DIVISION S-5—SOIL GENESIS,MORPHOLOGY, AND CLASSIFICATION

The Characteristics, Classification and Genesis of Some Tropical Spodosols1

K. H. TAN, H. F. PERKINS, AND R. A. McCREERY2

ABSTRACTMorphological, chemical, and mineralogical properties are

presented for three tropical spodosols. Based on the occurrencein different climatic zones, the soils were distinguished as low-land podzols and mountain or highland podzols.

The lowland podzol had a low organic matter content, aweakly developed Bh and a well developed argillic horizonbelow the spodic horizon. The name Humic Alfic Tropoferrodis proposed for this type of podzol. The A horizon containedpredominantly amorphous clay, but the B horizon had appre-ciable amounts of kaolinite.

Highland podzol I was high in organic matter, had a welldeveloped Bh, but lacked an argillic horizon, and was classi-fied as a Typic Tropohumod. Highland podzol II had similarproperties, but was relatively young in degree of developmentand was classified as an Entic Tropohumod. The clay fractionof the humods was characterized by high amounts of amorph-ous clay, probably allophane. Kaolinite was not detected.

Additional Key Words for Indexing: lowland podzol, high-land podzol, mountain podzol, Tropoferrod, Tropohumod,allophane.

THE SPODOSOLS, better known as podzols in the Canadianand European literature, are of wide occurrence in the

cool and temperate regions of the world. Considerable atten-tion has been devoted in the past to studies of podzols (8,12), and in recent years the concept of podzols has beenreviewed and reevaluated by many investigators (3, 4, 5,13, 14, 15, 19).

Recent investigations indicate that these soils are notlimited to cooler climatic regions, but occur also in tropi-cal zones. Tropical podzols have been described in the Ama-zon basin of Brazil (9), in Africa (18), in Ceylon (7), andin East Malaysia, Serawak (1).

Spodosols have been found in Indonesia (11, 17) also,but they have not been surveyed and mapped. The totalarea occupied by podzols in this country is still unknown,although in some areas they may constitute relatively impor-tant agricultural and forest soils. More information concern-ing results of studies on the genesis, characteristics, andclassification of these soils appears desirable.

It is the purpose of this paper to discuss the occurrenceof tropical podzols in Indonesia with attention to theirgenesis, chemical, and mineralogical properties and possi-ble classification in the Comprehensive System.

1 Journal Series Paper no. 684, Univ. of Georgia College ofAgr. Exp. Sta., College Station, Athens, Ga. Received Dec. 5,1969. Approved May 20, 1970.2 Asst. Professor, Professor, and Associate Professor, respective-ly, Dept. of Agronomy, Univ. of Georgia, Athens, Ga. 30601.

CLIMATE

The podzols in Indonesia appear to be restricted to themountainous regions (1,500-2,000 m above sea level) andto the lowland areas (0-25 m above sea level). The moun-tains, where podzols occur, are characterized by a warmtemperature dry summer climate, whereas the lowland areashave a humid tropical climate. Detailed climatic informa-tion of the specific areas is provided in Table 1. Based ontheir distinctly separate occurrence, the soils will be dis-tinguished in the following discussion as: (i) the highlandor mountain podzols, and (ii) the lowland podzol.

PARENT MATERIAL

The mountain podzols were derived from residuum ofliparitic or rhyolitic tuff under a tropical mountain rain-forest vegetation. They have not been found on the lessacidic parent material. Residuum of andesitodacitic tuffusually resulted in the formation of andosols. At lowerelevation the podzols graded into brown podzolic or redyellow podzolic soils (17).

The lowland podzol originated from sand deposits in theMahakam River delta under heath vegetation. The finertextured and more productive material at higher elevationswas usually under tropical rainforest and yielded red yellowpodzolic or lateritic soils. A similar condition was reportedby Klinge (9), who described podzols in the Amazon basinof Brazil being developed also on the poor coarse sandymaterial bearing heath vegetation. Loamy sediments wereunder a tropical rainforest and gave rise to the develop-ment of "brown soils".

SOILS AND ANALYTICAL METHODS

MorphologyThe soils investigated were lowland podzols of Kalimantan

(Borneo), and highland or mountain podzols of Sumatra. For

Table 1—Climatic types of podzol regions according to thenearest weather station

LocationNorth SumatraDolok SanggulSl-Borong!

BangkaMuntokPangkalpinang

East KalimantanSamarindaTenggarong

RainfallAltitude < 60 mm > 100 cm

m Months

1,451 3.5 6.11,320 1.4 9.0

Sea level 1. 0 9.720 1.3 8.6

Sea level 0.7 9. 4Sea level 1. 2 8. 9

Type of climateKoppen*

CsiCshi

AfaAfa

AfaAfa

S/Ff

AB

AB

AA

Mean annualrainfall

mm

1,7142,088

2,8632,324

1,9351,862

775

Mean temperatures: A*=coldest month > 18C; C=between 18C and-3C; a=warmestmonth > 22C; h«annually > 18C; i=dtfference between coldest and warmest month< 5C; f=humld; s=summer dry.Schmldt and Ferguson (Berlage, 1949) divided climate Into 8 classes from the formulaavg. no. dry months/ avg. no. wet months x 100%; Class A=0-14 3%; Class B=14 3-33.3%.

776 SOIL SCI. SOC. AMER. PROC., VOL. 34, 1970

morphological details the following three descriptions areoffered:

The lowland podzol of Tandjung Bangko (Samarinda, Kali-mantan) occurred on a rolling plain in the Mahakam Riverdelta at approximately 10 m above sea level with A (coldestmonth > 18C), f (humid), a (warmest month > 22C) climate(Table 1). The vegetation was heath and consisted of Tris-tania, Callophyllum, and Vatica species. Parent material con-sisted of residuum of alluvial sand. Soil colors given belowrefer to field-wet Munsell color notation.

Depth,Horizon cm Description

Al 0- 9 Brown (7.5YR 4/2) loamy sand, strong finegranular, very friable, many roots and fungimycelium, extremely acid, abrupt smoothboundary.

A21 9- 21 Reddish grey (SYR 5/2) sand, single grained,loose, white spots, few roots, medium acid,gradual smooth boundary.

A22 21- 38 Light grey (10YR 7/2) sand, single grained,loose, pinkish grey spots, few roots, mediumacid, gradual smooth boundary.

A23 38- 43 Light grey (10YR 7/2) loamy sand, singlegrained, pinkish grey spots, very few roots,slightly acid, abrupt smooth boundary.

Bh 43- 59 Reddish brown (SYR 4/3) loamy sand,compact, slightly firm, no roots, slightlyacid, abrupt smooth boundary.

Btir 59-103 Very pale brown (10YR 7/4) loamy sand,compact, firm, no roots, neutral, gradualsmooth boundary.

B3 103 + Very pale brown (10YR 7/4) loamy sand,single grained, friable, reddish brown spots,no roots, neutral.

Highland Podzol I occurred on Mount Sibartong (Tapanuli,north Sumatra) at 1,600 m above sea level, with C (temp,between 18 and —3C), s (summer dry), h (humid), i (differ-ence between coldest and warmest month < 5C) climate(Table 1). The vegetation was primeval tropical mountain rain-forest. Parent material consisted of residuum of liparitic tuff(17, 19).

Depth,Horizon cm Description

Ol 0-20 Dark reddish brown (SYR 3/3) partly de-composed raw humus, extremely acid.

A2 20-30 Very dark gray (SYR 3/1) sandy loam,weak fine crumb, very friable, many roots,very strongly acid, abrupt smooth boundary.

Bh 30-50 Very dark gray brown (SYR 3/2) sandyloam, moderately thick platy to subangularblocky, firm, dark reddish gray (5YR 4/2)mottling, few roots, strongly acid, abruptsmooth boundary.

Bir 50-55 Reddish yellow (7.5YR 6/8) loam, irregu-lar subangular blocky to platy, very firm,no roots, medium acid, gradual smoothboundary.

C 55 + Pale yellow (2.5YR 7/4) sandy loam, mas-sive, friable, yellowish red (SYR 5/8) andyellow (10YR 7/8) mottlings, few pumiceremnants, medium acid.

Highland podzol II occurred at Haririanpintu (Tapanuli,north Sumatra) at 1,800 m above sea level with Cshi climate(see Table 1). The vegetation was old secondary tropical moun-tain rainforest. Parent material consisted of residuum ofliparitic tuff.

Depth,Horizon cm Description

Al 0-10 Very dark brown (10YR 2/2), silt loam, weakmedium granular, very friable, many roots,extremely acid, abrupt smooth boundary.

A2 10-20 Dark gray (10YR 4/1) silt loam, weakmedium granular, firm, extremely acid,abrupt smooth boundary.

Bl 20-40 Dark yellowish brown (10YR 3/4) siltloam, moderately subangular blocky to pris-matic, slightly firm, yellowish red (SYR5/8) mottlings, strongly acid, abrupt smoothboundary.

B2 40-60 Red (2.5YR 4/6) silt loam, moderate coarsesubangular blocky, compact and firm, darkred (2.5YR 3/6) mottlings, strongly acid,gradual smooth boundary.

C 60 + Strong brown (7.5YR 5/6) fine sandy loam,very firm, pinkish gray to pink (7.SYR 7/3)and dark reddish brown (5YR 3/4) mot-tlings.

It is probably necessary to state, that the Bl horizon was avery young developed Bh horizon and the symbol Bl wasselected in this respect to indicate this condition.

Analytical MethodsThe analyses were made on soil samples of < 2 mm. Particle

size determination was conducted with the pipette method (17).Prior to mechanical analysis, the organic matter was destroyedwith 30 ml of 30% H2O2. Dispersion was with 0.0027V HC1.For differential thermal analysis DTA and X-ray analysis theclay obtained was dialyzed in seamless cellulose tubes againstdistilled water. Soil pH was measured in a soil-water (1:2.5)suspension using the glass electrode. Organic C was analyzedwith a modified Walkley-Black method employing solidK2Cr2O7 (6). Nitrogen was determined with the standardKjeldahl procedure (6). Total chemical analysis of clay wasdone by fusing clay samples with solid Na2CO3 (6, 17). TotalSiO2 was determined by volatilization weight loss with HF,A12O3 by titration with HC1 using thymolphthaleine and ali-zarine yellow mixture (2:1) as indicator, and Fe2O3 by EDTAtitration with sulfosalicylic acid as indicator. X-ray analysiswas conducted with clay samples, using an X-ray tube withcopper anode and 0.5-mm collimator. Differential thermal anal-ysis (D.T.A.) was carried out with H2O2 treated clay fractions,employing a manually operated instrument with a heating rateof 0.150 mv/minute. This corresponds to an average tempera-ture of 20 C/minute (16). Due to the development of verylarge low-temperature endothermic peaks, the analysis wascarried out mostly with samples diluted (1:5 or 1:2) withinert reference material.

RESULTS AND DISCUSSIONLowland Podzol

The profile description and the results of the physico-chemical analysis (Table 2) clearly indicated the phenom-enon of podzolization, characterized by the formation ofalbic and spodic horizons. An argillic horizon has also beenformed in the Bir horizon. The increase of clay contentin the Bir horizon meets the 3% criterion and clay skinshave been observed on the ped surfaces. The SiO2/R2O3,SiO2/Al2O3, SiO2/Fe2O3 molar ratios, which increased fromthe Al to A23 horizons, indicate the dissolution and trans-location of Fe and Al with depth in the profile, which gaverise to the formation of an albic horizon. The sharp increasein organic C content and decrease of SiO2/R2O3, SiO2/A12O3, and SiO2/Fe2O3 molar ratios from the A to Bhorizons were evidences for the accumulation of organicmatter, Al, and Fe, characteristic of spodic horizons. Theabrupt increase of the Al2O3/Fe2O3 ratio from the A23to the Bh horizon, on the other hand, indicated that Alwas accumulated in the Bh horizon. The trend in clay con-

TAN ET AL.: CHARACTERISTICS, CLASSIFICATION & GENESIS OF TROPICAL SPODOSOLS 777

Table 2—Physico-chemical composition of tropical podzols

Chem.

ProfileCla

%iy

PHC%

N%

CN

SIO;

K«l

comp. of claySiOj

Mfl,SiO,

F^Oj

AljO,FejO,

Kalimantan Lowland PodzolAlA21A22A23BhBtirB3

5.1.0.2.3.

13.11.

01810556180706

4.35.75.66.46.26.66.8

8.882.000.381.003.441.081.06

0.400.110.020.050.180.060.05

22.118.419.922.219.318.623.6

1.192.263.023.731.691.341.17

1.2.3.4.1.1.1.

36805749897035

9.1911.8119.5122.2216.436.288.82

6.764.225.464.958.693.686.52

Sumatran Highland Podzol IOlA2BhBlrC

._8.

10.10.10.

._24639

3.44.95.35.75.8

47.87.38

11.61.930.19

2.140.330.310.05tr

22.322.237.342.9--

_2.450.541.071.21

2.0.1.1.

_66562130

...32.314.8

8.8417.9

__12.226.5

7.3213.8

Sumatran Highland Podzol HAlA2BlB2

9.13.12.1.

15478

4.34.35.15.4

39.710.210.94.7

2.70.530.600.63

14.519.217.9

7.46

15.097.341.300.87

33.25.2,1.

676283

28.235.95.23.4

0.691.401.981.89

tents from A to B horizons expresses the common trendencountered in many podzols (12), and is self-explanatorywith regard to the formation of an argillic horizon in theBir horizon.

Results of D.T.A. analyses revealed that the clay composi-tion changed with depth (Fig. 1). Thermograms for samplesfrom the surface horizon indicate the presence of eitherhigh amounts of amorphous clay or organic matter. How-ever, the organic matter content in the clay fraction aschecked with the chromic acid method of Walkley-Black (6)was negligible, and according to Mackenzie (10) strong exo-thermic peaks between 200-500C could also be caused byamorphous Fe-oxide compounds. In samples from the Bhorizons, the thermograms had distinct endothermals at100-200C and at 500-550C, respectively, and weak to veryweak exothermals at 900-1,OOOC. These peaks were absentfrom samples of the surface horizon. The medium endo-thermic peak at 500-550C suggests the presence of kaoli-nite, while the weak exothermal at 900-1,OOOC probablyindicates the presence of 2:1 type clay minerals or weakcrystallization due to interstratification with amorphousmaterials. X-ray analysis supported these results, by showing

V200 400 600 800 1000°

CFig. 1—D. T. A. thermograms of organic matter free clay

fractions in Kalimantan lowland podzol (diluted 1:5 withinert sample). (I) Al horizon; (2) A21; (3) Bh; (4) Bir;(5) B3.

Table 3—Total chemical composition of clay (in % )

Profile SiO2 Al,0, Fe,0, CaO MgO K2O

Lowland PodzolAlA21A22A23BhBtir

A2BhBirC

Al

24.740.449.365.935.243.5

28.312.726.432.7

27.29

30.824.523.425.931.643.3

18.138.836.243.0

30.27

7.29.16.77.95.7

18.4

Highland Podzol I2.352.307.774.89Andosol9.76

tr.0.33tr.

2.51.30.65

(18)nd—----

2.65

0.190.100.080.060.200.09

nd_-----

nd

0.230.340.150.070.541.06

nd—-_--

0.864

very diffused patterns for the clay fraction of the surfacesoil, indicative of amorphous material. Medium weak 7.2-and 4.3-A reflections were obtained for the clay fractionsof the B horizons, indicating the presence of kaolinite. Noevidence was obtained to support the presence of 2:1 lat-tice minerals since neither 14- nor 17-A reflections couldbe detected.

A similar condition was reported by Brydon, Kodama,and Ross (3) , who noticed a difference in mineralogicalcomposition between A and B horizons of Canadian pod-zols, with an apparent absence of kaolinite in the Aehorizon.

Results of total chemical analysis of the lowland podzolclay compared with those of allophanic clay of some ando-sols showed that the clay in the surface soil of the lowlandpodzol had an almost similar composition as that of allo-phane (Table 3).

Highland or Mountain Podzol

In the highland podzol, the process of podzolizationwas somewhat difficult to follow due to the absence ofseveral A horizons in the profile. However, an abruptdecrease in SiO2/R2O3, SiO2/Al2O3, and SiO2/Fe2O3molar ratios from A to B horizons could still be foundwhich indicated the development of albic and spodic hori-zons. The clay contents in these profiles were somewhatmore uniform from A to B horizons than in the lowlandpodzol.

The trend in thermal reactions (Fig. 2 and 3) were againindicative of the presence of high amounts of amorphousclay, especially in the A horizons. The latter showed somesimilarities with clay of the surface horizon of the lowlandpodzol. In the B horizons, the thermograms of the clay frac-tions possessed a weak exothermic peak at 900-1,OOOC.X-ray analysis revealed very diffused bands for both the Aand B horizons, which also supports the presence of amor-phous materials.

CLASSIFICATION

The following classification and correlation of theseSpodosols should be viewed at as very tentative in nature,since not all of the criteria proposed for recognition ofSpodosols in the new Comprehensive System have beenapplied.

Based on criteria of the Comprehensive System (13, 14)

778 SOIL SCI. SOC. AMER. PROC., VOL. 34, 1970

200 400

Fig. 2—D. T. A. thermograms of organic matter free clayfractions in highland podzol I (diluted 1:2 with inert sample).(1) A2 horizon; (2) Bh; (3) Bir; (4) C.

classification of tropical spodosols is incomplete. The low-land podzol meets the temperature requirements of theTropoferrods and has characteristics of the Ferrods. Theincrease in pH with depth from 4.3 to 6.8 indicates anincrease in base saturation within the control section toabove 35%, therefore it is intergrading toward an Alfisol.At the same time it has some properties of the Humods.In view of the characteristics of this soil including theweakly developed Bh horizon and the presence of an argil-lie horizon below the spodic horizon, a classification ofHumic Alfic Tropoferrods is proposed. This division is notpresent in the Comprehensive System, but appears to de-scribe this podzol better than other terms of the system.

The highland podzol I has a well developed Bh andappears to meet requirements of the Typic Tropohumods.Although the Bir horizon is very firm, it is not cemented.Morphological studies of podzol II from the Sumatra high-lands indicate the presence of a Bh horizon. This horizonis not well defined if only chemical data are used. TotalC is comparable for the A2 and Bh horizons but the markeddecrease in SiO2/Al2O3 in the Bh as compared with theA2 indicates high Al. General properties of the two high-land podzols are similar except podzol II is not as highlydeveloped and has more than 0.58% C in the matrix of thefirst 30 cm below the top of the spodic horizon. Theproposed classification of this soil is an Entic Tropohumod.

CONCLUSIONSDifferences existed between three tropical Spodosols of

Indonesia. Those restricted to the mountain or highlandareas of Sumatra were high in organic carbon and had ahigh content of amorphous clay, probably allophanic. Theorganic matter of one highly developed soil was charac-terized by a lower C/N ratio in the A than that of theB horizons. The proposed classification of the highly devel-oped mountain soil is a Typic Tropohumod. The othermountain soil having weakly defined horizon characteristicsis classified as an Entic Tropohumod.

The Spodosol which occurred near sea level in Kaliman-

200 400 600 800 1000°C

Fig. 3-D. T. A. thermograms of clay fractions in highlandpodzol II and III (diluted 1:5 with inert sample). ( I ) High-land podzol II/A1 horizon, (2) B2; (3) Highland podzolIll/Al horizon; (4) Bl; this profile closely resembled thedescription of highland podzol II and was not included inthe discussion.

tan had a lower organic carbon content and containedconsiderable kaolinite in addition to amorphous compo-nents. No marked difference was found in the C/N ratiobut pH increased markedly with depth. It contained a welldeveloped argillic horizon with a high Fe content. Theproposed classification of this soil is a Humic Alfic Tropo-ferrod.

GERSPER & HOLOWAYCHUK: STEMFLOW WATER & MIAMI SOIL UNDER A BEECH TREE i. 779