans and the surface of deposition was rather sh aggregates and the s-matrix was diffuse. Fig. 15. Fhotomicrographs of illuviation cutans in the ®2lt horizon of the Paaloa soil.' 160x. Crossed nicols and plain light, respectively. ^These outans coat the walls of large channels and pores and sur- , faces of peds. 66 67 The pores were smooth and round and were usually filled with fine textured materials which were waxy. When observed by means of the microscope, they were light gray under reflected light suggesting that they were clay materials. These pore-fillings were usually unoriented, but the cutans surrounding the former were oriented in a circular pattern. The cutans associated with pore walls and aggregates occurred in greater amounts than those associated with channel walls. The s-matrix had a uniform, clayey texture and was reddish brown. On the other hand, the pore-fillings had a finer texture and was very light brown. In general, under crossed nicols, cutans were reddish yellow and had a higher birefringence than the s-matrix. Gibbsite was very common in this horizon. Goethite, which had a high birefringence of gibbsite but with bright red color (Cady, personal communication, 1968) was also observed. Grains of black opaque mineral believed to be magnetite or titano magnetite were also very common. B22t horizon—Illuviation cutans were also observed in the ®22t horizon. They were similar in appearance to those ob served in the B2Xt horizon. Although it is not so apparent in the black and white micrographs, these cutans were thick coatings on the walls of channels and pores and surfaces of peds ( Fig. 16). Aggregates of cutans were also observed but they were less V- Fig. 16. Photomicrographs of illuviation cutans in the B22t horizon of the Paaloa soil. 160x. Crossed nicols and plain light, respectively. -.i t . ^ -.-V ' 68 69 common than tha outans associated with channels, pores, and peds in the B21t horizon. Large pores were filled with uniform fine textured clayey material which were also coated with thick cutans. It appeared as though aggregates or peds of different sizes were developing from these fine textured unoriented clayey materials. The s-matrix were usually reddish brown due to iron oxide stain. Black opaque grains believed to be magnetite or titano- magnetite were common. They were unevenly distributed and were more common in certain areas than others. Goethite was also observed. There was a high degree of cracking in the s-matrix. ~ T ®23t horizon— Figxire 17 shows complex cutans in the 8234 horizon. Illuviation outans along walla of channels and large pores, cutanio remnants of different ages, and stress cutans were observed. The latter, similar to that observed in the Leilehua soil, was found in only very small quantity. The cutans associ ated with the channels and pores were moderately to highly birefringent and strongly oriented. The boundaries between the illuviation cutans and the s-matrix and between the cutanic rem nants and the s-maUrix were sharp, but that between the stress cutans and the s-matrix was diffuse. Channels I Fig. 17. Photomiorographs o{ illuviation outans in the ^22t lic>rizon of the Paaloa soil. 160x. Cx*osseci nicols and plain light, respectively. ; ■ ;■ * ' i : ,■ -V r - ? (, 70 71 occurrence and dietribution of other minerals were similar to those in the upper horizons. Olelo Silty Clay Loam ^ B22t horizon— Figures 18 through 21 show illuviation cutans in channels and pores. These cutans showed high birefringence and strong orientation. The boundary between the cutans and the s-matrix was sharp. Some cutanic remnants were found but they were not common. The texture of the s-matrix appeared very coarse and non-uniform. Gibbsite, goethite, and opaque grains h : believed to be magnetite or titanomagnetite were observed. The s-matrix appeared to be forming into granule-like aggregates cemented by dark brown material and gave indication of being in the initial stage of formedion of laterite soils. ^ B23t horizon— No photomicrographs are shown for this horizon. Illuviation cutans, however, were observed in large channels and pores. These cutans were thin and broken, indi cating a decrease in cutan distribution. Few cutanic remnants were observed in the s-matrix, and they were moderately to strongly oriented with high birefringence (bright red color). The boundary between the cutans and the s-matrix was sharp. The s-matrix was clayey, finer in texture than the above horizons. Gibbsite, goethite, and mineral grains believed to be magnetite or titanomagnetite were also found in this horizon. Fig. 18. PhotomicrograFtos of illuviation cutans in tha B22t horizon of the Olelo silty olay loam. 160x. Crossed niools and plain light, respectively. Cutans in pore showing layering and strong orientation. • • , • .v .-„ 72 -■ 'V, , • ■ , N.' . -‘^ -.- ; - v - . ■ Af-^ #*' ■ ' ’ •' 4 1 - ' ..r4 ’ ^~'i' *- '> ■ t - .. *' * V ■ '.J ’" ■. _ -■•a'*'•J* ’;■ , ■*v.t.-v^»-•»''■'"J- ■•',w* '''Is. k>f»- '•■‘■-A.'r ■'"..^>■.•£ *,^ '■ .'>' . *• - . ^ > 4T >• 41 : .-xft \«i- T.:• '■»■ ; ■: -■ii^^-:*-‘ ♦».•:' .>*- - K i • ■ 3 . •••V* ':;^ A ;r.,:'' v a a . .. ••■ ^ ; . •;. • e r r - ' J Fig. 19. Photomicrographs of illuviation outans in the B£2t horizon ol ttis Olslo silty olay loam. 160x. < Crossed nicols and r^ain light, respectively. Cutans coat chan nel walls and HU pores. 73 V' - Jt . ^i; Fig. 20. Photomiorographs of illuviation cutans {9 the B£2t horizon of the Oleio silty clay, loam. IGOx. Crossed niools and plain light, respectively. t Sti-r - VS- > V 74 - •• -V.--.XV ^ ■ ■ ' i ' Fig. 21. Photomicrograph ol UluviaHon cutans in tha B22t horizon of tha Olalo silty clay loam. 160x. Crossed nicols. . '-s. ' 75 76 Olelo Silty Clay B 22t horizon— The illuviation outans in this horizon were associated with channels (Fig. 22) and pores (Fig. 23). The cutans were thick and broken or cracked in many places. In fact, these broken outans may be the outanic remnants found in the s - matrix ( Fig. 22). The cutans were moderately to strongly oriented with high birefringence. The boundary between the outans and the s-matrix was sharp. The texture of the s-matrix was fine clay, but because of aggregation, the porosity was high. There were less opaque mineral grains than in die Olelo silty olay loam., and in general, they were smaller. ®23t horizon— No photomiorographs are shown for this hori zon. The occurrence and distxnbution of illuviedion outans were similar to those in the B22t horizon. In general, these cutans, however, were thicker. Cutanic remnants were less common. C horizon— No photomiorographs are shown for this hori zon. The thick illuviation cutans were associeded with very large channels amd ped surfaces. They were strongly oriented and highly birefringent. Some outanio remnants were observed in the line clay materials near the large channels. The boundary between the outans and the s-matrix was sharp. The latter was a fine oomipact material which indicated the development of a hard pan. Porosity was high with fine pores dominating. The pores were relatively free of fillings. Opaque minerals believed to be Fig. 22. Fhotomicrographs of Illuviation outans in the B22t horizon of the Olelo silty clay. 160x. Crossed nicols and F^ain light, respectively. Ciitcms coat channel walls. 't' 77 Fig. 23. Fhotomiorographs of illuviation cutans in the Bo2t horizon of the Olelo silty clay. 160x. Crossed niools and plain light, respectively. Cutans fill a pore. J ?'- 78 X- ♦ - ■' ‘ o •• W V A j: / .- ^ . '•P '-■> t* ^ •-? t \ rv*L-v'' ■:'Si; 79 magnetite or titanomagnetite as well as gibbsite were found associated with many peds. Comparison of the Argillic Horizons Table 8 shows some of the important characteristics of the argillic horizons of the four soils used in this investigation. The depth is measured from the surface of the mineral hori zons. The vertical distance is the distance between the A horizon and the B21 or B22 horizons. The thickness of the argillic horizon is the thickness of the B 21 or B 22 horizons. The data show that the depth of the argillic horizons of the four soils ranged from 51 to 99 cm, and the clay content ranged ??■“ from -2 to 14%.’ * The fine to coarse clay ratio (0.2u/2u) was higher than that in the surface horizons. Base saturation was low, ranging from 3 to 9%, and soil acidity was strong to very strong. The SiC ^/R 2O3 ratio of the Leilehua and Paaloa soils was betwaen 0 .4 and 0 .5 , while that of Olelo soils was between 0 .1 to 0 .2 . Stress cutans were observed in the Leilehua soils, but illuviation cutans were observed in other soils. Kaolin and gibbsite were the dominant minerals in the Leilehua and Paaloa soils, while a mixed layer mica was tha dominant mineral in the Olelo soils. The clay content of the Leilehua soil and Olelo silty olay loam does not saiiisfy the definition of the argillic horizon as proposed by the Soil Survey Staff (I960). Reasons for these Table 8. Soma Characteristics of the Argillic Horizons of Four Soils SoUs Depth Vertical Thickness Clay Fine/ Coarse Base pH SiC 2/R 203 Cutans Mayor Clay cm Distance cm Increase (0 . 2u /2u) Sat. 1: 1H2C Minerals from A (<2w) Ratio % cm % Leilehua 64 33 21 2 2.4 5.9 4.41 .505 Stress and Kaolin Illuviation Paaloa 59 18 33 14 1.6 2.5 5.05 .435 Illuviation Kaolin Olelo 99 18 39 -2 5.4 8.6 5.68 .104 Illuviation Mixed-layer ( sici) mica Olelo 51 13 13 8 0.548 3.3 4.88 .168 Illuviation Mixed-layer (sic) mica 81 differences are presented in the Results and Discussion of each soil. Field Relationships of Hawaiian Ultisols Leilehua and Faaloa Soils Both soils occur on Oahu, but the Leilehua soil occur at a lower elevation than the Faaloa soil. The former is derived from basaltic parent rock, while the latter is derived from, alluvium as well as basic igneous rock. The rainfall increases with elevation, and the present vegetation of the Leilehua soil is cultivated crops, pineapple, and sugarcane, while that of the Faaloa soil is sugar- ft w??-. cane, grass, ohia,^ and fern. These soils occur at different elevations, but the slope and s. drainage are similar. Although the Leilehua soil has a shallower and darker A horizon than the Paaloa soil, both have well- V ¥ developed subangular blooky B horizon. • i- CompaoHon of the upper horizon of the Leilehua soil by farm machinery may be one of the reasons why stress cutans were observed in this soil. Frequent wetting and drying of the soil may be another reason. Olelo Silty Clay Loam and Olelo Silty Clay The Olelo soils occur on Maui. The Olelo silty clay loam, ooour at a lower elevation than the Olelo silty clay. They are located on the same plateau of the West Maui Mountain and are 82 derived from the same parent material, olivine basalt (S C S , U SD A, 1966). The present vegetation of the Olelo silty clay loam is grass and herbs, while that of the Olelo silty clay is grass, herbs, ferns, and trees. Topography and drainage are similar. These soils appear to be at approximately the same stage of soil development. Tliey have a high concentration of oxides of aluminum, iron, and titanium, and a high bulk density in some portion of the B horizon. Except in the A horizon, the texture of these two soils are similar. Both soils also have illuviation outans. Oahu vs. Maui Soils ■r i Although the age of the parent material of the four soils is believed to be similar, the Leilehua and Paaloa soils occur in a higher rainfall The results of this investigation indicate thed the Maui soils are more weathered than the Oahu soils. Perhaps a contribution of volcanic ash to the former m.ay have led to such advanced soil development. The presence of materials with high degree of hydration, small amounts of kaolin, low 5 1 0 2 /^ 2 ^ 3 support this belief. SUMMARY AND CONCLUSION The argillio horizons ol four Hawaiian Ultisols, tha Leilehua and Faaloa soils from Oahu and the Olelo silty clay loam and Olelo silty clay from Maui were investigated. Some chemical, physical, and mineralogical properties were determined. Thin sections were prepared to study some of the characteristics of the cutans. Field relationship of these four soils were also studied. Based on the results of this investigation, the following conclusions are made: % 1. Argillio horizons have a high, clay accumulation and ' , I higher fine to coarse clay ratio than the surface hori zons but not necessarily the highest in both oases. 2. Argillio horizons have low base saturation and low S i0 2 /R 2 ^ 3 ratio but not necessarily the lowest ones in the profile. 3. Cutans formsd from kaolin and outans formed from mixed-layer mica cannot be distinguished from, each other. 4. Cutans may be transformed, but the m.eohanism is not understood. 5. Mineralogy of the cutans and the clay in the soils cme similar. However, the amounts of olay may differ. 6 . Soil pH in the argillic horizons is strongly acidic. UTERATURE CITED Brewer, R . 1956. A petrographic study ol two soils in relation to their origin and classification. Jour. Soil Sci. 7:268- 276. and Haldane, A . D. 1957. Preliminary experiments in the development of clay orientation in soils. Soil Sci. 84:301-309. 1964. Fabric and Mineral Analysis of Soils. John Wiley and Sons, Inc., N . Y . Buol, S . W. and Hole, F . D. 1959. Some characteristics of olay skin on peds in the B horizon of gray-brown pedzolic soil. Soil Sci. Soo. Amer. Proc. 23:239-241. ______and . 1961. Clay skin genesis in Wisconsin soils. Soil Sci. Soc. Amer. Proc. 25:377-379. Cady, J. G . 1965. Petrographic microscope techniques, pp. 604-631. 1a Methods of Soil Analysis. C . A . Black (ed), Amer. Soc. Agronomy, Madison, Wis. Day, P . R . 1965. Particle fraotioncdion and particle size an Fieldes, M. 1966. The nature of allophane in soils. N .Z .J . Sci. 9:599-629. Frei, E . and Cline, M. G . 1949. Profile studies of normal soils of New York: 11. Mioromorphologioal studies "of the gray-brown podzoiic-brown podzolic soil sequence. Soil Sci. 68:333-345. Fry, W. H. 1933. Petrographic methods for soil laboratories. USDA Tech. Bull. 344. Gardiner, H. C. Jr. 1967. Genesis of climosequenoe of soils in the Kohala region. Unpublished M .S . Thesis, Univ. of Hawaii, Honolulu. Grim, R . E . 1953. Clay Mineralogy. McGraw-Hill Book C o ., Inc., N. Y. 85 Hailsworth, £ . G. 1963. An examination of some factors affecting the movement of clay in an artificial soil. Jour. Soil Sci. 14:361-371. - Hendricks, S. B ., Cady, J. G., and Flach, K. W. 1962. Petrographic studies of mineral translocation in soils. Trans. Joint Meeting CommT IV and V . Intern. Soc. Soil S c i., New Zealand: 34-38. Jackson, M. L . 1956. Soil Chemical Analysis, Advanced Course. Published by the author. Dept, of'Soil S c i., Univ. of W is., Madison. Juang, T . C. and Uehara, G. 1968. Mica genesis in Hawaiian soils. Soil I Sci.« Soc. Amer. Proo. 32:31-35. Kilmer, V. J. and Alexander, L. T. 1949. Methods of making mechanical analysis of soils. Soil Sci. Soc. Amer. Proc. 68:15-24. Loganathan, P . 1967. The properties and the genesis of four middle altitude Dystrandepts from Mauna Kea, Hawaii. Unpublished M .S . thesis, Univ. of Hawaii, Honolulu. McCaleb, S . B . 1954. Profile studies of normal soils of Now York. IV. Mineral properties of gray-brown podzolic- brown podzolio soil sequence. Soil Sci. 77:319-333. Minashina, N. G. 1958. Optically oriented day. Soviet Soil Sci. (Translated 1959) 4:425-429. PeeeK, M-, Alexander, L. T. a[. 1947- Methods of soil analysis for soil-fertility investigations. US DA Cir. 757. Sherman, G. D. 1949. Factor influencing the development of lateritic and laterite soils in the Hawaiian Islands. Pacific Sci. 3:307-314. Soil Conservation Service, US DA. 1966. (Profile descriptions: Leilehua, Padoa, and Olelo series.) National Cooperative Soil Survey. U . S . A . Soil Survey Staff. I960. Soil Classification, A Comprehensive Systerri, 7th Approximation. U. S . Governmient Printing Office, Wash., D. C . 86 Soil Survey Staff. 1967. Supplement to Soil Classification System (7th Approximation). iS C S , U SD A, Wash., D. C. Stephen, 1. 1967. Clay orientation, pp. 342-349. in Selected Papers in Soil Formation and Classification. J. V . Drew (ed), Soil Sci. Soc. Amer. Special Publication Series No. 1. ' Stoop, W. A. 1967. Genesis of Naiwa and related soils. Unpublished research report. Dept, of Agronomy & Soil Science, Univ. of Hawaii, Honolulu. Suhr, N. H. and Ingamells, C . O. 1966. Solution Technique for Analysis of Silicates. Ancd. Chem. 38:730-734. Swindale, L. D. 1966. Classification, genesis, and morphology of the soils of Oahu. Unpublished manuscript. Dept, of Agronomy & Soil Science, Univ. of Hawaii, Honolulu. Thorp, J ., Cady, J. G ., and Gabble, £ . E. 1959. Genesis of Miami silt loam. Soil Sci. Soc. Amer. Proc. 23:65- 70. Uehara, G., Flach, K. W., and Sherman, G. D. 1962. Genesis and micro morphology of certedn soil structural types in Hawaiian latosol and their significance to agricultural practice. Trans. Joint Meeting Comm. IV and V . Intern. Soc. Soil Sci., New Zealand, pp. 264-269* Van Olphen, H. 1951. Rheological phenomena of clay soils in connection with the charge distribution on the micells. Feraday Soe. Diso. 11:82-84. Williamson, W. O . 1947. The fabric, water-distribution, drying-shrinkage, and porosity of some shaped disc of clay. Amer. Jour. Sci. 245:645-662.