CHARACTERIZATION, CLASSIFICATION AND USE INTERPRETATIONS OF A SEQUENCE OF SOILS ALONG THE TRANSAMAZON HIGHWAY, OF BRAZIL BETWEEN THE XINGU AND JACARE RIVERS BY Antonio M. Pires-Filho A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MAST ER OF SC IENCE Department of Crop and Soil Sciences 1978 ABSTRACT CHARACTERIZATION, CLASSIFICATION AND USE INTERPRETATIONS OF A SEQUENCE OF SOILS ALONG THE TRANSAMAZON HIGHWAY, OF BRAZIL, BETWEEN THE XINGU AND JACARE RIVERS BY Antonio M. Pires-Filho A sequence of four profiles (numbered from highest to lowest) was studied. The soils were relatively shallow, and physical tests show that the two better drained profiles have plinthite in their subsoil horizons. Chemical analyses show profiles 2 and 3 have high Al+++ saturation. All soils studied have low exchange capacity and percent base saturation.. Kaolinite comprised more than 95 percent of the total clay fraction. Aluminum saturation seems to have more influence on x-ray diffraction intensity than soluble iron oxides in the samples. Pretreatments of clay by dithionite and oxalate increased the kaolinite diffraction peaks in all subsurface samples; but, dithionite was most effective. Oxalate treatments were not effective on surface samples. Antonio M. Pires-Filho Taxonomically, these soils fit into Plinthic Paleudults (Profile 1), Plinthudults (Profile 2), and Aquic Paleudults (Profiles 3 and 4). The two more poorly drained soils (Profiles 3 and 4) had severe limitation for all purposes, but the two better drained (Profiles 1 and 2) had less limitations for some purposes. AC KNOWL EDGMENT S The author wishes to thank his major professor Dr. E. P. Whiteside for the patient guidance and assistance throughout the course of his study and preparation of the manuscript. Gratitude is due to Dr. Marcelo N. Camargo for his initial guidance at the beginning of this work, in Brazil, and some useful suggestions. He wishes to express his sincere gratitude to Dr. Raphael David dos Santos who described and collected some supplementary soil samples, and pnovided the author with many references. His appreciation is extended to Drs. Luiz Gonzaga de Oliveira Carvalho and Reinaldo Potter who helped in the field studies. He also wishes to thank Dr. Franklin dos Santos Antunes for making mineralogical analyses; and the labora— tory of SNLCS/EMBRAPA for other basic analyses. Acknowledgments are also due to members of the guidance committee, Drs. M. M. Mortland, J. C. Shickluna, and D. H. Brunnschweiler. ii Finally, the author deeply appreciates the financial support of the Empresa Brasileira de Pesquisa Agropecuaria-EMBRAPA, which made this study possible. iii TABLE OF CONTENTS Page LIST OF TABLES O C O O O O C O C O O I 0 Vi LIST OF FIGURES. O O O O O O O O O O O O Viii Chapter I. INTRODUCTION . . . . . . . . . . . 1 II. LITERATURE REVIEW. . . . . . . . . . 3 Historic . . . . . . . . . . . . 3 The Soils. . . . . . . . . . . . 5 Upper Amazon River Basin . . . . . . 5 Middle and Lower Amazon River Basin . . 6 Plinthite. . . . . . . . . . . 8 Measurement and Removal of Iron Oxides . . 14 Classification . . . . . . . . . . 15 III. MATERIALS AND METHODS . . . . . . . . 19 Soil Formation Factors . . . . . . . 19 Field Studies . . . . . . . . . . 20 Profile 1 . . . . . . . . . . . 23 Profile 2 . . . . . . . . . . . 26 Profile 3 . . . . . . . . . . . 28 Profile 4 . . . . . . . . . . . 30 Laboratory Studies. . . . . . . . . 31 Physical Analyses . . . . . . . . 31 Chemical Analyses . . . . . . . 32 Mineralogical Analyses. . . . . . 36 Laboratory and Field Methods for Plinthite Identification . . . . . 41 iv Chapter Page IV. RESULTS AND DISCUSSIONS . . . . . . . . 42 Physical PrOperties. . . . . . . . . 42 Chemical PrOperties. . . . . . . . . 44 Mineralogical Properties . . . . . . . 48 Plinthite Characterization . . . . . 68 Classification of These Soils . . . . . 69 Current Land Uses . . . . . . . . . 73 Interpretations for Engineering Purposes. . 74 Limitation of Soils for Town and Country. . 80 Soil Survey Interpretation in Brazil (for Reconnaissance Surveys) . . . . . 85 V. CONCLUSIONS . . . . . . . . . . . . 93 LITERATURE CITED 0 O O O O O O O O O O O 96 LIST OF TABLES Table Page 1. Level of Plinthite in Soil Taxonomy . . . . 18 2. Climatic Data According to Thornthwaite (1955) Altamira, Para, Brazil, Period 1931-1967. . 21 3. Some Physical PrOperties of the Soils Studies. 43 4. Some Chemical Properties (pH, Exchangeable Cations, and Available P) of the Soils studied. 0 O O O O I 0 O O O O O 45 5. Some Other Chemical Properties (Carbon, Nitrogen and Acid Soluble Components) of the Soils Stud ied O O O O O O O O O O O I O 4 7 6. Mineralogical Analyses, Coarse Fragments . . 49 7. Mineralogical Analyses, Sands . . . . . . 55 8. Clay Contents, Selected Soil Analyses from Tables 2 to 4 and Heights of Kaolinite Diffraction Peaks of Clay Fraction With or Without Pretreatments . . . . . . . . 65 9. Distinction Between Red Subsoil Mottles and Plinthite (in Laboratory). . . . . . . 70 10. Classification of the Soils According to the Systems Used in Brazil, FAD/UNESCO, and U C S O Taxonomy 0 O O I O O O O O O 7 1 11. Estimated Soil PrOperties Significant to . Engineering . . . . . . . . . . . 75 12. Engineering Interpretations. . . . . . . 78 vi Table Page 13. Limitations of Soils for Town and Country Planning . . . . . . . . . . . . 81 14. Guide Table for Determining Suitability Class of Soils Under Both Primitive and Developed Management in Brazil . . . . . . . . 87 15. Estimated Degree and Major Kinds of Limitations Affecting Agricultural Uses by Management Systems, of the Soils in This Study . . . 90 vii LIST OF F IGURES Figure Page 1. Legal Amazon Region Showing Transamazon Highway and Interval Studied ++ . . . . . . . 4 2. Hydrological Balance Registered at the Metereological Station at Altamira State of Para, Brazil, for the period 1931-1967 . . 22 3.. Scaled Diagrams of the Profiles Studies with Altitudes in Meters . . . . . . . . 24 4. x-ray Tracings of Total Clay of Selected Soil Horizons O O O O O O O O O O O O 67 viii I. INTRODUCTION During the soil survey process along the Transamazon Highway, of Brazil, soils with plinthite have been mapped on several parts of the highway (Santos et al., 1973). During the rainy season (January-July), these soil types have caused many problems to the traffic, because of the high water table in the soils of the lower parts and lateral movement of water in the soils of the higher parts of the slopes. Some researchers have studied plinthic soils in Brazil. Nevertheless, they remain not well characterized in the soil survey of the transamazon highway, because some, by field observation of the profile recognize them as a plinthite feature, but some others do not. Therefore more study is necessary in order to clarify this problem. There is much controversy concerning the characterization of these soils in the field and by laboratory analyses. The present study started in 1973 and was sponsored by Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq). However, it stopped before completion because CNPq changed its policy. The main objective of this study is description, characterization, classification and interpretation, plus comparative evaluation among the profiles studied, in order to see how they vary. II . LITERATURE REVIEW Historic In 1965, the Ministry of Agriculture of Brazil, made an agreement with United States Agency for Inter- national Development (USAID) to make a Schematic (explora- tory in some areas) Soil Survey of the North, Middle North and Central-West Regions of Brazil (Brailian Amazon region is included) which comprises approximately 6,000,000 sq km (Camargo, Freitas, et al., 1975). Legal Amazon Region showing Transamazon Highway and interval studied 77, is showed in Figure 1. Since Marbut and Manifold (1926), chiefly after the second Wbrld war, and creation of the SPVEA (Superinten- déncia do Plano de Valorizacao Econ6mica da AmazOnia), new data on the Brazilian Amazon soils have been gathered. The Amazon region in Brazil is part of the middle and lower parts of the Amazon River basin. Some other soil researchers have done soil studies in the area, such as: Guerra (1952); Day (1958, 1959, 1961); Carneiro (1955); FAQ by Sombroek, and Sampaio (1962): Sombroek (1962a, 1962b); and IPEAN-Seccao de Solos by .++ pmficsum HmSnmucH can 133:on sonEsmcmua mewsonm sawmom cause—4 Hams In anasmwm a“Humsumuaoaomlnmaaamuumnsuaom aa>ovoa 183:3: Hudsonaaufleomunfiflsousageum 3.63s Apoeuaum Hu>uoucuv huasmwm couaaumsduanIOpupsunm onooua «cacoudadnsdue uw>ooom mn3nmwm sonoaumscuauIMOHcONdssmcuua aw>ovom musmwm lilfifiwn. [m ON. 0”” O°90% of the iron associated with the sodium dispersed clay size fraction but sampled horizons with plinthite often have more than half of the iron associated with the sodium dispersed sand and silt size fractions. An ”active iron" ratio, oxalate extractable/citrate- bicarbonate-dithionite extracable iron, is a possible indicator of plinthite. Seventy percent of the samples called plinthite have "active iron” ratios <0.05 indicating that <5% of the iron is amorphous” (Daugherty, 1975). McKeague and Day (1966), working with Canadian soils using dithionite and oxalate procedures extractable Fe and A1 as aids in differentiating various classes of soils, concluded: l. The oxalate extraction dissolved much of the iron and aluminum from the amorphous materials but very little from crystalline oxides, whereas the dithionite extraction dissolved a large proportion of the crystalline iron oxides as well as much of the amorphous materials. 2. Both oxalate and dithionite-extractable Fe and Al values are useful in studies of soil genesis and classification. The oxalate values give an approxi- mation of the degree of accumulation of amorphous products of recent weathering in the horizons of soils formed from materials varying widely in texture, color, pH, organic matter, and total iron oxides. Classification The types of soil in this study have precipitate many discussions (disagreements) among soil surveyers (mappers) and soil classifiers in Brazil and all over the world. Some studies of correlation and classification done by Jacomine, Camargo et a1. (1972) have proposed "if the 16 profile has plinthite as deep as 75 cm and the drainage is not more restricted than imperfectly, the soil should be considered as Red Yellow Podzolic plinthic." Jacomine, Camargo et a1. (1973) proposed a differ- entiation between: "Red Yellow Podzolic plinthic and Ground Water Laterite soils. Tentatively it was established that when plinthite is just below the A horizon, the soil should be called Ground Water Laterite. When the upper part of the B horizon, free of plinthite, is 'thick' or a whole B horizon is free of plinthite, but the plinthite is present in the C horizon, the criteria designate the soil with 'substrata plinthic' e.g. Red Yellow Podzolic . . . sub- strata plinthic. If the upper part of the textural B, solonetzic B, latosolic B or incipient (B), is free of plinthite but the bottom part has plinthite, the best way is to classify the soil according to type of the B horizon and add the qualitative term plinthic, e.g. Red Yellow Podzolic plinthic. The same criteria is used for AC soils such as Alluvium and Regosols. A soil taxonomy is a reflection of the current knowledge of soils and their genesis. A multiple cate- gorical system in the United States is based on a hierarchy of chosen soil prOperties. The level of generalization of the chosen property is used in forming classes. Plinthite is presently used at two levels of generalizations: the great group, where a continuous phase or greater than 50 percent of the soil volume, within 1.25 m of the surface, 17 is occupied by plinthite; and the subgroup with plinthite volume range of 5-50 percent, within different depths. There are 185 great groups in this multiple category system, of which 9 use the presence of plinthite as a major property, for differentiation and only one has an established series in the United States, Puerto Rico or the Virgin Islands (Soil Survey Staff, 1975). There are presently 23 subgroups with plinthite and 20 have recognized series in the United States, Puerto Rico or the Virgin Islands. Table 1 summarizes the use of plinthite in soil taxonomy (Soil Survey Staff, 1975). Daniels, Perkins et al. (in press), have suggested that slight adjustments in the amount of plinthite required for recognizing a plinthic soil must be made according to the form of plinthite present. For example: Ten percent or more discontinuous phase platy plinthite and its underlying reticulately mottled horizons will perch water in a humid climate for significant periods each year. The 5 percent plinthite by volume that is diagnostic for plinthic subgroups in Soil Taxonomy (Soil Survey Staff, 1975) is, on the basis of available data (Daniels, Gamble, et al., in press), too low to be recognizable for soils with platy plinthite. Neither the plinthite nor the underlying reticulately mottled horizons appear to have a signifi- cant effect on water movement, but its presence apparently does indicate that the underlying reticu- lately mottled horizons are restricting the downward flow of water. The 5 percent plinthite criterion seems appropriate for soils having nodular plinthite. Nodular and platy plinthite can occur in the same pedon, but one usually is clearly dominant and the classification should be based on the dominant condition. 18 Table 1.--Leve1 of Plinthite in Soil Taxonomy. r...~—~_-_=.. -—‘r—--'--—?-=-- .-__‘ _ ____S-... _.-._ Ordera Subordera Great Groupb SubgroupC Alfisols Aqualfs Plinthaqualfs* No subgroup or series in U.S. Udalfs Paleudalfs Grossarenic Plinthic Paleudalfs Plinthaquic Paleudalfs Plinthic Paleudalfs Ustalfs Plinthustalfs* No subgroup or series in U.S. Xeralfs Plinthoxeralfs* No subgroup or series in U.S. Inceptisols Aquepts Plinthaquepts* No subgroup or series in U.S. Tropaquepts Plinthic Tropaquepts Oxisols Aquox Plinthaquox* No subgroup or series in U.S. Orthox Acrorthox Plinthic Acrorthoxd Haplorthox Plinthic Haplorthoxe Utisols Aquults Plinthaquults' Oxic Plinthaquults Fragiaquults Plinthic Fragiaquults Plinthudic Fragiaquults Paleaquults Arenic Plinthic Paleaquults Plinthic Paleaquults Tropaquults Plinthic Tropaquults Humults Plinthohumults‘ No subgroup or series in U.S. Palehumults Plinthic Palehumults Udults Plinthudults‘ No subgroup or series in U.S. Fragiudults Plinthaquic Fragiudults Plinthic Fragiudults Paleudults Arenic Plintaquic Paleudults Arenic Plinthic Paleudults Grossarenic Plinthic Paleudults Plinthaquic Paleudults Plinthic Paleudults Tropudults Plinthaquic Tropudults Plinthic Tropudults Ustults P11nthustults' No subgroup or series in U.S. uaplustults ._—.._. .. Plinthic Haplustults 'No series have been established in the United States, Puerto Rico or the Virgin Islands (Soil Survey Staff, 1976). aPlinthite b CPlinthite d ePlinthite Plinthite Plinthite is not a differentiating criterion at the order or suborder level. must be continuous or >50% of the volume within 1.25 m of the surface. is noncontinuous and 5-50% of the volume within 1.5 m of the surface. is noncontinuous and 5—50% of the volume within 1.0 m of the surface. is noncontinuous and 5-50% of the volume with 1.25 m of the surface. III. MATERIALS AND METHODS Soil Formation Factors There are very few detailed studies available about soil formation (geology, climate, vegetation, and so on) along the Transamazon Highway that has only recently been built. According to "Esbéco geologico preliminar and Perfil geologico preliminar by Campanhia de Recursos Minerais (C.P.R.M.), in Falesi (1972), this sequence of soils are related to undifferentiated Pre-Cambrian gneiss and migma- tite—granites. The parent material of these soils are pro- vided by the decomposition of these materials, followed by some local reworking of materials, except for Planosols Plinthic, which are formed from clayey and sandy, recent or subrecent, colluvial sediments. The topography is gently undulating and elevations range from 40 to 80 meters. The vegetation is semi-evergreen forest (tropical rain forest). The climatic data at Altamira City, situated 70 km west from the Xingu River, are the nearest ones available to the sites studied. 19 20 According to depen, the climate of the area is the type Aw, having relatively high annual precipitation with a definite dry season (Bastos, 1972). This dry season generally occurs from July to October, having at least one month with less than 60 mm of precipitation. Climatic data are in Table 2. Galvao (in I.B.G.E.-C.N.G., 1959), made the following comments about Altamira's climate. "Really its mean annual temperature is very high (26.0°C) ranging from 25.5°C in July to 26.6°C in October. Its extreme values registered are: absolute minimum, 12.4°C (08-08-1938) and the absolute maximum, 39.9°C (03-14-1933). The thermal amplitude is only l.l°C which qualifies as a isothermic climate (Table 2). In spite of the fact that Altamira City is situated in the Am zone, in which annual total precipita- tion reaches 2000 mm in almost all meteorological stations, Altamira presents only 1700 mm. The hydrological balance is shown in Figure 2. In Koppen's diagram, Altamira is located very close to the diagonal which separates the climate types Am and Aw. This permits considering it as a transitional climate between these two types. Field Studies Field studies were made on two profile pits and two profile road cuts and comprised: morphological charac- terization and collection of soil samples, according to the standards established in the Soil Survey Manual (Soil 21 Table 2.--Climatic Data According to Thornthwaite (1955) Altamira, Para, Brazil, Period 1931-1967. Tmax Tmin Tm PP PE RE ......... ‘C—------- ----—---mm-------- January 30.3 21.2 25.8 216 143 143 February 30.2 21.0 25.6 275 128 128 March 30.2 21.3 25.8 346 130 130 April 30.1 21.4 25.8 278 146 146 May 30.3 21.4 25.8 176 149 149 June 30.6 20.7 25.6 77 139 128 July 30.7 20.3 25.5 51 140 100 August 31.5 20.7 26.1 26 150 64 September 31.7 21.0 26.4 33 153 50 October 31.9 21.3 26.6 48 157 60 November 31.4 21.3 26.4 65 155 65 December 31.2 21.3 26.2 106 151 106 Year 30.8 21.1 26.0 1697 1741 1269 Tmax = maximum temperature; Tmin = minimum tempera- ture; Tm = medial temperature; P = precipitation; PE = potential evapotranspiration; RE = real (actual) evapo- transpiration. 22 Surplus 5001 [C/7 Utilization 4 Recharge Deficit 4004 /M ..__.__...__... Precip. 1697 mm —" ''''' POt. Evap. 1741 m 3004 -——-— Real Evap. 1269 mm 5 Surplus 428 mm(Pp-RE) g \ Deficit 472 mm(PE-RE) -H c o ".1 I P I 53 200 I , '3 1 I .A , ! O 0 0 ! E J . '1 In Al _ _+_4 I, 100‘ i infll. OJFMAMJJASOND'J Months Figure 2. Hydrological Balance Registered at the Metereological Station at Altamira State of Para, Brazil, for the period 1931-1967. 23 Survey Staff, 1951) and Manual de Metodo de Trabalho de Campo (Sociedade Brasileira de Ciéncia do Solo, 1973). The samples were then analyzed for physical, chemical, and mineralogical properties as described in the next section. The results of the field studies of each profile follows Figure 3 of the diagrams of profiles and altitude. Profile 1 Classification in Brazil: RED YELLOW PODZOLIC ALIco1 low activity clay, moderately drained, moderate A horizon, sandy/gravelly,2 medium texture, semi- evergreen forest phase, plain relief, substrata plinthic. Location: Municipality of Altamira, State of Para; 19.6 km from Xingu River (Belo Monte) in direction to Maraba, to the left side of the highway, and 56.3 km before the Anapu River is reached. Situation and Slope: Pit on the top of an elevation with 0-0.5% slope. Altitude: 80 meters. 1ALICO means Al+++ saturation greater than 50%, in Brazil. 2Follows the Brazilian criteria for gravelly materials according to Manual de Metodo de Trabalho de Campo (Sociedade Brasileira de Ciéncia do Solo, 1973), that is related to amount of coarse fragments (2-20 mm). .very gravelly-—has greater than 50 percent. .gravelly--ranges from 15 to 50 percent. .with gravel--ranges from 8 to 15 percent. 24 .ooa om om 0v ON um um E mm +00 mp mm mm ma Um UN E 00 +om mm mm vv on ma .muouoz ca momsufiua< nufi3 .vofipsum moawmoum on» mo memummwo coamom ocon ovenucflam E om OOH Vom .om rov rON .9 "menuauaa OAHMOHQ .m museum mo u: qqdeg 24 .ooa 00 00 0e 0N um UN 6 mm .muoumz ca momsueuaé cues .powpsum moaflmoum on» «o masseuse anamom +om mh mm mm ma Um um E 00 moon muflnucflam +00 00 mm vv 0N ma E 05 E om .m magmas 00H .00 .00 roe fem 0 r "masseuse maauoua mo ur qqdag 25 Parent Material: Product of gneiss and migmatite-granite Relief: decomposition. Level on the top of elevation. Erosion: Slight laminar. Drainage: Moderately drained. Vegetation: Semi-evergreen forest. A1 - 0 - 7 cm, grayish brown (10 YR 5/2); sandy loam with grave13; moderate fine to medium granular and moderate very fine to fine subangular blocky; many fine pores; slightly hard, friable, slightly plastic and non-sticky; clear smooth boundary. - 22 cm, yellowish brown (10 YR 5.5/4): 9rave11y sandy loam; weak fine to medium subangular blocky with aspect of massive moderately coherent "in situ"; common fine pores; moderate common discon- tinuous clay skins; hard, very friable, plastic and very stickly; gradual smooth boundary. B2t - 22 — 35 cm, yellowish brown (10 YR 5/6), few fine B3tp1 Remarks: distinct red (10R 4/6) mottles; gravelly sandy clay loam; weak fine to medium subangular blocky with aspect of massive moderately coherent "in situ”; common fine pores, moderate common discon- tinuous clay skins; hard, very friable, plastic and very sticky; abrupt wavy boundary. - 35 - 80 cm+, brownish yellow (10 YR 6/8), red (2.5 YR 4/8), pale brown (10 YR 6/3) variegated with few coarse prominent brown (10 YR 5/3) mottles; clay; many fine pores; weak few discontinuous clay skins; 40% plinthite; hard, very friable, plastic and sticky. (a) A magnifying lens (10x) was used to check clay skins. (b) The plinthite present is a noncontinuous phase. 3See footnotes in Profile 1, page 23. (e) (d) (e) (f) (9) Profile 2 Classification in Brazil: RED YELLOW PODZOLIC ALICO 26 The B2t horizon contains some iron concretions. Roots: abundant at Al, common at Blt' few at B2t and rare at B3tp1' Distribution of color at B : brownish yellow 3tp1 45%; red mottles 5%, brown 5% and pale brown 5%, and plinthite 40%. The B3tp1 presented small amounts of material weakly weathered that showed the presence of parent material nearby. p1 designated a horizon with more than 5% plinthite. 4 plin- thic, low clay activity, moderately drained, moderate A horizon, sandy/gravelly clay texture, semi-evergreen forest phase, gently undulating relief. Location: Municipality of Altamira, State of Para; 19.8 km from Xingu River (Belo Monte) in direction to Maraba, to the left side of the highway, and 56.1 km before the Anapu River is reached. Situation and slope: Pit on lower 1/3 of the elevation with 5% of slope. Altitude: 70 meters. Ibid 0 27 Parent Material: Product of gneiss and migmatite-granite decomposition influenced locally by reworked material. Relief: Gently undulating. Erosion: Slight to moderate laminar. Drainage: Moderately drained. Vegetation: Semi-evergreen forest. A - 0 - 13 cm, dark brown (10 YR 4.5/3); loamy sand; moderate, fine to medium, granular and moderate, very fine to fine, subangular blocky; many fine pores; soft, friable, nonplastic and nonsticky; clear smooth boundary. 1 B - l3 - 26 cm, brown (10 YR 5/3); sandy loam with gravel5; weak, fine to medium, subangular blocky, with aspect of massive moderately coherent "in situ"; weak, few, discontinuous clay skins; slightly hard, friable, plastic and slightly sticky; gradual smooth boundary. It B - 26 - 44 cm, yellowish brown (10 RY 5/4); sandy clay loam with gravel; weak fine to medium subangular blocky with aspect of massive moderately coherent ”in situ"; common very fine pores; weak, few, dis- continuous clay skins; slightly hard, friable, plastic and slightly sticky; gradual smooth boundary. 21t B - 44 - 55 cm, yellowish brown (10 YR 5.5/6), few fine distinct yellowish red (5 YR 5/8) mottles, brown (10 YR 5/3) mottles; sandy clay with gravel; weak, fine to medium, subangular blocky, with aspect of massive moderately coherent "in situ"; common very fine pores; weak, few and discontinuous clay skins; slightly hard, friable, plastic and sticky; clear wavy boundary. 22t B3tp1 - 55 - 68 cm+, pale brown (10 YR 6/3), brownish yellow (10 YR 6/8), yellowish red (5 YR 5/8), red (2.5 YR 4/6) variegated color; gravelly clay; weak, medium to coarse, subangular blocky, with aspect of massive moderately coherent "in situ"; common very ‘fine pores; weak few discontinuous clay skins; 51bid. 28 greater than 50% plinthite; slightly hard, friable, plastic and sticky; abrupt wavy boundary. C - 68 - 90 cm+, pale brown (10 YR 6/3), brownish yellow Pl (10 YR 6/8), red (2.5 YR 4/8), yellowish red (5 YR 5/8) variegated color; clay with gravel; common very fine pores; greater than 50% plinthite; hard, friable, plastic and sticky. Remarks: (a) The plinthite present in a continuous phase. (b) A magnifying lens (10x) was used to check clay skins. (c) Roots: Many in Al; common in Blt’ few in Bth and rare in B3tp1 and Cpl' (d) pl designates a horizon with more than 5% plinthite. Profile 3 Classification in Brazil: GROUND WATER LATERITE ALICA6 (with textural B) low clay activity, abruptic, imperfectly drained, moderate A horizon, gravelly medium texture/gravelly clayey, semi-evergreen forest phase gently undulating relief. Location: Municipality of Altamira, State of Para; 21.9 km from Xingu River (Belo Monte) in direction to Maraba, to the right side of the highway, and 52.4 km before the Anapu River is reached. Situation and Slope: Road cut on lower 1/3 of the elevation with 5% of slope. Altitude: 60 meters. Ibid. 29 Parent Material: Product of granite decomposition influenced locally by reworked material of sandy clay nature. Relief: Gently undulating. Erosion: Slight laminar. Drainage: Imperfect. Vegetation: Semi-evergreen forest. Al - 0 - 15 cm? brown (10 YR 5/3); sandy clay loam with gravel ; weak, fine to medium, subangular blocky; many fine and medium pores; slightly hard, friable, plastic and sticky; clear wavy boundary. B1t - 15 - 35 cm, yellowish brown (10 YR 5/4), common fine prominent strong brown (7.5 YR 5/6) mottles, few fine prominent black (5 YR 2/1) mottles; gravelly clay; moderate, fine to medium, angular blocky; common very fine pores; hard, firm, plastic and sticky; clear smooth boundary. B2t - 35 - 55 cm, pale brown (10 YR 6/3), common medium prominent red (2.5 YR 5/6) mottles, common district prominent strong brown (7.5 YR 5/8) mottles; clay with gravel; moderate, medium, angular blocky; common very fine pores; weak, few, discontinuous clay skins; hard, firm, plastic and sticky; clear wavy boundary. B3 - 55 - 75 cm, pale brown (10 YR 6/3), red (2.5 YR 4/6), reddish yellow (5 YR 6/8) variegated color; clay with gravel; moderate, medium, angular blocky; few very fine pores; weak, fine, discontinuous clay skins; hard, friable, plastic and sticky; abrupt wavy boundary. t C - 75 - 90 cm+, very pale brown (10 YR 7/4), yellow (10 YR 7/6), red (2.5 YR 4/8), light brownish gray (10 YR 6/2) variegated color; clay with gravel; less than 5% plinthite, hard, friable, nonplastic and non- sticky. Remarks: (a) A magnifing lens (10x) was used to check clay skins. (b) The plinthite present is a noncontinuous phase. Ibid. 30 (c) Roots: common in the A1, few in the B1t and and rare in the B . BZt 3t Profile 4 Classification in Brazil: PLANOSOL plinthic, low clay activity, imperfectly drained, moderate A horizon, medium/clay with gravel texture, semi-evergreen forest of the bottom valley phase, level relief. Location: Municipality of Altamira, State of Para; 53.2 km from Xingu River (Belo Monte) in direction to Maraba City, to the right of the highway, and 22.9 km before Anapu River is reached. Situation and Slope: Road cut on level relief. Altitude: 55 meters. Parent Material: Clayey and sandy, recent or subrecent, colluvium-alluvium sediments. Relief: level (plain). Erosion: None. Drainage: Poorly drained. Vegetation: Semi-evergreen forest. A1 - 0 -20 cm,.grayish brown. (10 YR 5/2.5); sandy loam; many fine and very fine pores; friable, and non- plastic and nonsticky; clear smooth boundary. A2 - 20 - 40 cm, brown (10 YR 5/3), few fine faint yellowish brown (10 YR 5/6) mottles; sandy loam; many fine and very fine pores; friable, nonplastic and non- sticky; clear smooth boundary. 31 B - 40 — 60 cm, pale brown (10 YR 6/3); common fine faint yellowish brown (10 YR 5/4) mottles; sandy clay loam with gravel,8 common fine and very fine pores; friable, plastic and slightly stickly; abrupt smooth boundary. 2t B - 60 - 80 cm, very pale brown (10 YR 7/4), common fine prominent red (10 R 4/6) mottles, few fine distinct grayish brown (10 YR 5/2) mottles; sandy clay with gravel; less than 5% plinthite; friable, plastic and slightly sticky; abrupt smooth boundary. 3t C - 80 - 100 cm+, light gray (10 YR 7/1); many medium prominent red (2.5 YR 4/6) mottles; gravelly sandy clay; friable, plastic and sticky. Remarks: (a) The plinthite is present in a noncontinuous phase. (b) The profile was very wet. (c) Roots: common in the horizons A1, A and B 2' 2t' few in the B3t and rate 1n the Cg. Laboratory Studies The soil samples were air dried, crushed and passed through a 2 mm sieve. The fraction greater than 2 mm was separated into 20-2 mm (cascalho) and (calhaus) greater 20 mm fractions. The part less than 2 mm comprised the air dried fine earth. Physical Analyses9 Granulometric analyses: by sedimentation in a Koettgen cylinder, using NaOH as the dispersion agent and 81bid. 9The chemical and physical analyses were done by the laboratory of the Servico Nacional de Levantamento e con- servacfio de Solos (S.N.L.C.S.) da Empresa Brasileira de Pesquisa Agropecuaria (E.M.B.R.A.P.A.), Rio de Janeiro, Brazil. 32 shaking in high rotation. Four fractions were separated according to the classification of the International Method, and using 0.05 mm as upper limit of silt. They are: 2.0-0.2, 0.2-0.05, 0.05-0.002 and less than 0.002 mm. Natural clay or clay dispersed by water: is the percentage of clay obtained by shaking with distilled water. Flocculation degree: was obtained by comparing natural clay content with clay content (total) after dis- persion with NaOH, by the following formula total clay - clay dispersed by water total clay x 100 Moisture equivalent: was determined by the method of Briggs and McLane, centrifuging the moistened earth at 10009 for 40 minutes. Chemical Analyseslo Organic carbon, C: was determined by oxidation of the material with potassium bichromate, 0.4 N (method of Tiurin). Total nitrogen, N: was determined by digestion with sulphuric acid, catalyzed with copper and potassium sulphate. After transformation of all N into ammonia, it was collected in a solution of 4% boric acid and titrated with 0.01 N HCl. loIbid. 33 pH-H20 andng-KC1: were determined potentiometri- cally using a soil paste with ratio of soil to water or salt solution of approximately 1:1, using a glass electrode. Available phosphorus, P: was extracted with a solution of 0.050 N HCl and 0.025 N H SO4 (North Carolina). 2 The phOSphorus was colorimetrically determined by reducing of the phosphorous molybdate complex with ascorbic acid, in presence of the bismuth salt. stOL(d=l.47) soluble fine earth: under a reflux cooler, 2 g of air dried fine earth were boiled for an hour with 50 ml H2804, d=1.47. After boiling, the material is cooled, diluted and filtered into a receiver of 250 ml capacity. a. SiOZ: The residue of the sulphuric acid treatment is boiled for half an hour with 200 m1 of 5% Na C03. The 2 mixture is filtered, and in a measured part of the filtrate, the dissolved silica is precipitated by an excess of con- centrated HZSO4 and heated in a sand bath until smoking. The silica is determined colorimetrically. b. A1203, total aluminum: 50 ml of the filtrate from the sulphuric acid treatment are used for the determination of total aluminum subsequent to the separation of heavy metals by the addition of an excess‘of 30% NaOH. An aliquot of this filtrate is gradually neutralized with HCl and the aluminum determined volumetrically with EDTA. c. Fe20 total iron: was determined on 50 ml aliquot 3! of the filtrate of the sulphuric acid treatment by the 34 bichromate method, using diphenylamine as the indicator and tin chloride as the reducing agent. d. Ti02: was determined in the filtrate of the sulphuric acid treatment by the colorimetric method of H202, after elimination of the organic material by heating with several drops of concentrated KMn04. e. P205, total phosphorus: was determined colori- metrically on the filtrate of the sulphuric acid treatment, by reduction of the phosphorous molybdate complex with ascorbic acid in the presence of bismuth salt. Values Ki (SiOZ/Alng ratio), Kr (Si02/(A1203+Fe203) ratio) and A1203/Fe203: were calculated on a molecular basis from the data obtained from sulphuric treatment. It is assumed that Al and Fe are determined totally with the sulphuric acid treatment as described above. The data for these two constituents therefore represent the sums of the portions of Fe and Al occurring in exchangeable form, the portions occurring as free sesquioxides--including con- cretions--and the portions that are constituents of the silicate clay minerals. The determined Si comprises all that of the silicate clay minerals and also that which is present in free colloidal form. Quartz and other primary minerals are not, however, attacked, even when of clay- size. The determination of the Ki and Kr on the fine earth fraction generally gives the same results as the inter- nationally used determination on the clay fraction (Vettory, 35 1959). The Kr may be slightly different if concretions are present (Sombroek, 1966). Exchangeable metallic cations: a. The sum of exchangeable metallic cations, S: S + + . + represents the sum of the separately determined Ca+ , Mg , K+ and Na+. b. Exchangeable calcium, Ca++, magnesium, Mg++, and aluminum, Al+++: Extractant was a normal solution of KCl at a proportion 1:10. An aliquot of this solution is used for the determination of exchangeable Al+++ by titration of the acidity using Brometymol blue as the indicator. The same aliquot is subdivided into two equal portions, for deter- mining Ca++ and Ca++ + Mg++ by EDTA. In fact, the aluminum (Al+++) determination gives the "active acidity." Experience at SNLCS has however shown that the exchangeable aluminum, determined colori- metrically with aluminon after extraction with l N KCl is practically equal to the active acidity. c. Exchangeable potassium, K+, and sodium, Na+: are determined flame photometrically directly in the percolate of 0.05 N HCl. Potential acidity, exchangeable, H+ + Al+++: is determined by extraction with normal calcium acetate at pH 7 and titration of the resultant acidity with 0.1 N NaOH using phenolphtalein as the indicator. This value represents the "potential acidity." It includes the "active acidity," or the exchangeable 36 . +++ aluminum, Al . H+ alone represents the pH-dependent acidity. The exchangeable H+: is calculated by subtracting + from the H+ + Al+++. exchangeable Al++ Cation Exchange Capacity, T(CEC): Not determined separately but obtained by the addition of S (page 35) and H+ + Al+++ (page 35). As such, it is equivalent to the cation exchange capacity according to the NH4OAC method at pH 7. T(CEC) = S+H+ + A1+++ Base saturation, BS: is obtained by formula, B5 = loos/T(CEC) Aluminum saturation percentage: 100A1+++/A1++++S Mineralogical Analyses 11 The coarse fragments, The >20 mm and 20-2.0 mm, and sands (coarse and fine), were studied mineralogically. Identification of mineral species was by optical methods (Fry, 1933; Winchell and Winchell, 1959), using a polarizing microscope and counting the species over lined millmetered plates or lined millmeter paper. Amounts less than 0.5% by weight are indicated as "trace," tr. 11The analyses of sands and coarser fragments were done by Professor Franklin dos Santos Antunes. 37 Some chemical microtests (Feigl, 1954) were made for some opaque or weathering minerals. Qualitative analyses and estimation of dominance of mineralogical components for coarse fractions, >20 mm and 20-2.0 mm. Sand fractions (coarse and fine),12 obtained by granulometric analysis, were divided in two other samples with different densities by heavy liquid separations, using bromoform with density 2.83 and a Brogger funnel. The heavy minerals are concentrated in the group whose density is greater than 2.83 and the other fraction, with density less than 2.83 are where quartz and feldspars are concentrated with other constituents when present. The sample separation by density facilitates, the counting and morphological description and allows heavy mineral identifications whose percentages are very small in the sands of these soils. After homogenizing, the description and the counting of the mineral species are conducted using a stereoscopic microscope. Mineral identification was verified by petro- graphic microscope with transmitted light (Fry, 1933; Winchell and Winchell, 1959). Clay fractions and X-ray diffraction: Three methods were used: first clay samples were x-rayed without any pretreatment, second they were x-rayed after removing the organic matter and free iron oxides, and third they were 12Ibid. 38 x-rayed after treatment with acid NH4-oxalate. The removal of iron oxide was done by Dithionite-Citrate System Buffered with Sodium Bicarbonate as proposed by Mehra and Jackson (1960), and the acid ammonium oxalate treatment is as modified by McKeague and Day (1966). X-ray diffractometer: A Norelco X—ray unit with wide-range goniometer, and Brown recorder, was adjusted to 20 milliamperes at 35 kilovolts and used for scanning parallel oriented samples on glass slides. The X-ray tube contained a tungsten filament and a copper target. A nickel filter was used to filter out radiation of shorter wavelengths than the copper Kcl radiation of 1.54 A°. To obtain the necessary measurements, the gonio- meter was set at a scanning speed of 2°(26) per minute, and the sample was rotated to 28° (20). a. Without any pretreatment four grams of soil (Bg for A1 of profile 2, because it has very low clay content) were suspended in distilled water, mixed thoroughly, allowed to sediment for 24 hours, and pipetted onto a clean glass slide and air dried at room temperature. The dried material was then subjected to x-ray diffraction analysis. b. After removing the organic matter and free iron oxides 39 1. Removal of organic matter: Used about 49 of soil (less than 2 mm) and added 4 m1 of distilled water to the sample to bring the soil water ratio to 1:1 (89 for A1 of profile 2, because it has very low clay content). Five ml of 30% hydrogen peroxide solution was then added to the sample to oxidize the organic matter. A further addition of 5 ml hydrogen peroxide was also done. The sample was heated (digested) on the hot plate (about 70°C) for 15 minutes. Heating above this temperature caused decomposition of the hydrogen peroxide. The excess of liquid was evaporated to a thin paste (approx 1:1 ratio), but not to dryness. Distilled water was added to the sample to dilute the hydrogen peroxide present and it was evaporated again to about 1:1 ratio and then centrifuged for 20 minutes at 7,000 rpm. The supernatant liquid was decanted and the sample was washed twice with distilled water and centri- fuged. At the end of each washing, the supernatant was discarded (Kunze, 1965). 2. Removal of free iron oxides: With dithionite citrate, 40 ml of 0.3 M sodium citrate and 5 m1 of l N sodium bicarbonate were added to the wet soil. Four grams of soil were used except for A1 of profile 2, because it has very low clay content, 8 g were used. The suSpension was carefully warmed to 75-80°C in a water bath, about lg of sodium dithionite (sodium "hydrosulfide" Na25204) was added to the suspension, it was stirred continuously for about one minute, and occasionally during a period of 15 40 minutes. After this, the suspension was cooled and cex fuged. The supernatant was decanted and the sample was washed twice with distilled water and centrifuged. At the end of each washing, the supernatant was discarded. Only sample B from profile 1 needed additional treatment 3tp1 with sodium dithionite, because after first treatment the supernatant remained yellow. With acid ammonium oxalate; 200 ml of 0.2M acidified ammonium oxalate solution* (the pH of the solution had been adjusted to 3.0 with oxalic acid) were added to Zg of oven- dried, less than 2 mm soil (in plastic bottles) except for A1 of profile 2, because its very low clay content, 49 were used. The suSpension was then shaken continuously for 4 hours in the reciprocating shaker. The suspension was centrifuged. The supernatant was decanted and the sample was washed twice with distilled water and centrifuged. At the end of each washing, the supernatant was discarded. Separation of clay fractions and preparation of slides: After treatments above, the soil sample was put in a 400 ml bottle, and after sodium carbonate (Na C03) was 2 added until pH 9 and it was shaken for 24 hours in the reciprocating shaker. After this dispersion, the suspension *McKeague and Day (1966) have shown that ammonium oxalate at pH 2.0 and 3.0 can extract approximately the same amount of A1 and Fe, but pH 4.2 extracted somewhat less Fe and A1 from most of the samples they tested. However, pH 3.0 caused less breakdown of silicate minerals than pH 2.0. 41 was transferred to a 1,000 ml sedimentation cylinders graduated at 100 ml intervals, through a 300 mesh screen. The volume was completed with distilled water, stirred, and the suspension allowed to stand for 24 hours. At the end of this time, according to the depth determined by Stokes law for less than 2p clay, the suspension above this was siphoned into a bottle. Then a portion of the suspen- sion was pipetted onto a glass slide placed over two leveled glass rods. The slide was allowed to air dry overnight and then subjected to x-ray diffraction analysis. Laboratory and Field Methods for Plinthite Identification The methods by Wood and Perkins (1976a) and Daniels, Perkins et al. (in press), were only partially used. In the field, red mottles and plinthite were measured together. In the laboratory, the samples were soaked in water for 2 hours; also 15 cycles of drying and rewetting, were used. IV. RESULTS AND DISCUSSIONS Physical Properties The distribution of the separates (coarse fragments, sand, silt, and clay) in four profiles is given in Table 3. Amounts of coarse fragments are less than 22 per- cent, and they increase from the surface to the lower horizons. In the greatest amounts are in the two surface horizons of profiles 1 and 3, and in the smallest amount is in the lowest horizon of profile 3. The distribution of the silt in profile 1 showed a tendency to increase and in profile 4 to decrease with depth. Its percentage ranges from 12 to 23. The clay contents increase from the surface to lower horizons, in all cases. From an examination of each profile, it is evident that there was an accumulation of clay in the lower horizon of the sola. Clay movement was evident by clay skins.present in the subsoil of all profiles. Some researchers have also found that the clay content of similar soils decreases below a maximum in the B horizon, in the Amazon Region (Falesi, 1972 and Sombroek, 1966). 42 43 Table 3.--Some Physical Properties of the Soils Studied. Horizon Air Dry Sieves Granulometric analysis (NaOH) Natural Degree % silt Moisture Clay of Floc- --- equiva- Symbol Depth >20 20.2 <2 2-0.2 0.2-0.05 0.05- (0.002 \ culation % clay lent cm qunUI mm mm uni 0.002 mm % Profile 1 A1 0-7 3 10 87 45 32 12 11 6 45 1.09 10 B1t 7-22 0 16 84 32 32 19 17 13 24 1.12 15 B2t 22-35 1 16 83 36 23 18 23 3 87 0.78 16 B3tpl 35-80+ o 3 97 18 15 23 44 o 100 0.52 27 Profile 2 A1 0-13 0 7 93 46 36 10 8 6 25 1.25 8 B1t 13-26 0 10 90 39 32 14 15 l3 13 0.93 12 Bth 26-44 0 12 88 34 28 14 24 0 100 0.58 16 B22t 44-55 2 15 83 31 21 13 35 0 100 0.37 19 B3tp1 55-68 2 18 80 29 18 12 41 0 100 0.29 22 Cpl 68-90+ 0 8 92 22 16 15 47 0 100 0.32 25 Profile 3 A 0-15 0 14 86 27 28 19 26 19 27 0.73 18 B11: 15-35 0 18 82 17 21 19 43 0 100 0.44 24 B2t 35-55 0 8 92 16 15 17 52 0 100 0.33 28 B3t 55-75 0 9 91 16 14 17 53 0 100 0.32 27 C 75-90+ 0 13 87 18 9 22 51 0 100 0.43 26 Profile 4 A1 0-20 0 6 94 34 33 21 12 ll 8 1.75 12 A2 20-40 0 6 94 32 29 22 17 16 6 1.29 14 B2t 40-60 0 9 91 29 26 20 25 24 4 , 0.80 16 B3t 60-80 0 12 88 27 21 16 36 0 100 0.44 20 C 80-100+ 0 22 78 33 13 13 41 0 100 0.32 22 44 Table 3 shows considerable differences among these soils: depth to clay greater than 40 percent is 35 cm, 55 cm, 15 cm, and 80 cm, respectively, from profile 1 to 4; degree of flocculation of clay varies from 4 to 100 percent and depth to flocculation greater than 85 percent is 22 cm, 26 cm, 15 cm, and 60 cm, respectively, from profile 1 to 4; and the percentage of silt/clay ratio varies from 1.75 to 0.29 and decreases with depth in each profile, but the maximum is 1.09, 1.25, 0.73 and 1.75 in profile 1 to 4. Moisture equivalent is consistent with clay content. It varies from 8 (8% clay to 28 (52% clay). Chemical Properties Table 4 shows the pH, available P, and exchangeable cations of the profiles studies. The pH values, percent exchangeable bases and available P of the four profiles, were quite low. In each case there was not much variation with depth. Only profile 4 showed a slightly higher pH, available P, and base saturation in comparison to the others. Some investigators have used pH values as a measure of the approximate degree of base saturation, but at a given pH it may differ in soils of similar origin as has been demonstrated by Pierre and Scarseth, 1931. In all profiles the exchangeable hydrogen predomi- Imates in the exchange complex. The second most abundant exchangeable cation is A1+++, except in profiles 1 and 4 Table 4.--Some Chemical Properties (pH, exchangeable cations, and available P) of the Soils Studied. 45 Horizon Symbol Depth Exchangeable cations (meg/1009 soil) Base satur- Satura- +++ pH ition tion + P cm 820 m1 Catt MgM x” Ra+ s(5mn) Al+++ 11+ T(CEC) “6):; 103:: pm Profile 1 A1 0-7 4.9 3.4 0.8 0.07 0.02 0.9 0.6 2.3 3.8 24 40 3 B1t 7-22 4.7 3.6 0.4 0.06 0.02 0.5 0.6 2.2 3.3 15 55 <1 82t 22-35 4.7 3.7 0.6 0.06 0.02 0.7 0.5 1.8 3.0 23 42 <1 B3tp1 35-80+ 4.6 3.7 0.5 0.10 0.03 0.6 0.7 2.0 3.3 18 54 <1 Profile 2 A1 0-13 5.0 3.5 0.7 0.09 0.02 0.8 0.4 2.8 4.0 20 33 4 B1 13-26 4.6 3.4 0.3 0.05 0.02 0.4 0.6 2.1 3.1 13 60 1 Bth 26-44 4.4 3.4 0.3 0.04 0.03 0.4 0.8 2.0 3.2 13 73 <1 B22t 44-55 4.5 3.5 0.3 0.04 0.03 0.4 0.9 2.0 3.3 12 69 <1 B3tpl 55-68 4.4 3.5 0.3 0.05 0.03 0.4 1.0 1.9 3.3 12 71 <1 Cpl 68-90+ 4.7 3.8 0.4 0.04 0.02 0.5 1.0 2.1 3.6 14 67 <1 Profile 3 A1 0-15 4.5, 3.8 0.2 0.05 0.05 0.3 1.0 2.7 4.0 8 77 1 B1t 15-35 4.6 3.8 0.2 0.05 0.04 0.3 1.3 2.7 4.3 7 81 2.83): Heavy fractions were com- posed by heavy minerals resistant to weathering such as: zircon, ilmenite, and magnetite among others. One exception was the Bth horizon of the profile 2, that showed a small amount of biotite (6.7%). A lithologic discontinuity could be inferred from this factor or perhaps preservation of a less resistant mineral in concretions could have occurred. Iron concretions are also common secondary com- ponents of the coarse sands in the heavy fractions, parti- cularly those from the better drained profiles 1, 2, and 3 are commonly the most abundant constituents of the heavy fractions. These are less abundant in the light fraction of the coarse sands and in the heavy fractions of the fine sands. Ferruginous clay fragments may also occur in the lighter sand fractions of profiles 1 and 3. 49 Table 6.--Mineralogical Analyses, Coarse Fragments. A1 1t 2t Profile 1 >20 mm broken quartz, showing signs of crushing, reddish grains due to iron oxide. 20-2 mm Large percentage of transparent and milky quartz, less reddish grains due to iron oxide; several grains show signs of crushing; subrounded grains of hematite, ferruginous concretions; fragments of clay-ferruginous material, red, several with inclusions of transparent quartz; fragments of clay-milky material; rare goethite concretions; rare fragments of coal and roots. 20-2 mm Large perCentage of quartz, crushed grains, reddish due to iron oxide; rounded ferruginous concretions; fragments of the clay-iron material with inclusion of transparent quartz; rare fragments of coal; creamy clay material with spots (stained by iron oxide). >20 mm Ferruginous concretions; crushed quartz, reddish grains due to iron oxide, the grains look like fragments of quartzite. 50 Table 6.--Continued. 20-2 mm Large percentage of quartz, crushed grains; reddish due to iron oxide; fragments of the iron-Clayey material with inclusions of quartz; material with Clayey aspect, white and red mottles; rare ferruginous concretions; fragments of the iron- clay material with inclusions of very small plates (blades) of weathering mica. B3tpl 20-2 mm White and milky quartz, several of them are crushed; fragments of the iron-clayey material with inclu- sions of quartz; fragments of the iron-clayey material with inclusion of plates (blades) of weathering mica; fragments of the material with clayey aspect with white and red mottles. Profile 2 Al 20-2 mm Large percentage of quartz, some grains are crushed and the majority are colored by iron oxide; rounded ferruginous concretions with inclusion of quartz; rare fragments of detritus; rare fragment of coal. B1 20-2 mm The same as above. 51 Table 6.--Continued. B21t 22t B3tp1 20-2 mm Large percentage of quartz, some grains are crushed and the majority are colored by iron oxide; rounded ferruginous concretions with inclusions of quartz; rare grains of quartz are rounded and subrounded. >20 mm Ferruginous concretions (like Bir horizon); quartz colored by iron oxides. 20-2 mm Large percentage of quartz, several grains are crushed, the majority are of milky appearance, and some are colored by iron oxides; ferruginous con- cretions, some are rounded with inclusions of quartz; fragments of iron-clayey material, some with inclusions of quartz, others with inclusion of plates (blades) of weathering mica. Observation: The crushed grains of quartz look like fragments of quartzite. >20 mm Ferruginous concretions with few quartz grains included (look like Bir horizon); crushed quartz colored by iron oxide (look like fragments of quartzite). 20-2 mm The same as above. 52 Table 6.--Continued. Cpl 1t 2t 20-2 mm Quartz, the majority of the grains have a milky appearance, many crushed (some of them look like fragments of quartzite); ferruginous concretions, and some are rounded; rare rounded and subrounded grains of quartzite; rare fragments of iron-clayey material with inclusions of quartz; rare fragments or mottled iron-clayey material. Profile 3 20-2 mm Large percentage of quartz, many grains are colored by iron oxide, when crushed look like quartzite fragments; few grains of milky quartz or quartzite like fragments. Presence of fragments of quartz with appearance of secondary origin. Some grains of quartz subrounded. Some fragments of red clayey- iron material, with inclusions of crushed quartz and transparent quartz not crushed. 20-2 mm Milky-quartz like, crushed, grains colored by iron oxide; fragments of ferruginous material with inclusion of crushed quartz. 20-2 mm Crushed milky quartz-like, crushed quartz spotted (stained) by iron oxide; fragments of ferruginous 53 Table 6.--Continued. t 2t 3t material with inclusions of crushed milky-quartz like; rare ferruginous concretions. 20-2 mm The same as above. 20-2 mm Crushed milky-quartz like, fragments of ferruginous material some with inclusion of quartz; fragments of clayey-iron material with red and white color (mottles). This material is not consistent. Profile 4 20-2 mm Large percentage of quartz, the majority are milky- quartz like, some look like quartzite fragments, others slightly colored by iron oxide; rare ferru- ginous concretions with inclusions of quartz. 20-2 mm Large percentage of quartz, the majority are milky- quartz like, many of them crushed, some look like quartzite fragments, other grains slightly colored by iron oxide. 20-2 mm The same as above. 20-2 mm Large percentage of quartz, some grains crushed, some look like quartzite fragments. The majority 54 Table 6.--Continued. of grains are milky-quartz like; some ferruginous concretions. Cg 20-2 mm Large percentage of quartz, many grains milky- quartz like, some slightly colored by iron oxides, some grains crushed, look like quartzite fragments. 55 .ucmonom m swap mmmallmomuu momma x x mcoflumuocoo hmau x ouchEHH o.o~ mcoeuonocoo msocemsuumMImmHU x oueumcmmz m o.om Nunmso o.ooa mcoflumuocoo msocemsunmm a umm m.m~ Nuueso n.0m mueuocmce m.m maceumuocou one muecmfiae oeumcmmz o.em unease o.om msoeumuocoo msocwmsuumm umm x muecmmo m.v mcofluouocoo msocflmsuumMImmau o.m muwummm one coouem N.n mCOeumuocoo msocflmsuuom H.m mueumcmme one muHcmEHH o.mm Nuance o.va mcoHumHocoo msocemsuumm HSm x ouopemm o.m coouflu 0cm muflpmme m.nH Nuance m.¢ mc0euouocoo mDOCHmQHHCMImCHU o.m~ muflumcmme H.h mcoflpmuocoo msocfimsuumm 0cm Aoeumcmmfiv wuHcmEHH o.mw apnoea m.Hm meowuouocoo moosemsuumm He REE ~.|~v poem omumoo H maemoum sesame imm.~vec consumes sesame xme.~Aec souanom an m unmeq 0cm Edeowz he w coauomum m>mwm .mocmm .mmmaamcd HmoemonchflzII.n magma 56 o.m ouHcmEHH o.hH mCOeuoHocoo 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mcoHumuocoo msocwosuumm a umm x mCOAuoHocoo msocwmsuummuhmao x unused o.m oueumcmmz o.oa muwcmEHH umm o.ooH Nuance o.mw mGOADmHocoo moosemsuuwm m ¢.N coouwu . 5.0 mueuoem x msuwuuoo o.oH muecmeHH o.ooa Nausea o.om maceumuocoo msochsuumm uHmm o.m muecoEHH o.mm mGOHuoHocoo H o.ooa Nuance . moosemsuuowlmuHDCEmm m o.m~ muecmEHH x msueuumo 0.0m muwumeomz o.ooa Nuumso o.ov Nuueso He ASE N.1~V comm mmumoo m daemoum names: Amm.~vov coHuumum brooms Amm.mxpv acneuom an s names new suave: an a soanomum s>mmm .emssausoouu.e magma 58 x mueuon x maeusm 0.0 muflummm 0cm cooueu 0.H~ mcoHumHocoo msochsuumm 0.0 opecoEHH 0.0m mueumcmmfi 0cm muecmsaH 0.00 Nuumso 0.0v Nausea ado 0.mH muwummm one COOHHN 0.0m muecmfiaw 0cm mueumcmmz 0.N mcoflumuosoo 0.0m maceumuocoo msocemsuumm d 0.0m Nunmso 0.He Noumea H umm x mafiusm 0.0 muflummm 0cm COUHHN 0.0m mcoeumuocoo msocemsnumm 0.0 mcofluonocoo Cam ouHcmEHH 0.0m wuHcmEHe 0cm oueumcmmz o.mm sparse 0.08 Nausea ummm 0.0 mcoflumuocoo msocflmsuumm 0.0 muecoonfin Cam mueumme 0.0 muecmEHH 0.0m Nuumso Dam 0.00 Nunmso 0.00 ouwumcome one ouHcmEHH m 0.0 cooueu 0cm mueumme 0.0 muecmEHH 0.mm Nuumdo a 0.00 Nuumso 0.00 oueuocmmfi 0cm muHcmEHH m x mcoeumuucoo 0.0 muflpmmm use GOUHHN x msueuumo 0.Hm Nuumso O . 00 H NDHMDO o . mm OUHUOCUME @Gm OuHCOEHH HAN ASE 00.IN.V comm mean sesame 1mm.mvev seahorse sesame 1mm.~Aee sosasom >n w named 0cm Edwomz an m COeuomHm >>mmm .Cosceuc0011.> oHQmB 59 0.0a mnoHueHonoo mnonemnuumMImeHo 0.00H enceumuonoo one mnoHueuonoo mnonemnuuom euenpeom one .eufluefien 0.00 Nuneno .muenOEHH “moonemnuumm U 0.0 Nuueno 0.0 noouen one .eueuenmefi .euwnefiaH x mnueuueo 0.00 mnOeueHonoo 0.~ mnoHuononoo wdonemnuuem euenumoo one eueueaen 0.00 Nuueno muwnoefia amnonemnunem one x mnufiuuen 0.0a Nuueso one 0.N mnoeueuonoo .eueuonmee .euflneEHH moonwmnuuemnheao 0.00 mnoeumnonoo ouenueom one 0.00 Nuueno euenOEHH Amsonemnuuem 0mm 0.0 Nuueno x mnufluumo 0.0a noouen one 0.~ mCOeumuonoo .eueuenmes .euwneEHH womeao .euHDOen 0.00 enceueuonoo .mnoHueuonoo mnonemnuuem openueom one .euenOEeH 0.00 Nuneno .eueueEen amnonwmnuuem Dam 0.0a eueaouneum one x oeHHeEeH unnumono noouwu .eueneEHH oeuenmez x oueuowm 0.00 mnoHueHonoo eueueeen mnuenueo waaemeonenm one .euenueom 0.00H Nuueno oanOEHH xenonfimnuuom He AEE 0.100 onem emneoo m eHemoum unmask A00.mvo0 noeuoeuh anodes A00.~Ao0 noNHnom 0n 0 unmfiq one Edeoez an 0 noHuoeHm w>eem .oenneunoouu.e manna 60 0.0 nooueN 0.0a Nuueno x mnuereo 0.0m euwuenmee one eveneEHH 0.0a mnOeumnonoo 0.00 mnoflueuonoo moonwmnuquImeao openneom one.~muwueeen 0.00 Nuueso .euwnOEHH “muonwmsuuem umm 0.0 mueueme one eueuown .noouem 0.0a evenefiaH 0.0m Nuueno 0.0a mnoHumnonoo 0.00 mnOfiueuonoo moonwmnuumwlmeau euwuenoefi one .euwuefien 0.00 Nuueso .euenoEfiH "mnonemnuuem umm 0.~ eueueme one noouwu x mueuoam o.oa munumsmme one muesmsaH x mnuwuuea 0.00 mnoHuouonoo 0.0 mnowuononoo openueom one .eueueeen mnonflmnuquImeHU euenoEHH ”mnonemnuuem 0.00 unease 0.04 muenoen ere unease unm x euooflmm x mnuwuueo 0.0a eueueme one noouwu 0.0m nuueno x mnueuueo 0.0m eueueeem 0.00H Nuueno 0.00 oueuenmee one openeEHH H4 ASE 00.1N.0 onem enem assess xm0.~ve0 conuomun prose: xm0.~Ae0 souanom 0n 0 unwed one Eneooz 0n 0 nowuoeum >>eem .eessfinnoouu.e wanes 61 0.N nooHHN x openeEHH 0.0 Nuueso x msnenuwo 0.0 mueumnmez 0.00H Nuumso 0.00 mueseeHH 0o x eueuefiem 0.0 nooueN x epfl>oomnz one euwuenmez 0.0 mueuenmez um 0.00H Nuueno 0.00 meeneEHH m 0.0 Nuueno 0.0 noouwm x mnueuueo 0.0 epeuenoez u o.oon Nassau c.00 muesmeHH mm 0.~ enceueuonoo mnonflmnuuem 0.0 nooueu x mnueuuea 0.0a euwuenmez o.ooH unease 0.00 muaemsaa 04 0.0 mnoeueuonoo eueueEem x openeEHH 0.0 nooues x mnueuueo 0.0a epeuenmez a 0.00H Nuueno 0.00 openeEaH 4 REE 0.100 onem emueoo v maemoum 0.0 noonen 0.0a mnoflumuonoo 0.0a Nuueno mnonemnunewlmeao 0.0a eveneEHH one mnoeuenonoo moueueEem 0.00 mnoflueuonoo muenueom 0.00 Nuueno one .euwuefien .euenOEHA U sesame xm0.~ve0 sonuomun unseen nm0.~Ae0 sounuom an s semen ere eseems an a consumes 0>mmm .omnnwun0011.0 wanes 62 0.0 Nuueso x openoEHH 0.0 nooueu x mnueuueo 0.0 eueumnmez 0.00H Nuueno 0.00 eveneEHH mu x mnueuueo x mnueuueo 0.0 mueuenmez 0.H muflpenmee one muenoEHH 0.0a nooueu pm 0.00 Nuueno 0.00 eveneEHH m 0.0 Nuueno 0.0 enceuenonoo mnonemnuuem x mnueuueo 0.0a nooueu 0.H eueuonmee one openeEHH 0.0a eueuonmez u 0.00 Nuueso 0.05 mnecmeHH mm 0.0 Nuueno x mnuenueo 0.0a nooues 0.H ouenoEHfi one mueumnmez 0.0m oueuenmez m 0.00 Nuueso 0.00 euenoEHH a x openeEHH 0.0 Nuneno x Hemo 0.0 nooHHN x msnfiuumo o.m~ meanesmez H 0.00H Nuneno 0.00 eueneEHH e Ass mo.a~.0 esem mean prone: lm0.~ve0 soHuosnn prunes xm0.~Ae0 soanom 0n 0 unmeq one Eneoez an 0 noduoeum >>eem .emscnunoouu.e enema 63 Iron concretions were not observed in the A horizon of the profile 2, even in the heavy sand fractions. In profile 4, the most poorly drained, iron concretions were observed only in the heavy coarse sand of the A horizons and the heavy fine sand of the B2t horizon. Apatite is an infrequent heavy mineral observed in the coarse and fine sand fractions of the A1 and B1t horizons of profile 1; in the fine sand fractions throughout profile 2; and in the A1, B1 and B2t of profile 3. Bio- t! tite was also observed in the heavy fine fractions of the B and B horizons of profile 3. 1t 2t Medium and light fractions (d<2.83). The medium-and light fractions are the predominant components in both the coarse and fine sands. More than 90 percent by weight of the medium and light fractions were quartz. Quartz could thus be con- sidered the dominant constitutent of these sand fractions in all four profiles. However, small amounts of ilmenite were also observed in the fine sand fractions of profiles 1, 2, and 4. Secondary products were found in the light fractions of some horizons only. Thus, iron concretions and ferrugi- nous Clay fragments were observed in the coarse sands of profile 1, iron concretions were observed in the coarse sands of the subsurface horizons of profile 3, and ferruginous Clay fragments were observed in some of the fine sand fractions of the subsurface horizons of profiles 1 and 3. 64 Clays Fractions: For this purpose, only X-ray diffraction analyses of total Clay fractions were used, from 9 of the 20 horizons in the four profiles. The results are tabulated in Table 8. Two pretreatments were used: the first with dithionite-Citrate-bicarbonate and the second using ammonium oxalate. Besides the clay mineral characterization, the pur- pose of using these two treatments was to try to make some comparisons with the amount of the exchangeable Al+++ and acid soluble Fe203 on the differences in X-ray diffraction peak heights. Figure 4 shows X-ray tracings of total clay. The dithionite treatment is supposed to dissolve much of the iron from amorphous as well as from crystalline materials and the oxalate treatment is supposed to dissolve only iron from amorphous materials. The height figures on the table refer to the scale of the X-ray diffraction recording charts. The samples were X-rayed at three different times and they showed different peak intensities. Differences in intensities of X-ray diffractions (peak), probably are due to differences in amount of clay mineral, mineral particle orientation, and with the position of the mounted sample in the diffractometer. The following comparisons and conclusions seem warranted: First, it was evident that all profiles were 655 .0000 00000: as» no: 00 0000000 000 an uoo0>0o 00: 0o. .xeem 00:00: any we: pa emneoon .v oafiuoum mo nonauon 4 enu n0 Mano 0e. an ooo0>0o me: 000 00.0 0.00+ 00 00.0 0.00 000 0.00 00.0 00+ 00 00.0 000 000 00 00.0 00+ 00 00.0 00 000 00 00.0 00 000 00 mo 00.0 0.0+ 0.00 00.0 00 00 00 00.0 0+ 00 00.0 00 00 00 on 00.0 0+ 00 00.0 00 00 00 00.0 00 0 00 0 «00.0- 00- 00 000.0- 00: 00 00 .00.0- 00: 00 000.0- 00: 00 000 0 «00.0- 00: 00 000.0- 00: 00 00 00.0 00 0 00 0 0 00.0 00+ 00 00.0 00 00 00 00.0 00+ . 00 00.0 00 000 00 um 00.0 00+ 00 00.0 00 00 00 00.0 00 000 00 0 .00.0- 00- 00 00.0 00 00 00 .00.0u 00+ 00 00.0 00 000 00 .00.0u 00- 00 00.0 00 000 00 00.0 00 00 00 4 0 00.0 00+ 00 00.0 00 000 00 00.0 00+ 00 00.0 00 000 00 00.0 00+ 00 00.0 00 00 00 00.0 00 000 00 000 -u u- -1 00.0 00 00 00 n- u- n. 00.0 00 000 00 000 u- u: .n 00.0 00 . 00 00 00.0 00 000 00 0 .00.0u 00- 00 00.0 00 00 00 .00.ou 00- 00 00.0 00 00 00 0 .00.0- 00. 00 00.0 00 00 00 00.0 00 00 0 e 0 «0.0+ 0+ 00 00.0 00 000 00 .00.0. 00- 00 00.0 00 000 000 0000 00.0 0+ 00 00.0 00 000 00 00.0 00 000 00 0 0 000 000 000 0 o 0 o no» .02 o\~o elo n No .ueouu l£\00 eta u 0o .ueouu use! moNom .ueu noauedn ueao 1000: oaeu 00000 \0 Hosea unseen .0om +++0< uooo00 0ouoa noun oz e0o0 no 000000 mO0uem no 002000: xeem .uneaueoua mowuem no munm0em xeom .uneaueoua eueHexO|an0nan¢ evenonueowmnoueuua010u0n00nudo .munosuoouuoun 000:003 no 0003 :O0uoaum aeHU no exeem caduceMMNHQ eu0n000ex mo seamen: one 0 on N uOHAea noun 00000en¢ 00cm oouoeaom .nuneunoo 0e0011.0 eHQee Figure 4. 66 X—ray Tracings of Total Clay of Selected Soil Horizons. Treatment: (1) No Treatment (2) Ammonium Oxalate Procedure (3) Dithionite-Citrate System Buffered With Sodium Bicarbonate Scale factor is 32 for all tracings. 67 Figure 4. 66 X—ray Tracings of Total Clay of Selected Soil Horizons. Treatment: (1) No Treatment (2) Ammonium Oxalate Procedure (3) Dithionite-Citrate System Buffered With Sodium Bicarbonate Scale factor is 32 for all tracings. 68 mostly kaolinitic (greater than 95%), as shown by diffrac- tion peaks at 7.18A°. After dithionite treatment, the diffraction peaks showed greater heights than they did after oxalate treat— ment in all horizons. After oxalate treatment, the A horizons had smaller diffraction peaks than with no treatment. That is the reason for their negative ratios in the last column of Table 8. The A1 of the profile 4 showed the highest kaolinite peak with no treatment. This horizon had the smaller amount of exchangeable Al+++ saturation, 17 percent, and the clay had a low degree of clay flocculation, 8 percent. Even the dithionite treatment decreased the diffraction peak height of this sample. The relative order of increase of the intensities of the kaolinite peaks in the subsurface horizons is about the same for the two treatments, but the dithionite treat- ment was most effective. The B sample from profile 4 had 2t the lowest peak height without treatment. Both treatments increased the peak heights more of this sample than would have been expected from its lack of flocculated clay, its +++ . - low Al saturation, and low soluble iron content. Plinthite Characterization A great limitation for plinthite characterization in the laboratory, was the amount of soil samples in 69 undisturbed (natural) conditions. Even so, some conclu- sions can be made from the results of the slaking and fifteen wetting and drying cycles in the laboratory. Table 9 shows the results of the distinction between red mottles and plinthite after slaking (being immensed in water for 2 hours) and the test of hardness after 15 drying and wetting cycles. These tests should be made in the field, but it was impossible. For the slaking test, it does not make any difference. But for the drying and wetting cycles it probably does because the investigators mention that soil material hardens especially if it is exposed also to heat from the sun. From the table it is evident that the most red material is actually plinthite in the better drained pro- files (1 and 2), but they harden only after 15 cycles. Sanches (1973), has indicated from 5-10 cycles should be sufficient. Classification of These Soils Table 10 shows the classification of the soils in this study according to the systems of classification used in Brazil, FAQ/UNESCO, and the U.S. Soil Taxonomy. Currently, in soil surveys carried out by SNLCS in Brazil, plinthite has tentatively been considered necessary to quality for a Ground Water Laterite. But, probable some .0030000>m 00: 0003 mmafifidm ownusumwocs anamomn q mafimoum 5003 0608 mm: 0000 muouwuonma ozm 70 00 on 00 00A 0 0v 00 o 0: 00 000 0 0 00 00 0: 00 000 0 0 00 00 0 0000 0 0v 00 00A 00 000 00 0000 0 0v 00 00A 00 0 00 on 0 000 0 0 0 0000 0 00 0000 0 00 00 00 00 0 00 on 0 000 0 0 0 00 0 0000002 000 000000 00 0 0000002 000000 00 0 000000000 00 000000000 000 00 0 00 0 mo m000003 0M0M0WMMW0M0 0000002 000 000000000 000000 0000000 0000000 umum< mmwcoumm mason 0 Mom AmHQEMw unwoz 00 away Imzwmom 00003 :0 vomumsaH .00000000000 :00 000000000 000 0000002 0000000 000 0003000 00000000000--.0 00000 .m500um0uommv mmawmoum no 000000000 mmmnu00umnm 00 cowumo0u000000 Hm>mum 000 000000: 05000 000 000000000000 .00um:ommoum« 00050000 06 muwmawmmnm 000005fludmummcou m 000050000>wq 00 00000002 ouw>ummnnmuqzm .A.ouw .mmmc0xoou .mmmCflcoum .mmwamu .cowumummm>v 000 000: :00 0000:00 71 .muduxmu 005000000002000 am>mum £003 5:0no5\>0500 .4 .05000000m .h5moa 00000005 .nwcwmuu hauoom .mmao 1000M .005050000 uwsvm 0000000< 000000 >00>0uum 300 .UHnucwam 00000000 0 .musuxmu >000 xdam>muo\550©05 aaam>mum .0 00000605 .0050006 aauommummafl .owumdunm .hmao >00>0000 000000000000000 .0000000000 300 .00 00000000 00030 .xmxmao .005030000 005U¢ 0000000¢ 000000 .000dm 00000000.H0003 cadouo m .mnauxmu >000 >HHm>mum\>cqmm .0 00000005 005umsuumm>£000 .050000000 .vmcwmuv aamumuvaE .00n000am .00000n0000 .00000000000 00000000 00000000 .00000 00000000 300000 000 N .oanucwam mumuumnzm 005umzuummmzomw .musuxwu 550605 >HHm>mum\hvGMm .030000000 .w5000lmcwm .¢ 00000005 .hmao >u0>0uom 300 0096:0000 00305000 maomwuufl Oflnucfiam n.oofla< uaaonvom 300000 60% 0 000000 00000000 .0.0 000000 oommza\000 0000000\<000020\0o020 0000000 00 ammo mcawm 000m no 0000000 4050000080. {0.5 can .oummzs\000 .00qum :0 wow: meumwm may 00 mcwouooud maflom 030 no cowumo0m0mmMHUI|.oa manna 72 of these soils already mapped could not be classified as Ground Water Laterite because tests for identifying plinthite and its measurements have not been done. For example, profile 3, was previously classified as a Ground Water Laterite in the field, because of the presence of red mottles. After laboratory tests it has less than 5 per- cent of what could be called plinthite. Likewise profile 4, called Planosol plinthic does not fit well into this class of soils. It also has less than 5 percent that could be called plinthite. These two soils show the evidence that plinthite develops more in better drained soil conditions. Profile 1 was classified as Red Yellow Podzolic . . . substrata plinthic, due to presence of plinthite below 75 cm at the bottom of the Bt. Profile 2 is Red Yellow Podzolic plinthic, because plinthite is within that depth and occupies a large part of the B horizon. In regards to the FAG/UNESCO system, all profiles fit into Acrisols. The plinthic soils are classified as plinthic Acrisols and the non-plinthic as Ferric Acrisols. Finally, in U.S. Soil Taxonomy 3 profiles (1, 3, and 4) were classified as Paleudults because the clay content increased from the surface to the lower horizons. Profile 2 fits in Plinthudult, with plinthite as a con- tinuous phase. The U.S. Taxonomy has not differentiated any subgroups for this great group. However, profile 2 could be classified as an Oxic Plinthudult, because it 73 shows a high degree of clay flocculation and a low activity clay (after correction for carbon). Bennema, 1964 indicated that one gram of carbon often is equal to approximately 4.5 millequivalents of cation exchange capacity. The equation for 100 grams of clay based on CBC and carbon (C) of a sample is: 100 Current Land Uses This sequence of soils has not had any agricultural use in the Amazon Region. However, Plinthic Paleudults and Aquic Paleudults, have been mapped in Sierra Leone, west Africa and some indications of their value for agri- cultural uses have been recognized (Odell et al., 1974). Plinthic Paleudults are used for both annual and perennial crops, such as: upland rice, maize, groundnuts, cassava, coffee, oil palm, and citrus. Dry season irrigation is desirable, but not feasible in most-places. The Aquic Paleudults are used for swamp rice during the rainy season, with bunding and water control; and vegetables are grown during the dry season. With supplementary drainage a variety of crops can be grown. At the family level, the Plinthic Paleudults in Sierra Leone are fine-loamy over clayey-skeletal, mixed, isohyperthermic. The Amazon soils are in the fine-loamy, siliceous, isohyperthermic family. The Aquic Paleudults are 74 in the clayey, kaolinitic, isohyperthermic family, in. both areas. Plinthic Paleudults have also been mapped in Puerto Rico, but they are in oxidic, instead of siliceous, families. They present very severe limitations for cultivated crops. Agricultural uses are not recommended for the Brazilian soils, because of the high investment that would be required and the large area of relatively better soils in the Amazon Region that could be so used. Interpretations for Engineering Purposes* These interpretations provide information about engineering properties of soils, Table 11; the suitability of soils as source materials, and the factors affecting various engineering uses of soils, Table 12. The soils also are related as to their degree of limitation for residences, recreational facilities, as well as farm crops, farm trees, structures for light industry, trafficways, and gardens, Table 13. The purpose of these interpretations is to give ideas about the potential uses for the soils represented in four profiles. Estimated soil properties significant to engineering interpretations, are given in Table 11. Explanation of *Basically from guide for Interpretations for Engineering Uses of Soils by S.C.S.-U.S.D.A. and Michigan Agricultural Experiment Station. '75 .muaaooau 0» unannuan o>oam muammmm manucH m case mama unmouom a o.mua.v oaumv mauma ooa cod sun o a snao sauna ooanoa a o.mum.a oauav mauma cod ooa sun 0 a snao sauna oauoa an: o.mna.a mmumm oauoa ooH cos au~uu o a Enos snao sauna oauov z a.m-H.m canon osuoa ooa ooa vu~-< z a anoa sauna oauom and m.mua.m canon osuoa ooa ooa annuu z m anoH sauna o~-o no a a o.m-m.a maumm ooanoa ooH ooH sun a z ano oauas a o.mum.v mmumm ooauoa ooH ooH sun : z snao manna a o.aua.v amumm ooanoa ooa ooa sun a s snao mmuam u o.mnm.a amuam ooauoa ooH ooa sun a z ano amuaa aoz o.aum.v amnma oauoa ooa ooH anmuu o a anon snao sauna mfluo can m a o.mum.v mmnms coauom ooa ooH sun 3 z snao omuaa a m.an oauma aauma ooa ooH sun 0 a snao sauna aaumm an: o.m-m.v oanaa mmnma ooH cod s.n o a snao sauna amnav aoz m.ax mmumm oauoa ooH cod auauu o a unoa snao sauna ovum" sou o.mua.v canon osuoa cos ooH vumau z a snag sauna amuma sou o.aum.v cmnms apnea cos ooa eunun : a auna sunoa mane oaA m m-= o.aum.a ma-ms ooauom ooa OOH sun a z snao omuaa ao: o.m-m.v amumm oanoa ooH ooa auauu o a unoa ana sauna mmnmm sou o.m-m.a canon osuoo ooa ooa vunsn z a anoa sauna nuns sou o.m-a.a carom ossoa ooa ooH vuauu z a unoa sauna s-o can H was. a a. a as 4 ms 2... aaunoouo anuonom ommam aosmauo uxaeuuomo uonauom swans swam .oz sua>wmouuoo aquamomm Hwom .auauaaunmum on uunoaaauaaa aaauaamoaa Haoa aounuauamnu.aa manna 76 terms: Depth to seasonally high water table--Listed is the shallowest depth to which free water rises at least once a year, generally during the winter (in Amazon region this is about 6 months). Depth from surface--the depths given in this column correspond to the top of the soil horizons. USDA texture--the texture indicated corresponds to the textures given in the technical description of each soil profile of the sequence (USDA Handbook No. 18, SOIL SURVEY MANUAL). Unified C1assification2--The Unified Soil Classifi- cation system is based on identification of soils according to their texture and plasticity and their performance as engineering construction material (Corps of Engineers, U.S. Army, Technical memorandum No. 3-357, vol. 1, March, 1953). In this system, soil material is divided into 15 classes: 8 classes are for coarse-grained material (GW, GP, GM, GC, SW, SP, SM, SC), 6 for fine-grained (ML, CL, CL, MH, CH, OH), and l for organic material (Pt). AASHO Classification2--Most highway engineers classify soil materials according to the system approved by the American Association of State Highway Officials. (High- way Research Board Proceedings of the 25th Annual Meeting, 2Unified and AASHO classifications were taken from guide sheet 15--General relationship of systems used for classifying soil samples (USDA-Soils Memorandum--45 Rev. 2). Guide for Interpreting Engineering Uses of Soils.) 77 1945). This classification is based on the gradation, liquid limit, and plasticity index of the soil. Highway performance has been related to this system of classifi- cation. All soil materials are placed in seven principal groups. The groups range from A-l (gravelly soils of high bearing capacity, the best soils for subgrades) to A-7 (clay soils having low strength when wet, the poorest soils for subgrades). Percent of Material Passing Sieve3-—The measured or estimated percentages of material passing the numbers 4, 10, 40, and 200 sieves are given for each major horizon. When there is very little gravel size material (No. 4 and 10 sieves) present, the percent passing the 200 sieve approxi- mates the amount of silt and clay. Soil Reaction--soil reaction or the intensity of soil acidity or alkalinity is expressed in pH--the logarithm of the reciprocal of the H-ion concentration. A pH of 7 is neutral, lower values indicate acidity and higher values show alkalinity. Shrink-Swell Potential-~indicates the volume change to be expected of the soil material with changes in moisture content. It is low in all cases. Table 12, part A, presents a summary of the Engineering Interpretations for topsoils, sand, and gravel, or road fills. 3Percent of Material Passing Sieve were taken from guide sheet 2 of the same Soils Memorandum 45 previously mentioned. .muaaOOam 78 .pmuamuo sauoom .manmu umumz swam ou uoonnsm mason ume>mm a .auaaooaa .pouamun sauommumeH .manwu Hmum3 Amam on unonQSm .mmmsum3 “wum>mm m .Hmum3 nonoumm .Houmz “pmcflmnp Hamz mamumumvoz omnoumm .muwsucaam .HHOmQSm swab "mumuopoz N .Hmumz omsoumm .Hmum3 .munuumnsm nowcamuo Hams sawumumcoz vmnonmm .muwnuuwam swab "mumuwooe ou unmaam H mandamuo anusuasoaubfi amoum uw0>ummmm mummuum was modem Hmooq . . . muwuoowmm wuzummm maaom Amy IIIIIIIIII .oanmu mounMIIIulnnnlnlnn .owuamup .uumm o: «nouadmuo swan decommmm auumucoo sauoom “Room .onSOm manmnoumsH Mounds oacmmuo 30H “noon v .ucoucoo swab swan um3 .ocmm o: «wouasmco nuuwuuou Hmuuma oacmmuo 30H .an0 oauHuwHomx «swam .woudom manmnoumEH «muumfimmum mammoo "Room m .Haomnsm .Hoom .usmucoo umuuma smao oeuauflaomx "saws .oou50m manmnoumEH oacmmuo 30H «spawn "Moon N .HfiOmndm .uoom uuwucoo Hmuuma oaummuo snao owuwufiaomx “Hams .wUHDOm wandaoumaH 30H «muumaqmum mammoo “Moon H Haas anom Ha>nuo aun auna Hecamoe .oz asaoa . . . mo mousom mm suaHaQMuHsm “my .mcoaumuoumumucH mcaummsamCMIu.ma manna 79 Explanation of Items: Topsoil--The organic matter content, thickness, texture, and natural fertility of the surface layer determine the suitability of a soil for use as topdressing for lepes, road shoulders, and other earth structures that require a plant cover for protection. The rating terms used are: GOOD, FAIR, POOR, AND VERY POOR. Sand and gravel--This column gives information about the soil as a possible source of sand and gravel for con- struction purposes. The ratings are: Probable source (GOOD, AND FAIR), AND IMPROBABLE SOURCE (POOR, AND UNSUITED). Road fill--This column rates the soil material of the solum (surface layer and subsoil) and of the substratum. Road fill is subgrade material that is used to support the subbase and base, or surface course. Soil properties con- sidered in making the ratings are soil texture and its effect on compressibility, shrink-swell potential, and moisture content. The suitability of a road fill depends largely on its texture, moisture content, and location. Normally wet, plastic, clay is rated poor for road fill, and sand is rated poor or fair, depending on its location. Sand is difficult to compact and needs close control of moisture during compaction. Table 12, part B, summarizes soil features affecting local road or streets, reservoir areas, and agricultural drainage. Explanation of Terms: Local roads and streets-—The limitation ratings given in this column apply to use of 80 soils for construction and maintenance of improved local roads and streets. Consist of: (l) underlying local soil material, whether cut or fill, that is called "the sub- grade"; (2) the base material of gravel, crushed rock, lime-stabilized soil, or soil-cement-stabilized soil; (3) the actual road surface or street pavement that is either flexible (asphalt), rigid (concrete), or, in some rural areas, gravel with binder in it. Major factors considered are: soil drainage class, flooding hazard, slope, depth to water table, and shrink-swell potential. Reservoir areas--consideration is given primarily to the sealing potential of the soil, but shallowness to bed- rock and the susceptibility to overflow in flood plains are also considered; so the reservoir areas of farm ponds are adversely affected by rapid permeability, seepage, and flooding. Agricultural drainage--Among the soil features listed are natural drainage, permeability of the soil in place, susceptibility to flooding, and the presence of a seasonal high water table. Limitation of Soils for Town and Countrerlanning These limitations are summarized in Table 13. The following explanations apply to that table. Explanation of Items for: Residences--Residences refer to dwellings of three stories or less. They may be single houses or in a large subdivision. The limitations 81 .mmmcumz "mumumooz .mmmsuma "wumumboz .mmmsumB "mumumwoz a auaaaa auaaaa uuaaaa m unmaam .mmoam "mumumpoe ou usmHHm unmaam m aumsaa uumaaa numasa a mocsoum oacoam mnmum hmam m>wmcmucH mmuflmmfimu . . . mOHUHHHOMM HMSOA$GOHUO¢ Amy .ausaooaa .auaaooaa “magma swum3 zmfls Hmcommmm "mum>0m “wanna Hmum3 amen Hmsommmm "mum>mm a .mannu noun: amen Hmcommmm "mum>mm .manwu Hmumz swan HMGOmmmm "mum>mm m .m>onm mm mEma mnu "mum>mm unmaam m .auON annuauaaa us sunfish ImmEumm 30Hm samumumooa "mum>mm unmflam H mpamsm nouaflm xcmu oeummm mamumsm mmm3mm suassasoo Ho beansm .oz mHHom . . . spas mmoamoflmwm Adv .mcwccmam mnucsou can c309 How mawom mo msowumuflfiaq|l.ma maan .mmmmu Haom mmmnu CH manammomEa maamoauomum ma cowummuomu Assn“ mcouum mo mauuoE mv unusaz map mcausp mmsmoon Mano Umnmpamuoo mm3 Adams mo Duncan mama .mnuu08 my wEHu seesaw was .coHuomm mans uomm 82 .auaaooHa .auaaooaa .muaaooHa .muaaooaa “manna Hmum3 amen amcommmm .muaaooHa “maamu swum3 saw: Hegemmmm “manna nouns “magma Hmum3 “manna kum3 «wuaafluumm “wuwafluuww swan decommmm swan Hmuommwm amen Hmuommmm amusumc amusum: 30H "mum>mm ”mum>mm "wum>mm 30H “mum>mm "muo>mm >Hm> a .oanmu Houmz so“: HMGOmmmm .manmu umum3 .manmu Hmuuz .manmu Houm3 usuaaauumm swan Hmcomwmm 30H: Hmuommmm swan HMGOmmmm mum>0m amusumu 30H "wum>mm "mumumcoz "munumooz ou mumumooz "mum>mm sum> m sufl>auoso cosmouuoo suaaauumm loud 30H mumuouoo no“: Hmuoumu "monumooz usmflam "oumumpoz mumumpoz 30H "mum>mm m sua>fluosc coflmonuoo mafiafiunmm Iona 30H mumuouoo swan amusum: "monumpoz unmflam "mumnwooz mumsmooz 30H "mnm>mm H asumsUCa uumaa now .02 mumpumo msmsoammmue mmusposuum momma Eumm amouo Esau aaaom aaan aaaao for .aauuauuoo-n.MH manna 83 are rated for dwellings served by public or community sewage system and for dwellings that are served by septic tank filter fields. The significant soil properties are bearing strength, shrink-swell potential, depth to seasonal high water table, flood hazard, and lepe. Flooding is a major limiting factor. If a septic tank filter field is required, a high water table and slow percolation rate are major limitations. Increase in slope makes the soil less desirable for construction of sewage disposal fields. Slopes over 12 percent have severe limitations for the layout and con- struction of sewage disposal fields. Side-hill seepage is a problem on sloping areas. Very sandy soils may allow unfiltered effluent to enter and contaminate shallow water supplies. Clayey soils and soils with a high water table may become saturated during wet periods and prohibit proper functioning of the filter field. Recreational facilities:4 Campsites—-are they suitable for tents and camping trailers. It is assumed that little site preparation is needed. Suitability for septic tanks is not a requirement. Soils prOperties that affect this use are depth to seasonal high water table, flood hazard, permeability, surface soil texture, and slope. 4For this section, the summer time (6 months, less amount of rain) was considered only, because during the winter (6 months of strong rain) recreation is practically impossible in these soil types. 84 Intensive play areas--ratings apply to areas to be develOped for playgrounds, athletic fields, and organized games such as volleyball and tennis. All areas are subject to heavy foot traffic. They require nearly level surfaces, good drainage, freedom from flooding during use periods, and a texture and consistence that provides a firm surface. Areas should be free of coarse fragments and rock outcrOps. Picnic grounds-—ratings apply to areas to be used for picnic areas and extensive play areas. Ratings are based on soil features only and do not include other features such as presence of trees or ponds, which affect the desirability of a site. The same properties as for intensive play areas are significant, although wider vari- ation within some properties can be permitted. Other uses: Farm crops--soils are rated in terms of their limitations for common farm crops and pasture. Properties of the soil, erosion hazard, wetness hazard, climate, slope, and general fertility are items considered in this evaluation of the soils. Farm trees--ratings apply to the use of trees for ornamental production. Available water capacity, depth to root restricting layers, and natural drainage are major factors in determining the limitation of the soil. Structures for light industry--include buildings that are used for stores, offices, and small industries; none of which are more than three stories high nor require more than moderate bearing strength. It is assumed that 85 sewage disposal facilities are available. The properties important in evaluating soils for this use are lepe, depth to seasonal high water table, flood hazard, bearing strength, shrink-swell potential, and erosion potential. Trafficways--refer to low-cost roads and residential streets. It is assumed that construction involves limited cut and fill and limited preparation of subgrades. The properties important in evaluating soils for such traffic- ways are slope, depth to seasonal high water table, flood hazard, shrink-swell potential, and traffic supporting capacity. Gardens--include the production of both vegetables and flowers for homes. Properties important in evaluating soils for this use are productivity, depth to seasonal high water table, flood hazard, droughtiness, tilth, lepe, erodibility, and permeability. Soil Surveyjlnterpretations in Brazil (For Reconnaissance Surveys)5 The soil survey interpretation system for reconnais- sance surveys develOping in Brazil comprise: a. A list of properties of soils and environment, such as: mapped area, occurrence, climate, altitude, parent material and litholoqy, natural vegetation, relief, erosion, and so on; 5Bennema; Beck and Camargo, 1964. 86 b. Soil limitations for plant growth and agricultural use; c. Land capability classification. Estimated degree and major kinds of limitations affecting farm uses shown in Table 14 are used as a guide for determining suitability classes of soils, under both Primitive and Developed Management. Explanations of the items considered are discussed next. Estimation of Items: Deficiency of native fertility-- in this case meaning chemical fertility, depends on: 1. The availability of the macro- and micro-nutrients in the soil, and 2. The absence or presence of toxic substances. Usually only soluble salts, and especially sodium salts, are regarded. Other important toxic sub- stances, such as soluble aluminum and manganese, may depress the availability of some mineral nutrients. These toxicities are considered as part of point 1. Deficiency of water--generally is determined as a function of the amount of available water to the plants and of the climatic conditions, especially, precipitation and transpiration. The climatological factors are the only factors of importance, in extreme cases as in the desert and in some super-humid areas, but in the other cases soil factories also have an influence. .ao>osau sHauonsoo on uouuno auoHunuHsHH unuu ounoaauH auaxonun uqu auanssu oaauesm. aun .Hv .suHHHuHaaom oasocoom mo some» may canvas HHHum usnv 3onlsocx Hmoaunoou no Hmuamno anmumvacoo saw: van .mHnHmmmmN H .uuoau>oumaH mo sUHHHnHmmou usonqud .BOHmuo>o ou anaummomsm uuomoum mHHon on» cog: .suaHanduasm mo mmnHo was» uH coHuuuaaHH wouuwahomx .3onl3ocx Hmoacnoou can Hnuwmmo mo wanna couoHuumou nua3 .OHnHmnmu hHHmmm £37 umum>om Hounuouoz couo>om cwuo>om suo> umuo>mm H .umwuH wunumaoz u m Hm manna ouo>om a mum . can no u «No a H u aoz u Hwy u a0: m a0» . u m ASou—sumac: x.H~Vmunuovoz uuaHHa uuaa a u a a aunuuaaoz ma .uana E E H E a 3 u E»: a a chuumHHm aunuaaoa 0:02 one o On oco . H H z AHvu: HHm and up: .Hm H z u aooo .uoHuanuHH usonquv m .QOHo>mo .sounsm unusumnumz ouo>wm sum> wum>mm sum> 0H0>om wum>mm >uo> muw>wm sum> H .ummcH xmuo>oa ouo>mm muo>om ou oumuouoz ouo>om ouo>om m .vouowuummm munuwaoz munuoaoz ounnovoa ou uanHm ounuoaoz munumvoz m .anm ounuovoa uuaHHa uuaHHa aun auoz auaHHa aun auoz aun uuaHHa uuaHHa 0» auoz a .aoou <63fl5fl.8$$u553§z suauauonz uoaaoum on among Hanna suHHHuuaa aaaanHo HMH=UH50Hum¢ suHHHQHumoomsm mo mmooxfi mo 0>Humz mo suHHwnmuwzm now was socoHoHuoo houmwoauoo aaaa suns you aHHoa no uoHunuHaHa .HHunum ca uuoammmcuz vomoHo>wo can 0>HuHaHum nuom Home: mHHom no mmnHo suHHanduHsm mcflcasuouoo How oHnma ocasoul.vH anma 88 In well-drained soils this is especially the amount of available water which can be stored, and this amount depends on a set of single soil properties, among which are texture, kind of clay, carbon content and effective soil depth. Excess of water or deficiency of oxygen--is mostly related to the drainage class, which is the result of climatological conditions (precipitation and evaporation), local relief, and soil properties. In soils with low water table the more important are: structure, permeability, and depth to a less permeable layer, if present. The depth of water table, in soils with high water table, is important too. It is evident that, in general, a direct relation must exist between drainage class and deficiency of oxygen, because the drainage classes are essentially defined in terms of excess of water. Some discrepancies may, however, exist in practice because the essential point in the classes of deficiency of oxygen is the reaction of plant- life, while in the drainage classes soil profile character- istics are taken to determine the drainage class. This relationship does not persist if the soil is artifically drained. Susceptibility to erosion--consideration is given here to erosion by water, only. Susceptibility to erosion by water depends, besides climate, on topography and soil, also on the land use, and on the vegetation of the land. The standard for susceptibility to erosion is the erosion 89 which would occur if the land would be used for cultivated agriculture, such as growing crops which are not soil protectors and neglecting to take measures to prevent erosion. Use for agriculture machinery--This agricultural factor depends on slope, absence or presence of stones or rocks, absence or presence of extreme shallowness of the soil, at least if underlain by consolidated material or by material unfavourable if ploughed up, bad drainage con- ditions, and extreme in properties of the soil material, such as clayey texture with the presence of 2:1 layer silicate clays (often together with drainage conditions), organic soils, or loose sandy soils. In the case of mechanization, it should be noted that an area which has no impediments to mechanization should have a minimum size to be of importance. Table 15 lists the estimated degree and major kinds of limitations for farm uses of soils, and how these relate to suitability classes with primitive or developed management systems. MANAGEMENT SYSTEM, PRIMITIVE, A This system is characterized by using traditional methods of tiallage which reflect a low level of technical operational knowledge. There is no capital input (invest- ment) for fertilizers and corrective applications, as well as for maintenance and improvement of soil conditions and of the tillage. The land use is not permament, because it .ousuau unauououm ou uouocu00u mom "ouoz 90 .unm 1+2 domv .ancun .ausduuv .mucmucoo .muduouoa sHuoom mucoauudu m m .2235 on £38 0:02 ouoz 53330: .9825 0:02 auoz 5.23% 30H .333 a 093 +++H¢ fiomA .Ho>duo .aocauuu .muuouuoo .ounumaoa sHuoomuomld uuoHuusu 30H m m .wvusmHHm ou uanHm Hocoz unmaHm AuvusmHHm ..oumuoooz ocoz ouoz vaoumuovoz .ouo>0m >uo> m 093 .Ho>uuu +++H¢ vomA aud.v:au .muuoucou .ouauoaoa anemones uuoauus: 30H m H 3338 on £38 Houoz 3 238 333 uu3Hm £38 233 A338.302 655a suo> a .uum .Hgnua +++Hn aomv can nude .uuuouuoo oumuocos ucoauuau a n 3233 3 £33 Houoz £33 £38 £31.... 233 9:38 .8333 30H .3255 H m d m d m 4 m 4 m a n a nlllllllllllll .oz mamumhm uqummmuu: suocanouz cowmoum ou nouns mo mmooxfl nouns auHHHuumh 0>Humz oHHmoum ha momunHU >UHHHnduHsm HausanOHuma we was huHHHnHumoomam uo hucowoauoo mo sucoaoamoo .aHHow on» no .wauumsm uucswmusdz sh mono HausuHsOHumd muauuouua ucowunuHsHH no mvuax scan: and acumen nouosaummul.mH «Hana 91 is native fertility dependent, so when the production goes down, the land is abandoned for recuperation. Animal power and only the more simple farm imple- ments are used. Suitability classes CLASS l--GOOD, G. None of the soils of the sequence was classified in this class; CLASS 2--FAIR, F. None of the soils of the sequence was classified in this class; CLASS 3--RESTRICTED, R. The soil conditions present moderate limitations for growing a large number of climatically adapted crops. It is possible to foresee a medium harvest during the first years, but they rapidly decrease to a low level within a 10 year period; and CLASS 4--INAPT, I. The soil conditions present severe and very severe limitations for growing a large number of climati- cally adapted crOps. It is possible to foresee low to very low harvest in the first years already. MANAGEMENT SYSTEM, DEVELOPED, B (without irrigation). This system employs a high level of technical- operational knowledge, including experimental data. There is a high input of capital for maintenance and improvement of soil conditions and of the tilth. If necessary and 92 feasible, artificial drainage and erosion control are done as well as the employing of fertilizers, correctives of the acidity, insecticides, and herbicides. The tractor which includes the whole set of power-operated equipment is used. Suitability classes CLASS l--GOOD, G. None of the soils of the sequence was classified in this class; CLASS 2--FAIR, F. The soil conditions present slight limitations for growing a large number of climatically adapted crops. It is possible to foresee that 329d harvest can be obtained in most areas, but the Option for crops, income maintenance, and a selection of management practices are restricted by one or more not feasible limitation of correction or can be partially corrected only; CLASS 3--RESTRICTED, R. The soil conditions present moderate limitations for maintenance of climatically adapted crops. The harvests are seriously reduced and the option for crops is very restricted by one or more limitations that cannot be removed; CLASS 4--INAPT, I. None of the sequence was classified in this class. V. CONCLUSIONS Four Ultisols of a soil sequence in the warm, humid tr0pics of Brazil were studied. The parent material varied from granite-gneiss to relatively recent sandy-clay colluvium or alluvium sedi- ments. In soils of the slopes, some reworked materials have had an influence in soil formation. The soil sequence has been developed under very acid conditions. They are dystrophic and have low activity clays. The low cation exchange capacity, low exchangeable calcium, magnesium, and potassium, low base saturation, and relatively high amounts of free iron oxides (as well as extractable Al+++) all indicate strongly weathered soils. Variations among profiles in this sequence are accounted for by differences in topography and parent materials. Coarse fragments are composed mostly of quartz and quartz is prevalent in the coarse and fine sands. Some horizons also contain iron concretions and ferruginous clay fragments. Kaolinite is the predominant clay mineral (greater than 95%). This is consistent with the observations of 93 94 Sanches and Buol on well drained soils in the upper Amazon Basin in Peru. Dithionite pretreatment was more effective than ammonium oxalate in removing coatings from the clays in the subsoil horizons. This is shown by greater increases in X-ray diffraction peaks of kaolinite, in comparison with no treatment. In the A horizons dithionite normally increased the kaolinite peaks much less than in the B horizons in com- parison with no treatment. The A1 of profile 4 showed higher peaks with no treatment than with dithionite. In the A horizons ammonium oxalate decreased the kaolinite diffraction peaks, in comparison to no treatment. In- creasing of the peak heights was associated with high per- centages of Al+++ saturation and high degrees of clay flocculation. Presence of plinthite was confirmed only in the two better drained soils. Thus, in the future during soil descriptions, better observations should be made by soil scientists where plinthite is suspected to be present. Plinthite must be separated from red mottles and the amount present measured or estimated. Profiles 1, 3, and 4 were classified as Paleudults, due to the clay increase from the surface to the lower horizons. Profile 2 fits in Plinthudults, due to plinthite forming a continuous phase. The U.S. Taxonomy has not differentiated any subgroups for this great group. However, 95 profile 2 could be classified as an Oxic Plinthudult, because it shows a high degree of clay flocculation and a low activity clay (after correction for carbon). Profile 1 is in the Plinthic Paleudult subgroup due to more than 5 per— cent Plinthite in a non-continuous phase. Profiles number 3 and 4 are in the Aquic Paleudults. The soils with more restricted drainage (profiles 3 and 4), present moderate and severe limitations for agri- cultural uses. Under primitive management systems pro- files 1 to 4 fit into restricted, inapt, restricted, and restricted classes. Under developed management systems they can improve only one class. Profiles 1 to 4 then fit into fair, restricted, fair, and fair classes, respectively. LITERATURE C ITED LITERATURE CITED Agrochemical Methods in Study of Soils. Translated from Russian 4th ed. 1965. Published for the USDA- §g§ and The Indian National Scientific Documentation Centre. New Delhi, pp. 61—68 and 586-588. Alexander, L. T. and J. C. Cady. 1962. Genesis and Hardening of Laterite in Soils. SCS-USDA. Tech. Bull., No. 1282. Arshad, M. A., R. J. St. Arnaud, and P. M. Huang. 1972. Dissolution of Trioctahedral Layer Silicates by Ammonium Oxalate, Sodium-Bicarbonate and Potassium Pyrophosphate. Can. J. Soil Sci., 52:19-26. 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