Soil Transitions in Central East Botswana (Africa)

SOIL TRANSITIONS IN CENTRAL EAST BOTSWANA (AFRICA)

W. SIDERIUS This thesis will also be published as a publication of the International Institute for Aerial Survey and Earth Sciences (ITC) — International Soil Museum. Soil Transitions in Central East Botswana (Africa) Printed by Krips Repro Meppel Scanned from original by ISRIC - World Soil Information, as ICSU World Data Centre for Soils. The purpose is to make a safe depository for endangered documents and to make the accrued information available for consultation, following Fair Use Guidelines. Every effort is taken to respect Copyright of the materials within the archives where the identification of the Copyright holder is clear and, where feasible, to contact the originators. For questions please contact [email protected] indicating the item reference number concerned.

Soil Transitions in Central East Botswana (Africa)

Proefschrift

ter verkrijging van de graad van doctor in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit te Utrecht, op gezag van de Rector Magnificus Prof. Dr. Sj. Groenman, volgens besluit van het College van Dekanen in het open- baar te verdedigen op woensdag 2 mei 1973 des namiddags te 2.30 uur

door

Woutherus Siderius

geboren op 13 augustus 1940 te Baarn PROMOTOR: PROF. DR. IR. F. A. VAN BAREN ACKNOWLEDGEMENTS

This study was conceived thanks to the co-operation of many who directly or indirectly were associated with its development. I am, Prof. Dr. F. A. van Baren, in particular indebted to you for your scientific advice and organizational endowments that enabled me to follow up my work in Botswana at the Soils Institute at Utrecht, and to use the facilities of your Department. Your concurrent effort and personal concern made it possible to bring this study to its conclusion.

I owe sincere thanks to you, Mr. W. L. P. J. Mouthaan, B. Sc, not only for your valuable suggestions in the field of the sand mineralogy, but moreover, for your philosophical insight relative to soil genesis and your guiding support.

It is a pleasure to thank J. G. Pike, M. Se, FAO project manager, for his interest and help towards the accomplishment of this investigation, and also my colleagues of the FAO integrated survey team, of which I owe special thanks to H. J. van Rensburg, M. Sc. for valuable suggestions concerning the description and recording of the vegetation.

I am grateful to the UNDP Office in Gaborone, Botswana, for their assistance in the realization of this study and to the Department of Surveys and Lands for permission to use cartographic material. My gratitude is further extended to Dr. R. Dudal and A. J. Smyth, Esq. of the FAO Land and Water Development Division, for their comprehension comparative to the subject, and to Dr. R. F. Loxton, consultant, for his constructive ideas made during his sojourns in Botswana.

Professor Dr. J. I. S. Zonneveld and the Staff of the Department of Physical Geography (Utrecht State University), Prof. Dr. D. J. Douglas and Prof. Dr. J. F. M. de Raaf, I acknowledge the profound scientific teaching received during my University education.

I express gratitude for the valuable critisism of Dr. L. Bal, D. Greutzberg, M. Sc, Dr. J. J. Reynders and N. M. de Rooij, M. Sc, on selective chapters of the manuscript. The help of G. A. E. M. Hermans, M. Sc. and Dr. P. Maaskant in the determination of the rock specimen is appreciated, and the latter is thanked for his part in the electron microprobe determination. Discussions with j. i>. Al, B. Se, J. H. V. van Baren, M. Se, J. A. . Boertna, M. Se. and S. P. Tjallingii, M. Se, prevented imperfections. I am grateful to the following persons for their expertise help, Mr. J. Drenth, Mr. H. E. Renaud, Mr. J. D. Schreiber, Mr. D. de Vries, Mr. J. van der Wal and Mrs. I. W. J. Wolters.

Thanks are also due to Mr. F. Henzen and Mr. I. Santoe for their assistance in drawing most of the diagrams and the reproduction of many illustra- tions.

I am grateful to A. Muller, M. Se, and his Staffat the Soils Laboratory of the Royal Tropical Institute, Amsterdam, for the able way in which a number of analyses were carried out, and for the facilities made available to me. The pleasant company of Mr. L. Lebodi on many field trips is memorized with great appreciation.

I thank Miss Weia S. Smid for her efficient typing of the manuscript. My grateful thanks go to Madame V. Balikci-Ossent and to my wife, for the correction of the English.

This research was for the major part financed by the Netherlands Foun- dation for the Advancement of Tropical Research (WOTRO), The Hague. Its publication was supported by a grant from the Netherlands Ministry of Education and Sciences.

Sincere appreciation is bestowed to the Ministry of Agriculture of the Government of Boswana for their authorization to undertake this investigation and permission for its publication. CONTENTS

INTRODUCTION CHAPTER I ENVIRONMENTAL CHARACTERISTICS 15 1.1. Climate 15 1.1.1. Atmospheric climate 16 1.1.1.1. Precipitation 16 1.1.1.2. Temperature 17 1.1.1.3. Evaporation 18 1.1.2. Soil climate 19 1.1.2.1. Soil temperature ,20 1.1.2.2. Soil moisture 23 1.1.3. Paleoclimate 24 1.2. Geology 28 1.2.1. General 28 1.2.2. Parent material 30 1.3. Geomorphology 39 1.3.1. Topography 39 1.3.2. River systems 40 1.3.3. Landscapes 43 1.4. Vegetation 47 1.4.1. Natural vegetation ,47 1.4.2. Human induced vegetation 51 1.4.3. Vegetation patterns 52

CHAPTER II TYPICAL SOILS 55 11.1. Location of sample sites 55 11.2. Field observations 56 11.3. Soil properties 84 11.3.1. Bulk density 84 11.3.2. Soil reaction • 84 11.3.3. Exchange capacity 85 CHAPTER III SOIL COMPOSITION 89 III. 1. Fragments coarser than 2 mm 89 111.2. Grain size distribution in the fine earth 89 111.2.1. Sand 90 111.2.2. Silt 91 111.2.3. Clay 91 111.3. Elemental composition of the fine earth 95 111.3.1. Major elements 95 111.3.2. Trace elements 100

7 111.4. Mineralogy of special constituents 103 111.4.1. Mineralogy of the sand fraction 103 HI.4.1.1. Heavy minerals 104 III.4.1.2. Light minerals 109 111.4.2. Mineralogy of the clay fraction 112 111.5. Organic matter 116 III6. Salinity 118

CHAPTER IV ARRANGEMENT OF SOIL CONSTITUENTS 121 I V.l. Micromorphological observations 121 IV.2. Evaluation of the field data 140

CHAPTER V ROCK WEATHERING AND SOIL FORMATION 147 V.l. Rock weathering 147 V.2. Soil formation 152

CHAPTER VI SOIL CLASSIFICATION AND LAND USE 167 VI.1. Soil classification 167 VI.2. Land use 171

APPENDIX I METHODS 175 1.1. Survey methods 175 1.2. Laboratory methods 175

APPENDIX II SOIL PROFILE DESCRIPTIONS AND LABORATORY DATA 182

SUMMARY 245

SAMENVATTING 247

REFERENCES 249

CURRICULUM VIT AE 260

UPPER CATCHMENT OF THE MAHALAPSHWE AND BONWAPITSE RIVERS * North

iliiilllip ridge

i^. J. Location map of the investigated area INTRODUCTION

The importance of natural resources for Botswana, as expressed by this country's export data, but even more as the basis for the life of more than 95% of its population, is well understood by the present Government. Inventarization of these resources has proceeded rapidly since the country's independence in October 1966. Within this programme, integrated surveys were initiated in Northern and Eastern Botswana from 1968 to 1972 as part of a FAO/UNDP-SF project. One aspect of these were a number of soil surveys carried out by the author on different levels of intensity. Although much data was gathered, advanced soil research on genetic and related fields of interest could not be conducted within the current project programme. This was felt to be necessary, however, in order to come to a better understanding of the soil's properties and characteristics. For that purpose, an area was selected in Central East Botswana (fig. 1). The area located just north of the Tropic of Capricorn at 26° 18'—26° 50' E and 22°45'—23° 18' S comprises the upper catchment area of two tributaries of the Limpopo river, namely the Mahalapshwe and the Bonwapitse. In these catchment areas a number of representative soils were selected after the area was surveyed on semi-detailed level. Differentiating environmental characteristics played an important role in locating the sample sites. A total of 154 soil samples was collected and they form the raw material for this study, together with four samples from streambeds and ten rock specimens. Under the present semi-arid climate, a number of soils or soil characteristics seem allochthone and questions about their present development and potential are better answered by looking into the past. The factors influencing the pedosphere are dealt with in Chapter I. Decisive information concerns particularly the sections on climate and geology. The bulk of the soil data is presented in Chapter II, field descriptions and laboratory data provide the necessary background for further detailed studies. The results hereof, with special reference to the mineral constituents of the soils which account for more than 99% of their assemblage, is the subject of Chapter III. As a logical development, the arrangement of these soil constituents are then discussed and described in Chapter IV. Together with the material from the foregoing chapters, main conclusions about rock weathering and

13 soil formation are presented in Chapter V. The last chapter deals with some aspects of the soil classification, also a short assessment is given on the agricultural use of the investigated soils. Although a great amount of information was gathered and used, a substan- tial field of research of these or similar soils lies open. Present findings do however close a gap between much fieldwork and laboratory data and may form the foundation for further research on Botswana soils, of which previously little was known. The relevance of our results in stressed not only to the area studied but also to similar areas in the world. This concerns the soil's morphology in the field as well as the laboratory approach. New procedures for the computing of the data were applied and these and other results are a novelty in the research on these soils. Apart from the scientific approach and its worth, may this publication be an aid to a better utilization of the land, creating thus a more prosperous sphere for the people living on it.

14 CHAPTER 1

ENVIRONMENTAL CHARACTERISTICS

I.I. Climate

1.1.1. Atmospheric Climate The central land-locked part of Southern Africa to which Botswana belongs is affected by a wide range of climates. Greatest contrasting differences occur in the country from the extreme southwest to the northern part of the Chobe region, viz. from arid to sub-tropical conditions. The eastern part of the country in which the survey area is located has a semi-arid climate, classified by Koppen (1931 ) as BSHw and characterized by Finch et al. (1942) as a dry climate of low latitudes-Bsh. This climate is also known for the summer rainfall when unstable equatorial air masses are farthest poleward. Recent work has revealed six characteristic synoptic situations which are responsible for the weather conditions in this part of the Southern Hemisphere (Schulze, 1965; Pike, 1971). The main factors that control in first instance these climatic conditions are as for any place on earth: 1) its latitude, which determines the amount of solar radiation (just north of the Tropic of Capricorn), while the amount of solar radiation expressed in cal/cm2 per year is about 281.000; 2) its position relative to the distribution of the sea and the land, most of the South African subcontinent is under the influence of the westerly circulation; 3) its height above sea level (Schulze, 1 965). Grouping these situations, Pike (1971) recognizes the following succession of air masses and their result when they approach the fairly flat table land of the interior. First come tropical continental air and superior air which have subsided from high latitudes within the anticyclones of the subtropical high pressure belt. In winter the superior air is brought to Botswana by NW winds and gives rise to warm and sunny days and cold clear nights. This weather prevails from April to September. The tropical air mass comes as NE and N winds in summer. The air is generaly warm and moist as the original subtropical high pressure belt becomes moistened over the humid lowlands of the East of Southern Africa. Thunderstorms commonly develop. The effect of the equatorial air mass is occasionally felt in the North of the country and in general tends not to pass south of 20 S latitude, if so,

15 the southernmost limit of the inter-tropical convergence zone brings more rain. At the beginning of the winter the superior air may be disturbed by cold polar and sub-polar air masses from the Antarctic, occasionally causing frost. The rythmic change in the weather conditions gives rise to the recognition of a number of seasons. Of these the summer and the winter are the most outspoken. Summer: December—January—February Autumn: March—April—May Winter: June—July—August Spring: September—October—November The effect on the ground resulting from the circulating of the different air masses is expressed in a number of climatological data such as precipitation, temperature and evaporation. As key metereological station for the study area Mahalapye with a thirty-year record was chosen, while for comparison a second station was selected in the southeastern part of the country, Gaborone.

1.1.1.1. Precipitation The rainfall in the northern part of the country is received due to the attenuated effect of the inter-tropical convergence zone, in the eastern part it is dependent upon the positions of the tropical continental air. Thus rainfall in the eastern part of Botswana is brought about by a weakening of the anti-cyclone which promotes the flowing in of moist air from the Indian Ocean.

Table 1. Mean monthly and annual rainfall in mm over the period 1939/40— 1968/69

Month J F M A M J J A S O N D Year Station

Mahalapye 73.0 91.8 67. 5 33.7 12. 9 6.3 0.6 1.4 7.2 29.5 70.1 82. 6 476 .4 Gaborone 81.7 80 .6 68. 6 51.4 15.3 10. 5 4.4 3.1 12.9 43.8 58.7 87.9 518..7

The location of the stations is Mahalapye 23° 04' LAT. and 26° 48' LONG, and altitude 1001.0 m and Gaborone 24° 10' LAT. and 25° 55' LONG, at an altitude of 980.0 m. Although the yearly total precipitation (table 1) compares favourably with other semi-arid areas, a high degree of variability and intensity is recorded, which reduces the effect of the rainfall with regard to soil

16 moisture and groundwater conditions. The variability expressed as the coefficient of variation was calculated on a decade basis as selected by Pike (1971) for a number of key stations. This percentage is 33.5 for Mahalapye and 28.6 for Gaborone. The coefficient of variation is generally inversely proportional to the annual rainfall. In the survey area the annual rainfall in the East exceeds 450 mm with a 60% probability that the rainfall will exceed at least 400 mm in any one year. Similar calculations were carried out by Jackson (1970). In extreme cases of limited rainfall, drought may occur. They are defined as such if the probability of the annual rainfall is less than 60% of the mean annual rainfall. Drought periods in Mahalapye may occur in one out of every eight years and in Gaborone in one out of every 15. Apart from the amount of rainfall its mode of precipitation is important. Unfortunately the rain falls often as heavy showers (up to 125 mm) causing rapid run-off and erosion, with little contribution to the storage of water in the soil. Continuous spells of soft penetrating rain are relatively scarce. Over the year there are: 40—60 days/annum with 0.25 mm or more rain, and 10—20 days/annum with 10 mm or more rain. In addition, dry periods within the rainy season are common especially in late December and early January. Long term prediction about the trend of the rainfall is difficult to make. However, there are indications that the mean annual rainfall is decreasing; if this turns out to be exact it might have a disastrous effect on the current farming practices.

1.1.1.2. Temperature The air temperature, and to a large extent the soil temperature, is almost entirely determined by the sun energy transmitted as visible and heat rays. The incoming energy is governed by a number of environmental factors such as cloudiness, vegetation, slope and latitude (Russell, 1961). The average solar radiation for the two stations is given in table 2.

Table 2. Average solar radiation in calclcni1 day-monthly

Month J F M A M J J A S O N D Station dahalapye 558.5 550.2 476.8 402.3 372.5 327.0 350.6 420.2 454.3 513.1 529.2 532.2 Gaborone 594.5 470.8 499.8 417.1 383.7 341.8 268.6 433.5 510.6 554.0 570.7 588.8

The duration of bright sunshine falls between 70—90% of the total possible. The values recorded in the summer months are somewhat lower

17 due to cloudiness, the higher values of duration occur during the winter season (Schulze, .1965). The resulting air temperatures are presented in table 3.

Table 3. Mean monthly and annual temperature \n C.

Month J F M A M J J A S O N D Year Station

Mahalapye 25.,2 24.8i 23.4 20.4 16.5 13.2 13.2 16.1 20.5 23.5 24.6 24.4 20.5 Gaborone 25..5 25.1 23.3 19.4 15.2 12.0 12. 1 15.3 20.3 23.3 24.5 24.7 20.1

The temperature range reveals the distribution of the seasons, but hides the occasional extremes that may occur. An example is the occurrence of groundfrost, caused by active terrestrial radiation. Lowest temperatures are recorded in June and July (13.2° C). The highest mean values are registered in January for both stations. The maxima and minima temperatures are furthermore presented in table 5 (section 1.1.2). With reference to the main westerly circulation, it is noted that the maximum temperature over the oceans is retarded by approximately two months in relation to the maximum of the solar radiation at the summer solstice, which falls on 21 December (Pike, 1971). The combination of rainfall (P) and temperature (T) has lead certain authors to define the dry season (Gaussen, 1963). By application of the formula P = 2 x T as the definition for the dry period, this period would occur in East Botswana for six months, with emphasis on the period from May to August. Chemical weathering during this period will be considerably reduced. Physical weathering, being the breakdown into smaller fragments while the chemical composition remains unaltered, may be increased due to sharper diurnal temperature contrast.

1.1.1.3. Evaporation The resulting effect of rainfall and temperature calculated for the evapotransporation shows a deficit in all months of the year for the Mahalapye station. Data on the evaporation (Eo) and the potential evapotransporation (Ept) are given in table 4.

As shown by Pike (1971), a factor of 0.68—0.75 must be applied to the evaporation figures from pans to obtain real natural open water rates. A composite diagram of the mean precipitation (P), air temperature (T) and potential evapotranspiration (Ept) (fig. 2) demonstrates clearly the marginal conditions for intensive agricultural use of the land with regard to cropping.

18 Table 4. Mean monthly and annual evaporation data in mm for Mahalapye

Month J M J J Year open water (Eo) 212.8 181.6 165.3 123.9 91.4 68.0 77.6 109.8 154.9 197.5 198.5 203.8 1785.1 short green crop (Ept) 168.3 140.8 128.2 94.7 65.5 48.3 54.9 77.7 120.7 157.3 176.9 161.7 1395.0 wet bare soil (Ept) 157.2 131.8 119.6 87.4 59.5 42.6 49.6 73.9 112.6 146.9 149.6 151.1 1281.8 pan (Eo) 247.5 207.8 210.9 157.1 130.0 102.5 119.8 154.0 214.2 264.1 247.3 242.0 2297.2

The occurrence of rainfall during the summer season promotes high evapotranspiration rates, which results in a limited improvement of the moisture conditions in general.

mean monthly rainfall in mm. ,, „ Ept short green crop in mm. „ ,, „ wet bare Soil in mm. ,, ,, air temperature in °C STATION : MAHALAPYE

Fig. 2. Composite diagram of mean P, T and E„( values for Mahalapye

1.1.2. Soil Climate The climate of the pedosphere may be characterized by two factors, namely soil temperature and soil moisture. Both factors have considerable influence on a) the kind of soil processes that takes place and b) the rate at which these processes occur (Mohr and Van Baren, 1959).

19 1.1.2.1. Soil Temperature Soil temperature data are available for the Mahalapye station and are used as an indicator for the soil climatic conditions in the study area. Unfortu- nately, these data cover only one season. Comparative data are therefore also given for Gaborone which has an eight-year record. These data are comprised in table 5 while temperature graphs are given in fig. 3. The temperature readings were both taken in a reddish brown sandy clay loam comparable to profile 3, as described on page 47, with a bare surface.

Tin °C 40 I

20-

JFMAMOJASOND STATION: GABORONE years 1962-1970

T.in°C 40 ï

20-

3FMAMJJAS0ND

STATION: MAHALAPYE year 1968-1969

mean monthly air temp „ ,, soil at. 10 cm ,i ii 60 „ , „ 120 „

Fig. 3. Mean monthly air and soil temperatures for Mahalapye and Gaborone

20 Tabel 5. Soil temperature data in C

Station Mahalapye depth yearly monthly mean absolute difference cm mean highest lowest max. min.

10 25.1 34.2 14.7 38.9 10.4 28.5 30 25.0 32.6 18.3 34.2 16.7 17.5 60 25.0 32.2 17.3 32.3 17.2 15.1 120 24.9 29.9 19.1 30.7 18.6 12.1 air temperature 20.5 25.2 13.2 27.5 10.4 17.1

Station Gaborone 10 25.3 35.5 10.8 39.7 5.6 34.1 20 25.0 35.4 13.3 36.6 11.1 25.5 30 25.0 34.4 15.4 36.1 13.6 22.5 60 24.9 31.7 16.6 35.0 13.8 21.2 120 24.8 30.0 18.9 31.7 16.7 15.0 air temperature 20.1 25.5 12.0 35.1 1.8 33.3

The fluctuations of the soil temperature generally follow those of the air temperature. Maxima and minima are, however, delayed by about one month. The mean total soil temperature closely follows the values obtained at a depth of 60 cm (fig. 3). The amplitude of the variation of the soil temperature decreases with depth. Lowest monthly soil temperature data are recorded at both stations in July while highest temperatures occur in January. Changes in soil temperature, which become apparent upon comparison of summer and winter data, are considered characteristic of the climatic conditions at this latitude (fig. 4). The temperature decline in autumn and the temperature rise in late winter and spring have implications for the behaviour of water as vapour or liquid in the soil (see section 1.1.2.2).

The monthly fluctuations are of equal importance as the amplitude and regime of the soil temperature on a daily basis. The latter was taken at 08.00, 14.00 and 20.00 GMT at five different depths, mean values are calculated and presented in table 6.

Daily variations are greatest at or near the soil surface but decline beyond 60 cm depth. This is the result of the conductivity of the soil and shows how soil temperatures are influenced by atmospheric conditions. From figure 3 it is evident that soil temperature closely follows air temperature depending on cloudiness, amount of radiation, rainfall and cooling off in

21 T.,n°C 40T

10 cm ^ .—

_.__ Tr.6Q.en) 120 cm 30-5

JANUARY

120

60 ^^ ^——-"TJI-— —*~c^^

DUNE

1 — . i 20,00 hrs. G.M.T.

mean daily soil temperature at 10 cm depth ,. „ ,, „ 20 ,, ,, 30 „ .. , 60 ,, „ ...... „120,,

Fig. 4. Mean daily soil temperatures for the months January and June the evening and night hours as a result of strong surface radiation. Taken over the year, the mean soil temperature is 4.9° C warmer than the mean air temperature in Gaborone (25.0 versus 20.1° C), while the difference in Mahalapye is 4.5° C (25.0° C for the soil and 20.5° C for the air). This is a departure from the usually accepted rule that the mean soil temperature could be deducted from the mean annual air temperature by adding one degree Celsius to the latter value (Soil Survey Staff, USDA, 1.970). A similar temperature course has been reported in other notably semi-arid countries (Buursink, 1971). In terms of classifying the soil temperature regime the criteria of the 7th Approximation (1970) have been applied. As such the soils may be described as having a hyperthermic temperature regime. The effect of the soil temperature on biological and mineral processes in the soil has been and still is the subject of considerable research (Kai et al., 1969;Mueleer, 1970; Power et al., 1970).

22 Our readings of the soil temperature suggest favourable conditions for biological life, germination and weathering. Summerizing, Russell (1961) states the optimum conditions for germination between 18—22° C. The recorded temperatures in Botswana indicate that during summer this value will be exceeded at the topsoil. Optimum temperatures for the development of soil microbes are present (24—35° C), but higher values are probably at the soil surface.

Table 6. Mean soil temperature in Cat Gaborone over the period 1962—1970

Month J FMAMJ J AS OND depth in cm

10 31.8 31.8 30.3 25.3 20.2 15.9 16.1 19 .9 23.8 27.8 29.9 30.7 20 32.9 31.3 29.4 24.3 20.1 15.9 15.8 18.8 23.8 26.6 30.0 31.2 30 32.4 31.6 28.9 24.6 20.4 16.4 16.2 18.8 23.7 26.9 29.6 30.5 60 31.6 30.4 29.0 25.1 21.5 17.6 16.9 19.1 23.3 25.8 28.5 29.5 120 30.0 29.4 28.2 25.7 23.4 20.2 19.2 19.7 22.4 24.8 26.8 27.8

The high soil temperatures do however accelerate the decomposition of plant material as was demonstrated by Mohr and Van Baren (1959). A complete and rapid decomposition of organic matter is recorded at 32° C, a slower rate of mineralization at 24° C, and one third of the 32° C rate, when the temperature is 1 5.5° C. Subsequent low carbon and nitrogen percentages in the soils encountered seem to support these findings. It is understood that many of these processes are considerably slowed down when soil water is insufficient.

1.1.2.2. Soil Moisture Soil moisture conditions in the encountered soils do not only depend on the amount of precipitation and its intensity and distribution, but even more so on chemical and physical soil characteristics. Of the latter the soil texture is an important factor as it affects to a considerable degree the amount of water that will penetrate into and be held by the soil (Abrol et al, 1968). Data on infiltration rates of topsoil in Botswana is scarce and are held to range between 8.89 and 12.19 cm/hr for a sandy loam texture (Siderius, 1972). No moisture readings were carried out in the soils encountered; field observations suggest, that at the end of the dry season (late September) the top 60 to 90 cm of moist soils are dry. In any case they are far below field capacity (1/3 atm.) and close to the wilting point (15 atm.).

23 Some moisture may be encountered below this depth, but it is question- able if this water can be consumed by plants. Observations in riverbeds of a coarse sandy texture confirm the depth of 90 cm to which the soil may dry out due to evapotransporation. If soils are covered by vegetation their water balance may be even less favourable. Related to soil moisture obtained from rain water is the fact that in none of the soils groundwater was observed, so that the water supply from a subsoil may be disregarded. Perched water tables may occur at low topographic positions during the rainy season but are not persistent. The water storage in the soil is therefore thought to be nil. This is theoretically exact if moisture values are obtained according to the procedure as outlined by Thornthwaite and Mather (1957) ranging from the surface to a depth of 90 cm. These data also support the calculation by Black et al. (1970). Rainfall is apparently sufficient to support the vegetation as described in section 1.4., meaning that the available water holding capacity of the soils during the growing season (from October to March) is adequate. During the rest of the year the vegetation is dormant and adapts itself to the dry conditions. In terms of the USDA (1970) classification, the soils have an ustic moisture regime. This is defined as a limited amount of moisture present in the season when the soil is warm. The amount of soil water, particularly water vapour, and its rate of movement are in turn influenced by the soil temperature. On an annual basis, the soil temperatures have an upward gradient from June to January and a downward gradient during the late summer and autumn. As soil water vapour tends to move from warm to cold soil masses, the infiltration rate of water may be opposed by the upward temperature gradient in the spring and early summer. In the latter part of the summer and in autumn, water may be transmitted more easily through the soil (Rose, 1969). Similar interpretations can be applied to the daily temperature gradients. Little is known about the implications for the application of water, for example for irrigation.

1.1.3. Paleoclimate The study of the climatic past of Africa has yielded a number of different opinions and is still controversial in many ways. A point that led to confusion is that the initial geological stratification for the Quaternary was also used for climatic interpretations (Cooke, 1957). In addition, much of the salient discoveries were made in the Southern Hemisphere, notably in East Africa where a correlation could be established between geological formations and the dwellings and remains of the early hominid.

24 The subdivisions of the Quaternary in Kageran, Kamasian (divided in Kamasian sensustricto and Kanjeran) and Gamblian were consequently used to indicate pluvial periods. Temptation was great to link these pluvials with the glacial periods in the Northern Hemisphere, especially with the well-known sequence in Western Europe. Frenzel (1967) indeed suggests that climatic changes were syn- chronous in both hemispheres. Other workers are more cautious as to the exact dating of the periods in Africa, especially in the southern part of the continent where it remains difficult. Flint (1959) made an excellent contribution in an attempt to unravel the confusion in chronology and correlation. Since then numerous factual studies have been published. Those by Van Zinderen Bakker (1963, 1964) contributed much to the exact dating of the stages of the Pleistocene by means of pollen analyses through which temperature changes could be better detected. Suggate (1968) and Morrison (1968) base their conclusion mainly on the weathering and state of weathering of the geosol, as does Kubiena (1963). The opinion of the latter that the change in temperature foremost induced a change in precipitation is supported by many workers. An attempt to absolute chronology was undertaken by De Heinzelin (1964). However, lack of data prevents a complete record of successions in Southern Africa, especially since it is unlikely to discover remains of humans in an environment which was hostile to them at the beginning of their era due to very dry conditions (Korn et al., 1957). Thus precise equivalence of glacial and pluvial periods in both hemispheres is improbable, but may in some areas be closer than in others (Cooke, 1957; Fairbridge, 1963). That changes in climate have taken place in Central Southern Africa was proved in addition to paleo-botanical research by a number of landscape and geological studies (Bond, 1957 and 1963; Korn et al, 1957; Mabbutt, 1957; Bosazza, 1957; Flint et al., 1968; Netterberg, 1969). To summarize, Bond (1964) states that a wet (more humid) climatic phase may show an increase in rainfall of 50%, while during a dry phase minimum rainfall is less than 50% of the normal. Geological evidence suggests a greater variability in rainfall than paleo-botanical data (Van Zinderen Bakker, 1963). According to this author temperature fluctuations are believed to be more widely spread with a range of six degrees Celsius (-1 to+5°). The Quaternary history of Botswana has been the object of a limited amount of studies. The main contributors are Wayland (1954), Bond (1964), and Groove (1969). The following table of Pleistocene successions is modified after Bond (1964).

25 Table 7. The Pleistocene in Botswana

Geological Relative Suggested Absolute Cultures Period Succession Rainfall Rainfall in mm

present rainfall about 375—500 mm/year J^resent black soils and slightly 450-500 Late Stone Epi-Pl. calcrete nodules wetter Age blown sands drier less than 375 Magosian Nata delta wetter ? 500-625 blown sands drier less than 375 Middle Stone Age calcrete si.wetter 450-500 ? 7 Fauresmith/ Upper Sangoan PI. blown sands very dry 125-150 calcrete si.wetter 450-500 blown sands drier less than 375 Middle gravels of fossil wetter ? plus 625 Old Stone Age rivers, silcrete blown sands drier less than 375 Lower Pi.

(Period indication according to Harmse, 1967).

The succession of events is comparable to an outline as proposed by Harmse (1967) for the Highveld region in South Africa, but full correlation is not justified at this stage due to lack of data. From the combined data it is evident that in the past the climate did differ considerably in spells from the present situation. The rate of soil evolution was accelerated during the wetter periods (Harmse, 1967; Watson, 1969). Evidence thereof is also discussed in Chapter V. 1.1. It is difficult to assess to which extent the Tertiary did influence the formation of soils. Whereas landscapes of Tertiary age were detected in the area, the correlation with the soils encountered on them at present is uncertain (Moss, 1968). Soils and landscape suggest that soil formation has taken place for a long time and was intensified during the wetter periods of the Pleistocene (Frenzel, 1967).

26 Changes in climatic conditions are, however, not restricted to the past in Southern Africa (Hofmeyer et al, 1963), but modulations have occurred in historic times. Verbal accounts from people in the study area reveal moister conditions than at present. This is in agreement with Pike, who in a recent account (1971) on the rainfall data, demonstrates the decrease in mean annual rainfall since 1958 for all stations in Botswana.

27 1.2. Geology

1.2.1. General The eastern part of Botswana including the study area is fairly well exposed for geological survey work. The geology of the remaining part of the country is largely masked by a thick cover of Kalahari sand, where exposures are rare. The stratigraphy of the country is varied and the age of the geological units range from Archaen rocks of the Basement Complex, dated as Precambrium, to the recent pan-sediments and sands of the Kalahari Beds. The geological sequence originated as the depression in the ancient Afri- can shield, to which Botswana essentially belongs, and became filled at various stages with sediments and volcanic deposits (McConnell, 1959). The ancient shield has been detected only in the southeastern part of the country. The first stratigraphical table was prepared by Poldervaart and Green (1954) and is mainly based on work by Du Toit (1954). Further refinements and additions were made by McConnell (1959), Boockock and Van Straten (1962) and Frakes et al. (1970). Hyde (1972) summarizes the previous work in a clear review. The stratigraphy may thus be described as follows. The terminology is adapted partly from Krumbein et al. (1959). partly from Krumbein et al. (1959). The Archaeozic Era is strongly represented; the oldest rocks are connoted in the term Basement Complex. The complex is divided into: 1) undifferentiated gneisses with minor inclusions of intrusive granite (for example the Mahalapye Formation) and metamorphosed sedimentary and volcanic rock, 2) various schists and associated sedimentary rock types often metamorphosed such as marbles, banded ironstones, quartzites and amphibo- lites. Rocks of both formations are exposed extensively in eastern Botswana. The succeeding rocks of the Kanye Volcanic Group and Ventersdorp System occur mainly in the southeast of the country. They consist of massive felsitic lavas, dark slates, quartz-feldspar porphyries, grits, sandstones and conglomerates. North and west of Gaborone an intrusive porphyritic granite underlies a large area. The intrusion is tentatively dated as Post-Kanye Volcanic Group and Pre-Ventersdorp System. The Proterozoic Era is represented by the Transvaal System, the Water- berg System, the "Ghanzi Group" and the Damara System; the Palaeozoic by rocks from the Karroo System (Ecca and Dwyka Series). The Transvaal System occurs mainly in the south and southeast of the country. Two formations are recognized, the lower one consists of dolomites, banded ironstones, cherts, shales, quartzites and arkose. The upper one comprises shales, quartzites, conglomerates, limestones, banded ironstones and

28 andesites. Certain sedimentary rocks in the Shoshong area are tentatively correlated with the Transvaal System. Dated as Post-Transvaal is a group of ultramafic intrusive rocks that occur in the southeast, south and southwest of the territory. The Waterberg System is extensive in southern and eastern Botswana; shales, siltstones, sandstones, limestones, grits and conglomerates are the dominant rocks. Dated as Post-Waterberg and Pre-Karroo are intrusives of dolerites, syenites, diorites and mafic rocks. Apart from their occurrence in southeast Botswana, these intrusives also occur in a large area around Shoshong, situated in the investigated region. The occurrence of the Ghanzi Group is restricted to northwestern Botswa- na. The Group is divided in two formations, the Ghanzi Beds Formation and the Kgwebe Porphyric Formation. The former consists of quartzites, shales, limestones and lavas, the latter of quartz feldspar porphyries and felsites. Rocks of the Damara System are also restricted in their outcrop to the northwest of the territory. Known rocks include quartz schists, quartzites, dolomites, limestones and marbles. The lower Paleozoic Era is mainly represented by the Karroo System. The Karroo System is similar to the same formation in adjacent countries, notably South Africa, from which its name was derived. The System is widespread in Botswana and underlies younger formations over most of central and southwestern Botswana, including also a strip along the border with Rhodesia. The general trend of the Karroo basin is northeast to southwest. A number of series is recognized of which the most important are the Ecca, Dwyka and Stormberg series. The grouped Ecca and Dwyka series consist of shales, sandstones, grits, mudstones, limestones, tillites and coal. The Stormberg series represent the Mesozoic Era. They are further devided into the Cave Sandstone and the Drakensburg Lava Stage. The main constituents of the former is a massive false-bedded eolian sandstone of various colours. It may also comprise some shales, mudstones and marls. The Drakensburg Lava is locally an up to 400 m thick uniform flow of basaltic lava. The Tertiary in Botswana comprises the Kalahari System. Rocks belonging to this System may also be of recent age and therefore cover the whole of the Cenozoic Era. Because of the uncertainty relative to the interrelationship of the various units of the system, the geological survey uses the term Kalahari Beds. The oldest rocks consist of reddish, calcareous clayey marls, usually encountered near ancient drainage lines. They are succeeded by calcareous silicified sands and sandstones. Exposures are frequently encountered in ancient drainage lines and occasionally near pans. The rocks cover vast areas in the interior. The Upper Tertiary is represented by the eolian Kalahari sands, ranging in colour from reddish-brown to greyish-white. These sands are very exten-

29 sive over most of the Kalahari except where there are pans, drainage lines or rock outcrops. The sands may be consolidated to varying degrees, depending partly on the amount of silt and clay. During the Pleistocene, sands from older cycles of deposition have been reworked (Poldervaart, 1957), while younger sands may have been derived from disintegrated Cave Sandstone (Boockock et al., 1962).

The stratigraphy of the rocks is fairly well known, the structural geology of the territory is however less clear. Folds have been detected in the oldest formations (Du Toit, 1954), while in a recent study Green (1967) indicates two sets of Post-Karroo faults in Botswana. One set is roughly directed from the northeast to the southwest and the other set from the northwest to the southeast. The major fault trend in the investigated area has the latter direction. The dating of the renewed folding is still a subject of argument. Mason (1969) postulates that the Post-Karroo movement of the majority of faults in (the eastern part of) the country is merely rejuvenation on very old fractures. It is therefore that suggestions by Vail (1968) and Fairhead et al. (1969) as to the extension of the East African Rift System into southern Africa should be considered with great care.

1.2.2. Parent Material The soil parent material is derived from the following geological formations: 1) the Mahalapye Formation, described as an intrusive granite of the Lower Precambrium, mainly consisting of migmatites and granites. The main outcrop in the survey area is formed by the Morale Hills. 2) Post-Basement Complex and Pre-Karroo intrusives, and therefore of Upper Precambrian age, consisting mainly of dolerites, syenodiorites with subordinate areas of syenites and ultrabasic rocks. The dominant outcrops form the Shoshong and the Marutlwe Hills. 3) The Ecca series of the Karroo System consisting of grits, shales, mudstones, sandstones, conglomerates and coal. They emerge mainly in the northwest of the survey area and form partly the Kalahari escarpment. 4) Younger Kalahari sand.

1) The Mahalapye Formation in the area comprises the foliated roof zone of a large Precambrian pluton and is correlated with the Messina series in South Africa (Poldervaart et al, 1954; Grubb, 1961). The biotite granite with parallel, tabular phenocrysts of microcline is intrusive in the Base- ment schists and gneisses in the Mahalapye area. Migmatisation of the Basement Complex by this younger granite is observed. Crockett (1965)

30 considers the Mahalapye Formation of palingenetic origin. The autoch- thone migmatites and gneisses are so advanced through granitization and mobilization that origin and affinity of much of the xenolithic material is obscured. Where exposed, this material consists largely of biotite-rich rocks as observed in the Morale Hills exposures. In the northern part of the catchment area of the Mahalapshwe river the mobilized homogeneous granite is pale-pink to white with a medium to coarse texture. The dominant feldspar is microcline. Of other minerals garnet occurs and biotite may be present if the granite is associated with xenolithic material. Migmatites are occasionally excellently exposed and consist of dark schists intruded upon by granite (Jennings,,1963). Amidst the granite rocks the occurrence of a calcium-rich epidote-garnet rock sample (specimen 12 A) is to be noted. Neither the extension of this type of rock nor its metamorphic facies are well known at present. The rock is classified tentatively as metadolerite. The elemental composition* of a number of rock samples of the Mahalapye Formation is given in table 8. They include samples from the Morale Hills as well as from the granitic area around the Marutlwe Hill.

Me 8. Elemental composition of rocks from the Mahalapye Formation (% by weight) Loss on impie Rock type SiO2 Al2O3 Fe2O3 TiO2 CaO MO K2O Na2O P2O5 ignition

syenodiorite 61.0 11.4 2.4 0.80 5.62 13.59 1.93 3.10 0.13 1.0 SA leucogranite 81.1 7.6 1.3 0.32 2.53 2.20 2.05 2.90 0.08 0.8 >A metadolerite 57.6 5.7 5.5 0.69 15.11 14.89 0.07 0.08 0.36 1.6 ?B leucogranite 76.4 10.1 0.8 0.28 1.91 2.18 5.40 2.71 0.18 0.8 'C granite 78.6 8.3 1.6 0.46 2.82 3.22 1.94 2.96 0.09 1.5 'D granodiorite 81.6 7.5 1.1 0.29 2.20 2.03 2.41 2.76 0.07 1.2

The composition of the granites is similar to the one given by Crockett (1965) of granites a little south of the survey area and deviates only slightly from data given by Tyrell (1929), Dana and Ford (1932), Grout (1932), Wahlstrom (1948) and Mohr and Van Baren (1959). Microscopical qualitative analysis of thin sections made from the rock specimen reveals the following. The granodiorite consists primarily of quartz, followed by plagioclase and some orthoclase. Plagioclase in largely sericitised; biotite is partly transformed to chlorite, while epidote and colourless mica occur as secondary

* The element concentration is given as oxides.

31 products. Zircon is observed accessorily, pumpellyite occurs occasionally. Quartz is also the chief component of the leucogranite, followed by orthoclase. Plagioclase occurs but is also strongly sericitised. The small amount of biotite is largely chloritised. Apatite and hornblende together with epidote are present in subordinate amounts. The epidote-garnet rock consists mainly of epidote with pumpellyite succeeded by chlorite, serpentine and garnet. Also present are titanite, quartz, and colourless amphibole. The rock composition and its occurrence does suspect the metamorphic facies of an originally calcium-rich rock, such as dolerite or gabbro, therefore the rock is named metadolerite.

2) The second source or parent material forms rather a contrast to the first one and consists of basic intrusive rock. The age of the intrusions is believed to be 590 ± 24 and 660 ± 26 m.y. as determined on two samples of the Shoshong sill (Jones et al., 1966). This determines their origin as Post-Waterberg and Pre-Karroo and as such of Upper Precambrian to Cambrium. Of the same age, but of rather variable composition are several dykes, exposed particularly in the central catchment of the Mahalapshwe River (Grubb, 1961). The Shoshong Hills and the Marutlwe Hill are the two most extensive sills in the survey area. Both sills dip approximately 10° to the south, thus causing a drainage system to develop into this direction. Much of the weathering products are therefore deposited on the south side of these hills. Origin and composition of these sills have been subject to a number of studies (Grubb, 1961;Cullen, 1961; Jones et al., 1966). Comparative research on similar intrusives in southern Africa was exe- cuted by Cox et al. (1967). These studies suggest that the Botswana dolerites belong to the southern province. The difference with the northern province is mainly based on the high values of K, Ti, P, Ba, Sr, Zr in the northern province. The rocks are mainly dolerites and syenodiorites, with subsidary syenites and peridotites (Cullen, 1961). According to Grubb (1961) the Shoshong sill is a multiple intrusion formed by two successive influxes of basic magma. On the basis of differentiation within the sill (increase of orthopyroxene phenocrysts towards the base) five pétrographie zones can be recognized. Accompany- ing contact metamorphism was usually low-grade, although in the Shoshong sill a roof zone of about three meters granophyric granite occurs, with a very coarse basal zone of red granite beneath the sill. Total thickness of the sill is estimated at 400 m, with 150 m exposed. The elemental composition of three random rock samples from the sills eluci- date the differences with the acid rock suite:

32 Table 9. Elemental composition of three rock samples from the Shoshong and the Marutlwe sill (% by weight) Loss on TiO CaO MgO KfO Na2O No. Rock type SiO2 Al2 O3 Fe2O3 2 P2O5 ignition

L2B Dolerite 50.8 15.3 9.8 0.63 11.26 9.27 0.86 2.81 0.10 0.8 S3B Dolerite 52.9 15.1 11.2 0.80 9.82 7.32 1.08 1.56 0.15 1.2 Î7A Dolerite 51.9 14.0 10.5 0.59 9.84 10.38 0.75 1.12 0.07 0.2

The above data are in general agreement with values given by Grubb (1961) and Cox et al. (1967). The trace element composition of the sills is not known, but some data are available from similar sills in Swziland and from Karroo intrusives in the Tuli syncline (tables 10 and 11).

Table 10. Trace element composition of some dolerites in Swaziland (ppm)

Trace element mean range Trace element mean range

Ba 235 85-390 Pb <10 Be <3 — Rb <50 _ Co 31 30- 35 Sc 36 20- 65 Cr 159 95-230 Sr 300 250-330 Ga 18 15- 20 V 263 200-350 Li 12 10- 20 Y 26 10- 35 Mo 4 3- 4 Zr 79 35-100 Nb 24 10- 30 Source: Cox et al., 1967.

In a recent account on the geology of the Karroo basalts in the Tuli syncline, which also touches Botswana in the northeast, Vail et al. (1969) report the presence of shoshonite. This alkali feldspar-bearing rock, presumably named after the Shoshong dolerite sill, is described as a pheno- cryst basalt that contains abundant groundmass alkali feldspars as over- growth on plagioclase. Augite varies between trace to 3% and the percentage plagioclase ranges between trace and 10%. Although the majority of the basalt in the Tuli area is classified as belonging to the northern province as defined by Cox (1967), the shoshonite clearly belongs to the southern province as described for the basalts in Swaziland. Trace element data from the Tuli basalts differ considerably from the Swaziland rocks. For the two rock samples of the shoshonite the amount of trace elements is given in the following table (Vail et al., 1969):

33 Table 11. Trace element composition of the Karroo basalt in the Tuli syncline (ppm)

Element Rb Sr Ba Zn Zr Nb Co

118 1332 2160 86 317 133 36 1183 1273 2035 82 331 14 30

The above data may be more in agreement with the general composition of the dolerite sills that form the Shoshong and Marutlwe Hills. Microscopic investigations of the dolerites disclose that the dominant mineral in sample 12B of the Shoshong sill is plagioclase, followed by pyroxene; a fair amount of epidote amd amphibole is observed. Augite does occur to a limited amount but is somewhat amphibolized locally; some biotite and quartz is observed. The second sample from the same area (No. 83B) is dominated by pyroxene, that may be uralitised locally, followed by plagioclase. The amount of amphibole is extremely low, while biotite, chlorite and serpentine occur as accessory minerals. The rock sample from the Marutlwe Hill is similar to the latter described sample. Pyroxenes are dominant except augite, while plagioclase occurs in subordinate amounts. Biotite, chlorite and serpentine occur infrequently. There has been little alteration while the optical structure is weakly expressed. The process described as uralitization may explain the low percentage of pyroxenes in the weathering products of the dolerite. Although no data are available on the content of rare elements in the granites and in the basic rocks in the area, information herefrom is made available by Edge et al. (1962) for comparable rock types in South Africa. The results are summarized in table 12 and supplement the knowledge about the parent material of the soils.

Note: The processes of sericitization and saussuritization that have effected the feldspars of the granitic and doleritic rock suites imply in petrographical sense the formation of sericite (fine scaly colourless mica) respectively of epidote (from calcium-rich plagioclase) during the late hydro- thermal phase. Uralization signifies the alteration of pyroxenes to amphiboles (fribrous hornblende).

34 Table 12. Content of some rare elements in granitic and basic rocks in South Africa (PPm)

Rock type Element Molybdenum (Mo) Tin (Sn) Gallium (Ga) Scandium (Sc)

mean range mean range mean range mean range granitic 1.9 0.96-4.5 3.2 1.5-5.6 16.9 10.0-22.0 4.5 1.4-11.0

Yttrium (Y) Lathanum (La) Cerium (Ce) Niobium (Nb)

mean range mean range mean range mean range granitic 32 5-55 85 29-177 525 135-790 79 17-141 basic 26 13-33 27 17- 36 47 35- 67 33 24- 44

3) The sedimentary rock of the Ecca series are encountered in the northwest of the area; arenaceous and argillaceous types are dominant within the large variety of rocks that occur in this formation. Although no bedrock sample was collected from this rock type, the elemental composition of the C material from a soil underlain by the Ecca series is given (table 13).

Table 13. Elemental composition of the fine earth fraction of a weathered rock from the Ecca series (% by weight)

Loss on

Element SiO2 A12O3 Fe2O3 TiO2 Cao K2O Na2O P2O5 ignition

Rock type S,chist 73.8 21.6 2.1 0.77 0.13 1.28 0.34 0.00 8.2

The trace element composition of the same sample in ppm indicates a low amount of Mn (60), Cu (26), Zn (4), Co (18), Ni (30), and Sr (7), while Cr (146) and Ba (200) are slightly higher. The mineralogical analyses of the clay fraction indicate that kaolinite makes up almost the entire composition. Heavy mineral determination on similar rocks in South Africa (Harmse, 1967) show low zircon and tourmaline percentages. The garnet percentage is high, epidote and hornblende are rare, some rutile occurs.

4) The vast cover of Kalahari sand forms the parent material for a variety of less developed soils in the interior. The soil under consideration is located on the eastern edge of the Kalahari sandveld and is probably

35 developed in redeposited Kalahari sand (Wayland, 1953; and Poldervaart, vaart, 1957). The source of the sand has not been retraced sufficiently to make any binding comments. However, it seems possible that especially the younger sands may have been derived from the disintegration of Cave Sandstone (Boockock et al., 1962). Elemental composition of a specimen from this sandstone is given in table 14.

Table 14. Elemental composition of a rock specimen from the Cave Sandstone (% by weight) Loss on K O Na O P O Element SiO2 A12O3 Fe2O3 TiO2 CaO MgO 2 2 2 5 ignition

Rock type Fine-grained 93.8 3.3 0.3 0.08 0.51 0.84 0.87 0.17 0.10 0.9 sandstone

Microscopical evaluation of the sandstone confirms the very high amount of quartz, while it is also detected that SiO2 is the dominant cementing agent. Plagioclase is rare, the amount of zircon and tourmaline is very low. The sorting of the grains is moderate and the roundness is poor. Data on the heavy mineral assemblage of the Cave Sandstone Stage as collected by Harmse (1967) indicate a fairly low percentage of zircon (15%) and garnet (3%), but the percentage of tourmaline is high (41%). An almost opposite picture is obtained while looking at the data on the heavy minerals as available from a soil developed in the Kalahari sand. Zircon is dominant (43%), succeeded by tourmaline (28%); rutile is slightly less (7% versus 10%). The reason must be sought in the higher resistance to weathering of zircon causing it to occur frequently in the weathering product of the Cave Sandstone. The source of the parent material for the majority of the soils is related to the granitic rock suite. The dolerite and associated rocks follow, while the rocks of the Ecca series and the younger Kalahari sands form the parent material only in a few cases. To procure insight in the relation between the bedrock material and the weathered rock as encountered in a number of profiles, ratios as introduced by Jenny (1941) were applied. Two reservations must be made. Firstly, the obtained picture is approximate as in no case was unweathered bedrock material (R) included in the soil samples encountered, and secondly, alteration of the weathered parent material (C) is possible because lateral or certical mineral transport is not accounted for. The SiO2 /Al2 O3 and the K2 O+MgO+CaO/Al2 O3 indices indicate the

36 Fig. 5. Relation between rock and weathered rock based on leaching values

37 removal or accumulation of the cations of the numerator, if we assume that the solubility of Al is negligible in the soil reactions encountered (Krauskopf, 1967).

As illustrated in figure 5, a number of distinctive groups occur. The first group comprises the bedrock samples. The ratio SiO2 /Al2 O3 for the doleritic rocks (Nos. 12B, 83B, 87A) varies less than for the granitic rocks (Nos. 1, 83A, 87B, C, D), the latter range between 3 and 6 and the former between 3 and 5. A sharp distinction is present between C material from a number of Ultic and Oxic Haplustalfs; a Haplustalf (15), an Entisol (1.7) and an Inceptisol (5) on one side and two Oxic Haplustalfs (29, 32) and some other Alfisols on the other side. The former group shows a high SiO2/Al2O3 ratio of 7 or more while the base metals are indicated between 0.30 and 0.80; the last group has a ratio of 2—4 with base metals less than 0.30. The C material from most of the remaining granitic soils (Nos. 3, 4, 6, 8, 13, 14, 18, 23, 33) not only has a far lower SiO2/Al2O3 ratio, in fact comparable to the one encountered in soils derived from the doleritic rock suite (Nos. 22, 25, 26), but also has a lower base metal index. These data suggest that the development of soils derived from granitic material undergoes a stage in development in which an increasing amount of SiO2 is accompanied by a lower percentage of base metal ions. Further evolution indicates a lowering of the silica content together with a lower amount of basic cations. Remarkable is also the correlation between the highly calcareous material from three profiles (1.0, 24, 31.) and the epidote-garnet rock (No. 12A), tentatively classified as metadolerite. Parent material from one soils presumably derived from rocks of the Ecca series (No. 29) have an identical Sio2/Al2O3 ratio, with a slightly differing status in base metal cations. Loughnan (1969) reports on a similar loss of cations from the environment. A comprehensive account on the mineralogy of the soils is given in section 11.3.1. Remarkable is the presence of highly calcereous material (calcrete) in the deep subsoil of profiles 10, 24 and 31. In the latter, overlying soil material has developed as a Vertisol, while profile 10 is classified as an Alfisol. Although a relation seems to exist between the calcium-rich matter and the metadolerite (see Fig. 5) their affinity can be doubted on basis of the overlying soil material and keeping in mind the very old age of the granitic rock and "younger" basic formations. Micromorphological observations suggest the displacement of the calcium-rich material in profile 25, but do not consider such action relative to profile 10.

38 1.3. Geomorphology

1.3.1. Topography Compared to the remaining flat to almost flat profile of the Botswana countryside, the Eastern part has a variable topography. This is particularly true for the study area where incised rivers, rock outcrops and hills give rise to undulating to rolling relief alternating with level stretches of land. This is partly due to the different geological formations that occur in the area, while river activity has been and still can be relatively active as part of the Limpopo drainage system. As a result of the interaction between various agents a topography of the following diversity is encountered. In the southeastern part the countryside is flat to almost flat with an altitude between 1050 and 1130 m. The most outstanding topographical feature are the Morale Hills, a granitic rock outcrop that rises to about 1370 m above the surrounding country (Bawden et al., 1963). Therein shallow pans and drainage channels are distinguished, the latter determined by the hills. The majority of the pans is observed in the Southeast of the area and the East. In addition to the origin of the pans described by Harmse (1967) as eolian and by Boockock et al. (1962) as eolian and caused by animals and as part of an older drainage system (Geyser, 1950), the solution of the underlying calcrete in the area under consideration could induce the formation of pans. The Bonwapitse River is the most conspicuous drainage channel in the area. In some places an incision of two to three meters in the flood plain is observed. In the immediate surrounding of the river-bed gully erosion occurs. This type of erosion is limited in the area and is often initiated by man through destruction of the vegetation, or along roads. Sheet erosion seems more common although its results are often masked. The percentage of rock outcrops and the difference between high and low increase towards the North and Northwest. This section of the area has in parts a rolling topography, although flat tracks of land do occur on the divides. Local relief differences may be 50 m or more, the general altitude of the area is between 1130 and 1310 m. Gully erosion is common along the drainage channels from the Mahalapshwe River and its main tributary the Mmitle, often resulting in truncation of soils. The topography becomes less differentiated in the headwaters of the Mahalpshwe River. Gently rolling topography prevails, although near the drainage lines 1—2 m deep gullies may be encountered. The most remarkable feature is the watershed between the Mahalapshwe River and the internal Kalahari drainage system. The divide has taken the form of an escarpment in some areas, while in others a slow rise marks the transition towards the Kalahari sandveld. The

39 differences are mainly ascribed to changes in the geological formations. The scarp may stand 20—30 m above the surrounding areas. The westerly and south-westerly part of the survey area is again characterized by a succession of level to almost level topography of 1130 m altitude only interrupted by the Shoshong and Marutlwe Hills. These may rise to about 150 m above the surrounding land. Gully erosion is again confined to the area near the headwaters of the Bonwapitse River and its tributaries. The river itself is incised 2—3 m in the flood-plain. The hills are flat on top with raised edges. The debris slope usually has a gradient of 25—30°. Granitic rock outcrops are rare in this area but some occur East of Mutane and Southwest of Shoshong. The inexperienced observer may find the local differences in topography rather insignificant; however, together with the other soil forming factors they are the cause of variable soil profile development (Mabbutt, 1966).

1:3.2. River Systems The area is drained by two rivers, the Bonwapitse and the Mahalapshwe, which are classified as ephemeral streams because heavy precipitation is needed to cause enough run-off for streamflow. These flows seldom last longer than a couple of days and often not longer than hours, after which the river is dry, except for its saturated bed. Depending upon rainfall, the magnitude of the flows measured for the Mahalapshwe River at peak discharge is 752 m3/sec. (Hyde, 1972). The developed drainage pattern of this river is classified as dendritic (Lobeck, 1939; Finch et al., 1942). The stream is occasionally controlled by the structure of the geological formations and may then be rectangular. The pattern as a whole reflects the situation such as can develop on granitic rock. The Bonwapitse River is divided into two branches. The northerly, originating near Kalamare, has a similar pattern as the Mahalapshwe River. The southern one, which developes near Shoshong, is classified as rectangular. Weakened zones in the bedrock caused by faults together with the slight dip of the hills to the south has resulted in a number of streams running north to south. These flow together south of the hills and then form the southern branch of the Bonwapitse River. The overall direction of the drainage is to the southeast following the opposite direction of a broad, low westerly pitching anticline, which is the major structural unit of the area (Cullen, 1961) and embraces rocks of the Basement Complex, the intrusives and the Transvaal and Karroo Systems. There is no evidence that streamflow was once directed towards the west. In the northern part of the Limpopo catchment in Botswana there is, on the contrary, topographical evidence that east flowing rivers may have been decapitated in the headwaters, approximately in the zone

40 Table 15. Data of stream deposits.

Granulometric analyses. sample gravel sand silt clay >2000 2000- 1000- 500- 200- 100 50- 20- /im 1000 500 200 100 50 20 2 <2

fim fim /lm flm flm txm /im flm

sample A 7.4 7.8 3.8 5.2 2.4 1.8 19.7 24.8 34.5 sample B 30.6 39.8 19.7 15.7 24.0 0 0 0.8 0 sample C 19.3 21.4 13.2 14.4 13.2 5.9 8.2 11.4 12.3 sample D 22.5 30.9 19.6 19.2 12.0 2.6 1.9 3.1 10.7 sample E 16.4 28.9 21.7 27.2 15.5 0.9 0.5 2.2 3.1

ChemicaI data

org.C % N% C/N pH-H 2O pH-KCl sample A 3.28 0.30 10.9 7.5 6. 5 sample ß 0.03 tr - 7.7 7. 1 sample C 0.05 tr - 8.3 6. 1 sample D 0.23 0.02 11.5 8.8 7.6 sample E 0.06 tr — 9.0 8. 1

Heavy mineral composition of the sand fraction (50—200 micron) o c Ö o u u u — 0 EJ 'c r- b- § 1 t ra _O c >-. O. o CU 15 Q sample A 7 tr 9 1 tr 8 2 51 3 tr - 1 18 23 sample B tr tr 4 1 1 9 2 59 2 tr — 1 21 14 Sample C 6 1 1 1 52 1 28 - — 6 — 4 37 sample D 17 tr 8 2 29 11 19 - 2 — - 12 61 sample E tr tr 7 1 16 2 16 1 17 - - 40 30

Elemental composition of the clay fraction Loss on

SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2O; ; ignition sample A 52.0 25.6 11.3 1.38 0.24 4.97 2.19 0.15 0.83 12.5 sample C 54.8 17.9 13.8 1.81 0.65 4.98 4.60 0.77 0.59 9.6 sample D 56.0 24.9 12.1 1.11 0.23 2.55 2.55 0.00 1.38 5.4

41 where the Kalahari escarpment is featured nowadays. The dating ot these events is still tentative but is probably older than Miocene (Dixey, 1943).

The nature of precipitation together with soil and topographical factors has resulted in a highly varying sediment load ot the rivers when in flow. Stream-bed samples taken from the two rivers at the outflow of the area show a dominant very coarse textured composition. Alternating therein are the finer sediments deposited in the tranquil environment at: the end ot the main flows. High and low stream velocities and consequently chanijinii carrying capacities arc the main cause of the textural differentiation. The overall character of the deposits are strongly influenced by the nature of the hinterland, such as geology, topography and vegetation. The locution of the samples is given on fig. 1. Details on sample sites are: Sample A : depth 0 — I).5 cm (fig. 6) Sample B : depth 5-15 cm Sample C : depth approximately 400 cm Sample D : depth 0 - 10 cm Sample E : depth 0-10 cm Some chemical and physical data ot the deposits are given in tabel 15.

f:-

Fig. 6. Flood residue of a flow in the Malmlapslnrc river

42 The granitic component in the river samples is dominant in the sand fraction, particularly in the medium and coarse sizes. The finer components are chiefly provoked by the presence of basic rock. Although this may be evident for the southern branch of the Bonwapitse River that originates in the doleritic sill, such is also the case for samples taken from the Maha- lapshwe River and is ascribed to the doleritic dykes that occur in that catchment area.

The interpretation of the Röntgen diffractograms yield the following relative to the composition of the clay fraction: sample A is mainly composed out of montmorillonite; in sample C kaolinite with montmorillonite, chlorite and quartz are present; sample D is almost entirely composed of kaolinite with some quartz, while sample E contains kaolinite with montmorillonite, chlorite and quartz and is thus similar to sample C. The sandy loam deposit found 500 m upstream of the Mahalapshwe road bridge at a depth of 4 m (sample E) underlies a mainly coarse sandy and gravelly bed. It presumably overlies bedrock, although in or just above the deposit a coarse gravelly layer may be present. Similar successions have been reported from other rivers in East Botswana. The sedimentation of this kind of finer textured sediment, which is estimated at least 1 m thick, was most likely caused by other environmental conditions in the catchment area than prevail at present. They indicate a denser vegetative cover and a more evenly distributed rainfall regime (Watson, 1969). Further research on stream-bed deposits might contribute valuable knowledge about the history of this part of Botswana and possibly for the country on the whole.

1.3.3. Landscapes The division of the landscapes as given below resulted from an evaluation of the environmental factors that create these forms directed towards their usefulness in soil survey work. The use of land systems, land units and other variable scales of morphological entities in practical survey work is well recognized by a great number of workers and was successfully applied in Australia (Mabbutt et al., 1963) and was also adapted by Bawden et al. (1963) in Botswana.

The observed morphology calls for the recognition of a number of landscapes, which are indicated on figure 7. I) The landscape of the Morale Hills which is made up of the following elements: the granitic rock outcrop, represented as a series of more or less well developed domes that undergo strong exfoliation; the associated debris slope, also called colluvium (Swan, 1970) or hill slope (Young, 1972), and the succeeding pediments. The latter are

43 Fig. 7. Landscapes and geology of the investigated area

44 well developed and of such an extent that their coalescence gives rise to a pediplain (King. 1967) of a slope between 0.5-3°. The slope angle between the upper part of the pediment and the lower part of the hill slope is well marked. To the north and the south the transition of the pediplain to an almost level erosion surface is not distinct. The whole area was classified by Bawden and Stobbs (1963) as belonging to the land system of the Central Plains. In an account on the presence of peneplains in Botswana, Jennings (1962) states that the plains belong to the Late Tertiary erosion surface, as defined by Dixey (1943) and King (1967) for Southern Africa. An altitude of 820 m to 1210 m is maintained for this surface. These observations on the succession of landscape elements is similar to those made by Fair (1949). Mabbutt (1955), Pallistcr (1956), Moss (1963) and Young (1972). The landscape of the upper Mahalapshwe catchment and northern branch of the Bonwapitse River is essentially an eroded peneplain of an altitude between 1130 m and 1280 m, on the basis of its topography the transition to the Kalahari sandveld is indicated differently (lia). The main elements are rock outcrops (basic and acid)

Key to fig. 7.

Svmbal Geomorphology Geology

hills, colluvmm. Archacn rocks of the Basement Complex, mainly pediment and pediplain granites from the Mahalapye Formation

dissected peneplain Arcliaen rocks of the Basement Complex un- differendated granites occurrence of dolcritic dikes

II.. slightly eroded peneplain as II with some areas of Ecca Series

tlat copped hills with asso- Post Waterberg-Pre Karroo basic intrusices, mainly ciated scarp and colluvium dolcrite

pediment Undifferentiated granitic rocks from the Basement Complex with subordinate occurrence of dolc-ritc

flood-plain Pleistocene to recent calcareous clayey deposits

alluvial fan Holocene to recent undifferentiated deposits

IV plain (sandveld) Pleistocene to Holocene eolian sands

45 with their associated areas as described for the Morale Hills, but on a smaller scale. The granitic rock outcrops may have the '"kopje" torm or are classified as "whale backs" [Watson. 1964). The direction of fractures and joints seems foremost responsible for the shape of hill developed (Hurault, 1967). Here also the piedmont angle is well defined. Depending on the density of the drainage the interfluvcs may carry a variable thickness of soil overlying weathered rock. Convex to straight and then transitional to concave slopes are common, gradients of more than 3° occur. Alluvial deposits in the drainage channels vary considerably, mainly depending on the rate of erosion. Overlooking this part of the investigated area, the imaginary surface formed by the summits of the rock outcrops seems to occur below the skyline, which is made up by the contours of die associated higher areas ^ landscape III). Similar observations were made by Moss (1968) in West Africa. Jennings (1962) dated the eroded plain as Late Tertiary, however it is not clear which surface is meant, the summit level of the hills or the planation surface around the rock outcrops. HI) The landscape of the doleritic hills is characterized by the almost flat summit level of the hills, followed by the "scarp" that is composed out of the outer upper rock boundary, the associated hillslope

; *&&?•-*£$*

l~ig. 8. I he eastern slope of The Mtirntlwe hill with associated pediment formed by colluvium and pediments (Ilia), (fig. 8). The transition to the Bonwapitse flood-plain (Illb) is on a very gradual slope. Concave slope forms are dominant near the hills whereas the gradient becomes flatter towards the stream. Granitic pediments are well developed on the northern side of the hills, while on the southern side smaller pediments (sub-alluvial) and occasionally alluvial fans ( 11 Lc) occur. The hill tops showing an altitude between 1300 — 3 350 m were correlated by Jennings (1962) with the Early Tertiary cycle of erosion as described by King (1962). To what extent the summit of the Morale Hills (1370 m) belongs to this surface is still a matter of speculation. IV) A similar postulation is made for the Kalahari sandveld, that rises about 1350 m above sea-level. The plain, underlain by a Mesozoic or late Tertiary erosion surface (Groove, 1969), is encountered in the extreme northwest corner of the study area. The transition to the Limpopo drainage system is variable, but often takes the form of a pediment at an altitude between 1280 m — 1320 m. In the interior, rock outcrops in the form of sandstone mesas occur, while old drainage channels and pans are a common feature in some parts of the Kalahari (Boockock and Van Straten, 3962; Groove, 1969). In the area concerned, such topography is absent and the landscape elements limited to level or almost level "sandveld".

The genesis of the various landscapes has not been touched upon inten- sively as it falls outside the scope of the present study. The morphody- namical aspects are well described in more recent literature (Weise, 1970; Swan, 1970; Biidel, 1971). However, if applicable references to the relationships between the soils and the various landscape elements are given (see also Chapter II).

1.4. Vegetation

1.4.1. Natural vegetation The term "natural vegetation" is not without double meaning and was used to indicate a stable type of vegetation in complete equilibrium with climatic and soil conditions (Eyre, 1968). Nowadays the term "climatic climax vegetation" is used in a situation implying that among other conditions, no human activity has influenced the vegetation. As such, the vegetation of the whole area under consideration does not satisfy the requirements of this definition. However, in an attempt to make a distinction between areas in which human influence is strong and those where conditions have changed relatively little, the term "natural vegetation" has been maintained to indicate the latter.

47 This vegetation that developed under semi-arid conditions was described by De Beer (1962) as a tree savanna, wherein Acacia species and Com- bretum varieties are dominant. On the revised physiographic vegetation map of Botswana (Weare et al., 1971), the area is classified as an Acacia nigrescens/Combretum apiculatum tree savanna (unit 21). The use of the terms "savanna" and "steppe" to indicate vegetation types in Africa has led to confusion about the exact definition and meaning of these terms (Acocks, 1951; Aubreville, 1957; Richards, 1961; Cole, 1963; Walter, 1964). Much was clarified by Eyre (1968) who recorded three types of savanna in Africa, namely 1) high grass/low tree savanna, 2) acacia/ tall grass savanna, and 3) acacia/desert grass savanna. The second type is recognized in the area. Within a certain type of savanna, the grass cover and tne tree density may vary considerably. It was found necessary therefore by Philips (1969, 1970) to introduce a more detailed terminology with special regard to Southern Africa. Consequently, terms as "woodland" and "grassland" with their variations came into use. In his study, Philips defines woodland as a community of trees and large woody shrubs, occurring either singly or in a single or several storeyed clumps of varying size, separated by appreciable distances, but crowns not usually more than thrice the height of the trees, the intervening growth from stem to stem being grass with or without sub-shrub and forbs (Philips, 1970). An important sub-division of the woodland is the shrub open woodland defined as "open woodland in which the widely scattered elements are large shrubs set in a matrix of grass." This woodland may occur naturally where edaphic control is marked, such as poor drainage, or may be induced by man or animal, (see 1.4.2.) The overriding importance of the climate for the vegetation has been recognized for a long time in the world and in Africa in particular. Differentiation in composition and character of the vegetation within the climatic regions is however caused mainly by edaphic factors such as soil and topography (Cole, 1963). In an attempt to clarify the long lists of vegetation species that seem to result from ecological surveys within a vegetation type, Van Rensburg (1971) designated a number of trees, shrubs, herbs and grasses as indicator species. Each species or combination thereof as characteristic for a certain combination of factors can be applied distinctively to indicate differences between for example, soil and topography. During soil surveys in the area, emphasis was placed on the recognition of the woody species and the grasses with relation to the different soils encountered. As a result of intensive ecological research in the terrain, the overall classification for the vegetation by Van Rensburg is named an "Acacia mixed woodland and

48 Fig. 9. ,'lfjcia mixed woodland dominated by Acacia nigrescens with some Comhretum apicu- laturn, site of profile So. 1 ; m the background one of the exfoliated domes of the Morale Hills

Combretum apiculatum woodland", (fig- 9). The Acacia mixed woodland consists of the following acacia species: Acacia nilotica, A. grandicornuta, A. gerrardii, A. tortilis, A. tenuespina, A. karroo and A, nigresceus. These species are often associated with Albi- zia harveyi. Combretum apiculatum occurs of ten together with Tenuinalia scricea (tig. 10). The correlation between the woody species and the soils is illustrated in table 16. The grasses may also be divided and correlated with different soil types and vegetation communities. A very broad distinction is made between the sweet and the sour veld. Whereas the former covers the grasslands of the warm areas, the latter comprises the cooler and wetter areas. The sweet veld ramains palatable during the winter while the sour veid does not (Acocks. 1964). The 625—750 mm isohyet is taken as approximate boundary between these two types, a considerable transition zone does exist. Due to human interference much of the indigenous perennial grasses

49 r/ij. /(). Omikrefitm iijiiculututn and 'Vcrmmalui sericea woodland, site of profile No. 2

Table 16. Relation between woody species, soil and topography

Vegetation ^woody species) Soil Topograph)

Acacia uilotica deep. dark, cracking clay drainage lines A Ibizia harveyi deep. dark, cracking clay drainage lines Acacia nigrescens shallow to medium deep, blocked pediplain sandy loam Combretwn apicuhitttw as above and ;ilso on deep. pediplain sandy loams Terminalia sericea shallow, blocked sandy loam. pediplain deep loamy sands and sands A. grandieornuta deep, dark, cracking and pediment and A. tcnuispina mulching clay flood-plain Indigo fera schim peri Lintonia nutans A. tort His deep, reddish-brown sandy pediplain (clay) loam Kirkia accuminata very shallow and stony colluvium and Sclerolcarya caffra soils hill summit Commiphora. spp. Albizia rhodesica (modified after Van Rensburg, 1971).

50 that make up the sweet veld in the central pare of East Botswana, have been replaced by annuals. The original grass vegetation is visible only at places outside the reach of animal or man. The preference of the main grass species for a certain soil is illustrated in the following table.

Table I 7. Relation between soils/woody vegetation and grasses

Soils/Woody Vegetation tirasses

Kalahari sandfTcrminalia Anthephora pnbescens sericea woodland Aristidü stipitata Digitaria milanjiatia Eragrostis pullens Vrochloa brachyura Sandy [oamiConibretum Digitaria )iii!anjiana apiculatum woodland Eragrostis rigidior. E. supcrba Sclnuidtia pappophoinoides Clay loams with or without Ccnchrus ciliuris calcrete along drainage Digitaria criant ha lities/.-lftiCJtJ mixed woodland Panicutn coloratura and P. )}ttixi)niwi t'rochtoa tricJiopis Clay loams and clays along Diclianthimti papiltosuw drainage lines/.4c

Clay soils of flood-plains-pediment/ Bothriochloa htsculptia \ caria mixed woodland C\mbopogon exacavatus (fig. 11) Themeda triandra (modified after Van Rensburg, 1971

1.4.2. Human induced vegetation Vegetation is not only modified by humans through the introduction of crops, fodder and legumes in a certain area, but even more evidently by the effects of associated settlement activities, particularly in areas where the holding of livestock is a main source of income. These effects include destruction of the vegetation by trampling, uncontrolled grazing, often resulting in overgrazed almost bare areas: uncontrolled cultivation including cutting and burning. As a result of the aforementioned activities the encroachment of bush is a serious problem in the Eastern part of Bots- wana. Woody species that readily encroach include Dichrostachys ccucrea, Fig. 11. Acacia mixed woodland on clay soils dominated by Acacia grandicormita, site of profile No. 25

Acacia fleckii, A. mellifera, A. nigrescens, A. temiespiua, A. tortilis and liuclea umiulata (Van Rensburg. 1971 ). Grazing potential is thus considerably lowered while the costs for the clearing of land for cultivation or other purposes rise accordingly. An additional factor is that original woodland or grassland that has been disturbed is often permitted to rc-develop into shrub open woodland or suchlike. Additional sub-divisions are then necessary to term the vegetation accordingly.

1.4.3. I'egetation patterns Vegetation patterns have been identified and described in many areas, as reported by Wickens et al. (1971). These patterns seem to occur mainly in semi-arid and arid areas (Langdale-Brown, 1968). where soil moisture is the most crucial factor for die development of vegetation (Wickens et al.. 1971: Worrall, 1960; Harrison et al., 1958). Most patterns appear to consist basically of alternating areas with and without vegetation. Minor differences in topography and textural composition of the soils in the areas seem to determine the variety in the vegetation. In the survey area three vegetation patterns can be detected on the aerial photographs. The first pattern consists of alternating light and dark spots.

52 Ground examination revealed the light spots to be bare or almost bare of vegetation while the darker spots correspond with patches of vegetation. This pattern seems largely confined to the Termiualia sericea woodland (fig. 12j.

Fig. 12, Aerial photograph of the vegetation pattern at profile No. It

The second pattern that evolves consists of alternating light and darker stripes, which are disconnected and not continuous (vegetation around profile 7). The explanation of the colour contrasts on the photos is similar to that for the first pattern. This second pattern is mainly encountered in Coinbretiim apiculatum woodland with Terminalia sericea. A third and less clearly defined type consists of alternating dark and light lines, perpendicular to the slope (see fig. 23, profile 31). In these areas the controlling factor may be the run-off along the cattle tracks, which follow an established pattern between the grazing grounds and the watering points. From our information may be deducted that patterns in vegetation in the area are more likely to originate on coarse- textured soils, that are sensitive to soil moisture for plant growth than on the other, in general more loamy soils. In addition, soil depth can play an important role in the suitability of a soil for vegetation. Depth considerably determines soil moisture properties, especially in the survey area where a rather undulating blockage in the subsoil is common. Woody species as Tcrminalia sericea and Combretum apiculatum are readily correlated with coarse-textured soils (fig. 10).

53 Where the vegetation could follow up the pioneer species, the soil environment becomes more suitable for continued plant growth, particularly as the infiltration rate of the topsoil under the canopy increases (Lytord et al.. 1969). How far the human factor is responsible for the origin ot vcgetational patterns could not be established. It appears, however, tliat the patterns of the indigenous vegetation persist even in cleared fields. Vegetation patterns due to a particular soil-slope relationship or to slope exposure giving rise to catenary vegetation successions are well observed in Africa (Thomas. 1945; Harrison and Jackson, 195&). Their occurrence is however not marked well enough in the survey area to be applicable over large regions. With regard to the vegetation on hill slopes, it was observed that ou a slope exposed to the north it is more luxuriant than on a slope with exposure to the south. This variation is locally clearly visible in the Shoshong Hills. Little is known about the existence of the vegetation patterns in past or historic times, if edaphic factors are mainly responsible for their genesis, then it is not unlikely that the patterns may have existed for a relatively long time. The composition and distribution, however, of the various vegetation types in Southern Africa in the Pleistocene did differ considerably from the present natural vegetation especially during the drier periods of that era. During those times the extent of the Kalahari grassland increased notably with a decrease in the distribution of Brachy- stegia in particular. When wetter conditions prevailed Brachystegidj- .\cdcid/Cü)iiHÜphora woodlands tended to increase (Cooke. 1964).

54 CHAPTER II

TYPICAL SOILS

II.1, Location of sample sites During and after a semi-derailed soil survey of the area a number of soils was selected for this study. The sites chosen are as much as possible representative of the natural environment of the soils, although in some cases human influences could not be excluded. The essentials o^ the soil descriptions and some soil properties are given in the following paragraphs. The described and sampled soil pedons are located in a number of sample areas, which coincide largely with the gcomorphological units as dealt with in Chapter 1.3.3. The majority of soil profiles is situated on four traverses in general perpendicular to the slope, whereas the remaining profiles are chosen individually within the units. The lines on the aerial photographs are soil boundaries, often delineating vegetation boundaries and to a lesser degree gcomorphological and geological units. Sample area A exhibits the terrain of the Morale Hills (fig. 13j with the profiles 1 to 4 on a traverse and the profiles 10 and 1 1 separately east and south of these hills on the pcdiplain. In sample area B the soils from the peneplain are located, the profiles 5 to 9 (fig. 16) represent the different soils. Sample area C is part of the eroded peneplain where the profiles 1 2 to 18 are located on a cross-section through the landscape (fig. 19). Sample area D represents the region of the doteritic sills and the associated granitic pediment with the flood-plain of the Bonwapitse River (Kg. 21 ). The soil profiles 19 to 28 are situated in this area on a traverse. Sample area E covers the extreme northwest of the survey area and is the transition from the Mahalapshwe catchment area to the Kalahari sandveld. The soil profiles 29 to 33 represent the soils in this area; of these the sites 31 to ?>3 are located on a cross-section (fig. 23). The sites arc also indicated on figure 1 and 7. The description of the soils in the field is in accordance with the guidelines set by the FAO (1966). which are largely based on the Soil Survey Manual (1951 and 1961). For additional terminology the glossary of the SSSA (1964) is applied as well as the definitions suggested by the FAO/ UNESCO (1968, 1970). The soil description was set to a depth of two meters or a lit hie contact, whichever shallover (Van Wambeke. 1962; Smith. 1965). The soil morphology controlled in first instance the frequence of sam-

55 plins;. In general a vertical distance up to 30- 40 cm was taken per sample, below a depth of 100 cm this thickness may be somewhat larger. It felt necessary the sampling by soil auejcr was continued below a deptli of 200 cm. Colour indication is for moist conditions unless stated otherwise. For complete soil profile descriptions and analytical data see Appendix 11. References to the soil genesis are resticted and fully discussed in Chapter V.

11.2. Field observations The observations in the field arc çiven in the following sections according to the sample areas as outlined in 11.1. The environmental characteristics of the soil profiles in an area are given in tables 18 to 22.

Sample area A: Soils of the Morale Hills toposequence and associated pediplain (fig. I 3).

Fig. 13. Part of sample area A

56 Brief description oj profile So. 1 - Ultic Haplustalf The dark brown A horizon of a slightly gravelly coarse sandy loam texture is underlain from 20-60 cm by a reddish brown slightly gravelly sandy clay loam (B21j. which gradually transists to a B22 of similar nature: a blockage of boulders is encountered at 110 cm. The soil is structureless and with a neutral soil reaction, root development is confined to the top 40 cm. Horizonation is weakly developed, smooth gradual boundaries prevail. The analytical data indicate a low CEC/soil that increases with depth from 6.1 to 1 2.2. calcium is the dominant exchangeable cation followed by magnesium. The base saturation is above 50% and increases regularly with depth to 8y/(.- in the 1322. The percentage organic carbon is low and decreases with depth.

I i riefdescription of profile So. 2 — Ultic Haplustalf The dark brown loamy coarse sand that makes up the A horizon overlies a deep, brown B horizon of a slightly gravelly coarse sandy loam texture, the clay percentage and the amount of coarse fragments increase regularly with depth; strong brown mottles are observed in the upper part of the B horizon (B21), while red mottles occur in increasing amount between 88—120 cm depth: quartz gravel blocks further examination at 145 cm; structural development is confined to the top 23 cm. weak subangular blocky structures are common, while root development is at the maximum in the top 60 cm: the soil reaction is slightly to medium acid- Chemical data of this soil reveal a very low CEC/soil between 3.50 and 6.61, that increases regularly with depth, the dominant exchangeable cations are calcium and magnesium: the base saturation varies around 43% in the A and is at a minimum in the mottled B horizons (23'/f), but increases in the B23 and B3 horizon to respectively 37% and 40%. The organic carbon percentage is highest in the topsoil and decreases with depth.

Uric f description of profile No, 3 — Ultic Haplustalf (fig. 14) The dark reddish brown A of coarse sandy loam texture overlies a homogeneous, dark red to reddish brown B horizon from 2] to 98 cm, in which a regular increase (if clay is encountered, giving rise to a coarse sandy loam texture in ehe Bl and a sandy clay loam texture in the lower part of the B, cutans are well expressed in the B2t (62—98 cm); red mottles in a brown matrix form the contrast in the B23 from 98 - 1 1 8 cm; structural development is weak to absent while root development is mainly confined to the top 40 cm; the soil reaction is slightly acid; a

57 lig. 14. Vltic Haplnsmlf, profile No. J Jïg. 75. "A^nic" ILiplitftiilf, profile -\'i.'. 4 blockage of coarse angular gravel occurs at 133 cm depth. Yellowish red mottlin" in a brown matrix différenciâtes the B3 horizon ( 11 H- 1 33 cm). According to the analytical data the dominant exchangeable cations are Ca and Mg. rhe CEC/soil value is very low, but increases regularly with depth from 3.95 to 9.09 in the B2t, followed by a decrease in the deep subsoil. The base saturation percentage is above 50'.' for all horizons and increases with depth to 73'.r in the B3. The organic carbon content is very low and insignificant in the deeper soil horizons.

Brief description of profile Xo. 4 • ".\ijuic" Haplu^talf (fig. 1 5) The horizonation of the soil is fairly well developed and expressed as follows. A dark brown AI of a coarse sandy loam texture is underlain from 16-78 cm by a reddish brown B horizon of sandy clay (loam.i texture: from 78 cm onwards yellowish red mottles occur in the brown matrix, followed bv dark ^rey mottles in a brown matrix, B2g (7H—97 cm): below 1 12 cm depth the matrix colour is a very dark grey in which brownish mottling appears, the transition to the C horizon is marked by the presence of calcium carbonate accumulations of varying hardness; the amount of CaCOj increases considerably with depth. Ar a depth of 1 25 cm extremely hard mottled granite is encountered. The structure is weakly developed and mainly confined to the top 43 cm, as is the root development; cutans are clearly visible in the lower part of the B horizon, notably in the B2g; the soil reaction is neutral in the topsoil and the upper part of the B horizon and mildly to moderately alkaline in the B2ca and the C horizon. The supporting chemical data show a clear increase in the CEC/soil from 4.39 in the Al to 26.7 in the lower subsoil. The dominant exchangeable cations are calcium and magnesium followed by potassium. The base saturation is very high, 80% or more, and increases irregularly with depth. Clay mineral and salinity data suggest a deviation from the profiles 1 to 3 most likely due to its physiographic position.

Brief description of profile No. 10 — Typic Rhodustalf Below the shallow A (0 — 10 cm) of a reddish brown colour and a coarse sandy loam texture, a deep, dark reddish brown to dusky red B horizon is situated till 91 cm. The amount of clay and coarse fragments increases regularly with depth, resulting in slightly gravelly sandy clay loam textures; the B is underlain by calcrete of varying hardness. The horizon boundaries are gradual but for those in the subsoil; subangular blocky structure is common in the topsoil, while root development is normal in the top 50 cm. The soil reaction is neutral to moderately alkaline in the C horizon. The analytical data of this profile demonstrate the low CEC/soil increasing with depth from 7.96 to 17.8; calcium and magnesium are again the dominating exchangeable cations, the base saturation of the soil is above 80 throughout and approaches 100% in the C. The percentage of organic carbon is above the average in the topsoil (0.6%) but decreases considerably with depth.

Brief description of profile No. 11 — Oxic Haplustalf The A horizon has a coarse sand texture and is from 16—108 cm underlain by a homogeneous, dark brown to yellowish red B horizon with a uniform slightly gravelly loamy coarse sand texture; below 108 cm the B3 horizon is characterized by a brown colour and a slightly gravelly coarse sandy loam texture, red mottles are clearly visible in the matrix colour, the following C horizon has a brown colour in which the contrast is formed by yellowish brown mottling. At 173 cm depth the soil is underlain by coarse and very coarse angular gravel. Horizonation is gradual, structural development is weak, and roots are best distributed and dense in the upper 50 cm of the soil, the soil reaction is strongly acid to neutral. The accompanying chemical data show an extremely low CEC/soil (between 1.75 and 2.63) in the A and B horizons; calcium and potassium are the dominant exchangeable cations, the percentage organic matter is very

59 low indeed. The base saturation is variable, while high in the A horizon (52%), it decreases to 29% in the B21 and subsequently increases to 46% in the lower part of the B horizon.

Marked profile differentiation is observed in soils at low topographic sites (profile No. 4) and where the parent material deviates from the commonly present granitic rock or its weathering products (profile No. 10). The general decrease in coarse fragments in and on the soils away from the Morale Hills is further noted. The soils of the pediplain are also characterized by a considerable soil depth in comparison to soils on the associated (erosion) plain (see Sample area B), while in a number of cases the profile is underlain by gravel and not by weathering rock, although it is feasible that the latter was not reached because of extreme depth of the bedrock. The differences in the remaining soil profiles were more noticeable than expected, considering the common origin of the parent material and the prevailing climatic conditions. While vegetation marks the various soils in the terrain, field observations suggest a stage difference in profile development mainly due to changing soil moisture conditions.

60 l'jblc 18. Sample area 1, information on the profiles 1 to -I. 10 und I i tit time of sampling

Profile 10

date examination July 1970 July 1970 July 1970 July 1970 July 1970 July 1970 elevation I 150 Tn 1140 rn 1123 m 1107 m 1082 m 1041 m l.mdform concave hillslopc gently sloping almost flat almost flat flat pediplain flat pediplain (phys.pos.) y/r- pediment pediplain drainage charmai Lmdform surroun- hilly to the soutli gently sloping flat almost flat flat ding country gently sloping to the north

micro- few shallow gullies occasional nil tew gullies, deep nil nil topography 10-20 cm deep. shallow rills 50 cm, 1 m wide 30 cm wide vegetation AMW* AMW AMW AMW AMW Terminalia sericea A. nigrescens A. nigrescens A. erubescens, A. A. Tortilis, A. nigrescens, A. open woudl. A. tortilis Combretum apicu- nigrescens, A. Dichrotachys tortilis la tu m tortilis cenerea, encroaching, A. erubescens parent material granitic colluvial granitic granitic granitic mcta-docriti- granitic drainage well drained well drained well drained poorly drained well drained somewhat excessively (cl. 4) (cl-4) (cl.4) (cl. 2) (cl.4) drained (cl. 5) moisture slightly moist dry throughout dry throughout dry () 71) cm 0- 80 cm dry. dry throughout conditions throughout moist below moist below surface stones very stony nil nil nil nil nil (cl. 3) evidence of slight water some water nil moderate water nil nil erosion erosion erosie; n erosion human nil nil nil nil nil nil O\ influence

AMW = Acacia Muted Woodland Sample area ß: Soils ot the granitic plain associated with the pediplain of the Morale Hills (fig. 16). In table 19 information on the sites and the soils is tîiven.

•S«

62 The soil connotation reads as follows:

Brief description of profile No. 5 — Lithic Vstropept A dark brown coarse sandy loam (Al ) is underlain from 21 - 36 cm by a dark reddish brown gravelly coarse sandy loam (15). which changes abruptly to altered granitic rock with sharp distinct mottles at 36 cm: extremely hard rock is encountered at 55 cm. A weak subangular blocky structure is present in the A horizon, to which most of the roots are also confined: the soil reaction is neutral. The chemical data belonging to this profile indicate a very low CEC/soil that increases with depth from 3.50 to 4.83; the base saturation is high in the A (79/?) but decreases in the B and C horizons to respectively 41% and 35'r; calcium and magnesium are the dominant exchangeable cations; the organic carbon content is normal (0.55f/v) and follows the usual trend with depth.

Brief description of profile No. 6 — "Aqitic" Haphtstalf The A horizon (0 — 23 cm) is dark brown and has a coarse sandy loam texture, it overlies a (dark) reddish brown sandy clay loam that merges into a sandy clay in the B21 from 43 — 69 cm: prominent dark red mottles are observed in the lower part of the B21 and increase in amount and prominence in the B2g (69—105 cm); this horizon is underlain by a grey, slisihtlv gravelly coarse sandy loam in which black mottles arc abundant; the boundary with the C at 150 cm is abrupt; structurai development is confined to the topmost soil, the soil reaction is slightly acid. Accompanying analytical data indicate an increasing CEC/soil with depth from 5.27 to 9.77, the base saturation increases regularly with depth from 40'v to 69'/. while calcium and magnesium arc the dominant exchangeable cations; the amount of organic carbon is similar to the one in profile 5.

Brief description ofprofile No. 7 — Ult'tc Haplustalj (fig. 17) The topsoil is a dark loamy coarse sand and underlain from 15 to 34 cm by a dark brown loamy coarse sand (B21); the B3 is encountered from 55--Ó9 cm. characterized by a slightly gravelly coarse sandy loam texture and of a brown colour: this horizon abruptly overlies the C horizon. The soil is structureless, while the soil reaction is medium acid, horizonation is faint, the dry soil colours differ considerably from the moist colours. Additional chemical information reveals a low fluctuating CEC/soil (between 3.07 and 4.79). while the base saturation percentage varies between 90'Y in the A to 55'/r in the B21. Calcium is the dominant exchangeable cation followed by magnesium and potassium, the percentage of organic carbon is low and decreases regularly with depth.

63 K*.

Pig. 17. Detail of the transition from the lïg. IS. \quic Haphtstalf, profile No. 8 B horizon to the C horizon in profile No. 7, Vltic Haplustalf

Brief description of profile No. 8 — Aquic Haplustalf {(is.. 1 8) The Ap horizon is composed of a coarse sandy loam dark brown in colour; it overlies a dark reddish brown sandy clay loam (B21. 21 —47 cm) which in turn is underlain by a dark reddish brown and dark brown sandy clay from 47 — 104 cm, the B2g: grey mottles are encountered in the upper part ot the B2g, while red mottles appear increasingly in the lower part; the transition to the B3 is clear at 104 cm, the subsoil has a brown colour and a slightly gravelly coarse sandy loarn texture; C material occurs from 1 22 - 1 44 cm, in which the amount of coarse sand is considerable. Struc- tural development is poor, the soil reaction is neutral to mildly alkaline in the B3. Noteworthy is the animal activity in the soil. Analyses performed on the samples indicate a CEC/soil from 7.14 to 16.2, while the base saturation increases regularly with depth from 65 A to 857r. calcium and sodium are the dominant exchangeable cations followed bv magnesium and potassium, the amount of organic carbon is low.

64 Brief description of profile No. 9 — "Aquic" Haplustalf Under a very dark greyish brown coarse sandy loam (Al from 0—16 cm) a B of dark brownish colours and of a sandy clay (loam) texture is encountered; below 56 cm depth the colour changes to very dark grey, in which strong brown mottles occur, the texture is a sandy clay; this horizon is underlain by the B2g of a sandy clay texture in which distinct red mottling is visible in a dark grey matrix; the C horizon commences at 112 cm, hard granitic rock is reached at 140 cm depth. The structure is well developed, the soil reaction changed from neutral to mildly and moderately alkaline in the B. From the additional chemical data it appears that the CEC increases irregularly with depth from 5.27 to 14.2, the base saturation percentage is above 50% throughout and at a maximum in the B2g horizon; calcium, magnesium and potassium are the dominant exchangeable cations; the percentage organic carbon is low and diminishes in the subsoil.

The soil morphology indicates an increase in profile development in soils encountered at slightly lower topographical sites under the same climatic conditions and the same parent material. In some areas, especially in the bottomlands, the presence of water together with poor drainage caused anaerobic soil conditions, whereas in other areas restricted soil moisture conditions are expressed partly in limited soil depth.

65 Table 19. Sample area B, information on the profiles 5 to 9 at time of sampling as Profile 5 6 7 8 9

date examination July 1970 August 1970 April 1970 September 1970 June 1970 elevation 1115m 1107 m 1108 m 1126m 1140 m landform flat plain flat plain flat plain flat plain flat plain at (phys.pos.) slight elevation slight depression bottom land landform flat flat flat flat flat surrounding country micro-topography nil nil nil nil nil vegetation AMW with AMW with AMW with AMW with AMW with A. nigrescens, encroaching A. grandi- Combretum A. Nigrescens, A. A. tortilis and Combretum apiculatum cornuta and apiculatum, robusta, Dichros- Dichrostachys A. tortilis and Dichrostachys encroaching tachys cenerea, cenerea encroaching A. erubescens cenerea A. tortilis encroaching A. tortilis parent material granite granite granite granite granite drainage imperfectly drained poorly drained somewhat excessively moderately well poorly drained (cl. 3) (cl. 2) drained (cl. 5) drained (cl. 3) (cl. 2) moisture conditions dry throughout dry throughout 0—15 moist, dry 0-70 dry, slightly 0-30 dry, slightly below moist below moist below surface stones nil nil nil nil nil evidence of erosion nil nil nil nil nil human influence not cultivated cultivation nil cultivation nil at present The soil profiles 1 2 to 18 are located in sample area C, representing the eroded plain (fig- 19). Descriptive information on the soil sample sites is given in table 20. The brief soil descriptions read as follows:

l'ig- 19. Sample area C

Brief description of prof île \!o. 12 — Ultic Haplustalf Below a dark brown slightly gravelly coarse sandy loam topsoil (Ap), occurs a fairly homogeneous B21 (from 15—32 cm) and a B22 (from 32 — 59 cm) of sandy clav (loam) texture and with a reddish brown colour. This upper B is underlain by a dark reddish brown mixed with yellowish red clay, the B2t from 59—87 cm, which overlies a gravelly sandy clay of the same colour; coarse fragments increase with depth; the B3 is underlain

67 from 102 cm onwards by decomposed granitic rock of a gravelly clay texture. Horizonation is well expressed, but structura! development is poor: the soil reaction is neutral. The report on the chemical analyses indicates a regular increase in the CEC/soil (from 8.81 to 20.00) in the C. while the percentage base saturation follows the same trend: an increase from 70% to 91% in the deep subsoil. Calcium and magnesium are the dominant cations on the exchange complex, the organic carbon percentage is above average in the topsoil (0.64 and 0.61%), but decreases considerably with depth.

Brief description of profile No. 13 — Ultic Haplustalj The dark reddish brown A horizon of slightly gravelly coarse sandy loam texture overlies from 21 cm onwards a dark reddish brown gravelly coarse sandy loam, the B21 ; the B22 is characterized by an increase in clay not manifested as cutans, and in coarse fragments, while also distinct yellowish red mottles occur; the B3 commences at 76 cm depth and has a gravelly sandy clay loam texture and a reddish brown colour, this horizon is underlain by the C from 118-175 cm. Horizonation is moderately well defined but the structure is poorly developed, root distribution is confined to the top 50 cm, the pH water indicates a medium to slightly acid soil reaction. Supporting chemical data demonstrate a varying CEC/soil with values of 1 5.7 in the Al and 26.6 in the C and a range from 6.70 to 9.38 in the B horizon; the percentage base saturation increases from 20 to 79%; calcium, magnesium and potassium are the dominant cations on the exchange complex, the percentage of organic carbon is low.

Brief description of profile No. 14 — Ultic Haplustalf A dark brown gravelly loamy coarse sand forms the Al (0 — 18 cm), the following horizon is a reddish brown slightly gravelly coarse sandy loam (B2. 18—56 cm) that overlies a yellowish red gravelly coarse sandy loam with distinct red and black mottles, while the C horizon is reached at 90 cm depth. Horizonation is clear, structural elements are absent to weakly developed, the soil reaction is slightly acid, root development is largely confined to the top 50 cm. Accompanying chemical data show a very low CEC that increases slightly with depth from 3.59 to 5.81. the base saturation percentage is fairly constant between 55% and 59% but increases sharply in the C. The dominant exchangeable cations are Ca. Mg and K, while also Na is present in a small amount, the percentage of organic carbon is very low.

Brief description of profile No. 15 — Typic Natraqualf The succession of soil horizons commences with a black to very dark grey

63 A horizon of coarse sandy loam texture followed, from 43—69 cm, by a very dark ^rey sandy clay loam with columnar structure in which dark red mottles occur: this horizon overlies a B2g. respectively from 69-91 and from 91-127 cm of a (dark) grey slightly gravelly sandy clay texture with common distinct yellowish and red mottles; the B3 commences at 1 27 cm, is greyish brown and has a slightly gravelly sandy clay loam texture; from 158-180 cm the C horizon occurs, consisting of decomposed granitic rock. Structural development is well expressed in the. top 60 cm of the soil, but is poor in the subsoil, the soil reaction changes from slightly acid in the A to neutral in the B2 and strongly alkaline in the B2ç and the C horizon. The analyses report a slow increase in the CEC/soil with depth from 7.15 to 18.8 in the C (apart from the value in the All); the base saturation percentage increases from 60% in the topsoil to fully saturated conditions in the subsoil. Ca and Na are the dominant cations on the exchange complex followed by Mg and K; the organic carbon percentage is unusu- ally high (1.84) in the All.

Brief description of profile So. 16 — Typic Vstorteut (fig. 20) Dark brown slightly gravelly coarse sand (the AI ) is underlain from 12—46 cm by a gravelly loamy coarse sand of a brown colour (B21): texture and colour change slightly in the B22 (46—67 cm) which overlies a brown gravelly loamy coarse sand, while decomposed granitic rock is encountered at 98 cm. Structural development is poor to absent, root development is confined to the top 60 cm, the soil reaction is medium acid throughout, dry colours differ considerably from the moist ones. Chemical analyses of the samples indicate an extremely low CEC/soil. varying between 1.75 and 1.31, while the base saturation percentage is also low, increasing with depth from 1 1% to 22%; Mg and K are the major cations on the exchange complex, the organic carbon content is extremely low.

Brief description of profile So. 17 — Lithic Ustipsamment The All (0 — 15 cm) consists of loamy coarse sand and has a very dark greyish brown colour; coarse fragments increase with depth in the A12 (15 —34 cm) which is abruptly underlain by coarse rock fragments and quartz gravel at 34 cm; structural development is absent, the soil reaction is slightly acid, the moist colour values are two units lower than the dry ones. The accompanying chemical data reveal a low CEC of 3.14, while the base saturation percentage is 45% and 56% respectively in the All and A12: the dominant cations on the exchange complex are calcium and potassium, the percentage organic matter is low.

69 L. • , ' t

;. 20. Typic [Tstortent. profile So. (6

Brief description of profile Xo. 18 - "Aqiac" Haplustalf The Ap (0-15 cm) consists of dark reddish brown coarse sandy loam overlying; a dark brown coarse sandy loam to 36 cm, the B21. below this depth the B22 of brown sandy clay loam texture with distinct red mottles occurs, the boundary at 5 5 cm to the underlying B2g is clear. This horizon is marked by a greyish brown matrix in which red and yellowish red and strong brown mottles occur: downwards trom 104 cm, the B3 of slightly gravelly sandy clay texture and grey colour marks the transition to the decomposed granitic rock. Structural development is confined to the B2g (moderate to weak medium columnar structure), horizonation is clear, while the bulk of the roots is encountered in the top 36 cm; the soil reaction is slightly acid in the topsoil and neutral to mildly alkaline in the subsoil. The CEC/soil increases regularly with depth from 5.26 to 16.70. while a

70 similar trend is observed in the percentage base saturation (increase from 48% to 95%); Ca and Mg are the major exchangeable cations, followed by K and the Na; the latter cation is of importance in the B and the C horizon, the percentage organic carbon in the topsoil is average (0.55%) and decreases with depth.

The variety in soils is well expressed when comparing soils at different physiographic positions. An additional factor in this area is soil erosion that induces the shallow soils on the higher sites, while decomposition of soil material is encountered in the lower areas. The occurrence of rock outcrops is common, while some soil properties such as salinity and structure are well expressed in lowland soils. Soil differences also become apparent through changes in vegetation.

71 Table 20. Sample area C, information on the profiles 12 to 18 at time of sampling

Profile 12 13 14 15 16 17 18

Date examination June 1970 February 1971 February 1971 February 1971 February 1971 September 1970 February 1971 elevation 1170 m 1167 m 1180 m 1172m 1170 m 1185 m 1180 m landform flat divide gently sloping flat divide gently sloping gently sloping gently sloping gently sloping (phys.pos.) concave slope valley bottom concave slope valley bottom 3% 3% landform flat gently sloping flat flat to almost gently sloping gently sloping gently sloping surr, country flat micro-topogr. plough ridges nil nil few shallow nil nil nil gullies, 50 cm deep, 1 m wide vegetaion Acacia Mixed AMW with A. Combretum AMW with A. Terminalia seri- Terminalia seri- AMW with Dios- Woodl. with nigrescens and apiculatum/A. karroo, A. nilo- cea Woodl. with cea with A. tor- pyros lycioides encroachment A. tortilis nigrescens W. tica and Dichro- Orozoa panicu- tilis and Dios- of A. tortilis encroaching with encroach- stachys cenerea losa and A. pyros lycoides ment of A. nilotica erusbescens parent material granite granite granite granite granite granite gravel granite drainage mod. well well drained well drained poorly drained well drained somewhat ex- poorly drained drained (cl. 3) (cl. 4) (cl. 4) (cl. 2) (cl. 4) cess, drained (cl. 2) (cl. 5) moisture 0—15 cm dry, dry throughout dry throughout moist throughout 0—12 cm dry dry throughout 0—15 cm dry conditions si. moist below si. moist below 15-55 cm si. moist, 55 + cm moist rock outcrops nil nil occasional nil nil kopje and whale nil whale back back exposures exposures evidence of nil nil nil some water nil nil nil erosion erosion human influence dry land nil nil nil nil nil dry land farming framing practices .practices Sample area D (fig. 21) comprises the soil profiles 19 to 28. comprehensive information on the soils and the sites are given in table 21. while brief descriptions arc documented in the following paragraphs.

F-'ig. 21. Sample urea I)

73 îiriej description ot profile Xo. 19 - ÏAthic l'storthent A shallow 10-15 cm1 dark reddish brown clay loam rests directly on hard dolcrite; the soil reaction is neutral. The chemical data indicate a CEC/soil ot 27.1 and a base saturation of 69''; calcium is the major cation on the exchange complex, the percentage organic carbon is high ( 1.28%).

liricj description oj profile \'o. 20 - Vdic Vstocrept The AI 1 from 0 30 cm consists of a dark reddish brown gravelly coarse sandy loam and merges gradually to the A12 ot the same texture and colour; at 65 cm coarse 'Travel occurs, the soil reaction is neutral. Analyses performed on the samples taken reveal a low CEC/soil value, respectively 9.64 and 8.10 in the A1 1 and the A12. while the percentage base saturation increases with depth from 78''r to 87''; the dominant exchangeable cations are Ca and Mçr, the percentage organic carbon is normal. liricj description of profile .\o. 21 - Vltic Haplustolf The topsoil has a reddish brown colour and a coarse sand texture, it overlies a yellowish red loamy coarse sand {B21 j from 33-80 cm; the 1322 (80—129 cm ! has a coarse sandy loam texture and is ot a dark reddish brown colour: the transition to the C (sec Chapter 1.2.2.) is similar to the B2. but coarse fragments increase with depth, the soil reaction is slightly acid throughout, while structural development is weak to absent; major root development takes place in the top 80 cm. The analytical data show a slight increase of the CEC/soil with depth from 3.91 to 4.78, the percentage base saturation varies irregularly between 36'/' and 4 l'i- ; Ca is the main cation on the exchange complex, the amount of organic carbon is very low in the topsoil (mean 0.1 7?c).

Brief description of profile So. 22 — Typic Pellustert The topmost soil (0-2 cm) is formed by a very dark greyish brown sandy clay, which is the beginning of a deep A horizon of a very dark grey colour and a clay texture: from 67 cm onwards calcium carbonate accumulations occur, while the profile at 1 27 cm is underlain by dark reddish brown clayey 1IC material: a gravel blockage is encountered at 170 cm. The structure is coarse prismatic from 2 -28 cm and determined by vertical cracks, the remaining part o^ the solum is massive, the soil reaction is moderately alkaline throughout and increases a little with depth from pH water 8.2 to 8.5. Roots are confined to the top 60 cm. Results of analyses indicate fairly high CEC/soil values throughout, ranging between 32.9 to 39.5: the base sa uur at ion increases regularly downwards, and is always above 80' 'c.th e soil is fully saturated in the Aca:

74 calcium and magnesium arc the main cations on the exchange complex; the organic carbon percentage is fairly high throughout (0.5'/ or more).

Brief description of profile ,\'o. 23 — Udic Rli odi is talf (plate I) The dusty red sandy clay A horizon is succeeded below 1 2 cm depth by a homogeneous deep, dark reddish brown to dusky red B horizon of clayey texture; the B3 has a fine gravelly sandy clay loam texture and is dark red in colour; it commences at 122 cm, while a blockade of calcrete is encountered at 175 cm depth: weak medium subangular blocky structures arc confined to tbc topsoil in which also the main root development occurs; the soil reaction is slightly acid to neutral. According to laboratory data, tiie CEC varies with depth between 18.1 and 21.2; a similar trend is observed for the percentage base saturation •: decrease from 7(Y/f to 71%) with exception of the B3 horizon: the dominant cations arc Ca and Mg followed by K and a trace of Na. The amount of organic carbon is above average in the topsoil (1.26/r), but sharply decreases to normal values below 12 cm.

Brief description of profile i\ro- 24 — 1'ypic Chromustert The A horizon is a dark brown colour and has a sandy clay loam texture; it overlies a dark brown calcareous sandy clay loam (the A from 19—45 cm), the succeeding A horizon is a very dark greyish brown, slightly gravelly calcareous sandy clay loam which is underlain, from 76 cm onwards, by a brown, highly calcareous slightly gravelly coarse sandy loam; the pcdon is blocked ut 170 cm by hard calcrete. Structure is moderately developed in the top 76 cm. horizonation is well defined, the soil reaction is moderately alkaline in the topsoil and strongly alkaline in the subsoil. According to analyses, the CEC in the soil ranges between 32.9 to 35.9 in the Al and AC horizons, but decreases to 25 in the C: the percentage base saturation is HH'A in the Al and is at a maximum in the remaining part of the soil. Calcium and magnesium arc the dominant cations on the exchange complex, the percentage organic carbon is 0.58'' in the A and decreases with depth.

Briej description of profile Ao. 25 — Typic Pellustcrt (fig. 22) The topmost surface horizon (All, 0 — 3 cm) is very dark grey and has a clayey texture: it overlies a deep, fairly homogeneous very dark grey clay (loam) Al 2 and Al 3: below 67 cm the soil colour changes to black, while calcium carbonate is encountered in increasing amounts; the AC from 96 cm to 142 cm is a very dark grey silty clay loam; it overlies a red and very dark grey, highly calcareous, very gravelly coarse sandy loam, the (Il)C: structural elements are observed in the top 67 cm. cracks and roots arc

75 Fig. 22. 'i'ypic Pellnstcrt, profile No. 25 also common in this part of the soil. The soil reaction is moderately to strongly alkaline, horizonation is gradual. Chemical analyses demonstrate a high CEC/soil that increases regularly with depth in the A from 52.3 to 77.6. but decreases sharplv in the IIC (45.4); the base saturation is fairly constant between 82r/c and 857c with exception of the AC horizon for which a saturation of ll'/r is obtained. The percentage of organic carbon is above average throughout the A horizon (0.83—0.44*7r). the percentage of CaCO3 increases irregularly with depth.

Brief description of profile No- 26 — Typic Haplttstalf A dark reddish brown sandy loam (A, 0-24 cm) is underlain by a fairly homogeneous dark reddish brown B of a sandy clay loam texture, coarse fragments increase with depth, giving rise to gravelly sandy clay loam and a highly calcareous B2ca.

76 The solum is blocked at 120 cm depth by coarse gravel. The soil reaction is neutral in the Al, changes the mildly alkaline in the B21 (24—48 cm) and increases to moderately and strongly alkaline in the subsoil. Structural development is weak, the bulk of the roots is confined to the top 40 cm. The chemical data indicate an increase of the CEC, with depth from 12.5 to 20.9, and also show fully saturated conditions; calcium, magnesium and potassium are the main cations on the exchange complex.

Brief description of profile No. 27 — Lithic Ustorthent A dark reddish brown clay abruptly overlies dolerite at 20 cm depth; the soil reaction is neutral. As shown by the chemical data the CEC is 33.1 and the base saturation 79%, calcium and magnesium are the major cations on the exchange complex.

Brief description of profile No. 28 — Lithic Ustorthent A black clay rests abruptly on dolerite, commencing at 38 cm depth. The soil reaction is strongly alkaline. The analytical data shown a CEC of 46.2 and fully saturated conditions, calcium and magnesium are the main exchangeable cations. Contrasting soils are mainly due to the different soil parent materials, the doleritic versus the granitic rock suite. Shallow and stony soils are confined to the hills and the areas immediately surrounding them. Slight changes in soil topography seem responsible for differences in soil moisture conditions and associated development of soils derived from granitic parent material.

77 Table 2t. Sample area D, information on the profiles i9 to 28 at time of sampling

Date examination 19 20 21 22 23 24 25 26 27 28

Date examination July 1970 July 1970 Febr. 1970 Febr. 1970 Febr. 1970 Febr. 1970 Febr. 1970 July 1970 July 1970 July 1970 elevation 1320 m 1148 m 1131 m 1123m 1125m 1126 m 1131 m 1147m 1280 m 1 270 m landform flat hill base collu- pediment flat pediment pediment pediment base flat hill flat hills (phys.pos.) top vium, gently flood-plain gently gently gently colluvium, top sloping sloping sloping sloping sloping sloping landform flat top steep to S gently flat gently gently gently steep N flat to flat surrounding steep gently sloping sloping sloping sloping gently broken country sloping to sloping S the N. micro- nil shallow old plough faint nil nil faint nil nil faint topography gullies ridges gilgai gilgai gilgai 20-50 cm deep, 50 cm wide vegetation open Wdld. AMW, Aca- Combre- AMW, Aca- AMW, Aca- AMW, A. AMW, A. AMW, Bos- open Wdld. grassland Commi- cia nigres- apicula- cia grandi- cia tortiles Grandicor- grandicor- cia albi- Commi- phora afri- cens and tum/Aca- cornuta, A, Dichrosta- nuta, A. nuta, A. trunca, A. phora africana, Kir- Commi- cia nigres- tenuspina chys karroo, A. karroo, A. tortiles cana, Kir- kia accu- phora cens encroach- cenerea tenuespina, tenuespina, kia accuminata, africana Wdld. ing A. Dichro- Dichro- minata Scleroca- tortiles stachys stachys rya caffra cenerea, cenerea Boscia albitruca Table 21. Continued

Date examination 19 20 21 22 23 24 25 26 27 28 parent dolerite colluvial granite calcareous granite dolerite dolerite colluvial dolerite dolerite material derived alluvia derived from from doleritic doleritic and grani- rock tic rock drainage well well poorly modera- imper- poorly well drained drained drained tely well fectly drained drained (cl. 4) (cl.4) (cl. 1) drained drained (cl. 1) (cl.4) - (cl. 3) (cl. 2) moisture dry 0-20 cm dry 0-50 cm si.moist dry 0-30 cm 0-20 cm dry dry conditions dry, through- dry si. moist, si. moist, si. below moist out moist moist moist below below below below surface exc. stony very stony nil nil nil nil very stony exc. stony exc. stony exc. ston] stones rock out crops extr. nil nil nil nil nil nil nil extr. extr. rocky rocky rocky evidence of slight moderate nil nil slight nil nil slight nil nil erosion water water sheet sheet human nil nil once clear- nil nil nil nil nil nil nil influence ed for dry farming The soil profiles 29 to 33 are located in sample area E. A part of this area is shown in figure 23. Comprised site and soil in formation is presented in table 22; brief soil descriptions are given below.

Fig. 23. Part of sample area E

Brief description of profile No. 29 — Oxic Haplustalf Below a brown A horizon of loamy sand texture occurs a reddish brown sandy loam, the B21 from 22—36 cm; this horizon is underlain by a fairly homogeneous yellowish red sandy clay loam in which dark red mottling and coarse fragments increase with depth, giving rise to a prominent red mottled, gravelly sandy clay loam, the B3 (80—95 cm); weathered schist is encountered from 95 —113 cm. The soil reaction is neutral in the A, but slightly acid in the B and medium acid in the B3 and C horizon. Horizonation is gradual, while the soil has no visible structure and the bulk of the roots are found in the upper 50 cm of the soil; cutans are rather clear from 50—80 cm depth (B2t). The accompanying chemical data show a low CEC/soil slightly increasing from 3.23 to 5.23 in the B, but subsequently decreasing in the deep subsoil and the parent material to respectively 4.34 and 4.78. The percentage base saturation is between 43% and 53% in the topsoil and decreases slightly with depth. Calcium and magnesium are the dominant cations on the exchange complex, the percentage of organic carbon is low: 0.29%.

Brief description of profile No. 30 — Typic Ustipsamment A very dark greyish brown sand (All) is underlain from 23 cm downwards by a homogeneous brown sand; the A3 is encountered at 120 cm

80 depth and has a strong brown colour and the same texture as the overlying A horizon; the transition to the C is gradual, the latter consists of sand, strong brown with faint yellowish red mottles. Structure is absent (single grained) apart for a weak subangularblocky structure in the All, main root distribution is in the top 80 cm, the soil reaction is slightly acid and becomes medium acid in the A3 and C horizons. Chemical analyses of the samples taken indicate an extremely low CEC/ soil of 2.19 in the All, 1.31 in the A12 and 0.87 in the remaining part of the solum; the base saturation is 73% in the All, 31% in the A12 and varies between 14% and 17% in the remaining part of the A and C. Magnesium and potassium are the main exchangeable cations, the percentage of organic carbon is extremely low. Brief description of profile No. 3i — Entic Chromustert A dark greyish brown sandy loam overlies a dark greyish brown sandy clay, the All, from 15—39 cm; the succeeding A horizons are greyish brown and of a slightly gravelly sandy clay loam texture; below 116 cm depth the AC is represented as a brown, slightly gravelly sandy loam, while calcrete forms a blockage at 176 cm; the soil is highly calcareous throughout with a moderate alkaline soil reaction, structure is moderately developed; horizonation is gradual, the bulk of the roots occurs in the top 40 cm, pressure faces are best observed in the A12 from 36—67 cm. 7 Additional chemical data show a fairly uniform CEC/soil ranging between 20.7 and 25.4; the soil is fully saturated, while calcium and magnesium are the main exchangeable cations. The percentage of organic carbon is high in the A (0.85%) and remains at 0.5% till a depth of 67 cm; the percentage of calcium carbonate is above 10%. Brief description of profile No. 32 — Oxic Haplustalf Below a dark brown, coarse sandy loam a reddish brown and yellowish red B horizon occurs of a uniform clayey texture with dark red mottling increasing with depth, forming respectively the B21 from 30—61 cm and the B22 from 61—88 cm; the lower part of the B is underlain by a strong brown, slightly gravelly clay, the B3 (88 — 110 cm), which merges clearly to the C horizon. Red and blackish mottling increases in amount and prominence with depth as does the amount of coarse fragments; the soil reaction is medium to slightly acid. Structural elements are weakly developed to absent, major root development is restricted to the upper 60 cm of the soil. Supporting data from the chemical analyses visualize a low CEC/soil varying between 3.9 and 9.8, while the percentage base saturation is between 50—60% in the B and 68% in the A. Calcium and magnesium are the best represented cations on the exchange complex, the amount of organic carbon is normal.

81 Brief description of profile No. 33 — Ultic Haplustalf The soil has a dark brown, coarse sandy loam A horizon that merges at 30 cm into a dark brown coarse sandy loam which is underlain by a dark brown, slightly gravelly coarse sandy loam with reddish brown mottles, respectively the B21 (30-58 cm) and the B22 (58-99 cm); weathered granitic rock is encountered from 99 — ] 30 cm, horizonation is fairly well developed, structural elements are weak to absent, the soil reaction is slightly acid. Data of the analyses illustrate a very low CEC/soil that increases slightly with depth from 4.38 to 7.06, the percentage of base saturation increases from 42% in the A to 73% in the lower B; calcium followed by magnesium are the main exchangeable cations, the percentage of organic carbon is about average (0.48%) and decreases sharply with depth.

Under a uniform climate the interaction between the parent material and the topography is the most important factor of soil development. The soil differences are also well indicated by the changes in vegetation that the soils carry. Different soil moisture conditions are thought to be related in the first place to the time of sampling, summer with rain versus the dry winter. However, moist soils sampled in the dry period are commonly observed at depressional sites.

82 Table 22. Sample area E, information on the profiles 29 to 33 at time of sampling

29 30 31 32 33

Date examination Sept. 1970 Sept. 1970 Febr. 1970 Febr. 1970 Febr. 1970 Elevation 1320 m 1350 m 1320 m 1300 m 1280 m Landform (phys. gently sloping flat plain almost flat almost flat almost flat pos.) pediment pediment plain plain Landform surr. gently sloping flat flat flat flat country micro-topography nil nil shallow gullies nil nil 30—50 cm deep, 1 m wide vegetation Combretum apicu- Terminalia seri- Acacia Mixed Combretum apicu- Terminalia scri- latum/Acacia ricea Woodland Woodland with latum Woodland, cea Woodland, nigrescens Mixed with A. fleckii, A. gerrardi and some A. robusta some A. robusta, Woodland with A. Diospyros lyciodes. Chretia caerulea and Commiphora Ehretia caerulea fleckii, A. robusta Grewia retinerois mollis and Euclea un- Commiphora mollis, dulata Dichrostachys cenerea parent material schist eolian sand metadolerite (?) granite granite drainage well drained (cl. 4) well drained (cl. 4) moderately well well drained (cl. 4) well drained (cl. 4) drained (cl. 3) moisture conditions dry throughout dry throughout moist throughout moist throughout 0—10 cm dry, moist below evidence of erosion nil nil some gully erosion nil nil human influence may have been old nil nil nil nil cultivated land CO II.3. Soil properties

Subjects discussed in this section are: 1) bulk density, 2) soil reaction and 3) exchange capacity. The relation between these properties, the soil constituents and their arrangement, is a factor that controls soil characteristics to a great extent.

11.3.1. Bulk density The range of bulk density measurements expressed as g/cm3 for 43 samples, is between 1.1 and 1.8. The lowest values are obtained from the very topsoil of a granitic bottom land soil (profile 15, 0—2 cm), as well as from the sandy soil of the Kalahari (profile 30). In the latter, the bulk density ranges between 1.2g/cc in the topsoil and increases slightly to 1.4 g/cc in the subsoil. Similar values are commonly observed in the topsoil of all soils encountered. The deeper horizons of soils derived from granite, in which also an increase of clay with depth is noticed, represent the highest bulk density data from 1.5 to 1.8 g/cc. The black clay soils derived from doleritic rock have a bulk density of between 1.4 and 1.7; these data largely correspond with other figures on similar soils (Dudal, 1965). A regular, gradual increase in bulk density with depth occurs mainly in the granitic soils which show reasonable profile development; sharp changes are merely restricted when reaching the C material. The lower bulk density values in the topsoils are ascribed to the higher volume of soil taken up by the root system, the amount of organic matter in these horizons and to intensified biological activities. Corresponding with higher bulk densities in the subsoils of most hydromorphic Alfisols are changes in clay mineralogy. These include an increase in the 2 : 1 lattice Al-silicates. In addition, the compaction of the subsoil horizons through the weight of the overlying soil must be taken into account while reviewing the higher bulk density values in deeper parts of the soil.

11.3.2. Soil reaction Measurements of soil reaction expressed as pH-H2O and pH-KCl indicate acid to neutral conditions for most granite soils and neutral to alkaline environment for soils derived from the basic rock suite. Exceptions for the former include the subsoils of a number of bottom- land soils, such as profile 4, 15 and 18, as well as the subsoils which are characterized by a high percentage of CaCO3 (profile No. 10). The pH-H2O is 1.0 unit higher than the pH-KCl for all samples. The overall trend of the pH values with depth varies considerably and cannot be taken as a characteristic applicable to all the soils, if, however,

84 the profiles are grouped according to their profile development, it appears that in soils with a more pronounced morphology the pH regularly increases with depth, while in soils with faint horizonation the pH stays fairly constant. This feature is also best observed in soils derived from granitic parent material. In the sandy soil from the Kalahari the pH decreases considerably in the subsoil, while also in less developed soils the pH is in general lower than in their better-developed counterparts. This may be illustrated while comparing the soil acidity data from the profiles 11, 12 and 14 with those of profiles 4, 13 and 31. The correlation between the pH values, the C.E.C. and base saturation is summarized in table 23; see also section II.3.3.

Table 23. Correlation between pH values, C.E.C. and base saturation

X y r ;ression equation st. err. x st. err. y.

CEC pH-H2O 0.771 y = 0.05 x+ 6.16 8.77 0.56 CEC pH-KCl 0.676 y = 0.04 x+ 4.82 10.16 0.67 Sat. pH-H2O 0.759 y = 0.03 x+ 4.95 15.57 0.58 Sat. pH-KCl 0.735 y = 0.03 x+ 3.55 16.20 0.61 pH-H2O pH-KCl 0.920 y = 0.94 x- 1.02 0.35 0.35

In a semi-arid environment acid to neutral conditions are encountered in the majority of granitic soils that have been subjected to leaching. This means that the bases in solution accumulated to lower sites and/or that only but a small amount of metal cations was made available through the weathering of the parent material.

11.3.3. Exchange capacity Directly related to the pH is the percentage base saturation (Scheffer and Schachtschabel, 1970). The percentage indicates the relative proportion of the adsorbed bases and hydrogen on the exchange complex. The trend of the percentage base saturation is variable, in some soils a definite increase of the saturation is observed, for example in profiles 1, 8, 10, 12 and 18, while in other soils a clear decrease of the value is apparent (profiles 30 and 32). There are soils in which the base saturation percentage decreases at first, only to increase at a greater depth, or there are others where it remains fairly constant throughout the solum. The mean values of the saturation percentage was taken to investigate the possibility of grouping soils relative to their adsorbed cations. The criteria

85 for the groupings were partly derived from suggestions made by the FAO/UNÉSCO (1970). Soils with a high base saturation percentage (75 — 100%) are Vertisols, Entisols (basic) and most hydromorphic Alfisols. Those with a low base saturation (0—25%) include the Entisols (acid). Most of the Haplustalfs have a base saturation between 50—75%, some Oxic, Ultic and Typic Haplustalfs have however a lower saturation of bases (between 25—50%). The fluctuations in base saturation percentage in the granitic soils is commonly related to their stages of development. The relation between base saturation and pH is shown in figure 24 and correspond with findings by Scheffer and Schachtschabel (1970).

• • o o o o •i

3.91

cf^iö 25 50 75 bata aaturatlon (l)

Fig. 24. Scatter diagram and regression line for pH-KCl and base saturation percentage

86 As the organic matter content in the soils is low, the cation exchange capacity depends almost entirely on their mineral fraction. Of th'ese the colloids with the fine silt, and to a lesser extent the coarse silt and the sand fractions, control the ion exchange properties (Wiklander, 1969). The dominant exchangeable cations are calcium and magnesium, followed by potassium and occasionally soidum. The C.E.C. expressed as the total quantity of cations that a soil can adsorb shows a wide range (Buckman et al., 1967). This is not only due to the environmental factors, but also to the stage in soil development. In general the data indicate a slight increase of the G.E.C. with depth. On the basis of the values obtained and partly according to the USDA criteria (7th Approx. 1970) the following divisions can be made.

Table 24. CEC$oii as related to different soils

GEC/meq/100 g soil Soil Order Profile No.

50+ Vertisols 25 25-50 Vertisols, Entisols on basic material 22, 23, 24, 27, 28 and some Alfisols 10-25 Subsoils of hydromorphic Alfisols, 4,8, 9, 10, 12, 13, Rhodustalf and some Haplustalfs 15, 18, 19,26,31 0-10 Inceptisols, Entisols on granitic 1,4, 13, 14, 16, material, other Alfisols 18, 20, 21, 29, 30, 32, 33

The correlation coefficient between the CEC ^ and the grain size fraction is variable. For example, this coefficient is 8.07 between the CEC ^ and the fine silt + clay fraction except for the soils that have a coarse texture (loamy sand or sand), while the correlation is 8.56 between the CECsoil and the silt fraction not taking into account the profiles 21, 30 and 31. The correlation coefficient between the CEC u and the clay fraction is best expressed in medium-textured soils. Thus, generally speaking, the correlation between the CECsoil and the clay fraction is low in coarse-textured soils (respectively the profiles 3, 30 and 33). Similar findings were reported by Syers et al. (1970) for sandy soils in New Zealand. The decisive factors are the type of clay and the amount of clay present. This is evident when the CEC .. is recalculated as CEC meq/100 g clay. In three profiles only the CECcl is below 24 meq/100 g clay in the •greater part of the B horizon.

87 Furthermore, in most soils where other than smectite clay minerals are present, the CECc|a varies between 25 — 50 meq/100 g clay, which corresponds well with data from Scheffer and Schachtschabel (1970). The data are summarized in table 25.

Table 25. Correlation and regression equation between CEC i and various particle sizes

x y r regression equation st. err. x st. err. y

CEC 2-50/im 0.856 y = 0.45 x + 5.99 7.32 3.81 CEC <20 /im 0.807 y = 0.86 x + 22.38 8.58 9.11 clay CEC 0.888 y = 0.62 x - 2.69 6 68 4 .67

Similar high correlations, especially between the CEC u and the silt fraction, were reported by Buursink (1971) and were also quoted by Ruellan et al. (1967). The above data stress once more the importance of the textural composition of the soils in relation to their exchange phenomena. The above mentioned soil descriptions and related soil properties allow a classification of the soils according to the 7th Approximation (1970), in order to facilitate their discussion in the following Chapters. Eight groups are recognized (nos. 1 to 8), while symbols indicate these groups on the graphs in the text. Further information on the soil classification is presented in Chapter VI.

Key to fig. 24, 28, and 29. Symbol Group Order Subgroup Profile

D 1 Vertlsols Typic Pellustert 22, 25 Typic Chromustert 24 Entic Chromustert 31 + 2 Inceptisols Lithic Ustropept 5 Udic Ustocrept 20 e 3 Entisols Typic Ustorthent 16 (acid) Lithic Ustipsamment 17 Typic Ustipsamment 30 a 4 Entisols Lithic Ustorthent 19, 27, 28 (basic) o 5 Alfisols Ultic Haplustalf 1,2,3, 7, 12, 13, 14, 21, 33 • 6 Alfisols Oxic Haplustalf 11, 29, 32 Typic Haplustalf 26

A 7 Alfisols Aquic Haplustalf (4), (6).8, (9), (18) Typic Haplustalf 15 A 8 Alfisols Typic Rhodustalf 10 Udic Rhodustalf 23

88 CHAPTER III

SOIL COMPOSITION

Soil composition and mineralogy was assessed according to particle size distribution in the fine earth. The last two sections of this chapter deal with organic matter and salinity. The judgement of the soil texture in the field embraces all these constituents and comparisons between field and laboratory data are therefore influenced by the nature of analyses performed to determine the texture in the laboratory. As is common practice, the fine earth fraction of the soil was treated with diluted HCl and with H2O2; as such the laboratory data on the particle size distribution reflect the textural composition of the mineral particles only.

111.1. Fragments coarser than 2 mm The indication of this fraction is given according to FAO Guidelines for Soil Description (1966) and mainly refers to the fine, gravelly part of the soil, which is also called grit. In a number of profiles, this gravel represents a considerable percentage of the total soil, which is for the greater part attributed to the nature of the soil parent material. Thus soils developed from the granitic rock suite have a higher percentage of coarser material than soils derived from doleritic material and from schist and sandstone. In most solums the amount of coarse fragments, if present, increases with depth, thus indicating the activity of the soil forming processes. In the immediate surrounding of rock outcrops the topmost soil contains a high amount of coarse material, mainly due to gravity transport from the hills nearby. The study of the composition of material coarser than 2 mm indicates that, apart from whole pieces of rock that resemble the rock composition, the smaller fractions between 2—5 mm are mainly composed of quartz, while in some cases feldspar contributes. To a certain extent, the occurrence of these constituents indicates their resistance to weathering processes (Chap- ter III.3).

111.2. Grain size distribution in the fine earth

The following texture classes are applied: sand (2.0—0.5 mm), silt (50 — 2 /im) and clay (smaller than 2 ßtn), (Soil Survey Manual, 1951).

89 III. 2.1. Sand The grain size limits assigned to facilitate a subdivision of the sand fraction are the following: coarser sand (2.0—0.5 mm), medium sand (0.5-0.02 mm), fine sand (0.02-0.01 mm) and very fine sand (0.01-0.005 mm). The sand fraction as a whole is an important constituent in the majority of the soils, often representing more than 50% of the fine earth fraction. This feature is clearly detectable in a number of texture graphs, constructed on the basis of the mean values of the different fractions for the whole soil. In addition, the dominant sand grade is indicated in a sand triangle, constructed through the recalculation of the particle size distribution for the total soil on a 100% sand basis (fig. 25).

100AO

% coarse sand

Fig. 25. Sand triangle

Summarizing, it is seen that soils derived from the granitic parent material contain a higher amount of sand than soils derived from the doleritic rock suite. Within the granitic soils, the dominance of coarse sand is recognized above the other sand grades. In addition, a decrease in the amount of coarse and medium sand is accompanied by an increase in the clay fraction and occasionally in the silt fraction in the better developed soils. This is in agreement with findings from Thompson (1961). The soil derived from the Kalahari sand mainly consists of medium and fine sand, which is in accordance with the textural composition of the

90 parent rock (Chapter 1.2) and confirms earlier statements made by Polder- vaart (1955).

IU.2.2. Silt The silt fraction is subdivided into coarse silt (50—20 /urn) and fine silt (20 — 2 pm). The total silt fraction plays a subsidiary part relative to the texture composition of the soils. In soils derived from granitic parent rock, the combined percentage is about 1.0%; however, this percentage is considerably higher in soils developed from or on doleritic rock (25%). The lowest percentage of silt (0.5—2%) is encountered in the soil from the Kalahari sandveld (profile 30) and the highest percentage (mean 33.1%) is found in profile No. 25 (Vertisol). The ratio of fine silt and coarse silt is variable. In soils derived from granitic material, the amount of coarse silt is slightly higher than the amount of fine silt. Soils developed on more basic rock show a little higher percentage of fine silt, as is also the case for soils on Kalahari sand and schist.

III. 2.3. Clay The clay fraction comprises particles smaller than 2 micron; no subdivision within this fraction was made. The texture diagrams show an interest- ing trend of the clay fraction relative to the development of the soils and their origin. Greatest contrast between the total clay percentages is found in profile 22, black, cracking, clay soil from the Bonwapitse floodplain, and the sandy soil from the Kalahari, profile No. 30 (45.8% clay versus 3.7% clay). An increase in clay within the soils derived from the granitic rock is commonly observed but the degree of augmentation varies considerably. In general, the soils with a wetter soil moisture regime have a higher clay percentage and also a more pronounced clay distribution curve. In addition, granitic soils near the kopje have a higher clay content than the associated soils further down slope (profile 1 versus profile 2). This feature was correlated by Thompson (1961) with differences in the mineralogical composition. This was found to be only partly true (Chap- ter III.4).

The most typical Vertisols, profiles 22 and 25, have an amount of clay comparable to most of their counterparts in the rest of the world (Dudal, 1965). The difference between the lithomorphic and the topomorphic position of these soils could be responsible for the slight variation in the distribution of the clay through the profile, see also fig. 26. Relative to the particle size distribution, profile 25 closely resembles the margalithic soil as described by Mohr and Van Baren (1959, p. 261).

91 Fig. 26. Particle-size distribution for selected soils in weight percentages. 1 : coarse sand, 2: medium sand, 3 : fine sand, 4 : very fine sand, 5 : coarse silt, 6 : fine silt, 7: clay

The relation between the clay and the other fractions was computed for all soils. A very high degree of correlation was found to exist between the clay and the fine silt fraction (r = 0.971); this is mainly caused by the very low percentage of the 20—2 urn fraction in the soils (see III.2.2.). A fair negative correlation was observed between the clay and the fine + medium sand (r = —0.772).

The shape of the clay distribution curve was found to be closely related to the differences in the soils. The relevance of this curve is supported by the fact that the majority of soils are developed on homogeneous parent material. Four types of clay curves are recognized: 1) clay-constant, 2) clay-bulge, 3) clay-pyramid, and 4) clay-step(s).

92 The application of the type nomination may vary if used for the total soil depth and is here limited to the clay distribution in the A and B horizons to a depth of 1 50 cm; if the C horizon is included no depth limitation is used (fig. 21).

% clay 0 10 20 30 40 5C

• i \N \ \ X \ X • \ i \> • '\ v 50 i (15) \ V \ i (16)| s (29 i \ 1 V i A \. 1

/ '• \ 100 |

1 è

depth cm

type 1 profile no in ( ) 3 4

Fig. 27. Clay curves

Type 1, clay-constant: this curve is encountered in coarse textured soils of the Inceptisol and Entisol Order, such as profiles 5, 16, 20 and 30. The absolute increase of clay with depth varies between 0 — 2.5% clay, while the relative increase in clay may be as much as 50%. This is due to the very low clay percentage of the soils. The increase in clay in absolute terms seems therefore more appropriate than the relative indication. The constant trend of the clay curve in the Vertisols is merely attributed to

93 the effect of churning that causes a fairly even distribution of the clay with depth. Sharp changes in the amount of clay in these soils are restricted to the topsoil (Type 4, clay-step). Similar observations were made by Smyth (1963) and Fölster et al. (1967), who comment that textural differentiation not only increases with the age of soil formation but also with the rising clay content of the parent material. The impover- ishment of clay in the surface horizon is ascribed to surface wash.

Type 2, clay-bulge: this type occurs in the medium textured soils derived from granitic parent material; the following profiles (all Alfisols) are relevant: 3, 6, 7, 8, 9, 23 (weak), 29 and 32. The absolute clay increase with depth may be as much as 30% clay, but commonly varies between 10 — 20%. The relative increase in clay in the B horizon varies between 20—50%, while a subsequent decrease in the lower part of the B differs less than 20% from the clay percentage in the upper part of the B. Here again it is preferable to indicate the clay increase in absolute rather than relative terms. The "clay-bulge" has been widely recognized and used to designate texture B-horizons (Bt); its occurrence became almost synonymous for a clay illuviation horizon in the early years of European soil science. As soil genesis was better understood it became evident that weathering of soil material in situ could also cause such a distribution (Laatsch, 1937). Similar soils with this type of clay distribution curve were reported in other parts in Southern Africa (Thompson, 1 965; Van der Eyk, et al., 1971).

Type 3, clay-pyramid: soils with this type of clay distribution are commonly found on granitic parent material and include the profiles 1, 2, 4, 10, 13 and 33 and is weakly expressed in profile No. 11. The positive curve indicates the increase of clay with depth while the negative curve represents the regular decrease of clay with depth. The absolute increase in clay varies between 15 and 40%; a subsequent decrease or increase in the C-horizon may equal this amount; if expressed relatively, the increase in clay may reach 50—100% clay. A combination of this type and the clay-constant is sometimes observed (profiles 12, 15 and 21); after a regular increase of the clay percentage with depth the amount stays constant. The pyramid type of clay distribution has been recognized by several scientists; its development has been attributed to pedogenesis (Scholz, 1968) as well as to internal stratification of parent material (Fölster et al., 1967).

Type 4, clay-step(s): the clay curve reflects the sudden increase or decrease in the clay percentage followed again by either increase or decrease. It often occurs in combination with other types. If applied to the control

94 section from 0 — 100 cm the profiles 15, 25, 26, 31 and 32 are considered. The change in clay percentage is variable but is often more than 10% clay (absolute). In the studied soils the sudden change in the clay curve is caused by admixture from allochthone material (sand), or removal of soil material through the effects of wind and water erosion on the topsoil, which may result in profile truncation. In some horizons the change is due to different stage of weathering. This type of curve frequently occurs in alluvial soils, then resulting from differences in the dynamism of sedimentation.

The pedogenetic processes that cause differentiation in the clay distribution of the soils under consideration are illuviation, vertical as well as lateral, and formation of clay minerals (in situ), in some parts of the solum i.e. subject to more intense chemical weathering of primary minerals (Scholz, 1965). A more detailed account of these processes is given in section V.l. if the criteria are applied as suggested by the USDA 7th Approximation (1970) with regard to the clay movement in the argillic horizon, the following remarks can be made. In soils of which the eluvial horizon has less than 15% clay, the argillic horizon must contain at least 3% clay (absolute) more than the eluvial horizon. This is the case in profiles 2, 4, 7, 10, 11, 13, 14, 18, 21, 29, 32 and 33. If the eluvial horizon has between 15—40% clay, the ratio between the clay percentages in the argillic and the eluvial horizon must be 1.2. This is the case for profiles 8, 9, 12, 15, 23, 24, 25 and 31, but not for profile 22. Above 40% the absolute increase of 8% is considered to be sufficient for an illuvial horizon to be classified as argillic. Neither conditions are met for profiles 5, 18, 16, 20 and 30 and the lithic Entisols. How far the suggested criteria are representative for a clay illuviation resulting in an argillic horizon is discussed in Chapter IV. It is however pointed out that the limits as set by the 7th Approximation do not cover the clay distribution below the control section (0 — 100 cm), which may be an important soil characteristic.

III.3. Elemental composition of the fine earth

III.3.1. Major Elements Nine major elements were determined by Röntgen fluorescency techniques of the fine earth fraction, in addition to a number of trace elements dealt with in Chapter III.3.2. The elements consituting the largest proportion of the fine earth are Si, Al

95 and Fe; these are followed by the oxides of Ca, Mg, K and Na. Titanium and phosphate occur only in subordinate amounts. The amount of SiO2 ranges from 62.3% to 100% for all soils. The lowest values are encountered in the hydromorphic Alfisols and the highest percentage occurs in the granitic Entisol. The sharpest contrast in SiO2 concentrations is obtained within the Entisol order, notably the granitic Entisols versus the basic ones. Similar trends hold true for the amount of Al2O3 and Fe2O3.

The influence of the rock suites is clearly evident in the concentration of the major elements in the Entisols (basic). Mutual differences on a mean basis do not show any marked variations. The concentration of Al2O3 varies between 1.1 and 24.4%; the Vertisols have values in the higher level of this range (7.2-16.5%) in addition to Inceptisols (8.2-17.7%) and the Entisols on material rich in bases (17.8-20.1%). The concentration of Fe2O3 varies little in the soils, major variations occur in the Entisols developed on granitic material (0.8 — 1.2%) and those developed on doleritic material (10.7-10.9).

Table 26. The concentration of Si'O2, Al2O3 and Fe2O3 in the soils (% by weight)

SiO2 A12O3 Fe2O3 soil range range range

Vertisols 69.0- 85.8 7.2-16.5 2.0- 6.8 Inceptisols 68.0- 90.4 8.2-17.7 2.0- 8.2 Entisols (acid) 83.6-100.0 1.1-10.7 0.8- 1.2 Entisols (basic) 63.0- 65.6 17.8-20.1 10.7-10.9 Alfisols (Haplustalf) 63.2- 95.2 4.6-24.4 1.0- 8.4 Alfisols (hydromorph) 62.3- 89.1 6.1-21.0 1.9- 8.9 Alfisols (Rhodustalf) 70.1- 83.3 8.7-19.1 2.4- 7.4 all soils 62.3-100.0 1.1-24.4 0.8-10.9

Changes in the concentration of SiO2, Al2O3 are reflected in the SiO2/ Al2O3, the SiO2/R2O3 and the Al2 O3 /Fe2 O3 ratios. Highest SiO2 content is usually encountered in the A-horizon(s) resulting in high ratios. The concentration of SiO2 commonly decreases with depth, while the concentration of Al2O3 increases, thus giving rise to considerably lower SiO2/Al2O3 and SiO2/R2O3 ratios. The amount of iron, indicated as ferri-oxide in all analyses, shows usually a regular increase with depth. Corresponding Al2O3/Fe2O3 ratios are fairly constant and only in some cases increase in the soil, as for example in profile 15. The concentration of elements other than silicium, aluminium and iron is

96 greatest in the Vertisols (7.4%) and basic Entisols (6.4%) and smallest in the Inceptisols (2.0%) and hydromorphic Alfisols (1.6%) and ranges between 3.2% and 4.3% in the other soils. More information concerning the above is presented in the following table. le 27. The concentration of bases and Ti and P in the soils (% by weight)

TiO2 Cao MgO K2O Na2O P2O5 >up range range range range range range

0.40-0.78 0.19-9 .66 0.00-2.92 0.67-4.89 0.00-2.28 0.03-0.12 0.49-1.06 0.26-2 .02 0.31-2.32 2.91-4.29 0.00-1.55 0.02-0.20 0.18-0.40 0.09-0 .24 0.00-1.96 0.27-5.23 0.00-1.53 0.00-0.10 1.06-1.24 1.32-5 .31 2.75-3.38 0.48-2.04 0.00-0.28 0.04-0.54 0.25-1.28 0.10-2 .52 0.00-3.35 0.00-4.71 0.00-4.49 0.00-0.22 0.31-1.03 0.18-2 .02 0.42-3.73 0.00-4.18 0.00-1.01 0.04-0.19 0.39-0.79 0.44-0 .70 0.00-1.41 2.80-4.00 0.00-2.08 0.03-0.12 s 0.18-1.28 0.09-9 .66 0.00-3.73 0.00-5.23 0.00-4.49 0.00-0.54

The information does not differ as much as could be anticipated from the composition of the parent rock. The amount of potassium is considerably higher in soils derived from granitic material. The concentration of the various elements depends largely on the composition of the parent rock which in turn is reflected in the assemblage of primary minerals. The data obtained on the composition of the fine earth of the investigated soils correspond well with values given by Jackson (1969) and Mohr et al. (1959, 1972). The relationship between the elements and the grain size fractions may provide useful

Table 28. Correlation coefficient between Si'O2, AI2O3, Fe^O^ and some grain size fractions

grain-size SiO, A12O3 Fe2O3 r

clay 0.70 0.82 0.89 clay + fine silt 0.87 0.87 0.86 c. silt + fine and 0.69 0.78 0.61 medium sand

97 indication for the evaluation of the soils. Computations were therefore carried out to see if such correlations exist. This was found to be only partly the case (see table 28). Of the found correlations one is visualized in figure 28. The graph is constructed for all samples except those from the Entisols and profiles 25 and 26.

y =0.112 » • 0.798 f = 0.B9

clay %

Fig. 28. Scatter diagram and regression line for concentration and clay percentage

In general, the finer fractions are more readily correlated with the elements than the coarser grain size fractions. The high correlation found between the three elements and the clay + fine silt fraction is partly due to the very low amount of silt in the soils, resulting in a high correlation between the clay and the clay + fine silt fraction (r = 0.97). Although other workers (Buursink, 1971) found more statisfactory correlations between the various elements and the textural composition of the soils, these studies were mainly conducted on alluvial soils, which have in first instance an inherited grain size distribution that is often influenced by the nature of the solid sediment load. The correlation between Si, Al

98 Table 29. Correlation coefficient and regression equations for the oxides of Si, Al and Fe, as calculated for the fine earth of all samples

regression equation st. err. x st. err. y

SiO2 A12O3 -0.88 y =-0.495 x+51.680 3.730% 2.138%

SiO2 Fe2O3 -0.87 y = -0.263 x +24.805 4.228% 1.220%

A12O3 Fe2O3 0.82 y = -0.915x+ 2.371 2.641% 1.329% and Fe was found to be of greater significance for the investigated soils. Results are given in table 29 and illustrated for one case (SiO2—Al2O3) in figure 29. In combination with table 29, the above-quoted correlations do point to the differentiation between the soils and are indicative for some soil- forming processes as dealt with in Chapter V.

y = -0.495 x + 51.680 r =-0.88

Fig. 29. Scatter diagram and regression line for the concentrations of AI2O3 and S1O2

99 III.3.2. Trace elements A number of trace elements were determined in order to evaluate the soils and to indicate the differences between the soils encountered. Apart from research by Nilsson (in Siderius, 1972), no data of trace element concentrations in Botswana soils were available. The information (presented completely in Appendix I) denotes the following range in trace elements in ppm: Ba, 100-1720 (mean 515); Co, 2-77 (mean 21); Cr, 4-300 (mean 81); Cu, 5-58 (mean 22); Mn, 4-2830 (mean 350); Ni, 4-104 (mean 27); Sr, 2-250 (mean 29) and Zn, 2-86 (mean 20). The variation in concentrations occurs within the "limits" proposed by Mitchell (in Bear, 1969), but the mean values indicate that the concentrations are in general on the low side, which is illustrated in figure 30.

frequency 70 -i

0-10 10-20 20-30 30-40 40-50 50"60 60"70 70"80 >80 (Co,Ni,Sr,Cu,Zn) ppm

0-100 100-200 200-300 300-400 400-500 500"600 600-700 (Mn.Cr) ppm I I I ' I I I 0-200 200-400 400-600 600"800 800-1000 »1000 (Bo) ppm

Fig. 30. Frequency distribution of trace elements

100 The nature and content of trace elements in the investigated soils can be traced back to their parent material, data relative to the latter are given in Chapter 1.3., which confirm the findings of Apostolakis et al., (1970). However, the various trace elements are not uniformly distributed among the different rock types and many show a preference for a certain rock (Mitchell, 1969). This trend can often be observed in soils that are derived from a certain rock type, although this does not necessarily mean that the amount of trace element of the soil can be readily deducted from the parent rock (Oertel, 1961). Investigations indicate that a relationship does exist between the concentration of the trace elements and the soil in which they occur, as is demonstrated in the following table.

Table 30. Relation between trace elements (ppm) and selected soils

Trace Vertisols Alfisols (Ultic Alfisols (hydromorph) elements Haplustalf) range range range

Ba 100-1720 100-2600 100-1260 Co 12- 58 2- 56 2- 58 Cr 5- 224 5- 256 25- 352 Cu 5- 58 5- 50 5- 54 Mn 370-1250 4-2830 86-2508 Ni 8- 68 2- 85 3- 104 Sr 2- 59 2- 80 2- 45 Zn 5- 60 3- 86 5- 45

While keeping in mind that the Vertisols are derived from the doleritic rock suite and the Alfisols (Ultic Haplustalfs) from the granitic rock, it is seen that the concentrations of Co, Cr, Mn and Ni are relatively high in the soils developed on basic material. The concentrations of Cu, Sr and Zn are more or less equal in the different soils, but Ba is well concentrated in the Alfisols. Tç> a certain extent the hydromorphic Alfisols indicate the influence of pedogenetic processes with regard to the trace element distribution, as they have most likely undergone changes in the original soil material being subject to a more variable soil moisture regime. An extremely low content of trace elements is recorded in the sandy Kalahari soil (Typic Ustipsamment, profile 30), derived from the Cave Sandstone. Our data corroborate results reported by Mitchell (1969) and do not vary widely from trace element data given in Chapter I. 101 The computed correlation between the amount of trace elements and different grain size fractions was applied to all samples, but yielded little result. The following statement can be made. The bivalent trace elements (Co, Cu, Ni and Zn) show a good negative correlation with a) the coarse sand fraction (r = —0.85), with b) the medium sand fraction (r = —0.80) and with c) the fine sand fractions (r = -0.75). The positive correlation is recorded when dealing with the fine fractions but only for some elements, notably Mn, Ba and Sr. These elements have a positive correlation with the coarse silt fraction of respectively 0.83, 0.98 and 0.79. The clay fraction correlates poorly with the various elements, but the fine silt + clay fraction has good positive correlation with the bivalent trace elements, especially if applied to the Vertisols (r = 0.81). The affinity of the trace elements for the finer grain size fractions, particularly fine silt and clay, in the investigated soils is evident and supported by the findings of Krauskopf (1972).

The distribution of the trace elements in the soils is variable. For Mn and Ba a decrease in the concentration with depth is noted in the majority of soils. The opposite is the case for Cu, Zn, Cr and Ni, their concentrations show a trend to increase with depth in most soils, although an initial increase may be followed be a decrease in the deep subsoil. No clear picture is obtained for Co and Sr, the amount of element varies irregularly. A clear change in trace element concentration in the soils is often connected with the B horizon and corresponds with the textural variation that does occur in that part of the solum, thus indicating the translocation of trace elements caused by migration of the finer particles (Norman, 1963). Relationships between the trace elements themselves and some major elements are known to exist in a number of cases. According to Krauskopf (1972), the similarity in ionic radii of Fe, Mn and Zn and the strong covalent bonds that Cu and Zn form with S are mainly responsible for this interrelationship. A computed correlation between Zn and Co, Cu and Ni is shown in figure 31.

The high positive correlation between Zn and these bivalent elements implies the relationship between them and indicates that nutrient application should be balanced with regard to all elements present.

102 250 PP Tr

y- 2.633 x * 34.224 200- r = 0.88

150-

100-

TO" 20 30 40 50 60 zn 70 Fig. 31. Scatter diagram and regression line for the concentration of Zn and some bivalent trace elements III.4. Mineralogy of special constituents

III. 4.1. Mineralogy of the sand fraction Mineralogical research of the sand fraction of soil materials is widely applied to characterize the relation between soils and their parent material and is a useful guide as to the uniformity of the material from which the soil has developed. In addition it may yield valuable information relative to^ the utilization of soils (Sherman, 1971). The sand fraction contains most of the primary minerals to be found. A convenient way of separating lighter and heavier minerals is to use the specific gravity of these minerals as compared to bromoform (s.g. 2.89). The variation in heavy minerals is much greater, a fact that is particularly advantageous in comparison to the few members of the light mineral suite, although both groups may be indicative of the source of the minerals.

103 The sand fraction commonly used (50—500 microns) for heavy mineral investigations was found to be of little value, as the coarser sand (200—500 microns) yielded practically no such components. The fine and medium sand fractions were therefore investigated (50—200 microns), this being similar to the procedure applied by Watson (1965). Regular checks were carried out in relation to the coarser material to make sure that no deviations of the applied research technique occurred. The mineral composition of some soils is given in table 31.

III.4.1.1. Heavy minerals Investigations of the heavy mineral composition of the soils led to the recognition of five assemblages (fig. 32). Assemblage 1 is characterized by the abundance of green hornblende, followed by epidote and zoisite, while garnet and staurolite occur in subordinate amounts. The presence of zircon and tourmaline is negligible when compared with their occurrence in assemblages 3, 4 and 5. Augite does occur as trace or in very small amounts, its presence is however of great importance as it is indicative of the proximity of basic rock. The amphiboles, in our counting identified as green hornblende, are firstly ascribed to the transformation of pyroxenes into amphiboles (Chap- ter 1.2.2.), while epidote is also mainly derived from ferromagnesium minerals. In addition, clino-zoisite is regarded as a secondary product of transformation from pyroxenes or of lime-soda plagioclase feldspar (Mil- ner, 1962). The presence of garnet further proves the influence of metamorphosed granitic rock. The heavy mineral suite as described above is commonly encountered in soils derived directly from dolerite, such as in profiles 14, 23, 27 and 28. In addition this assemblage may be found in soils amidst the granitic region. In the case of profiles 12, 24 and 13, the suite is indicative of the presence of intermediate or basic bodies of rock within the granitic complex, as for example dikes as referred to in Chapter 1.2.1. In assemblage 2 the same minerals as in the previous suite are present. The occurrence of the large amount of epidote however together with considerable amounts of amphibole, zoisite and staurolite, warrants its separation from the former suite. The high amount of epidote may also be derived from the transformation of plagioclase feldspar which may subsequently have caused the low percentage of this feldspar in the corresponding light mineral assemblage (see III.4.1.2.). The occurrence of garnet further indicates the nearness of gneisses and schists as recorded in the Basement Complex. Pyroxenes occur but as trace or in very small amounts. The staurolite, finally, is indicative of dynamo-metamorphic influence. This assemblage is common in soils derived from transported weathering

104 profile 23 profile 25 20 40 60 80 100 20 40 60 80 100

49,5

81,5

119

profile 10 166 5- : : : : : : : profile30 21.5- i:;;ijflji|v 0 20 40 60 80 100

11,5 43-

»:':';3i;l|j|j|jl - =j 62,5- 42,5

81,5- 91- profile 14 0 20 40 60 8,0 100 100

142,5

100 H 5 192,5

amphibole hornblende)

dysthene toermahne I epidote (kyanite) I garnet miscellaneous

Fig. 32. Heavy mineral composition of representative soils from each assemblage

105 products of doleritic rock, such as in profiles 20, 25 and 26. It is also encountered in profiles 1, 17 and 22 located in the chiefly granitic area. If such is the case the assemblage testifies the proximity of more basic rock. Assemblage 3 is typified by an increasing amount of zircon in the heavy fraction; this mineral is distinctive for assemblages 3 and 4. On the other hand the fairly large amount of minerals typical for the groups 1 and 2, such as amphibole and epidote, suggest that this assemblage may also be transitional to the first two groups. This is also deduced from the presence of small amounts of zoisite, rutile and staurolite. Soils with this heavy mineral composition are commonly situated in lower lands such as profiles 4 and 15. Other profiles, namely 2, 7, 16 and 18, are fairly close to those soils in which assemblage 1 or 2 is found. The most distinct changes in the amount of zirvon is often related to the A-horizon. Assemblage 4 is considered typical for the soils derived from the Cave Sandstone or which are under strong influence of the sandveld. This group is characterized by high percentages of zircon and tourmaline with subordinate but significant amounts of rutile, staurolite and kyanite (profile 30). Similar observations were made by Wayland et al. (1953) and Polder- vaart (1957) relative to the heavy mineral composition of Kalahari sand. The latter author further notes the possible occurrence of epidote, amphibole and garnet in fringe areas. Investigations on a number of profiles, that is 29, 31 and 32, located in such an area (sample area D) indeed showed the presence of these minerals in the heavy fraction. The amount of tourmaline decreases notably away from the sandveld as was observed in profile 33, while the amounts of epidote and green hornblende increase. This soil is thus considered to belong to assemblage 3. The presence of rutile is particularly indicative of eolian deposits of the Kalahari (Poldervaart, 1957, Harmse, 1967). Kyanite, often associated with staurolite, is indicative of the presence of metamorphic rocks, especially schists and gneisses. The heavy mineral composition of the Kalahari sand (profile 30, Typic Ustipsamment) points to the source of the variation of the associated soils in the catchment of the Mahalapshwe and Bonwapitse rivers. The admixture mainly consisting of zircon and tourmaline is however commonly restricted to the topsoil. Assemblage 5 is characteristic for the majority of soils derived from granitic rock. Typical is the very high percentage of zircon (variety mala con). Poldervaart (1956) reported similar percentages in granitic soils in South- Africa. Zircon and tourmaline are considered most stable minerals and are able to survive several erosional cycles. The presence of metamorphosed granitic rock and the admixture of other minerals is testified by the presence of epidote and amphibole, respectively rutile and staurolite. Sillimanite and andalusite occur as traces. 106 The status of weathering is also implied in the percentages of opaque minerals and alterites; whereas the former are iron compounds (mainly hematite), the latter are minerals altered to such a degree that their characteristics are concealed. The percentage of opaque minerals was counted separately as is common usage in the European school of sand mineralogy (Carroll, 1962; in Milner). The amount of opaque minerals is high and ranges from 91% in the deep subsoil of profile 7 to 28% in profile 1. High percentages are recorded also in profiles 11, 19 and 32 of respectively 70, 71 and 71% (arithmatic means), the majority of the soils contain between 50 and 70% opaques, while in the remaining soils this percentage varies between 30 and 50%. There is a trend that soils with a high opaque content have a low percentage of alterites. For example low alterite percentages occur in profiles 1, 11, 31 and 33 (1 — 2%), while a high amount of alterites is counted in profiles 2 and 26, respectively 16 and 15%. The majority of the soil materials however have an alterite percentage of between 2 and 5%. Although the exact nature of most of the alterites cannot be traced, there are indications that a fairly high percentage is in fact strongly weathered green hornblende. In general the original rock composition is well reflected in the heavy minerals observed in the investigated sand fraction, taking into account the vulnerability of these minerals to weathering. Thus a decrease in pyroxenes, apatite, biotite in the rock weathering products was observed. No studies were conducted on the affinity of the various heavy minerals to particle sizes. Research on this subject (Dougles, 1940; Van Andel, 1952) on alluvial pi sediments, gained variable results. Our findings indicate that almost the total heavy mineral load is limited to the fine and medium sand fraction, thus enhancing statements made by Pettijjohn et al. (1972) relative to fractionated mineral research.

If we pursue research as carried out by Brewer (1950), assuming equal heavy residues for both the topsoil and the subsoil for profiles 1 to 4, we arrive at the following conclusions (see fig. 33).

107 1220

4 scale 1 : 50.000

prof tie

_. tourmaline gar net epidote.zoisite t _ topsoil amphibole s _ subsoi I Fig. 33. Variations of the heavy mineral composition in the profiles 1 to 4

The heavy mineral assemblage runs parallel in the top and the subsoils, indicating its uniform distribution. Furthermore, a sharp relative increase in zircon from profile 1 to 2 occurs, whereafter the percentage stays fairly constant, but for the change in topsoil versus subsoil. The increase in the topsoil of profile 4 is ascribed to lateral supply in this drainage channel. A regular increase in tourmaline from profile 1 to 3 is seen, but also a subsequent decrease in profile 4. The percentage of epidote-zoisite decreases sharply from profile 1 to 2 and further decreases, followed by a small rise, in the subsoil of profile 4. However green hornblende increases relatively downslope from 1 to 2, followed by a decrease and subsequent increase in profiles 3 and 4 respectively. Garnet is present in considerably amounts in profile 1 only, but occurs in subordinate quantities in the other soils.

108 The largest changes occur in the zircon, tourmaline and garnet percentages. Taking into account the dominance of granitic rock, the changes in heavy mineral composition partly confirm findings by Thompson (1965). He states that "at the base of the (granitic) kopje there would be a local concentration of the heavier feldspatic and ferro-magnesium minerals" . . . "subsequently the weathering products of these minerals would give rise to a textural variation between the members of the transition downslope in such a way that the finer textured soils occur at the upper end of the sequence and the coarse textured ones at the bottom part." The grain size distribution in the profiles 1 to 4 partly shows a different picture in that the finest textured soil (profile 4) occurs at the lowest part of the transit. In this case lateral supply of finer constituents must however not be excluded. The coarsest textures are found in profile 2 encountered at the middle upper slope of the pediplain, while a sandy clay (loam) texture is encountered also in profile 1, it being the upper member of the sequence.

III.4.1.2. Light minerals The soil mineralogy is supplemented by the knowledge of the light mineral composition of the sand fraction (s.g. < 2.89). Investigations thereof were carried out on 50 selected samples. The result complements the data obtained from the heavy mineral composition and is summarized as follows: quartz, orthoclase, anorthite and albite are the dominant light minerals; oligoclase, microcline, muscovite, sericite and volcanic glass occur as accessory minerals. The presence of volcanic glass was also reported in soils in the Karroo, South Africa (Cox et al., 1967). Statistical calculations carried out on the dominance of the light minerals revealed the relationship with the heavy mineral assemblages, as given in sub a. On basis of the mean values of the percentages of minerals occurring in the investigated profiles, it appears that assemblage 1 is supplemented by quartz, anorthite and orthoclase in the light fraction, respectively 70, 15 and 8%. The presence of lime-bearing plagioclase feldspar implies the presence of basic rocks and as such confirms the conclusions based on the study of the heavy mineral assemblage. Very large amounts of quartz are further observed in the light mineral fraction associated with assemblage 2. The percentage orthoclase is low, while anorthite may occur as trace. The light mineral suite of the other three assemblages indicates high amounts of quartz and orthoclase with minor occurrence of albite. The percentage of orthoclase is about 20% in group 3 and 25% in group 5. The percentage weathering products is variable, the highest amount was encountered in the C material of profile 25 (45%), but normally varies between 0—10%. The investigations evince that the majority of these

109 Table 31. Mineral composition of the fine and medium sand fractions (50—200 micron) in mutual percentages for selected soils

Light mineral composition Soil Depth Profile Sä U 01 U c product s Weather i Anorthi t Quart z Orthocl a Albit e Microcli r Muscovi t Biotit e Sericit e Phytolit l Vole , gl a Oligocla s

25 0- 3 91 6 1 tr 1 — — tr 1 3- 33 — 90 7 1 tr 1 - tr — — 2 33- 67 same as above 67- 96 same as above 96-142 same as above 142-190 - 43 6 - 1 - tr tr - - - 45

20 0- 30 64 16 5 _ 2 tr 4 tr 9 30- 65 - 47 28 3 - 1 2 13 - - 6

30 0- 23 _ 94 4 2 _ tr — - _ _ tr — 23- 52 same as above 52- 80 same as above 80-120 same as above 120-165 same as above 165-220 - 92 5 3 - tr — - - - tr -

28 0- 38 tr 64 7 - - 3 20 tr tr - tr 6 14 0- 18 _ 53 29 11 1 2 - - 1 1 2 18- 56 same as above 56- 90 _ 55 29 4 2 tr — — — _ _ 10 90-110 - 58 22 6 - 2 - - 1 - - 11 11 0- 16 — 79 17 2 1 _ _ _ tr _ tr 1 16- 45 same as above 45- 82 tr 81 15 2 1 1 - - tr — tr — 82-108 — 81 14 2 1 2 - - — — tr — 108-140 same as above 140-173 tr 81 15 2 1 ^ - - tr -

15 0- 2 _ 76 21 2 1 tr - - tr _ tr _ 2- 43 same as above 43- 69 _ 73 23 2 1 1 tr _ tr _ 69-91 same as above 91-127 — 77 21 2 tr tr — — tr — tr - 127-158 same as above 158-180 - 73 24 2 1 tr - - tr - . tr -

10 0- 10 _ 79 18 2 1 _ _ tr 1 10- 33 same as above 33- 53 tr 82 15 2 1 _ _ _ — — tr 1 53- 72 same as above 72- 91 same as above 91+ tr 77 18 3 1 ------1

110 Os Os en Os L»J Os © en S) 4*. OO O sO Opaque

S3 Os Os 00 O H-* sO to 00 so so OS ^1 to Zircon

to to to to to to Ln Os H- OO 00 O OO Os -fr. OJ Os O OS Tourmaline

« ? S? S) H- I I I I N W H N M Garnet

L»J SJ \O Os -b- Rutile

I I I I 1 I I I I I I I I I I I I I I I I I Titanite

oo o> m * NI to 00 so ^1 Ui Ui OS OS OS ^. so Staurolite

I I Os 00 O H-» 00 h- P N H H M Kyanite

I I I I I I I I Andalusite I I I I I P l» U H I I

CO 00 W NJ 00 e»j o NI S3 en i-> oo M W *Û W Epidote

I I I I ( ^ I I I Zoisite

I I I I I O S3 Os 4». I-» H- U> Gr. Hornblende

I 1 I I I I I I I I I I | I ! I I i I I I I I I . Augite

I ! I I I ! I I I I I I I I I i I I I I I I Hypersthene

I 1 I I I I I i I I I I I I ! I t ' Si S Monazite

I I I I I I I I I OJ >—» U> Sillimanite

I I I H s] U CO Ui Alterite weathering products are altered biotite and intermediate and basic plagioclase. . • . The composition of the light mineral suite of the sand fraction once more focusses the attention on the relation between the dolerite and the granitic rock suite and further points to the strong degree of weathering that has taken place (see also Holmes, 1969). Relative to the first remark, the occurrence of basic plagioclase, anorthite, is only observed in material directly derived from the doleritic rock. The second observation leads to the conclusion that, of the light minerals, only those with a low to very low weatherability have persisted in the environment, such as quartz and orthoclase. The distribution of the heavy and the light minerals with depth in the soils does not show any marked changes other than some minor variations that may occur in the topsoils of soils in sample area D (profile 29) and in the soil developed on alluvial of the Bonwapitse River (profile 22).

In conclusion, the mineralogical research of the sand fraction confirms our findings of Chapter 1.3. relative to the origin of the soil materials and further explains the small variations that may occur. The percentage of weatherable minerals is low, only the more persistent minerals are encountered in large numbers. The uniform distribution of the minerals in the soils enhances and promotes sound interpretation of the chemical data with reference to the soil development (Reynders, 1964).

III.4.2. Mineralogy of the clay fraction In the former sections of this chapter and also in Chapter II.3. the importance of the clay fractions with relation to soil properties and characteristics has been emphasized. Not only the amount of clay (III.2.3.) but especially the type of clay mineral determines to a large extent a number of evaluation criteria, such as cation exchange and nutrient status, while clay mineralogy is also applied in the classification of the soils (USDA, 7th Approximation 1970). Further investigations warrant a better insight in the genesis of the soils. This research was carried out by means of X-ray diffraction techniques on all samples, while from 85 selected samples of A, B and C horizons the elemental composition was determined through X-ray fluorescency. An additional 29 samples were subjected to special treatments. Although suggestions were made on the identity of a number of clay minerals in Botswana soils (Siderius, 1972), these were hitherto not confirmed by data. Reports from adjacent territories indicate the presence of the commonly expected minerals in the clay fraction encountered

112 under similar conditions and derived from similar parent material. They comprise kaolinite, illite and montmorillonite (Harmse, 1967; Watson, 1965; Scholz, 1963, 1968). This general picture is confirmed by our investigations but some elaborations are necessary. Quantitative measurements oiLclay minerals would be premature in the light of the performed analyses. However, norm analyses carried out on a number of soil clays allowed a tentative approach (personal communication De Rooij). Weight percentages of the constituents of the clay fraction were recorded as follows: trace (tr), subordinate (10—40%) and dominant (more than 50%); for quartz a different standard was used: trace (tr), moderate amount (1 — 10%) and large amount (10 — 20%). Feldspar, mainly orthoclase, was not indicated separately but may occur in considerable amount in profiles 2, 7, 11, 14, 15, 16 and 17. Indications of the presence of iron compounds (hematite, goethite) was observed in profiles 13, 14, 21, 23, 24 and 27. The main source for the formation of clay minerals is provided by the weathering products of the primary minerals (Chapter III.4.1.). These in turn depend on the parent rock composition as was indicated in the previous section, the main minerals include pyroxenes and amphiboles, some biotite as well as feldspars and quartz. Their weathering products are the basis for the formation of kaolinite and montmorillonite as well as for the genesis of a number of clay minerals that occur in lesser amounts such as illite, vermiculite, chlorite and mixed layer minerals (Worrall, 1968; Scheffer and Schachtschabel, 1970). This expectation is further supported by the considerations of Mohr and Van Baren (1959, 1972) with relation to the basic and acid milieu specific of the development for the various clay minerals. In this context Kraus- kopf (1967) comments that "acid solutions favour the formation of kaolinite while basic solutions are a suitable environment for the formation of montmorillonite". The mineral composition of the investigated clay fraction of the soils confirms to a large extent these anticipations. Kaolinite, with subordinate amounts of illite, is observed in profiles 3, 5, 11, 17 and 32, all situated in the granitic area in addition to profile 30 developed on material from the Cave Sandstone. Kaolinite, with subordinate amounts of illite and montmorillonite, is found in other profiles located in the granitic region. A similar combination with lesser amounts of traces of mixed-layer clay minerals and/or chlorite and/or vermiculite is encountered in most of the hydromorphic Alfisols and in the subsoils of profiles 1, 2, 4, 15, 19, 20 and 24. In the doleritic region, the dominancy of montmorillonite was demonstrated in the Vertisols and in the subsoils of profile 10, together O with subordinate amounts of kaolinite and illite; some vermiculite and/or chlorite may also be present. Mixed-layer clay minerals mainly belong to the Mt-I type.

The distribution of the clay minerals in the soils is uniform in general; greatest changes in composition occur in the hydromorphic Alfisols and in those soils with contrasting subsoil material such as profile 10, Rhodustalf. The dominance of kaolinite in the soils derived from granitic material is indicative to the later stages of weathering (Watson, 1965).

The identification of the clay minerals is mainly based on the interpretation of the diffractograms. These graphic representations of the intensity and peak form of the basal spacing and other spacings serve as an indication for the internal structure of the various sets of planes in the crystal. The method is widely applied to identify minerals of known spacing (Worrall, 1968). The normal basal spacing of the 1 : 1 layer Al-silicate kaolinite at room temperature is 7.15 Â, while a second order reflection was occasionally observed at 3.57 Â (002). The normal basal distance between the crystal planes of illite is 10.3 Â, a reflection of second order at 4.98 Ä was observed in a few cases (002). Montmorillonite, vermiculite and chlorite show reflection at 14 Â. Charac- teristic peak areas for chlorite further occur at 7.00 Â and 4.72 Â. In general, the peak areas are well outlined, while the background is fairly low. Special treatments were carried out on 29 soil clay samples to confirm the interpretations made from normally treated soil clays. These treatments include 1) Mg saturation and ethylene-glycol solvation at room temperature; 2) the saturation of the clay specimen with potassium at 33° C. and 3) the subsequent heating of the K saturated sample to 550° C (Jackson, 1969). These experiments have one thing in common, namely the alteration of the crystal structure due to the exchange of metal cations in the lattice and/or possible sorption of organic compounds followed by decomposition or transformation of the clay mineral caused by heat. X-ray diffractograms of the clay specimen treated in such a way show basal reflections known to occur in the different clay minerals and as such are applied to identify the composition of the clay fraction in the investigated soils. The selected samples showed high reflection intensities at random between 10 and 16 Â or irregularities in this range, as well as those clays that show weak developed peak areas at 7 and 10 Â. Proce- dures of the treatments and their purpose are outlined by Jackson (1969) and adapted as follows. Mg saturation and following glycol solvation at 25° C induces the increase of the basal spacing of the Mg montmorillonites, the type as encountered in the investigated soil clays, to 18 Â, thus providing a clear differentia-

114 tion between montmorillonite on one side and vermiculite and chlorite on the other. Saturation of the clay with K at room temperature followed by heating is an additional check on the closure of vermiculite and montmorillonite interlayers, while the chlorite phases remain expanded. In addition, the 10 Â reflection peak of illite is better pronounced due to better basal orientation caused by improved dispersion. Heating of the K saturated samples to 550° C causes the decomposition of kaolinite, while montmorillonite and vermiculite close to 10 Â each. In addition, the 14 Â peak of chlorite is reinforced while the 7 Â reflection has weakened or disappeared. The mixed-layer or interstratified minerals (Mi) can be detected further by heating of the K saturated sample to 550° C. They proved to belong dominantly to the Mt-I type. The mixed-layer clay minerals Mt-V and Mt-I close to 10 Â, but Mt-Chl may vary between 10-14 Â. Glycol treatment brings about an increase in basal spacing between 14-18 Â for Mt-Chl and Mt-V, and between 10-18 Â for Mt-I. These methods proved successful for the differentiation between the various clay minerals. Additional investigations were carried out on sam- ß^ i«. pies from soil clays which were treated with diluted (2 N) HCl and H2O2 and comparisons between these diffractograms and the ones derived from the "normally treated" clays were made. The treatment causes the removal of sesquioxidic coatings, carbonates as well as organic substances and a fairly clean but possible corroded clay is obtained. In less than 50% of the cases the diffractograms of the pretreated clays showed a much higher background (up to twice as high) for the clays of the B21 horizons from profiles 3, 4, 6, 9, 12, 18, 31 and 33. Considerably lower intensities were measured for the same horizons in profiles 10, 17 and 22. The basal reflections for the montmorillonite were enhanced from none or poor reflection to distinct peak areas in all Vertisols and the Typic Haplustalf (respectively A and B21 horizon). The reflections of kaolinite in the pretreated samples were much more evident than in the normal soil clays in the B21 horizons of profiles 2, 3, 4, 6, 11, 15, 26, 30, 31 and 33. Much lower intensities however were observed in the pretreated samples of B21 horizons in profiles 7, 12 and 14, all Ultic Haplustalfs. The results imply that the removal of concealing material improves the reflection of montmorillonite considerably, while the clay mineral is good crystalline, as it is assumed that the very acid environment of the treatment is in contradiction to the field in which it is stable (neutral to alkaline). It is noteworthy that a relatively high amount of organic matter was recorded in these soils (Chapter III.5.). Also the reflections of kaolinite show much better or remain the same. In those samples were a decrease in intensity was observed, a fairly broad 115 peak area also occurs, which indicates poor crystallization of the mineral. These clay minerals are therefore more liable to be broken down in the course of treatment. The several types of clay distribution curves (Chapter III.3.1.), were compared with the clay mineralogy of the clay fraction with special reference to the clay pyramid, type 3. It is noted that in the soils where such a distribution occurs kaolinite is the dominant clay mineral but subordinate amounts of illite, montmorillonite and chlorite are present. In addition, the pH in these soils increases with depth from slightly acid to neutral or alkaline, while an increase in moisture was also noted in the field. This environment is thought favourable for the neo-formation of the 2 : 1 lattice clay minerals directly from the primary minerals as suggested by Millot (1972). A subsequent increase in the clay percentage may therefore be anticipated. In conclusion it appears that kaolinite with subordinate amounts of illite are the dominant clay minerals in the granitic region, whereas montmorillonite and related 2 : 1 clay minerals are dominant in the doleritic area. However, montmorillonite, chlorite, vermiculite and mixed-layer minerals may be present in the subsoils of some granitic Alfisols if conditions required for their formation are met. Further elaborations concerning the genesis of the various clay minerals is given in Chapter V.

III.5. Organic matter The soils have a low organic carbon and nitrogen content, the values range between 0.15% and 1.84% organic carbon and between 0.02% and 0.25% nitrogen. If a correction factor of 1.3 for the organic carbon is applied, as is suggested by American workers since with the wet Walkley-Black method only 77% of the carbon is being oxidized, the organic carbon data range between 0.2 and 2.39%. Although some doubt may exist as to the justification of this correction factor for semi-arid soils (Harmse, 1967), it has been used in this study to comply with the criteria for the USDA classification. The mean organic carbon content for 63 topsoil samples (average depth 42 cm) is 0.65% and the nitrogen percentage 0.06. Both values decrease considerably with depth in all soils except in the Vertisols, where mulching and churning provide a fairly regular distribution throughout the profile. When the soils are grouped as outlined in Chapter II, the following picture is obtained concerning the organic matter.

116 Table 32. Organic matter in soils.

Soil Organic carbon % Nitrogen % C/N

mean range mean range range

Vertisol 0.63 0.43-0.83 0.10 0.07-0.12 7 6- 7 Inceptisol 0.42 0.33-0.55 0.05 0.03-0.06 (10) 8-11 Entisol 0.27 0.15-0.35 0.03 0.02-0.04 ( 8) 8- 9 (acid) Entisol 1.14 0.94-1.28 0.19 0.10-0.25 7 5- 9 (basic) Alfisol 0.39 0.16-0.48 0.04 0.03-0.07 ( 9) 6-10 (ultic) Alfisol 0.33 0.08-0.76 0.05 0.02-0.08 ( 8) 7- 9 (oxic, typic) Alfisol 0.59 0.30-1.84 0.06 0.04-0.17 (10) 8-12 (hydromorphic) Alfisol 0.74 0.37-1.26 0.09 0.05-0.14 8 8- 9 (Rhodustalf)

The highest organic carbon contents occur in soils derived from basic parent material, followed by red Alfisols and those with hydromorphic characteristics. The percentage nitrogen corresponds with this trend. Extremely low figures for the obtained organic matter correspond with the Entisols, the Inceptisols and most of the other Alfisols. Taking into account the analytical error in the nitrogen determination, the C/N quotients are placed between brackets if the nitrogen percentage is below 0.05%. Comparable data on organic matter for soils in Southern Africa were made available by Harmse (1967); they correspond well with our information. The variations in organic matter content are in first instance ascribed to the different types of vegetation as outlined in Chapter 1.4. The Vertisols mainly support Acacia species, while the Entisols, Incepti- sols and Ultic Alfisols often carry deciduous Terminalia and Combretum species. The remaining Alfisols support dominantly a Mixed Acacia Wood- land vegetation. In addition, the grass cover, being a most important source of humus, is not identical on the different soils and may even be absent; see also Chapter 1.4. Thus the occurrence and nature of the organic litter is variable and depends largely on the interrelationship between the soil and the vegetation. The amount of organic matter is small when compared with areas in the humid temperate areas and the wet tropics (Kononova, 1961; Mohr and Van Baren, 1959).

117 Of the soil climatic conditions reduced and seasonally bound soil moisture is the most severe limiting factor for micro-biological activity. Taking into account the distinct dry and wet seasons, as well as the dry spells within the rainy season, the processes that affect the raw organic material may be considered as follows (Harmse, 1961; Finck, 1963; Pauli, 1964). During the dry season the soil surface temperatures are very high and a part of the organic material is indeed burned (loss of NH3, H2O and CO2). Deeper down where the soil temperatures are somewhat lower and some moisture may still be available, mineralization (chemical weathering) of the (fragmented) organic matter on a restricted scale may take place, even though little or no microbiological activity is anticipated in the topsoil. The activity of micro-organisms, which cause the litter to be broken down into elemental compounds, is greatly accelerated by improved moisture conditions during the rainy season. At the start of the dry period, however, microbiological activity is suppressed, while the disorganization of the enzymatic systems cause a more intensive humification to take place while the soil dries out (Harmsen, 1959; Kononova, 1961). The presence of humus could be verified in thin sections thanks to the occurrence of very dark brown to black coloured soil material. The brown- ing of topsoils is presumably caused by the coating of mineral grains by organic matter. A third process deserves attention: the fragmentation of organic matter. This may be caused by physical breakdown and/or by soil animals. The result of this activity (especially of mites) is seen in thin sections in particular. These Orbitatid mites, are also an indication for the poor quality of the raw organic material and/or the poor conditions under which it is formed (Bal, 1970). They prepare mainly the way for better humification at a later stage.

III.6. Salinity The presence of salts in the soils of eastern Botswana giving rise to saline/alkali conditions is not a common feature. Extensive saline areas are however encountered in the central northern part of the country, notably the Makgadikgadi depression. In our soils the EC5 of the 1 : 5 waterextract was determined to indicate possible salts. Solubles were determined if the value was 0.1 mmhos/cm or higher. This condition was met for the Vertisols, most of the hydromorphic Alfisols and the basic Entisols. Calcium, sodium, chloride and sulphate appear to be the main ions. The

118 total amount of solubles present in most soils is low as is indicated by the sum of the cations and anions, that vary respectively from 0.3 — 5.1 and 0.2-4.9 meq/100g. In addition the ECS of the 1 : 5 waterextract does not rise above 1.0 mmhos/cm for all 41 samples analysed. In fact, in three soils only, an ECS value of 0.5 or higher was measured. Determination of the solubles carried out on the saturation extract of these soils are given in table 33. ible 33. Electric conductivity of the saturation extract, ESP and soluble (meq/1 )

Cations Anions mple Depth Ec ESP Ca Mg K Na HCO3/ Cl SO4 mmhos/ co3 cm.

.71 69- 91 3.4 21 1.9 1.2 0.4 34.3 1.6 31.0 0.3 .72 91-127 3.4 23 1.6 1.0 0.4 36.1 2.5 34.7 0.5 .73 127-158 3.0 26 1.0 0.9 0.5 35.2 2.7 33.7 0.4 .74 158-180 3.8 27 1.2 1.1 0.6 37.8 4.5 32.6 0.3

.93 64- 97 5.0 4 16.5 17.2 0.7 29.6 4.3 55.5 2.7 .94 97-127 5.8 7 15.0 17.2 0.7 37.4 3.4 60.4 4.5 .95 127-170 5.8 6 16.0 18.9 0.8 36.1 3.6 59.8 4.3

.78 67- 96 3.1 9 3.5 3.3 0.4 24.3 3.6 21.4 5.6 !.79 96-142 3.3 7 3.5 3.7 0.5 27.0 3.2 24.8 5.4 ,80 142-190 3.9 10 5.0 4.5 0.5 32.2 2.3 30.4 6.3

The subsoil of profile 15 (Typic Natraqualf) is classified as alkali (ECe < 4 and ESP > 15). The subsoil of profile 22 (Typic Pellustert) is saline (ECe > 4 and ESP < 15), while the salinity and alkalinity as expressed in the ECe and ESP value are not sufficiently high in profile 25 (Typic Pellustert) to satisfy either definition (see also USSLS, 1954). The sodium chloride salinization as encountered in profiles 15 and 25 accompanies a high amount of sodium on the exchange complex of the Natraqualf because of very low Ca, Mg and K contents. In the topomorphic Vertisol of the Bonwapitse flood-plain, profile 25, Ca and Mg carbonates are encountered in addition to the chlorides and some sulphates. A similar trend is expressed in the Vertisols closer to the Shoshong Hills. The data confirm the varying degree of salinity, which changes considerably from one locality to another. The source of the solubles in case of the Vertisols is correlated with the doleritic rock and its weathering products, such as calcrete. The presence of sodium is partly accounted for as a weathering product of Na bearing feldspars such as albite (Leneuf, 1959). However the accumulation of chloride solely from a local source seems

119 unlikely, as the amount of chloride in rocks in the area is presumably too low to account for the amount encountered. An additional allochthone origin is therefore feasible. A second possible source of chlorides is the extensive depression located 100 — 150 miles north to northwest of the survey area. According to Bawden (1965) NaCl is the dominant salt of these former lake bottoms. Salt particles taken up during the dry season and carried by the dominant northerly to northwesterly winds may subsequently be deposited in southern regions. Thereupon carried in solution to low-lying areas, the accumulation of the sodium chlorides causes the saline/alkali conditions as met for example in profile 15. In granitic areas in eastern Botswana saline/alkali soils are merely restricted to the bottomlands. Their occurrence is patchy. Soil erosion often causes the exposure of the columnar natric B horizons, a feature also reported by Harmse in South Africa (1967). Summarizing a sodium chloride salinization seems dominant in the granitic area of the survey region, whereas carbonates, and to a lesser extent sulphates together with chlorides, form the major solubles in the doleritic region.

120 CHAPTER IV

ARRANGEMENT OF SOIL CONSTITUENTS

[V.l. Micromorphological observations

For the descriptions of the samples the terminology from Brewer [1964) is used, although in some cases deviations from that system were made if found desirable. The arrangement of the soil constituents was studied in 20 mammoth-sized (8x15 cm) thin sections made from undisturbed samples. The sample sites were selected according to macromorpholoçical information obtained in the field. A comparison between this information and the micromorphological data is given in section IV.2. A continuous series of samples was not taken and in some profiles only one sample was collected to represent a particular phenomenon such as clay illuviation, mottling, or animal activity. The descriptive information relative to the thin sections can be found in table 34; remarks on the possible genesis of the soil material is tfiven in the following paragraphs. The soil classification as outlined in Chapter 11 is employed to designate the soils.

From a Vertisol. profile 25, three samples were collected, rcspectivelv from the Al 3 (44-58), the ACca (74-88 cm) and from (109-123 cm)'. The pedality is visible as subangular peds of about 300 micron, size and grade of the peds decrease with depth. Plasma separations around the peds and occasional voids are the main cause for their detection. The development of the void patterns seems to be related to a great extent to the swell and shrink properties of the soils and is especially clear in the upper part of the soil. The related, distribution of the plasma with reference to the skeleton grains is porphyroskelic. Considerable difference in the concentration of skeleton crains however does occur in isotubules, in which the skeleton grains and the plasma are not aggregated. In addition, a large amount of coarse material is encoun- DC? o f tered in aggrotubules. while in the deep subsoil a granotubule is observed wherein the skeleton grains are free of plasma, or where the plasma occurs in the form of pedological features. The reason for the local concentration of the grains in these tubules is not easily explained, but may be related to the action of animals (termites) which consume the finer soil constituents but could not manage the larger grains. The plasma fabric of the Vertisol is expressed in the upper part of

121 lig. 34. Mascpic skehepic and hisepic plasmic fabric and stress cutans, 't'y pic Pelhtstert (profile 25, depth 76 cm). 'Hun section wnii'r crossed polarizers. 100 x.

I:ig. 35. Skehepic plasmic fabric, Typic Pellustert (profile 25. depth 56 cm). 'Fliin section under crowd polarizers, 100 x.

122 the solum as plasma separations, called plasma reorientations by Slager et al. (1970), see also Stephen (1960), with striated orientation that occur in isolated patches or islands (insepic plasmic fabric). In the lower part of the soil plasma separations occur also as zones within the s-matrix (masepic plasmic fabric), (fig. 34). Skelsepic plasmic fabric occurs throughout the soil and may be induced by the shearing of the soil material, especially between skeleton grains (fig. 35). The boundary of the plasma separation in this case is gradual, in contrast to the transition such as occurs around embedded grain cutans. The occurrence of neocutans along voids is also caused by stress. Vosepic plasmic fabric such as observed in the Vertisols of the Sudan (Blokhuis et al., 1970; Buursink, 1971) is very limited which is partly ascribed to restricted action of the swell and shrink. Important pedological features are pedorelicts. They have a light brown colour and are densely packed, their boundary with the s-matrix is sharp, but may be gradual in some cases. The latter is often associated with a decomposition of the pedorelict. The relict may sometimes be enveloped by a compound cutan consisting of an argillan, an organo-argillan and a skeletan. The presence of these pedorelicts, noteworthy in the top 90 cm of the soil, indicates: a) admixture of foreign soil material in the soil and/or b) former soil processes leading to their formation. Both are possible according to the physiographic position of the soil (Chapter II) and the changing climatic conditions (Chapter I). Movement of plasma from the s-matrix is thought to be the cause of the development of neoskeletans. Illuviation of plasma is seen sporadically as very thin void argillans in the A13 horizon. The occurrence of embedded grain cutans in the lower part of the soil brings up the question of the origin of the cutanic material and/or the enveloped grain. It is not excluded that its formation can also be derived from an eroded skelsepic part of the matrix, whose present form was initiated by the movement of the soil material. Carbonate nodules with a crystic fabric occur throughout the soil but increase in amount with depth. They are similar to the ones described by Blokhuis et al., (1968) but their occurrence is linked to other processes rather than released from the calcareous subsoil by churning, as this process is not considered to be very active. The origin of these nodules is associated to: 1) an allochthone source, for example exposed calcrete, whose weathering products were in due course transported into the soil material, 2) to pedogenetic processes causing the nodules to form out of a solution enriched by released carbonates from the soil matrix. Biologic activity in the Vertisol is very intense in comparison to for example similar soils in the Sudan (Buursink, 1971) and occurs in a much

123 larger degree than was anticipated from field observations. There are indications that voids and channels are transformed into tubules through animal activity as single and welded faecal pellets are concentrated in them (Ghitulescu, Stoops, 1970). The shape, size and the occurrence of these pellets testifies to the presence of Oribatid mites and possibly very small earthworm species (or termites), (Bal, 1970, 1973). The former seem to consume organic matter as well as mineral matter, a feature not known hitherto. The faecal pellets of the earthworms are about 200—400 micron. The pellets are often concentrated in tubules, but are not necessarily restricted to them. The amount of organic matter is remarkably high throughout the solum and was found to be fairly evenly distributed, although the greatest amount occurs in the topsoil, which is in agreement with the chemical analyses. The distribution pattern of the organic material is ascribed to the process of churning as well as animal activity.

The calcareous subsoil of a Vertisol was studied in a sample taken from profile 24 at the boundary of the ACca and the C-horizon (69—83 cm). The plasmic fabric is dominated by plasma separations that occur as a mosaic (mosepic plasmic fabric), secondly skelsepic plasmic fabric occurs (fig. 36). The occurrence of rounded pedorelicts, presumably existing out of ses- quioxides, is again ascribed to the admixture of allochthone material and/or former soil forming processes. The relicts have a similar appearance as the ones described in profile 25, but are more red in colour. In addition, some of these nodules do not contain plasma and they may be enveloped by a ferri-argillan. In general the pedorelicts have a higher amount of skeleton grains and are poorer in organic matter than the surrounding s-matrix. The plasmic fabric is described as silasepic. Car- bonate nodules with a crystic fabric occur increasingly with depth, they are rounded and do not seem to have been derived from weathered calcrete rock formed in situ, thus enhancing the hypothesis relative to their origin as proposed for their occurrence in profile 25.

The Udic Rhodustalfs are represented by profile 23 and the Typic Rho- dustalfs by the subsoil of profile 10. Three samples were taken from the following horizons of profile 23, the Al (1 — 15 cm), the B2t (51—65 cm) and theB23 (89-103 cm). The pedality of the soil material is variably expressed, usually as small (100—200 micron) weakly developed peds in the upper part of the solum. In the B23 horizon some larger peds were observed (fig. 37). The related distribution of plasma with reference to the skeleton grains is uniform throughout the soil, however, concentration of skeleton grains is occasion-

124

Plate I. I'dic Rhoditstalf, profile 23.

Plate 11. Iron stained material of the C horizon from profile 7, also showing compound channel ferri-argillans, depth 72 cm. Thin section under crossed polarizers. 48 x. Plate Hi. Graded compound cutan, Typic Natraqualf (profile 15, depth 58 cm). Thin section under crossed polarizers. 120 x.

Plate IV. Skelinsepic plasmic fabric, compound void ferri-argillans and papules. "Aquic"Haplustalf (profile 4, depth 115 cm). Thin section under crossed polarizers. 120 x. Hg. 36. Skelsepic plasmic fabric with occasional embedded grain cutans, Typic Chromustert (profile 24, depth 73 cm). Titin section under crossed polarizers- 100 x.

Fig. 37. Peds in an Udic Rhodustaif (profile 23, depth 97 cm). Thin section under crossed polarizers. 100 x.

129 ally observed in aggrorubulcs. In the topsoil there are virtually no plasma separations but anisotropic domains that arc not orientated in regard to each other; the matrix has a flecked distinction pattern, resembling the silasepic plasmic fabric as described by Brewer (1964). In the subsoil plasma separations in zones are more common, giving rise to masepic and related kinds of plasmic fabric. It is ot interest to no re that in the B23 horizon zones occur in which a small random crack pattern (craze planes) is developed, thus giving rise to extremely fine (less than 50 micron) peds. Evidence ot clay illuviation, seen as void argillans, is limited and mainly restricted to the B2t horizon. The cutans are otten discon- tinous, slightly adhesive and constitute only a subordinate amount of plasma. Embedded grain cutans are more common. Closer observation reveals that a gradual transition to the s-matrix occurs occasionally. In this case the cutanic material is relatively thick and may be deformed to a varying degree, which may be the cause of a gradual transition of the circumference to the s-matrix, thus causing it to resemble a skelscpic plasmic fabric. Noteworthy are also neoskeletans along channels and vughs; these are probably formed by a loss of plasma from the matrix which was subsequently deposited elsewhere. An increase in plasma may also be derived from tiie local weathering of minerals in the soil giving rise to skelscpic fabric and ultimately to the formation of papules. These arc occasionally observed in the B23 horizon. Sesquioxidic nodules are mainly restricted to the B2t horizon; their boundaries vary from sharp to diffuse. The nodules are in general densely packed and have a pronounced porphyroskelic internal fabric. In the reddish brown s-matrix of some nodules, fillings of plasma may be encountered. In this case the internal fabric of the nodules is similar to the one of the s-matrix. The occurrence of the plasma fillings points to a period in which the movement of colloidal material was stronger. The amount of organic matter is relatively high in the Al and is well distributed, the amount clearly decreasing with depth. Evidence o^ animal activity is greatest in the topsoil but still considerable deeper down in the soil. This can be deduced from the occurrence of single and welded faecal pellets (up to 300 micron in diameter), which are mainly produced by mites and earthworms. The pellets are found in varying degrees of decomposition and are finally taken up in the soil matrix. Their occurrence is mainly restricted to the aggrotubules. The transition in a Typic Rhodustalf (profile 10), from the dark reddish brown sandy clay loam to the highly calcareous C-horizon, is demonstrated in thin section taken at a depth of 84—98 cm. The amount of plasma decreases considerably with depth in the area of study, but the amount of carbonate nodules increases. Plasma is accounted for as free

130 grain argillans but also occurs frequently as embedded grain argillans. Some scsquioxidic nodules occur and the related distribution of the plasma with referencc to the skeleton grains in these nodules is porphyroskelic. They are characterized by their reddish colour. The carbonate nodules have a fine to coarse crystic fabric and contain considerably less skeleton grains than the surrounding s-matrix. The nodules are mainly sub-angular. In addition calcium carbonate may be present in cal cans. The animal activity is clearly noticeable because ot the occurrence of single and welded faecal pellets and the result of mining, mainly concentrated in aggrotubules. Some voids may have been developed through solution of the calcrete, tor winch the term "solution voids" is proposed. The micromorphology of some Ultic Hap lu s tal f s was investigated by means of a number of thin sections from profiles 2). 14 and 2. The first belongs to the sandy family and the last two to the coarse loamy family. Samples from profile 21 were taken from the B21 and the B22 horizons at respectively 49—63 and 96 — 106 cm depth. Being ag^lomcroplasmic, the related distribution of the basic fabric of the s-matrix deviates from those generally described hitherto, thus indicating the influence of the soil texture on the related distribution o^ the plasma with reference to skeleton grains. The amount of intertextic is subordinate but relevant in this context. The plasmic fabric of the B21 is seen as isolated patches or islands within the dominantly flecked plasma (insepic plasmic fabric), while in the lower part of the B horizon the plasma has a flecked orientation pattern expressed as two sets of short discontinuous plasma separations, usually perpendicular to each other (lattiseptic plasmic fabric). The presence of sesquioxidic nodules with a distinct porphyroskclic related distribution and of a dark red to reddish brown colour, indicates the admixture of foreign soil material and/or former soil processes. The size of these nodules may reach 0.5 cm. The second important pedological feature constitutes free as well as embedded grain cutans. which are classified as ferri-armllans. The amount of illuviated plasma is estimated less than \% in the study area. In addition, a certain amount of plasma may have been derived from the weathering of primary minerals, notably plagioclase and orthoclase. The distinction made by Mermut et al. (1971) between proper illuviation cutans and cutans developed in situ, based on the presence of small pieces of primary minerals in the clay cutan could not be verified. The degree of orientation of the ferri-argillans is variable. In addition, their thickness can hardly be described to illuviation only, which is thought to be very limited at present. Animal activity is accounted for by the presence of single faecal pellets,

131 i:tg. 38. Detail oj d gratwtubule, Ultic Haplustalf (profile 21, depth 59 cm). Thin section under partly crossed polarizers. 40 x. mainly from Oribatid mites, while possible termite activity is acknow- ledged in channels and may also be testified for in aggrotubules and granotubulcs (fig. 38). The amount of organic matter is extremely low, which is confirmed by the laboratory data.

The B3 horizon of profile 1 4 (Ultic Haplustalf. coarse loamy) was sampled from 68 — 80 cm. The plasmic fabric is characterized by dominantly anisotropic plasma with anisotropic domains that are unorientated with regard to each other and is therefore classified as argillasepic. Plasma is further observed around single skeleton grains (free grain-araillans and fern- argillans), while some embedded grain ferri-argillans also occur. The presence of free grain cutans is regarded as proof of illuviation of plasma, after which the enveloped grain was embedded in the s-matrix. Typical arc further matrans around (weathered) rock fragments, which are indicative of mass movement of soil material, most probably associated with the nature of the rainfall. There is a great deal of animal activity observed indirectly as single and welded faecal pellets, mainly confined to aggrotubules.

Additional information about the subsoil of a coarse loamy Ultic Hap- lustalf was obtained from a thin section prepared from a sample taken at a depth of 97-111 cm in the B23 horizon of profile 2. The arrangement of soil constituents is similar as described for profile 14. Moreover the presence of sesquioxidic nodules with varying circumference is noted.

132 Within the s-matrix well orientated plasma fillings are clearly recognized, indicating sufficient moisture to induce these flows (fig. 39). The dating of these nodules is subject to speculation. Considering the physiographic position of the profile, it is assumed that they were formed during a different stage in the soil formation and are regarded as pedorelicts.

The natric B2g horizon and the B2g horizon from profile 1 5, a Typic Natraqualf, are the next subject of study. The samples were collected from 51—67 cm and from 97—111 cm respectively. The structure expressed in individual units, showing a diameter of about 1 50 to 200 micron, is better developed in the B2g horizon than in the natric B2g. Planes, as well as reorientated plasma, outline the structural elements. The basic fabric is complex. The plasma is marked by distinct plasma illuviation and deformation (fig. 40), random plasma separations and outspoken plasma fillings. In addition mass illuviation occurs resulting in compound cutans. In the subsoil, reorientated plasma as well as larger amounts of plasma results in a dominantly mosepic plasmic fabric, in contrast to the mainly skelscpic plasmic fabric in the upper part of the B.

l:ig. 39. Oriented plasma filling in an Ultic Haplustalf (profile 2, depth 107 cm). Thin section in plain light. WO x.

133 Fig. 40. Plasma illuviation and deformation. Typte Natraqiialf (profile 15, deplh 63.5 cm). Thn section under crossed polarizers. 40 x.

Fig. 41. Void and channel argillans and sketinsepic plasmic fabric, "Aquic" Haplustalf (profile 4. depth 11 6 cm). Thin section under crossed polarizers. 40 x.

134 The amount of small skew planes increases considerably in the B2g; their presence corresponds with a change in the mineralogy of the clay fraction. Papules, often as large as 500 micron, are frequently encountered. Em- braced by the s-matrix, they occasionally arc deformed to such an extent, better regarded as patches of reorientated plasma. Illuviation void (fcrri-) argillans arc clearly visible, but they do not occur throughout the whole area of study. Mass illuviation occurs as compound cutans in addition to the type mentioned above. These cutans somewhat resemble the agricutans described by Jongerius (1970). but differ in the gradual zonation of the cutanic material that becomes coarser towards the s-matrix (Plate 111). This feature is similar to the graded bedding as described by Kuenen (1953) and resembles on a micro-scale the first layer in the complete sequence of a turbidite, known as "graded interval" (Bouma, 1962). The sedimentolo^ical processes that caused the development of these macro features are however hard to visualize in the soil material considered. It is not held impossible that animal activity may have played a part in the genesis of these graded cutans. Roads et al. (1965) describe the formation of biogenic graded bedding by deposit- feeding organisms in intertidal and shallow subtidal environments. Although these conditions are rather different from the one described by this author, the fact that animal acitivity may have been an additional cause to the development of this feature should not be excluded. Biological activity is considerable in the soils in which these cutans occur, in addition their physiographic position implies that sufficient moisture is available during some time of the year to induce the mass transport of soil material. Plate 111 shows a graded compound cutan, having an argillan on top of the graded material. However, if we assume that two processes are responsible for the genesis of these features, they are more appropriately classified as graded complex cutans. Apart from the physical factors that induce slaking and subsequent mass illuviation, the movement of plasma and skeleton grains in this soil is also caused by the peptization of the clay, due to the high amount of sodium on the exchange complex. The deformation is more strongly developed in the lower part of the soil, in this part more planes are also observed. These features are correlated with the types o( clay mineral (Chapter 111.3.1.). Iliuviation contributed to the formation of free grain argillans and indirectly to the occurrence of embedded grain argillans. A feature of special importance are ncoskelctans, occurring frequently along voids; their plasmic fabric may be described as silasepic and correspond with the "flecked background" as reported by Brewer (1964). The concentration of these lighter zones caused by subsequent closing of

135 i'iy. 42. Irregular sesquioxidic nodule ("pedorelict") with sharp circumphvrence, Aquic Haplustalf (profile 8, depth 91 cm). Thin section in plain light. 40 x.

I:ig. 43. Sesquioxidic nodule with gradual boundary, Aquic Haplustalf (profile 8, depth 56 cm). Triin section in plain light. 40 x.

136 the voids may result in fairly large, pale coloured areas. Sesquioxidic nodules do occur and sometimes resemble the pedorelicts as found in the Vertisols and Haplustalfs. A marked difference is however that in the samples from this soil the boundaries of the nodules are often diffuse which could be indicative for their present (de)formation. Some may have a weak concentric structure.

Information on the organization of soil material in some Aquic Hap- lustalfs was obtained from thin sections taken from profiles 8 and 4. From profile 8 two samples were collected from the B2g horizon, at a depth of 44—58 cm and 79—93 cm respectively. The increase in clay and its orientation causes the development of mainsepic plasmic fabric in the lower part of the B2g. The moister soil conditions may eventually lead to a more pronounced movement of soil constituents causing the genesis of void argillans (fig. 41) as well as graded compound cutans as described for the Natraqualf, but may be deformed in the lower part of this horizon (see also Plate IV). These cutans are more abundant in the upper part of the B2g. According to Brewer (1968) clay illuviation plays a subordinate role in particle size differentiation in soil profiles; the formation of clay in sity being foremost the cause for an increase in this grain size. Sesquioxidic nodules are red to reddish brown and may have sharp to gradual boundaries (fig. 42, 43). Some may contain flow structures. Feld- spatic weathering occasionally gives rise to the formation of skelsepic plasmic fabric. Especially in the lower part of the soil, pale coloured areas occur, which may be caused by the reduction of iron compounds and its subsequent removal from the matrix. These areas are most evident along voids. There is a great deal of animal activity in the soil mainly concentrated in aggrotubules (up to 1 cm long). Single and welded faecal pellets as well as mining are caused by the action of mites, earthworms and termites. Their activity is also widespread in the subsoil as confirmed by field observations. Additional information from an "Aquic" Haplustalf (profile 4) does not deviate widely from those obtained from profile 8. The plasmic fabric is better expressed and animal activity is less intense in the upper 90 cm of profile 4. Carbonate nodules with a crystic fabric occur in the deep subsoil.

An example of weathered granitic rock, saprock according to Bisdom (1967), was taken from profile 7 (60—74 cm). The original rock structure is only present in some rock fragments, which are also weathered to a considerable degree. In its totality the material has a porphyroskelic related distribution, voids

137 occur as planar voids and channels. Weathering of the rock is evident in the (micro-) cracks and along joints. The planar voids may contain a variety of material such as a) breccia-like material, b) compound ferri- argillans, c) yellowish void argillans or, d) they may be empty. Yellowish cutanic material is often observed on top of compound ferri-argillans and may indicate the last stage of clay illuviation (Plate II). X-ray analyses indicate the dominance of kaolinite with subordinate amounts of illite as minerals of the clay fraction. Heavy mineral composition denotes a large amount of zircon (55%) and amphibole (33%) with some tourmaline (8%), epidote (7%) and staurolite (2%), while orthoclase dominates the light mineral fraction. The weathering of the feldspar is similar to that outlined by Bisdom (1967); the significance of the (micro) cracks is evident. In comparison to the overlying B3, the fine earth of the C has a marked increase in total iron from 1.7 to 5.9%, while total SiO2 decreases from 85.8% to 78.0%. The amount of A.I2O3 increases from 9 to 11%. A similar trend is observed in the elemental composition of the clay fraction for Fe2 03 and SiO2, while Al2 O3 stays fairly constant. Iron stains are clearly visible in cracks and joints of the mineral fragments and in the breccia-like material between the rock and the mineral fragments and in plasma fillings (fig. 44). The related distribution of the s-matrix closely resembles some of those encountered in sesquioxidic nodules. The amount of iron in a number of plasma fillings was measured by electron micro probe. Areas for selective countings were chosen on basis of colour, as seen in thin section (see also LaFleur, 1970). Material with a very dark colour was found to contain about 30 to 35% of iron and the somewhat browner material between 25 to 30% of iron. Countings were also conducted on a sesquioxidic nodule in soil material, results were similar; in addition, yellowish material was found to contain about 5% iron. An X-ray scanning picture of a plasma filling in the C-horizon of the granite shows the alternating lighter and darker areas (lighter coloured areas contain more iron), (Fig. 45.) Microscopic investigation of the thin section implies the darker material to consist mainly ofJiematite, while the lighter coloured areas contain more hydrated iron compounds, such as goethite. No binding comments on the relation between the kind of iron and the percentage as found can be given, as no measurements were conducted on the other elements. The occurrence of well-orientated plasma fillings points to a moister soil regime, in which these flow structures could form. In the upper part of the study area (60-65 cm), pedological features

138 lig. 44. Iron stained plasma filling in weathered granite, C horizon oj profile 7 (L'ltic Haplitstalf, dvpth 12 cm). Thin HTtion in plain light. 100 x.

lig. 45. X-ray scanning picture of iron distribution in a plasma filling oj weathered granite, detail of fig. 44, (Profile 7. depth 72 cm). 750 x. include aggrotubules with organic matter, compound papules, skeletans and void argillans. According to Schmidt-Lorenz (1971 and personal communication), the material has been subject to laterization, although there is no evidence that this process is active at present.

139 IV.2. Evaluation ot the Held data

The description of the soils in the field is supplemented by the micromorphological data. Macroscopical observations are limited by the means used and often deviate considerably from the information obtained trom the study of thin sections. A tew examples arc mentioned to illustrate these differences. The pedality. described as "the physical constitution of a soil material as expressed by the size, shape and arrangement of peds" (Brewer, 1964) accommodates the concept of the USDA Soil Survey Manual (1951). In this handbook peds are described as part oi the soil structure defined as "the aggregation of primary soil particles into compound particles, or clusters of primary particles, which are separated trom adjoining aggregates by surfaces of weakness". Many soils arc described as structureless or apedal (massive-coherent soil material, single grained-non coherent soil material), however there are some remarkable exceptions (fig. 46). In thin section however pedality is often visible as small natural aggregates out-

Fig. 46. Coarse columnar structure in profile 15 {Typic Natraqualf).

140 lined by plasma reorientations or is less often indicated by voids. The related distribution of. the plasma with reference to skeleton grains is difficult to assess in the field, although the textural composition of the soils is readily obtained. This may aid to evaluate the amount of skeleton grains in relation to the amount of plasma and, as such, points to the type of related distribution to be expected (Brewer et al., 1969). The void pattern as observed in the field comprises biogenic pores and cracks; only macrovoids (larger than 75 micron) can be detected or implied by the presence of pores. Most of these were classified as tubular (FAO, 1966). A significant aspect of the microscopical investigations appeared to be the activity of animals which are responsible for a large amount of pores or their deformation. The plasmic fabric does not lend itself to field description with the means at hand. Related stress-induced features such as vosepic and masepic plasmic fabrics may be partly deduced from the presence of stress phenomena (slickensides, pressure faces), and to a certain extent by the illuviation of plasma. The presence of smooth ped surfaces does not necessarily imply clay illuviation (Reynders, 1972). Such surfaces as well as "cutans" were observed in the field around peds, grains and in voids. Micromorphological investigation of the thin sections revealed the limited occurrence of true illuviation cutans, although embedded grain cutans were readily observed, especially in most granitic soils. The majority of distinct ferri-argillans is confined to the B-horizons of most Aquic Hap- lustalfs. Reviewing the plasmic fabric of some oxic and argillic horizons, Bennema et al. (1970) conclude that there is no close relationship between the plasmic fabric and the morphology of these B-horizons. Our observations indicate also that plasmic fabric may be expressed differently in the various argillic horizons. In the majority of cases the appearance of mottles could be correlated, after microscopical investigation, with the presence of sesquioxidic nodules with diffuse boundaries. In addition the mottling may be attributed to the presence of "pedorelicts" in some soils where no hydromorphic conditions are anticipated. Animal activity was observed in the field as related to millipedes and termites. This picture was elaborated largely by thin section examinations and indicated the presence of mites and earthworms as well. The biological activity is far greater than was to be expected from field observations and contributes to a higher evaluation of the soils. In addition, the presence of tubules widess the concept of homogenization as described by Hoeksema (1953) and may also be valid for soils in semi-arid areas. This process may eventually be responsible for the fairly uniform grain size distribution, as for example in profile 8. 141 Table 34: Micromorpliological description

Profile Classification Horizon Depth Related distribution of Plasmic Fabric plasma with reference to skeleton grains

25 Typic Pellus- A13 44-58 porphyroskclic insepic with some mase] tert and skelsepic

ACca 74-88 porphyroskelic skelmainsepic

ACca 109-123 porphyroskelic skelmainsepic

24 Typic Chro- ACca/C 69-83 porphyroskelic skelmainsepic mustert

23 Udic Rhodus- Al 1-15 porphyroskelic silasepic with some inse talf

B2t 51-65 porphyroskelic insepic intergrading to bimasepic and molattisC

B23 89-103 porphyroskelic insepic with some latti- silasepic

10 Typic Rhodus- B3/C 84-98 porphyroskelic inter- skelmainsepic with som talf grading to agglomero- lattisepic plasmic

21 Ultic Haplus- B21 49-63 agglomeroplasmic with insepic with some lattis talf (sandy) some porphyroskelic or intertextic

B22 92-106 agglomeroplasmic lattisepic

142 Pedological features Remarks general biogenic activity- some carbonate nodules with crystic common welded and single faecal common distinct subangular fabric; occasional thin void argillans; pellets; few isotubules, some peds of about 300 micron; few skeletans and occasional aggrotubules much organic matter; some pedorelicts meta planes and skew planes common carbonate nodules with few single and welded faecal as above crystic fabric; some pedorelicts; few pellets; few aggrotubules neoskeletans; occasional neoargillan stress argillans; occasional neo- common single and welded few fairly distinct peds of skeletan and calcans; some embed- faecal pellets; few granotubules about 150 micron; common ded grain cutans; many carbonate and few aggrotubules calcrete fragments nodules with crystic fabric abundant carbonate nodules with varying crystic fabric; rounded pedorelicts; occasional compound cutans, papules and embedded grain cutans; common lithorelicts occasional embedded grain cutans common single and welded faint peds of about 100 and ped cutans faecal pellets; few aggrotubules micron; much organic material; common vughs and channels few faint void argillans; some some single and welded faecal fairly distinct peds of embedded grain argillans and ped pellets; few aggrotubules about 100-150 micron cutans; some channel ferri-argillans and some sesquioxidic nodules; some ped cutans and embedded some single faecal pellets; moderate peds of about grain cutans; some channel ferri- common aggrotubules 200 micron, occasionally argillans; occasional papules and 1200 micron; common neoskeletans small voids; some craze planes some sesquioxidic nodules; common some single faecal pellets; some peds of about 1 50 micron; embedded grain cutans; some free common aggrotubules some simple and compound grain cutans; occasional calcan; packing voids; common calcrete abundant carbonate nodules with fragments crystic fabric, slightly rounded occasional embedded grain cutans; few single faecal pellets; some weak peds of 75-100 micron; common free grain ferri-argillans; aggrotubules, occasional common compound and single some sequioxidic nodules isotubules and granotubules packing voids; some orthovughs and channels some sesquioxidic nodules; some occasional single faecal pellets; common single and compound free and embedded grain ferri- few aggrotubules packing voids; some orthovughs argillans; some papules

143 Table 34 (continued)

Profile Classification Horizon Depth Related distribution of Plasmic Fabric plasma with reference to skeleton grains

14 Ultic Haplus- B3 68-80 agglomeroplasmic with:rr argillasepic talf (coarse some porphyroskelic loamy)

Ultic Haplus- B23 97-111 porphyroskelic argillasepic talf (coarse loamy)

15 Typic Natra- B2g 51-65 porphyroskelic with skelsepic with vosepic qualf some agglomeroplasmic and insepic

B2g 97-111 agglomeroplasmic with mosepic with some skel- some porphyroskelic in-and vosepic

Aquic Haplus- B2g 44-59 porphyroskelic inter- argillasepic with some talf grading to agglomero- masepic plasmic

B2g 80-95 porphyroskelic mainsepic, some silasepii

"Aquic" Haplus- B22 62-76 porphyroskelic mainsepic with locally talf some skelsepic

B2g 81-95 porphyroskelic bimasepic with some lat and skelsepic

B2ca/C 104-118 porphyroskelic bimasepic, some latti- ar skelinsepic

144 Pedological features Remarks general biogenic activity

some sesquioxidic nodules; many many single and welded faecal common packing voids and free and some embedded grain ferri- pellets; common aggrotubules channels argillans; some matrans around rock and occasional striotubules fragments; occasional lithorelicts

some pedorelicts and lithorelicts; some aggrotubules some orthovoids occasional free grain ferri-argillans; and orthochannels some void argillans; occasional papule and compound cutans; fillings of plasma

many papules; common (deformed) some single faecal pellets; some few weak peds of about 100-150 embedded grain cutans; common striotubules and occasional micron; some planar voids and sesquioxidic nodules; common isotubules skew planes channel ferri-argillans; some graded compound cutans some embedded grain cutans; some few single faecal pellets; occa- moderate peds of about 150-200 sesquioxidic nodules; common sional striotubules micron; some orthochannels; papules; some free grain argillans, many skewplanes; strong some void argillans; occasional neo- illuviation and deformation skeletan

some embedded grain argillans; few many single and welded faecal some fairly distinct angular peds graded compound cutans; some pellets; common aggrotubules of about 100 micron sesquioxidic nodules; occasional void argillans

occasional compound cutans; some as above some orthovughs and some papules; some embedded and free channels grain argillans; occasional void argillans; some sesquioxidic nodules; occasional papules; some neoskeletans

common embedded grain argillans; some single and welded faecal weak angular peds of about 100- occasional papules; some sesquioxi- pellets; occasional aggrotubules 150 micron; some orthovughs and dic nodules; occasional channel channels argillans and stress argillans some sesquioxidic nodules; occa- common single and welded faecal as above with some planar voids sional embedded grain argillans and pellets; few aggrotubules skeletans and neo (stress) argillans and papules common embedded grain argillans many single and welded faecal common skewplanes, craze planes and sesquioxidic nodules; some pellets; few aggrotubules and channels; some vughs skeletans, void and free grain argillans; common papules; some carbonate nodules with crystic fabric

145 CHAPTER V

ROCK WEATHERING AND SOIL FORMATION

The environmental conditions in central East Botswana induced various stages in rock weathering as well as in soil formation. Physical weathering, or the breakdown of the rock into smaller fragments, leaving the original mineral composition virtually unchanged, occurs mainly as a result of the variation in the diurnal temperature. Chemical weathering requires the presence of water, not only to impel the chemical attack on the fresh rock, but also to carry the released components away. In addition, the wind-action and biological activity may play an active role in the disintergration of material. Water is a limited commodity in the pedosphere and its supply depends solely on the rainfall. Hence most intensive chemical breakdown of minerals and neo-formation of minerals is to be expected during the rainy season from November to April, and is then enhanced by favourable high temperatures. A wide range of materials is simultaneously affected by the action of the atmosphere. In the following sections the alteration of the fresh rock (R) as compared to the weathered rock (C), is dealt within section V.l., while processes that are active in the soil are reviewed in part V.2.

V.l. Rock weathering

The combined physical and chemical agents induce the disintegration of the fresh rock. The assessibility of water in cracks and joints, the structure, the texture and the mineral composition of the rock determine mainly the rate of weathering. Several forms of weathered granite are mentioned in Chap- ter 1.2. In addition, Pettijohn et al. (1972), remark on the presence of "granite wash" in the immediate surroundings of granitic hills, a feature also observed in corresponding locations in the survey area. In terms of soil formation the chemical weathering of the fresh rock and the constituents derived therefrom will be emphasized. This process comprises the transformation of minerals through a) the adsorption of water and/or hydration on the mineral surface, b) the hydrolysis of these surfaces caused by the dissociation of water in H3O and OH~ ions and c) liberation of the ions from the mineral structure. The dissociation of the water is considerably enlarged by higher temperatures; sixfold by a temperature increase from 1.0° C to 30° C (Mohr et al., 1959).

147 The presence of carbon dioxide in the atmosphere and its ionization in the surface waters caused its pH to decrease to about 5.7. This in turn makes natural water a better solvent of minerals (Krauskopf, 1967). The behaviour of minerals exposed to such a solvent is primarily dependent on the build up of the crystal framework. Early research, published by Goldschmidt in 1937, on the principles of chemical elements in minerals and rocks revealed not only that atoms and ions are combined in a regular arrangement to form lattices, but moreover that their formation implies a sorting of elements according to their ionic radii and valency properties. For the most common elements in rocks and soils these values are given in table 35, according to data from Loughnan (1969).

Table 35. Ionic radius, radius ratio cation I oxigen and Zlr values for some common cations in soils and rock.

4 3 Si * Al * Fe3* Mg2* Ti4* Fe2* Mn2* Na* Ca2* K* ionic radius (Â) 0.41 0.50 0.64 0.65 0.68 0.76 0.80 0.95 0.99 1.32 ratio/radius cation/oxigen 0.29 0.36 0.46 0.46 0.49 0.54 0.57 0.68 0.71 0.95 Z/r ratio 9.5 6.0 4.7 3.0 5.9 2.7 2.5 1.0 2.0 0.75

Similarity in ionic radius (r) and ionic charge (Z) may promote isomor- phous substitution, but only if the valency does not differ more than one and the lattice structure of the mineral is suitable. The formation of rocks from silicate melts was commented on by Bowen (reviewed in Bear, 1969 by Barshad and Jackson). The crystallization of the various minerals caused by decreasing temperature and pressure was found to take place according to the degree of polymerization of the SiO2 tetrahedron, which is considered to be the basic structural unit of most silicate minerals (Loughnan, 1969). In general two series are recognized: 1) the discontinuous mafic series and 2) the tektosilicate series (Jackson, 1969):

olivine -> pyroxene -*• hornblende -*• biotite. quartz, K-feldspar anorthite -»• oligoclase ->• albite -^ (Ca-plagioclase) (Na-plagioclase)

From left to right in the series the temperature and the basicity decrease. The stability in circumstances of 1 atm. pressure and at room temperature

148 increases if the difference with conditions at time of forming lessens. The arrangement of the SiO4 tetrahedron, in which Al may substitute Si, becomes exceedingly complicated in the later stages of crystallization. Its substitution causes the addition of, for example, Ca2+ or Na+ to guarantee electric neutrality of the mineral. Seven groupings of the tetrahedrons are visualized, from single tetrahedrons (neo-silicates) to the complex continuous framework of tetrahedrons in three dimensions (tekto-silicates), (Holmes, 1969). The formation of these clusters depend on the measure in which the O-atoms share one or more tetrahedrons.

Some attention was given to the structural framework of the silicate minerals as it determines to a large extent the vulnerability of the mineral to weathering. Goldlich (referred to by Loughnan, 1969) found the weathering sequence for the common rock forming minerals almost the same as the one given for the crystallization of minerals from a silicate melt. The tighter the oxygens are packed around the cations in positions other than tetrahedral, the more stable the structure at low temperatures and pressure, (Barshad, 1969.) In addition, the stability of the configuration is maintained if the sums of the positive and negative charges equate (Pauling, quoted by Loughnan, 1969). This is illustrated by the ratio radius cation/oxygen and the ionic potential (Z/r). Thus it is feasible to assume that the breakdown of the mineral structure will most likely take place where the weakest cation-oxygen bond occurs. The energy to induce liberation of the ions from the mineral structure is supplied if the equilibrium between the rock and its immediate environment is disturbed. This may be caused by hydrolysis, causing the disrup- tion of the weakest bond in the structure and is further promoted by a change in redox potential through the oxidation of Fe2+ to Fe3+. The reactions continue as long as released ions form a more stable system in a certain environment than the one from which they are liberated. The loss of constituents was found to follow the sequence Ca > Na > Mg > K > Si > Fe > Al. The seemingly anomalous position of K is explained by its being readily entrapped in secondary formed minerals, such as illite (Loughnan, 1969) as the ion does not readily hydrate in water, thus developing a field to weak to annex water molecules (Millot, 1970). An impression of the change in rock composition for the two major rock types in the area, e.g. granite and dolerite, is obtained while comparing the fresh rock specimen and its weathering products. The rock samples 87B (leucogranite) and 12B (dolerite) were taken while the C-horizons from profiles 7 and 13 (respectively sample Nos. 7.5 and 13.63) and profile 24 (sample 24.84) were used.

149 The soils 7 and 13 are classified as Ultic Haplustalfs while the C-horizon from profile 24 underlies a Vertisol. Two reservations as to the validity of the results are appropriate; firstly as a result of the analyses method, iron is given as Fe2 O3, and secondly the fresh rock was not obtained from the same profiles as the C-horizon. For the calculation of the various oxides the procedures as outlined by Krauskopf (1967) are applied. This implies that the aluminium concentration is assumed constant, as the element is considered rather inert to weathering cycli if the environmental pH is between 4.5 and 9 (Loughnan, 1969). Objections against the use of TiO2 as reference oxide may be raised on the basis of the very small amounts in which this element occurs in the investigated material, thus enforcing the analytical error. To arrive at the persentage loss or gain of constituents in the weathered rock as compared to the fresh rock (R), the following steps are carried out.

Table 36. Calculation of gains and losses during weathering

1 2 3 4 5

leuco-granite weathered change loss or percentage loss (87B) rock (7.5) Al = c gain or gain to 1

SiO2 76.4 77.0 72.7 -3.7 5

A12O3 10.1 10.7 10.1 0 0 Fe2O3 0.8 5.8 5.5 + 4.8 + 575

TiO2 0.28 0.38 0.36 + 0.08 + 29 CaO 1.91 0.17 0.16 - 1.75 - 92 MgO 2.18 0.87 0.82 - 1.36 - 62

K2O 5.40 4.23 3.99 - 1.41 - 26 Na2O 2.71 0.80 0.76 -1.95 - 72 P2O5 0.18 0.08 0.08 -0.10 - 61

Column 1 gives the composition of the fresh rock (R) and column 2 the composition of the weathered material (C) in weight percentages. In both cases the analytical error and the trace element concentration are taken into account, thus adding the totals up to .100%. Column 3 results from the calculations of weight in grams from each oxide in the fresh rock (R) on the assumption that Al is constant. The losses or gains of the oxides given in column 4 are computed by substracting the values in column 3 from column 1. Column 5 gives the same loss or gain in percentage of the original amount in R. In a similar way the variations from R relative to the C was calculated for the C-horizon in profile 13. The following values are

150 obtained: SiO2 : -36%; A12O3 : 0%; Fe2O3 : t275%; TiO2 : +46%; CaO: -89%; MgO: -80%; K2O: -64%; Na20: -79% and P2 OS : -72%. Firstly, it is noticed that the mobility of the macro-elements such as CaO, MgO, Na2 O is in accordance with the expectations raised above, while losses of SiO2 are also relatively high. Secondly, the increase in Fe2 O3 is manifest in the C material of the investigated profiles. Its rise can hardly be explained as to be derived solely from the weathering in situ of Fe bearing minerals such as biotite, of the granite. Micromorphological observations confirm the concentration of iron mainly as staining of the material (Chapter IV). Transport of iron from elsewhere as iron-rich plasma, also noticed in plasma fillings, is therefore feasible. There is no conclusive evidence, however, that the iron is derived from vertical transport through the soil as the enrichment may as well be caused by lateral supply. If the changes in composition of the C-horizon are taken as an indication for a process, it resembles closely the absolute accumulation of iron as described by D'Hoore (1953). The position of the profiles on to the fairly flat land surfaces in which drainage is restricted and fluctuating water tables (did) occur, is thought to be favourable for an accumulation of iron compounds (Magnien, 1959, Alexander et al., 1962, Sombroek, 1962, Stephens, 1971). This requires however a wetter moisture regime than is presently encountered. These conditions did exist in the past (Chapter 1.2.), hence the formation of the iron enriched material is thought to be a paleo-feature. A different picture is obtained from the comparison between the dolerite and its weathered counterpart (table 37).

Table 37. Gains and Losses of dolerite

SiO2 Al2 O3 Fe2O3 TiO2 CaO MgO K2O Na2O P;lOs

R (12B) 50.90 15.3 9.8 0.63 11.28 8.29 0.86 2.82 0.10 C (24) 68.4 11. 5 4.0 0.51 8.81 1.87 2.65 2.26 0. 12 % loss or gain + 80 0 -46 + 8 + 5 -70 + 313 + 8 + 58

The position of this profile differs considerably from the granitic ones as it is located at the bottom of the Shoshong Hills and, as such, subject to appreciable movement of constituents. The breakdown of minerals rich in bases led to a transport of Ca, Mg, Fe and Al. The tekto-silikates (Na and K-feldspars mainly) weather less easily, which result in a relative enrichment of Si, Na and K. The encountered weathering products i.e. calcrete and montmorillonitic type of clay minerals confirm these assumptions.

151 V.2. Soil Formation

The formation of soil is induced by factors such as climate, parent material, biological activity and topography, which instigate the soil- forming processes (Jenny, 1941). These processes operate in the soil; the soil constituents being the reagents. Inherent to the formation-of soils is the development of soil horizons; a layer of soil or soil material approximately parallel to the land surface and differing from adjacent genetically related layers. Recognition of these horizons and their subsequent definition led to a) a better understanding in the various processes operating in the soil, b) a basis for soil classification. The interrelationship between the various soil-forming factors is not a static one and is not always dominated by one and the same factor, for example climate. Thus similar soil-forming processes are not restricted geographically but occur where the operation conditions are fulfilled. This notion stimulated genetic soil studies on a world-wide scale and lead to better insight in notably the controversial concepts of processes as laterization and podzolization (Andriesse, 1971). The movement of soil constituents leading to the differentiation of soils is the subject of the next section. After general remarks on the mobility of these constituents, the genesis of soil is approached according to the landscape entities in which they occur.

The mobility of the components depends primarily on the presence of water. If this commodity is present, the constituents may go into solution as ions, as colloids or as complex-compounds. Early research by Gartledge (1928) and Goldschmidt (1937) on the mobility of ions, was reviewed by Loughnan (1969) and Millot (1970). Ions are thus divided into three groups based on their ionic potential (Z/r) and their ionic radius (r): Group 1: the hydrated ions; these are ions with a weak ionic potential (Z/r <3.0) such as Ca2+, Mg2+, Na+and K+, which tend to pass into true ionic solution during the weathering processes; Group 2: the ions with an intermediate ionic potential (Z/r between 3.0 and 9.5), such as Al3+, Fe3+ and Ti4+, which are precipitated and become concentrated in the residue; Group 3: ions with a high ionic potential (Si, P and N) may form soluble complex anions.

The solubility of the various ions may equally be influenced by a number of variables such as the pH and the redox potential (Eh) of the liquid- liquid and the liquid-solid phases, which are dominant in soil materials.

152 A summary on the solubility of the common cations released by silicate minerals in soils was, amongst others, given by Reynders (1964), Loughnan (1969), Millot (1970) and Segalen (1.971). Within a pH range of about 4.5 to about 9.0 which covers the values encountered in the investigated soils it appears that: Ca2+, Mg2+, Na+ and K+ are readily lost under leaching conditions; the rate of loss from the environment may be retarded for K+through fixation in the illite structure; Fe2+ may be lossed but the rate of loss depends on the redox potential and the degree of leaching, while Si4+ is slowly lost if 4+ adequate leaching occurs; Ti is considered immobile in the TiO2 form; Fe3+ is immobile under oxidizing conditions and Al3+ is regarded virtually immobile in the given pH range. Whereas the alteration of the fresh rock implies a loss of constituents, the B3 horizon may be marked by loss as well as a gain in components to vertical and/or lateral transport of materials. This fact concerning some alfisols is illustrated in table 38.

Table 38. Gains or losses of metal oxides in the B3 horizon as compared to the C. (in % of)

Molar ratios

Oxide SiO2 Fe2O3 CaO MgO K SiO2 A12O3 Profile A12O;i Fe2O3 C B3 - C B3

7 (Alfisol) + 33 -65 + 24 -26 + 7 12.1 16.3 2.9 8.1 12 (Alfisol) + 45 + 8 -39 -24 + 48 4.2 6.2 4.5 4.8 32 (Alfisol) -25 - 7 - 7 -38 _ 15 5.8 5.5 4.4 5.9 10 (Alfisol) + 3 -12 -96 _ 2 + 27 9.5 9.8 5.7 5.3

The variation in the SiO2 , Al2 O3 and Fe2 O3 percentages is reflected in the SiO2 and the Al2 O3 ratios. An increase is noted for SiO2 in the B3 Al2O3 Fe2O3 for all B-horizons except profile 32 while also losses are recorded for MgO ourlined above. The relation between the landscape and the soils was found to be of significance in dealing with the soil-forming factors (oilier, 1959), hence spil genesis is discussed according to the locations of soils in the sample areas. (Oilier, 1959).. In sample area A the toposequence of profile 1 to 4 is of special interest as the soils occur on a cross-section through' the Late Tertiary pedeplain. The

153 Sample area A

Sample area B

Sample area C

Sample area D

19 20

Sample area E

Fig* 47. Schematic diagrams of soils in relation to topography.

154 soil material has been subject to intense weathering, such as can be deduced from the mineral composition. In addition leaching caused the considerable loss of the more mobile constituents, resulting in low CEC and a low base saturation. Barridge et al. (1965). Comment that texture, drainage and topographic position mainly govern leaching, assuming the presence of sufficient moisture. Exceptions herefrom are encountered in soils near a fresh supply of primary minerals (profile 1) or where an accumulation of the leached constituents could take place (profile 4). The migration of clay is closely associated to the movement of water in lateral and/or vertical direction, subsequently the accumulation of clay in the B-horizon was partly ascribed to this process. It is particularly clear in the lower B-horizon of the "Aquic" haplustalf. Changes in the concentration of some major soil constituents were indicated by comparing the composition of the deepest B-horizon with a topsoil, preferable the upper B. To limit the influence from surface wash and wind erosion or deposition, the topmost horizon was not taken. The changes were calculated as outlined by Krauskopf (1967) taking Al2 O3 concentration as the reference oxide. The high concentration of MgO in the B22 of profile 1 is ascribed to its position, being close to the source of ferro-magnesium minerals (Chap- ter 3). The loss of Fe2 O3 may have led to subsequent enrichment of the lower B in profile 2 through lateral drainage. Overall losses in the B23 as compared to the Bl are reported in profile 3, which is located in the central part of the toposequence, whereas a sharp increase in the concentration of more soluble elements is noted in profile 4, positioned in a drainage channel as lowest member of the sequence. In this profile, an "Aquic" Haplustalf, a change in clay mineral composition as well as an increase in the amount of clay is encountered with depth. This presumebly caused the relative enrichment of MgO in the B2ca horizon. Restricted drainage provokes grey colours in the subsoil horizons of the Aquic Haplustalfs (Young et al., 1965). Changes in profile 11 are similar as indicated for profile 3, apart for Fe2 O3, while variations in profile 10 show the calcareous C material.

i, > !••( blockage by : •

(loamy) sand •.;.;.• iron mottles s stOnes, gravel

+ + P—I sandy Loam + calcareous g granitic rock

Illllll (sandy) clay Loam 6 gley d dolerite : f SX^ (sandy) clay • drainage c calcrete cracks • surface, wash sc schist en

155 Table 39. Gains and losses in the B horizon as a result of soil-forming' processes (in % to theBl)

Molair ratios

SiO2 Al2 o3 Profile SiO Fe O CaO MgO K O A1 O Fe 2 2 3 2 2 3 2 o3 u 1 u 1*

1, B21-B22 + 1 - 10 -21 + 191 - 5 7.5 7.5 4.9 5.5 2, B1-B3 - 15 + 17 -69 - 45 - 17 17.3 14.4 7.3 5.9 3, B1-B23 -29 0 -33 - 70 -39 13.3 9.5 5.8 5.8 4, Bl-B2ca -47 - 2 + 13 + 233 -46 10.3 8.0 4.7 4.5 10, B1-B3 -26 - 12 + 23 - 35 - 4 13.2 9.8 4.6 5.3 11, B1-B3 -26 - 11 -20 - 46 -29 33.8 25.1 6.9 7.3

* u = upper B 1 = lowerB

The development of profile 10, a Rhodustalf, was found to be incidental on the pediplain and its occurrence mainly ascribed to those processes that led to the genesis of its counterpart profile 23. In sample area B, part of the late Tertiary erosion surface, the profiles 5 and 7 are located on slightly higher topographic positions, whereas profiles 6, 8 and 9 are situated in the lower bottom-lands and drainage channels. It is thought that a temporary water-table could develop on the flat interfluves under sufficient rainfall. Presently however, a surplus of water is not observed in these areas due to high evaporation rates and decreasing precipitation (Chapter 1.2). A perched water-table may occur nowadays in the soils located in depressions, to which the lateral drainage is directed. This has in addition, led to a change in environment inducing the neo- formation of minerals and resulting in a higher base saturation and cation exchange capacity in these soils. The occurrence of graded compound cutans in Aquic Haplustalfs (Chap- ter IV) implies that the soil dries out sufficiently in the dry spells, to allow for the transmittance of saturated soil material through voids during subsequent wetter periods. Following the procedure as applied above for the calculation of the gains and losses for the C-horizon as compared to the upper B, we arrive at the following table for the profiles 5 to 9.

156 Table 40. Gains and losses in the C or lower B horizon as compared to the Bl (in %)

Molar ratios

SiO2 AI2O3 A12O3 Fe2O3 u 1 u 1*

5, B-C 10 +50-21 -50 +3 17.6 15.9 5.3 3.5 7, Bl-C 26 +219 -30 +46 -24 10.9 9.2 5.9 2.9 6, B1-B3 16 +102+5 -12 -15 10.9 9.2 5.9 2.9 8, B21-B2g 22 +24+37 +30 - 18 10.7 8.3 5.0 4.0 9, Bl-C -41 34 _ 13 + 29 n.d." 10.9 6.5 6.2 4.7

* not determined ** u = upper B 1 = lower B or C

As for the soils in sample area A, there is an increase in SiO2 towards the soil surface. According to the results of Chapter 3, a rise in the concentration of SiO2 is correlated with a decrease in the content of Al2 O3. Marked difference with the better drained profiles (such as 1, 2, 3, 11) on the pediplain, is the sharp increase in the concentration of Fe2 O3 in the C- horizon of all profiles encountered. Whereas in the profiles 5 and 7 the processes that led to this increase are hard to visualize in the present environmental conditions (see V.I), it may be envisaged in the bottom land soils. Conditions in the subsoil of these "Aquic" Haplustalfs may induce the release and redistribution of iron in reduced milieu during wet periods and its dehydration and crystallization in the drier spells (van Schuylenborgh, 1971). This has led to the occurrence of mottles in the subsoil of the investigated profiles (6, 8 and 9). These mottles were identified mainly as sesquioxidic nodules with sharp and diffuse boundaries. Similar features were observed by Blume et al. (1969), who remark on the accumulation of Fe and Al in these mottles. A fact confirmed for Fe by electron microprobe analysis of a "nodule". It is noteworthy that the movement of iron oxides or hydroxides could not be verified in thin section, for example as ferrans. In the only proper Aquic Haplustalf (profile No. 8) the material from the C-horizon is richer in CaO and MgO, probably caused by lateral addition. The relative loss of K2 O in the subsoils is ascribed to leaching ot this constituent from these horizons. Sample area C represents the eroded part of the Tertiary plain. Relief differences are greater and drainage channels more pronounced. A number

157 of soils (Nos. 12 to 15) are located on a toposequence, whereas profiles 16 and 1 8 occur in associated positions. The calculated changes in elemental composition for the upper B and the C-horizon reveals the following:

Table 41. Cains and losses in the C or B3(s) horizon as compared to the upper B or A horizon (t)

Molar ratios

SiO2 A12O3

Profile SiO2 Fe2O3 CaO MgO K2O A12O-) Fe2O3 t s t s

14, B2-C - 5 + 59 _ 2 + 27 - 1 8.6 8.2 4.9 3.1 16, B21-C - 33 + 118 + 31 + 7 - 23 17.3 11.7 15.3 6.8 12.B21-C - 49 - 4 + 58 + 232 - 44 8.3 4.2 4.9 4.9 13, B21-C - 39 + 9 -36 + 221 - 44 13.4 8.2 5.7 5.3 15, A12-C + 163 - 62 -73 - 17 + 373 7.4 19.4 3.0 7.0 18, B21-C - 31 + 20 + 17 - 35 - 30 12.4 8.6 5.6 4.8 15, A22-B3 + 20 - 47 - 70 - 34 + 167 7.4 5.9 3.0 5.7 12, B21-B3 -26 - 8 + 4 + 152 - 18 8.3 6.2 4.9 4.5

Soils on the interfluves, such as the profiles 14 and 16, have a similar profile development as the ones in analogous position in sample area B. Noteworthy is however the increase in MgO in the B3 or the C horizon of profiles 12 and 13, presumebly caused by the (lateral) supply of weathering products from Mg-bearing minerals, such as amphibole. The specific environment in profile 15; high pH values, anaerobic conditions caused by wetness in the rainy season, may have induced the movement of SiO2 and FeO, although redistribution of only the latter was observed in thin section. The considerable increase in K2 O in the C and the B3 horizon is partly expained by the variability in the concentration of Al2 O3 in the fine earth, as such once more indicating the reservation to the use of this element as a reference. For the greater part, however, the high amount of K-feldspar (40% of the light mineral fraction) in the C and B3 horizon is the cause for the reported enrichment. The increase in sodium has led to saline/alkali conditions, such as described in Chapter II, which led is its turn to movement of plasma. Especially in the lower gley horizons of the Typic Natraqualf there is strong evidence for the illuviation of clay as well as its deformation. This is ascribed to the clay mineral composition in these sou horizons (montmorillonite and chlorite in addition to kaolinite and illite) and to animal

158 activity. In analogy to the described wetter bottom-land soils in the granitic region a redistribution of iron is visible as mottles in the field. This was confirmed in thin sections through the occurrence of pale coloured areas in the B2t horizon and accumulation of iron in nodules. The variations in iron context are rather similar to those observed by Ahmed et al. (1962). Who found an average of 2% Fe2 O3 in bleached layers and about 24% Fe2O3 in mottled horizons (see also IV.1). Modifi- cation of the soil material in the form of sesquans or ferrans was however not noticed in the thin section.

Soil transitions in sample area D differ considerable from the hitherto described ones because of contrasting parent material and drainage. As was outlined in Chapter II, the weathering products of the sills give rise on their south side to the formation of soils rich in bases, whereas soils on the north side of these sills are in general poor in bases, for example profile 21. Intensities on the element concentrations are given in table 42.

Table 42. Cains and losses in subsoil horizons (s) as compared to topsoil horizons (t) (in %)

Molar ratios

SiO2 Al2 O3

Profile SiO2 Fe2O3 CaO MgO K2O A12O3 A12O3 t s t s

19, Al-20, B12 + 33 - 15 + 74 -56 + 139 5.3 7.1 2.9 3.5 21.B1-B3 - 7 + 3 + 23 + 17 - 15 16.5 15.3 5.1 5.0 23, B21-B3 + 18 -10 + 23 n.d. + 28 6.5 7.7 3.9 4.4 24, Al-C - 11 - 14 + 469 + 13 + 30 11.4 10.2 3.9 4.5 25, A11-(II)C -20 + 24 + 47 + 21 - 49 11.6 9.3 6.0 4.9 26, A12-B2ca - 7 - 7 + 31 -25 - 10 9.5 8.8 2.8 3.0

The relative gain in K2 O in the subsoil of profile 20 is ascribed to the high percentage of K-feldspar and (weathered) biotite in this horizon. The nature of the parent material represents itself in the enrichment of CaO and MgO in most soils, where poor drainage induces the formation of mainly smectite minerals in the profiles 24 and 25. The high amount of CaO in the C horizon of profile 24 testifies to the presence of a partly consolidated CaCO3 accumulation. The development of the Rhodustalf (No. 23) is attributed to a slightly different topography, somewhat better drainage and different parent material. Under the prevailing soil climate iron is released from ferro-magnesium minerals through hydrolysis in the

159 wet season and leaching of the iron compounds as organo-metal comp- lexes may take place on a restricted scale in the topsoil horizons (SiO2 /Al2 O3 ratio in the A = 8.4 and in the B21 = 6.5). However due to little organic matter in the deeper horizons leaching is virtually stopped and the iron compounds impregnate the soil. A partial dehydration of the iron compounds is induced by the dry season, thus resulting in a reddish colour. The intensity of this process is mainly controlled by the duration and amount of precipitation. These toposequences of red and black soils are well known in the tropics. The clay mineral genesis of the members is governed by the prevailing permeability and leaching conditions, as well vertical as lateral (Mohr et al. 1959, 1972; Kantor et al. 1 972). Soil formation in sample area E is complex due to contrasting parent material and strong differences in relief. Schist forms the parent material for profile 29, the weathering products of sandstone for profile 30, metadolerite for profile 31, while the profiles 32 and 33 are situated in the granitic region of the upper catchment of the Mahalapshwe River. Variations in elemental concentration for the upper and lower soil horizons are given in the following table:

Table 43. Gains and losses in the (A)C horizon(s) as compared to the upper B or A(t) (in %)

Molai: ratios

SiO2 Al2 O3

Profile SiO2 Fe2O3 CaO MgO K2O A12O 3 Fe2 O3 t s t «

29,B21-C -62 -52 -46 +867 -73 15.2 5.8 7.7 15.8 30, A12-C - 1 - 7 - 10 n.d. - 38 100 100 3.4 3.4 31.A12-AC 0 - 1 -21 n.d. + 5 16.5 15.2 4.0 4.0 32, B21-C - 9 +17 +8 -15-17 6.4 5.8 6.4 5.5 33, Bl-C -12 +17 -39 - 76 n.d. 11.9 10.5 7.1 6.0

The enrichment of MgO in the C-horizon of the developed Alfisol, profile 29, is ascribed to lateral supply of weathering products from ferro- magnesium minerals and the high amount of weathered biotite. The small changes in the element concentration in the Entisol is inherent to its formation. The variations of the CaO concentration in the Vertisol (31) is opposite to the one encountered in the other Vertisols (profiles 24 and

160 25). This is thought due to a) the poor supply of bases from the hinterland and b) topographic position. The relatively small changes in composition are further ascribed to churning. Soils in the granitic area such as profiles 32 and 33 are similar in their development as the ones in analogous position in sample area B and C.

The clay fraction of the soils was found of special importance (Chap- ter III). From recent reports (Proc. Int. Clay Conf. Madrid, 1972) it is evident that a common numerator has yet to be found to explain the occurrence of the various clay minerals in soils. According to Millot (1972) among the three mechanisms originating clay minerals-heritage, transformations and neo-formation- the weathering zone is at first characterized by neo-formation and secondarily by transformation. Clay minerals in the investigated soils are considered to originate through the last two processes. Barshad (1969) suggests the formation of

these minerals to depend on the Al _— ,-, ratio of the medium, its v Al2 O3 + Fe2 O3 pH and the presence of bases in solution. Thus a ratio of between 2 and 4, a pH of 7 or more with a high content of Ca and Mg in solution would induce the formation of montmorillonite; the same values but with a high amount of K in solution would produce illite and a ratio of 2 or less, a pH of 7 or less with a low concentration of bases would give rise to the formation of kaolinite. If Mg would be dominant in the solution under the same conditions then vermiculite would form. No actual measurements were carried out to verify this hypothesis, however, an approach was made on the basis of the SiO2 /Al2 O3 Molar ratio and the quotient K2O + MgO + Na2O/Al2O3 of the clay fraction, to investigate the possible correlations as mentioned above. In addition the correlation between the SiO2 /Al2 O3 ratio and the pH-KCl was found to be high (r = 0.84), while the one between SiO2 /R2 O3 and pH-H2 O is also good (r = 0.81). The findings, presented in figure 47, confirm largely the theory of Barshad and accommodate the statements made in Chapter III.2.3. The SiO2/Al2O3 and the SiO2/R2O3 ratios are more than 2 in all clays. High SiO2 /R2 O3 ratios, of about 3 to 4 are encountered in the Vertisols, while lowest values are found in the Oxic Haplustalfs (ratio of about 2). The ratio decreases in all soils with depth except in the Vertisols and the Typic Natraqualf. The variation of the SiO2 /Al2 O3 ratio within and between the soils is as follows:

161 Table 44. Variation of the S1O2 /Al2 O3 Molar ratio of the clay fraction

Soil mean range Soil mean range

Vertisols 4.4 3.9-5.1 Oxic Haplustalfs 2.6 2.3-3.0 Inceptisols 3.0 3.0-3.0 Aquic Haplustalfs 3.0 2.5-3.5 Entisols (basic) 3.4 3.1-3.9 Rhodustalfs 3.1 2.7-3.8 Entisols (acid) 3.1 2.9-3.2 Ultic Haplustalfs 2.9 2.5-4.0 Typic Natraqualf 3.3 3.2-3.5 Typic Haplustalf 3.9 3.4-4.6

SiO, AI2°3 5.0 clay y =4.47 x + 2.19 r =0.88

4X3

2.5

AI 20 2°3 0 0.10 020 030 0.40 Q50 0.60 0.70 clay

,,..„„,. , . , . ., .. , .. SiO, , K,O + MoO y Na, O ,, , big. 48. Relationship between the Molar ratios . ' and —1 An — °*( tne c'ay~ fraction

162 The SiO2 /Al2 O3 ratio of the clay fraction increases in the Vertisols with depth and may increase in some Alfisols after an initial decrease. For the majority of soils however the value decreases with depth, thus confirming the findings relative to the elemental composition of the fine earth fraction. In an account on the importance of the use of these ratios to identify soil-forming processes in the (sub)tropics, Schmidt-Lorenz (1971) comments that if these ratios are more than 2, the soil material is considered "siallitic", thus indicating that the stage of weathering is not advanced enough to deplete the amount of SiO2, which concentration is still high when compared to the contents of Al2O3 and Fe2 O3. However the fairly low SiO2/R2O3 ratio may be indicative for a fersiallitic trend in the weathering of the soil materials, thus giving rise to an enrichment of especially iron in some soils. As such most of the soils developed from the crystalline rocks of Basement Complex approach the concept of Tropical Ferruginous Soils (D'Hoore, 1964; Buringn, 1970; Duchaufour, 1970). In particular the movement of SiO2 either caused by present or past processes is or great significance in the tropics and requires further considerations. As was indicated in Chapter III an increase in clay with depth is clearly noticeable in many soils and was typified as a "clay-bulge" or "clay-pyramid" distribution curve. For a number of granitic soils with such a clay distribution the gains and losses were calculated according to the principles outlined above. Considered are the top of the B-horizon and that part of the B where a maximum of clay is encountered.

Table 45. Gains and losses in the B2t horizon as compared to the B(2)l (in %)

Molar ratios (fine earth) clay percentage

SiO2 SiO2 A12O3 Profile SiO2 Fe2O3 A12O3 R2O3 Fe2O3 B(2)l B21 B(2)l B(2)l B(2)l B2t,g

3. Bl-B2t -39 + 1 13.3-- 8.2 11.4 --7.0 5.8 - 5.8 20.2 38.1 4. Bl-B2g -44 -3 10.3-- 8.0 8.5 --6.6 4.7 -4.8 25.0 43.5 12. B21-B2t -24 + 6 8.3-- 6.3 6.9 --5.2 4.9 -4.8 29.6 43.0 29. B21-B2t -32 -7 15.2-- 10.3 13.4 --9.2 " 7.7 -8.2 21.6 32.6

The data show a similar trend as those obtained from the topmost B and the B3 horizons. As can be seen from the elemental composition of the clay fraction, there is little variation in the concentration of SiO2 and Al2 O3 in the considered horizons in the same soil. In addition it was found that the amount of SiO2 and Al2O3 changed little in the non-clay

163 fraction of the horizons in the investigated soils, for example in profile 33: 83% and 83%; in profile 29: 94% versus 95%; in profile 12: 86% versus 87% and in profile 4: 94% and 96%. Taking into account that the concentration of SiO2 in the clay fraction is lower than in the non-clay fraction, it is concluded that the considerable increase in clay in the lower B causes a decrease in the amount of SiO2 in this horizon of the Alfisols considered.

The variation in soil profile development as outlined above reveals the considerable influence of the parent material and the topography as soil-forming factors. Leaching governed by rainfall, topography and drainage varied under the climatic modulations. This process was however not so intensive that it led to complete depletion of SiO2 and bases. Soils in intermediate positions in the granitic region however may show a trend into this direction as is indicated by the "Oxic" and "Ultic" subgroup nominations of a number of Alfisols. Zones of accumulation are encountered in the bottom lands of the granitic pediplain and peneplain. Soils encountered in these positions are subject to impeded drainage, which under prevailing climatic conditions may lead to the redistribution of iron. The removal of constituents is counteracted by lateral supply of bases, which in many cases provokes the neo-formation of clay minerals. In extreme conditions, the excess of sodium in particular, may induce salinity. Higher clay percentages in the B horizon of Alfisols are only partly caused by accumulation through clay migration. This process is limited at present and probably was at a maximum in the past. The formation of clay in situ in thought to be an important factor to the clay increase as noted in many hydromorphic Alfisols. The presence of argillic horizons in soils that have at present a very dry moisture regime, indicates that the climatic conditions preserve rather than destroy these features. The pronounced dry season impels the formation of voids in the soils, a development enhanced by animal activity. The mass movement of soil material caused by heavy and erratic rainfall is thus made possible. The presence of iron enriched material of the C and B3 horizons in granitic soils at flat position on the present interfluces is furthermore an indication of other conditions than encountered today. Also the release of calcium from the doleritic rock and its subsequent accumulation at the base of the zones of departure (the doleritic hills) points to more favourable leaching conditions than met with nowadays. The poor drainage of the clay soils in the present position further lessens the removal of this constituent from these soils.

164 The enrichment of potassium and ocasionally magnesium in some subsoils is associated with the high amount of orthoclase and weathered biotite in these horizons. In the sense of Ruellan (1971) many soils contain relicts, especially those that have known a wetter soil moisture regime. However sharp transitions between the various horizons are mainly restricted to the B3 en C horizons; in the remaining part of the solum gradual transitions prevail; indicating the homogeneous and far reaching development of the soils. In general it is thought that the processes that induced these relicts have weakened rather than that they have stopped altho- gether or have been replaced by controversial ones.

165 CHAPTER VI.

SOIL CLASSIFICATION AND LAND USE

VI. 1. Soil classification

The approach to the classification of soils according to the absence or presence of diagnostic horizons is based on the classical concepts on soil formation. These concepts were conceived in Russia and documented by Dokuchaev in 1886 (Tiurin, 1965), while during the same period (1892) E. W. Hilgard made known similar ideas on soil formation and classification in the United States (in Jenny, 1961). Continued research on and surveys of soils, especially in the Western Hemisphere, led to a better understanding of soil forming factors and subsequently to improved definitions of units of various soil classification systems. That soil developed as a result of the interaction of a number of factors, such as climate, parent material, vegetation, topography and time, was clearly recognized by Jenny (1941), and this synthesis was admirably applied by Mohr and Van Baren in their studies of soils in Indonesia (1959). The publication of the 7th Approximation in 1960 by the Soil Survey Staff of the USDA introduced another dimension to the existing systems of soil classification, namely clearly defined morphometric criteria to identify the various diagnostic surface horizons (epipedons), as well as a number of diagnostic subsurface horizons. The principles of the system are universally applicable, thus providing a first outline for an international classification system as well as procuring a basis for world-wide soil correlation (Smith, 1965). That the system is subject to critisism, not only because of its linguistic ingenuity, but also with regard to its multiple attributes and class structure (Webster, 1968), would be foreseen. In reviewing the system, Cline (1963) points out the genetic aspects in relation to soil properties when he says, "soils thought to have had similar genesis are placed in the same group; the groups are defined in terms of soil properties ..." and further "thus the basis on which the classes have been formed are genetic considerations while the criteria by means of which the classes are differentiated are soil properties." Similar systems were brought out by the FAO/UNESCO (1968, 1970) in an attempt to correlate the different soil classification systems throughout the world in order to establish a legend for the Soil Map of the World. Regionally, the study of Van der Eyk et al. (1969) focusses attention on

167 Table 46. Soil Classification and Correlation

Profile Order Subgroup Family FAO/UNESCC No.

1 Alfisol Ultic Haplustalf siliceous, fine loamy Chromic Luvis 2 Alfisol Ultic Haplustalf siliceous, coarse loamy Ferric Acrisol 3 Alfisol Ultic Haplustalf siliceous, fine loamy Chromic Luvis 4 Alfisol "Aquic" Haplustalf kaolinite, clayey Gleyic Luvisol 5 Inceptisol Lithic Ustropept siliceous, coarse loamy, Dystric Cambi: shallow 6 Alfisol "Aquic" Haplustalf siliceous, fine loamy Gleyic Luvisol 7 Alfisol Ultic Haplustalf siliceous, coarse loamy Orthic Luvisol 8 Alfisol Aquic Haplustalf silieceous, fine loamy Gleyic Luvisol 9 Alfisol "Aquic" Haplustalf kaolinite, clayey Gleyic Luvisol 10 Alfisol Typic Rhodustalf siliceous, fine loamy Chromic Luvisi 11 Alfisol Oxic Haplustalf siliceous, coarse loamy Orthic Acrisol 12 Alfisol Ultic Haplustalf kalinite, clayey Chromic Luvisi 13 Alfisol Ultic Haplustalf siliceous, fine loamy Chromic Luvisi 14 Alfisol Ultic Haplustalf siliceous, coarse loamy Chromic Luvisi 15 Alfisol Typic Natraqualf siliceous, fine loamy Gleyic Solonet 16 Entisol Typic Ustrorthent siliceous, sandy Cambic Arenos 17 Entisol Lithic Ustipsamment siliceous, sandy, shallow Dystric Regoso 18 Alfisol "Aquic" Haplustalf siliceous, fine loamy Gleyic Luvisol 19 Entisol Lithic Ustorthent montm., clayey, micro Lithosol 20 Inceptisol Udic Ustropept siliceous, coarse loamy Chromic Camb 21 Alfisol Ultic Haplustalf siliceous, coarse loamy Orthic Acrisol 22 Vertisol Typic Pellustert mont., clayey, calcar. Pellic Vertisol kaolinite, clayey Chromic Luvis( 23 Alfisol Udic Rhodustalf 24 Vertisol Typic Chromustert montm., clayey, calcar. Chromic Luvisc montm., clayey Pellic Vertisol 25 Vertisol Typic Pellustert siliceous, fine loamy Chromic Luvisc 26 Alfisol Typic Haplustalf calcareous 27 Entisol Lithic Ustorthent montm., clayey, shallow Lithosol 28 Entisol Lithic Ustorthent mont., clayey, shallow, Lithosol calcareous 29 Alfisol Oxic Haplustalf siliceous, fine loamy Orthic Acrisol 30 Entisol Typic Ustipsamment siliceous, sandy Cambic Arenos 31 Vertisol Entic Chromustert mont., clayey, calcar. Chromic Vertis 32 Alfisol Oxic Haplustalf kaolinite, clayey Ferric Luvisol 33 Alfisol Ultic Haplustalf siliceous, coarse loamy Ferric Luvisol

168 the application of the concept of diagnostic horizons to local conditions. Prior to the work carried out by this author this new approach had not been applied in Botswana. Previous soil classification systems used in the country by Van Straten (1959), Van Straten and De Beer (1959), Bawden and Stobbs (1963) and more recently by Blair-Rains and McKay (1968) are mainly derived from the system developed by D'Hoore (1954). Many of the older classification systems are still extremely valuable although they may not do enough justice to the fact that the soil is an intergrated part of the biosphere. (UNESCO, 1968). In the following paragraphs the latest issue of the 7th Approximation is employed (1970) while correlations are made with the FAO/UNESCO system (1968, 1970) and other soil classifications if found necessary. It is not the intention to repeat all the differentiating criteria of the classification, but to point out some characteristics relevant to the soils. Useful information relative to the agricultural use of the soils may be gathered from the classification on Family level. Comprised information on the classification of the studied soils is given in table 46. Four soil Orders were distinguished: Entisols, Vertisols, Inceptisols and Alfisols

Entisols are mineral soils that show little or no evidence of development of pedogenic horizons, other than an Ochric epipedon or Histic epipedon or an Albic or Spodic horizon with or without a salic horizon, sodium saturation of 15% or more, a calcic or gypsic horizon, plinthite, buried diagnostic horizons or ironstone. The occurrence of Entisols in the area is attributed to the nature of the parent material, and not to the recent age of the material in which they are encountered. The parent material consists mainly of quartz grains resulting in coarse textured soils. The latter is the main criterion for the subdivision of this Order on suborder level, dividing the very coarse textured ones (Psamments) from the coarse loamy and loamy ones without further differentiation (Orthents). Soil depth and soil moisture regime further determine classification on the lower levels. The Vertisols are mineral soils that have no lithic, paralithic contact or petrocalcic or duripan within 50 cm of the soil surface and have: a) 30% or more clay in all subhorizons down to 50 cm or more after the upper 18 cm are mixed, b) at some periods in most years, cracks that open at the surface and are at least 1 cm or more wide at 50 cm depth, unless irrigated, c) gilgai and/or slickensides at some depth between 25 and 100 cm and/or wedged-shaped natural structural aggregates with their long axes tilted 10 to 60 degrees from the horizontal. In the area under consideration, the Vertisols are developed from rock

169 rich in bases and have inherited most of their properties from the rock weathering products. Environmental conditions led to the formation of dominantly montmorillonitic clay minerals. The Vertisol Order is subdivided according to a certain rhythm subject to the opening and closing of cracks and the soil moisture regime. The soil colour provides further divisions on the lower levels (Great Group). Thus Pellusterts have chroma of less than 1.5 in some part of the matrix and of the upper 30 cm in more than half of each pedon. Chromusterts have a moist chroma equal or superior to 1.5. In large parts of Southern Africa these soils are classified as Subtropical Black Clay Soils (Van der Merwe, 1969). Inceptisols are mineral soils with altered horizons that have lost bases or iron and aluminium but retain weatherable minerals, and that lack illuvial horizons either enriched with silicate clays that contain aluminium, or those enriched with amorphous mixtures of aluminium and organic carbon. In the study area these soils have an Ochric epipedon overlying a Cambic horizon. They are classified as Tropepts on basis of the soil temperature regime and are subdivided on a lower level on basis of the soil moisture regime and the occurrence of a lithic contact. One profile was considered to belong to the not yet defined "Udic" subgroup in analogy to its use in the Alfisol Order. These soils are tentatively correlated with the Grey Ferruginous Lateritic soils as described by Van der Merwe (1969). Alfisols are mineral soils that have an argillic horizon or a natric horizon and have a base saturation by sum of cations that is 35% or more at a depth of 1.25 m below the upper boundary of the argillic horizon or 1.8 m below the surface of the soil, whichever is shallower. Most Alfisols encountered are classified as Ustalfs because of their present soil moisture regime and the properties of the epipedon. As in other parts of the world, these soils tend to form a belt between the Aridisols on the one side, and the soils of warm humid regions on the other side. On Great Group level the soils are classified as Haplustalfs. Their definition reads that they are freely drained, moderately deep to deep soils with an argillic horizon of loamy or clayey particle-size, some 2 : 1 clay minerals and a high base saturation. On subgroup level the Ultic, Oxic and Aquic adjec- tives were appropriate to distinguish soils from the central concepts of the Typic Haplustalfs. The Ultic Haplustalfs refer to those soils that do not have a base saturation percentage in the argillic horizon of 75% or more in some part, and/or have no calcic horizon or soft powdery lime within a certain depth. The Oxic Haplustalfs have less than 24 meq cation exchange capacity per 100 g clay (with reservation to the cation retention from NH4Cl, that was

170 not determined). The definition for the Aquic subgroup is fully condi- tioned in profile 8, but is not satisfied for Haplustalfs in similar topographic position such as profiles 4, 6, 9 and 18. Differences with the original concept of "Aquic" are minor however. For example, in profile 4 mottles with chromas of 2 or less occur at a depth of 78 cm instead of 75 cm. Therefore the soils with gley horizons are indicated as "Aquic" in the text. Based on the colour of the matrix and associated mottles one Aqualf was recognized, which because of its natric horizon is classified as a Typic Natraqualf (profile 15). Rhodustalfs are differentiated on basis of their red colour. Two soils were thus classified (profiles .1.0 and 23). The Udic subgroup notation for one of them refers to the presence of a calcic horizon or soft powdery lime.

VI. 2. Land use

At present the majority of the land in the investigated area is used for grazing while subordinate parts are cultivated under rainfed conditions. In the past, however, cropped areas occupied a fairly large acreage despite the fact that most preparing of the land was done by hoe (Fosbrooke, 1972). The main crops included sorghum, melon, pumpkin and at present also maize, groundnuts and beans. Little was done to maintain the fertility of the soil in the early days of the settlers, who for the largest part came from South Africa. The departure of a large number of inhabitants from the Shoshong area in the latter half of the last century is partly attributed to the depletion of the soil and the shortage of water. Water is still the crucial factor for the development of the land. The unreliability of the rainfall (Chapter I) does not encourage the cultivation of crops on other than subsistence level. The holding of cattle is more appropriate to the environment although their number is restricted not only by the grazing potential of the land, but also by the availability of watering points and their location. Water assessment studies in the area are not optimistic with regard to a large aquafer that as yet may be tapped for domestic, agricultural and industrial use (Hyde in Fosbrooke, 1972). The complexity of land development is not only caused by physical factors, but even more so by human attitudes and economic considerations. Although difficult to evaluate, the attitude of the population towards development is of great importance and its misjudgment had led to failure of many a scheme. The economic factors are readily comprised in the terms "input" and "output" such as proposed for the development of a land utilization system, instigated to embrace all factors relevant to the development of a certain area (FAO, 1972; Beeketal., 1972).

171 The subject under study concerns physical factors of the land only, as explained in the preceding chapters. During a semi-detailed soil survey of the Shoshong area particular attention was paid to a number of physical soil factors such as soil depth (d), soil texture (t), drainage (w) and erodability or effects of past erosion (e). Chemical analyses completed the picture relative to the elemental composition of the soils, their exchange phenomena, fertility level, salinity problems and related characteristics and properties. In dealing with some of the main aspects of land use the division in landscapes as outlined in Chapter II is appropriate. In sample area A, for the most part sufficient soil depth is observed inherent to the soils developed on the pediment. The texture of some soils may not be optimum with regard to the water holding capacities, whereas exchange capacities are variable, being closely related to the amount of clay. Soils in the depressions, such as in profile 4, may be subject to a water surplus during the rainy season, whereas in addition salinity and clay mineralogy do not encourage cropping in these areas. Most soils in sample area B have a limited soil depth due to erosion or shallow profile development. However, in this area belonging to the granitic peneplain, the slightly lower parts have a greater soil depth, in addition to a better soil moisture regime. Gley features in these soils are expressed, but often not clearly, within 60 cm of the surface thus indicating a reasonable part of the soil to be suitable for plant root penetration. Areas in the immediate vicinity of profiles 8 and 9 have a regular cropping schedule. In this region especially the danger exists that, through the pressure on the land, less suitable soils may be included in the cultivation pattern, thus increasing the hazard of soil erosion and land misuse. In the more eroded part of the catchment area, sample area C, some cultivation is being carried out at present on parts of the broad interfluves; however the greater part of this area is mainly suitable for cattle. In addition to the problem of soil conservation there is another factor, namely the accumulation of salts in the lower lying areas. The saline areas occur in patches which makes a precise location of them is necessary. Moreover, the workability of the bottom-land soils is limited due to the presence of 2 : 1 clay minerals in addition to the fine texture of the soils, causing poor drainage and a surplus of water over prolonged periods. Much erosion is observed along old paths or cattle tracks. In several instances roads had to be re-routed, because gullies and exposed rock had made them impassable. Soil transition is fairly gradual in this area, with exception of the boundaries between the soils of the slopes and the ones of the valley floors. This picture is further complicated in sample are D, where the black clay soils of the Bonwapitse flood-plain are associated with similar or reddish soil on the pediment. Soil boundaries are sharp and clearly visible on the aerial

172 photographias well as otherwise. Only the soils which are fairly easy to work arc being cultivated at present, although there are indications that in early times the finer textured soils were cropped. The latter can be managed only with the right amount of moisture, i.e. when of a friable consistency. The Vertisols however offer excellent possibilities for grazing as the grass cover is fairly thick and rejuvenates soon after the dry season. The sandier soils on the pediment in certain localities have potential for cropping but need special crops that mature and ripen in a short time, before the soil dries out (fig. 49). The infiltration rate of most of these soils is such that a reasonable amount of water can be stored at greater depth on condition that it is consumed fairly quickly. The depletion of soil fertility seems to be the foremost reason for the abolishing of a number ol fields, on most of the sandly or coarse loamy Haplustalfs. Sample area E is used for pasture, mainly because the area is too far away from population centers to make cropping a feasible proposition. Of special interest is the sandy soil of the Kalahari, as such and similar soils cover a tremendous acreage in the interior of the country. As was shown in the investigations, the soil is poor in almost all substances that

tig. 49. Poor sorghum crop on an Ultic Haplustalf (coarse loamy), in the background the Marutlwe Hill.

]73 are needed kir plant growth. Thanks to its particular texture it is never- theless capable ot holding ;i fairly larme amount or water for a given time. Tliis allows decprooted plants to survive in the semi-arid conditions. Thus one point in the soil to its favour is its depth. Soils similar to the described PsammctK, but of a coarse loamy texture arc reported to sustain a fairly high yield under minted conditions and with some application of fertilizer. One aspect is the problem of wind erosion which deserves special consideration. Windbrakes arc a must, unless very small areas arc cropped. One property of most of the granitic soils is the hia;h amount ot quartz present which caused plow shares and other farm equipment to blunt in a short time. The data on the soil fertility indicate that the amount of nitrogen is low, whereas potassium is slightly higher. Available phosphorous was also found to be extremely low. The application of compound fertilizer yielded good results under sufficient precipitation, but if the rain fails or is not adequate for the crop to mature or even for the seeds to germinate, much effort is in vain. Experiments carried out by the FAO/UNDP in analogy to but on a broader basis than some local farmers, showed high yields under irrigation on coarse and fine loamy Haplustalts. thus in a way creating an additional controversial viewpoint, concerning priorities as to the use of water. Considering the physical factors of the area, emphasis should primarily be brought on beef production in combination with subsistence farming in smaller areas The delicate balance between the use and misuse ot the soil is a challenge to those who depend directly upon it for their existence. An exact appreciation of this equilibrium, which so much reflects the situation in the biosphere, should also be a major issue to all who might tend to forget the fundamental importance of soil for life.

174 APPENDIX I.

METHODS

I.I. Survey methods

1.1.1. Office methods A first impression of the area was obtained from aerial photographs (scale 1 : 40.000), looked at through a Wild stereoscope. The photographs were printed on glossy, double-weight paper. Landforms, geology and vegetation formed the basis for areas in which different soils were expected. These were outlined on the photographs with wax pencil. Map legends were finalized after field surveys and a first draft of the soil map prepared on an uncontrolled mosaic, after which additional field checking procured the final legend and map.

1.1.2. Field methods Soils were studied in the field in soil pits, road and river cuts and from material brought up by soil auger. Soil pits were 2 m deep unless a (para)lithic contact was encountered within this depth. The length of the pit was orientated to the North. The river-side or Thompson auger with a core diameter of about 7.5 cm was frequently used. Auger observations were set through to 125 cm but occasionally deeper if thought necessary. Soil descriptions were based on the FAO Guidelines for Soil Description, the Munsell Soil Colour Charts were used for the colour identification. Samples were exclusively taken from soil horizons as visible in the pits. Soil observations were made within the units as outlined on the aerial photographs and followed no fixed grid pattern. The density of observations is about one per hectare. Vegetation counts were carried out by Van Rensburg (1971) on a quadrant basis set up around each soil pit. Most of these data are summarized in Chapter 1.4. The survey procedure follows largely the suggestions made by Vink (1963).

1.2. Laboratory methods

1.2.1. Particle-size analyses The determinations were carried out on the fine earth of all samples by the pipette method and by sieving. Air dry samples were gently crushed, if necessary, and subsequently sieved through a 2 mm sieve. Particles coarser than 2 mm were retained and indicated as coarse fragments. Of the remaining material 20 g was used for the particle-size analyses. Organic matter was removed through treatment with H2O2; carbonates and iron coatings were destroyed by 0.2 N HC1. The thus created soil pastes were neutralized by successive washing with distilled water and wet sieved through a 50 micron sieve into a 1000 ml cylinder. A solution of 0.1 Mol. sodium-pyrophosphate and 0.04 Mol. sodium carbonate was used as dispersion agent. The cylinders were topped up to 11 mark with distilled water and thoroughly shaken for good dispersion. The size analyses determination continued than according to standard procedures. For clay mineralogical analysis samples of the fraction smaller than 2 micron were obtained from not pre-treated soil. Dispersion was obtained with the solution as mentioned above, while subsequent precipitation was induced by adding a solution of 1.4 N Ca-acetate and 0.3 N acetic acid. The main particle-size nomenclature is obtained from the USDA system with additonal limits at 500, 200, 100 and 20 micron.

175 ƒ.2.2. Determination of the pH-water and the pH-KCl The soil was shaken for two hours with distilled water or 1 N KCL in a 1 : 5 soil-water ratio c.q. 1 N KCl mixture. Readings were done in the suspension with a pH meter with glass electrode on all soil samples.

1.2.3. Bulk density value Undisturbed soil clods of about 7 g were taken from 46 samples. The paraffine wax method was used as coating material (Black, 1965) for the volume-weight determination; the results are presented in g/cm .

1.2.4. Water soluble salts and ions in soil-water 1 : 5 extract The soil was shaken with water (soil-water ratio 1 : 5) for two hours and the extract obtained by filtration. Salt content (EC5 ) was measured by electrical conductance with a conductivity meter, results expressed in mmhos/cm at 25 C. The following ions were determined: calcium, sodium, potassium, magnesium, (bi) carbonate, chloride, sulphate and nitrate. Ca, Na and K were determined by flame ; photometer and the Mg colorimetrically with thyazol yellow. The amount of (bi) carbonates is determined by titration with 0.1 N HC1; chloride is measured with a "Chlor-o-counter" (Marius), nitrate is determined colorimetrically with brucine and sulphate turbidimetrically. These analyses were carried out on 41 soil samples which had an EC5 of 0.1 mmhos/cm or higher, results are expressed in meq/100 g soil on an oven-dry basis. \

1.2.5. Water soluble salts and ions in the saturation extract Water was added to the soil till a saturated paste was obtained. An extract was obtained by centrifuging with a high speed centrifuge. In the extract the ECe was measured with a conductivity meter and results expressed in mmhos/cm at 25 C. Ca, Na and K were determined by the flame photometer and Mg colorimetrically with thyazol yellow; carbonate and bi-carbonate and chloride were determined titri- metrically and sulphate determination was done turbidimetrically. These analyses were carried out on 10 samples all having a EC5 of 0.5 mmhos/cm or more. The results are expressed in meq/1.

1.2.6. Phosphorous determination The method as outlined by Olsen was followed. The soil was shaken with 0.5 Mol. NaHCO3 for 30 minutes in a 1 : 20 soil-water ratio. In the extract, obtained by filtration of the suspension, P was determined by means of molybdenum blue/ascorbic acid. The results are given in ppm.

1.2.7. Free calcium carbonate determination The fine earth fraction was subject to treatment with 20% HCL, and the soil was then shaken for 1 hour in a "Scheibler" apparatus and the volume of evolved CO2 was measured. Results are given as %CaCC>3 of oven-dry soil, however MgCC>3 may also be present.

1.2.8. Organic carbon determination The soil organic matter was oxidized with potassium-di-chromate and sulphuric acid without application of external heat (Walkley-Black method). The amount of potassium-di-chromate used was determined by titration with ferrous sulphate. According to Jackson (1969) only 77% of the carbon in the organic matter is oxidized as compared to the dry combustion method, for most soils of the temperate humid zone.

176 Usually the factor 1.3 is therefore applied to calculate the amount of organic carbon. The organic carbon percentage was determined on all soil samples.

1.2.9. Percentage nitrogen determination The micro-Kjeldahl method was followed, the results are expressed as %N in oven-dry soil. The analyses were carried out on all topsoil and some subsoil samples, as the percentage was found to be extremely low in the deeper soil horizons.

1.2.10. Exchangeable metallic cation determination The soil was mixed with purified sand and put into percolation tubes and leached with 50% alcohol to remove the water soluble salts. Subsequently the soil was percolated with IN NH4 acetate 96% alcohol (1 : 1) atpH 8.2. In the leachate Ca, K and Na were measured by flame photometer, while for Mg the colorimetric thyazol yellow method was used. The results are expressed in meq/100 g soil on an oven-dry basis.

1.2.11. Cation exchange capacity determination Following the treatment of the soils as outlined under 1.2.10., the soil material was percolated with IN Na-acetate of pH 8.2 to saturate the soil complex with sodium. The excess sodium was then washed out one or more times with 96% alcohol. Lastly the absorbed sodium was replaced by leaching with IN NH4-acetate of pH 8.2. The absorbed sodium was then determined in the leachate by flame photometer. The results in meq/100 g of oven-dry soil give the CEC value at the equilibrium pH of 8.2.

1.2.12. Heavy and light mineral analysis Pre-treatment with H2O2 and HCl was carried out on 50 g of the bulk fine earth. Samples of the 50 to 200 micron sand fraction were obtained, as it appeared that the coarser sand yielded virtually no heavy residue. This material was cone-quartered down to amounts required for separation by bromoform (s.g. 2.89) and for mounting of the mineral grains on slides. Determination and line countings of the mineral species were carried out by means of polarizing microscope according to the methods as outlined by Kerr (1959) and Milner (1962). Of the heavy fraction the mutual percentage of opaque and transparant grains were determined first and subsequently 100 transparent grains identified; of the light minerals 100 grains were counted per sample.

1.2.13. Preparation of thin sections The procedures for the preparation of thin sections follow the outlines by Jongerius and Heintzberger (1964). The unsaturated polyester resin synolite 544 was used for impregnation. Samples were sawn and polished to a thickness of about 15—20 micron. Investigations on 20 mammoth-sized thin sections were done by means of transmutent and polarized light through a Leitz Orthoplan microscope.

1.2.14. Clay mineralogy Material from the not pre-treated clay fraction (see 1.2.1.) was dried either in a stove at 40 C or freezedried, and if necessary, ground. Random powder specimen of all samples were analysed using Philips X-ray diffraction equipment consisting of: a generator control cabinet (PW 1320/00), a stabilized generator (PW 1310/00) with wide range goniometer (PW 1050/25), a basic recording unit (PW 1352/10) with sealer-time combination (PW 1353/100) and a pulse height analyses combination (PW 1355/10).

177 The experimental conditions to obtain the pen-recorded X-ray diffractograms are: radition: CoKa detector: proportional detector probe High voltage: 35 kV scanning speed: 1° (20) per minute current: 30 m A full scale: 400 counts per second filter: Fe time constant: 2 seconds divergence slit: 1 sample holders: flat aluminium holder or glass slides receiving slit: 0.3 mm scatter slit: 1

Additional diffraction data were obtained from 29 parallel orientated specimens. The saturation with Mg and ethylene-glycol solvation, and saturation with K for heating treatments, were performed according to procedures outlined by Jackson (1969).

1.2.15. Elemental analysis The concentration of 17 elements was determined with X-ray spectrometric analyses and atomic absorption spectrophotometer investigation. Determined with the former technique were the oxides of the elements: Si, Al, Fe, Ti, Ca, Mg, K, Na and P. The following trace elements were determined by means of the latter method: Mn, Cu, Zn, Cr, Co, Ni, Ba and Sr. The analyses were carried out on the fine earth of all samples, while in addition, the oxides of the major elements were determined on 85 samples of the clay fraction.

1.2.16.a. X-ray fluorescency determination Analyses of the major elements were done by means of a Philips 1410 X-ray spectrometer with chrome tube consisting of the same basic units as described in 1.2.14. The results were recorded on paper tapes for computer analyses by means of a Tape Punch Control (PW 4206/01). To prepare the sample for analysis 4—6 g of the air dry sample was heated at 900 C for two hours and the loss on ignition calculated. From this sample 400 mg was taken to which as added LiOH and B2O3. The fusion reaction was made at 1300 C in a furnace in which the crucible made of platimum +3% gold was plced. The thus homogenized soil material was retrieved as a solid button on cooling. The sample flux ratio is 1 : 10. The experimental conditions may be summarized as follows: element 20 position crystal collimator pre-set time (seconds)

Na background 54.00 KAP coarse 100 standard, 40 sample Na peak 53.10 KAP coarse 100 standard, 40 sample Mg background 44.50 KAP coarse 100 standard, 40 sample Mg peak 43.50 KAP coarse 100 standard, 40 sample P background 90.50 PE coarse 40 standard, 10 sample Ppeak 89.30 PE coarse 40 standard, 10 sample Si peak 108.95 PE coarse 10 Al peak 144.75 PE coarse 10 K peak 136.70 LI F fine 10 Ca peak 113.15 LIF fine 10 Ti peak 86.18 LIF fine 10 Fe peak 57.52 LIF fine 10

178 The element concentration is calculated according to the formula: 9 f = i Mi.jl * C(j)U C(i) = [I(i) - B(i)] x K(i) x Ve x 100 + L Ve J in which: C = concentration i = number element I = peak intensity ) corrected for Dead Time B = background intensity ) K = apparatus constant, determined on samples with known concentration Ve= dilution of sample ai,j = correction factor (influence of element j on the measurement of element i) Cj = concentration of element j In first approximation Cj = o, in the second approximation Cj = Ci of the first approximation. The complete procedure to obtain the concentrations of the various elements by means of a computer programme, was developed by De Rooij (1973, in preparation).

I.2.16.b. Atomic absorption spectrophotometrie The method of analyses was outlined by De Vries (1971), the procedures applied were verified through analysis of U.S. Geological Survey rocks (second series; Flanagan, 1969), which are used as geo-chemical standards. Part of the fine earth of each sample was cone-quartered twice down to 20 g, this was subsequently crushed in an agate mortar. From it 500 mg was taken for analysis. The Na2CO3—Na2B4O7 fusion technique was used to prepare the soil sample for flame analysis. The sample was subsequently dissolved in acid solution according to Meyer and Koch (1959) and was shaken mechanically at room temperature to prevent coagulation of SiC>2. Lanthanum was added to 1% of the solution to be analysed to prevent chemical interferences. A Techtron Model AA4 spectrophotometer was used, consisting of the following major units: a) set of hollow cathode tubes, one for each element, as light source emitting the sharp-line spectrum of the element to be determined; b) a premix burner, featuring a burner chamber in which sample, fuel and oxidant are mixed before entering the flame where atomic vapor of the sample is produced; c) an Ebert type monochromator as wavelength selector, which can be set to pass any wavelength of about 1.860 to 10.000 Â; mechanical slits open to a maximum width of 300 micron; d) a HTV photomultiplier type R 213, whose output is fed into a A.C. amplifier whose signal is rectified and fed to a galvanometer as read-out mechanism, coupled to a 1 mV Hitachi recorder. The concentration of the elements in a sample measured from the atomic absorption followed the addition method of Zeegers (1959).

179 The experimental conditons are summarized as follows: element cathode current absorption flame fuel oxidant mechai (+ auxiliary current) wavelength slit wie mA Â u

Mn 10 2.795 oxidizing C2H2 air 100

Cu 4 3.247 oxidizing C2H2 air 50

Zn 6 2.139 oxidizing C2H2 air 300

Cr 10 3.579 oxidizing C2H2 air 100

Co 10 (+400) 2.407 oxidizing C2H2 air 25 Ni 10 (+400) 2.320 oxidizing C2H2 air 50

Ba 10 5.536 reducing C2H2 N2O 50

Sr 10 4.607 reducing C2H2 air 100

1.2.1 7. Electron microprobe analysis These analysis were carried out on selected areas of thin sections from the samples 7.20 and 8.55, with a Cambridge apparatus (type Geoscan) according to methods outlined by Veen and Maaskant (1971).

180

APPENDIX II

SOIL PROFILE DESCRIPTION AND LABORATORY DATA

DESCRIPTION OF PROFILE NO. 1

Al 0-20 cm Dark brown (7.5YR3/2) moist and dry, slightly gravelly coarse sandy loam; structureless; dry loose, moist slightly friable, wet non-sticky and non-plastic; common fine roots; smooth gradual boundary; (sample 1.11),

B21 20 — 60 cm dark reddish brown (5YR3/3) moist, reddish brown (5YR4/4) dry, slightly gravelly sandy clay loam; structureless; loose dry, friable moist, slightly sticky and slightly plastic wet; few fine roots; gradual smooth boundary; (sample 1.12),

B22 60 — 110 cm reddish brown (5YR4/4) moist and dry, slightly gravelly sandy clay loam; structureless; consistence as horizon above; increase of coarse fragments with depth; (sample 1.13).

Note: blocked by coarse gravel or boulders at 110 cm.

182 Laboratory data of profile No. 1

Particle size distribution (/i) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 20Q- FÖcT 50- 20- <2 pH l : 5 No. in cm. zon mm. 500 200 100 50 20 2 H2O KC1

1.11 0- 20 Al 9.0 33.5 23.3 15.6 8.3 5.4 4 .0 9.9 6.8 5.4 1.12 20- 60 B21 5.2 25.0 18.2 14.9 8.0 6.9 4.2 22.8 6.7 5.1 1.13 60-110 B22 8.6 20.9 15.9 12.9 8.2 6 .5 5.9 29.7 7.1 5.5

Sample Exchangeable cations in meq/100 g C.E.C. Base P2O5 Organic matter No. Ca Mg K Na Sum sat. (%) ppm %C %N

1.11 2.52 0.49 0.31 tr 3.32 6.10 54 8 0.47 0.06 1.12 4.56 1.06 0.31 tr 5.92 8.78 68 2 0.45 0.05 1.13 8.16 1.54 0.37 tr 10.07 12.20 83 2 0.29

Sample Elemental Composition of the fine earth (% by weight) No. Sum SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2o Na2O P Os Loss on ' ignition %

1.11 73.0 13.6 4.4 0.45 1.93 0.76 4.37 1.58 0. 15 100.1 3.2 1.12 70.4 16.0 5,0 0.65 1.74 0.69 4.71 1.40 0.09 100.8 4.9 1.13 69.5 15.7 4.5 0.54 1.35 1.97 4.37 1.14 0. 11 99.2 5.2

Sample Trace element content of the fine earth (in ppm) SiO SiO2 A12O3 No. Mn Cu Zn Cr Co Ni Ba Sr Al. .o, R2O3 Fe2O3 1.11 280 < 5 21 256 24 10 400 50 9.1 7.68 4.9 1.12 320 42 37 112 12 50 540 58 7.5 6.21 4.9 1.13 374 34 40 112 6 28 940 65 7.5 6.35 5.5

Elemental composition of the clay fraction (% by weight)

Sample SiO2 Al. Fe2O3 TiO2 CaO MgO K2O Na2O P2O5 No.

1.11 47 .3 27.2 11 .6 1.46 4.21 1.96 2.50 0.00 3.84 1.13 49 .8 29.8 12 .1 1.42 1.70 2.21 2.09 0.00 0.93

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi Q SiO2 SiO2 A12O3 No - ÄL^3 R^)3 Fe2O3

1.11 + X 3.0 2.32 3.7 1.12 ++ + X 1.13 ++ + tr tr tr 2.8 2.25 3.9

183 DESCRIPTION OF PROFILE NO. 2

Al 0 — 23 cm Dark brown (7.5YR3/2) moist and dark greyish brown (10YR4/2) dry, loamy coarse sand; weak fine subangular blocky structure; firm dry, loose moist, non-sticky, non- plastic wet; abundant fine and medium roots; common fine and medium pores; smooth gradual boundary; (sample 2.25),

Bl 23 - 39 cm brown (7.5YR4/3) moist and (7.5YR5/3) dry, loamy coarse sand; structureless; very hard dry, friable moist, nonsticky and non-plastic wet; common fine and medium roots; common faint fine and medium strong brown (7.5YR5/6-dry) mottles; common fine and medium pores; smooth gradual boundary; (sample 2.26),

B21 39 — 62 cm brown (7.5YR4/4) moist and light brownish grey (10YR6/2) dry, coarse sandy loam; structure and consistence as horizon above; few fine and medium roots; common fairly distinct strong brown (7.5YR5/6-dry) mottles; smooth gradual boundary; (sample 2.27),

B22 62 - 88 cm brown (7.5YR4/3) moist and pale brown (10YR6/2) dry, fine gravelly coarse sandy loam; structure and consistence as Bl; few fine and medium roots; common fine and medium strong brown (7.5YR5/6) and yellowish red (5YR4/6) mottles; common fine and medium pores; smooth gradual boundary; (sample 2.28),

B23 88 - 120 cm brown (7.5YR4/3) moist and pale brown (10YR6/3) dry, slightly gravelly coarse sandy loam; structureless; slightly hard dry, friable moist, non-sticky and non- plastic wet; very few fine and medium roots; common prominent dark red (2.5YR3/6) mottles; common thin broken cutans; common fine and medium pores; amount of coarse fragments increasing with depth; smooth gradual boundary; (sample 2.29),

B3 120 - 145 cm brown (10YR5/3) moist and pale brown (10YR6/3) dry, gravelly coarse sandy loam; structureless; consistence as B23; faint reddish mottling; abrupt smooth sloping boundary; (sample 2.30),

(II)C 145+ cm coarse to very coarse subrounded quartz gravel; (no sample taken).

184 Laboratory data of profile No. 2

Par % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H2O KC1

2.25 0- 23 Al 1.9 43.9 23.6 12.0 6.7 3.1 4.6 6.1 6.5 5.0 2.26 23- 39 BI 2.3 34.9 23.5 14.5 9.5 4.1 5.6 7.9 6.4 4.6 2.27 39- 62 B21 2.0 35.8 23.8 13.6 6.4 4.8 5.6 10.0 5.7 4.2 2.28 62- 88 B22 7.8 38.4 19.6 11.2 4.8 4.3 5.8 15.9 5.6 4.0 2.29 88-120 B23 7.0 36.3 18.9 8.7 5.9 3.9 5.5 20.8 5.7 3.9 2.30 120-140 B3 14.7 35.6 20.1 10.1 7.4 4.4 5.6 16.8 6.0 4.1

Exchangeable cations in meq/100 g Organic Matter

Sample Ca Mg K Na Sum C.E.C. Base P2OS % C % N No. sat. (%) ppm

2.25 1.11 0.20 0.21 tr 1.52 3.50 43 4 0.44 0.04 2.26 0.80 0.23 0.21 tr 1.24 3.50 35 tr 0.24 0.04 2.27 0.50 0.20 0.21 tr 0.91 3.94 23 6 0.30 2.28 0.61 0.46 0.31 tr 1.38 5.71 24 1 0.27 2.29 0.81 1.06 0.55 tr 2.42 6.61 37 2 0.19 2.30 0.61 1.06 0.44 tr 2.11 5.27 40 2 0.21

Elemental composition of the fine earth {% by weight)

Sample SiO, A12O3 Fe2 O3 TiO2 CaO MgO K2O Na2O P2OS Sum Loss on No. ignition %

2.25 87.9 7.0 1.6 0.33 0.19 0.97 0.00 1.00 0.06 99.0 2.2 2.26 84.4 8.3 1.8 0.49 0.36 0.47 3.89 0.31 0.03 100.0 2.3 2.27 85.4 8.1 1.8 0.41 0.18 0.75 3.90 0.65 0.03 101.2 2.3 2.28 88.6 9.1 2.3 0.49 0.16 0.78 4.02 0.44 0.03 106.1 2.8 2.29 86.8 10.1 2.6 0.42 0.14 0.32 3.94 0.80 0.03 105.0 3.0 2.30 85.0 10.1 2.7 0.50 0.14 0.27 3.93 0.81 0.04 103.4 2.6

Sample Trace element content of the 1fine earth (in ppm) SiO2 SiOj A12O3 No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2O3

2.25 96 < 5 < 4 19 12 < 2 380 25 21.3 18.58 6.9 2.26 64 12 10 19 8 10 1720 35 17.2 15.17 7.3 2.27 12 5 2 18 19 < 2 1720 10 17.9 15.69 7.1 2.28 4 < 5 3 28 15 3 380 12 16.1 13.91 6.2 2.29 18 5 10 28 15 10 <100 16 14.8 12.79 6.1 2.30 50 21 15 210 24 10 380 80 14.3 12.25 6.1

Elemental composition of the clay fraction {% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na,O P,O, No.

2.25 53.8 27.5 9.6 1.85 1.95 1.35 2.66 0.00 1.33 2.28 58.1 24.8 7.5 3.24 0.17 1.20 4.41 0.11 0.38 2.30 53.5 29.5 10.0 1.69 1.16 1.23 2.03 0.00 0.82

Mineralogy of the clay fraction Molar ratios

Sample K I Mt Mi V Chi Q SiO2 SiO, A12O, No. A1,O3 R,O3 Fe,O,>

2.25 ++ + + xx 3.3 2.72 4.5 2.26 ++ + + XX 2.27 ++ + + XX 2.28 ++ + + tr xx 4.0 3.33 5.2 2.29 ++ + + tr xx 2.30 ++ + + tr xx 3.1 2.53 4.6

185 DESCRIPTION OF PROFILE NO. 3

Al 0 - 21 cm Dark reddish brown (5YR2.4/2) moist, dark brown (7.5YR3.6/2) dry, coarse sandy loam; weak medium subangular blocky structure; firm dry, loose moist, non- sticky non-plastic wet; common fine few medium and coarse roots; common fine pores; very rapid permeable; wavy gradual boundary; (sample 3.19),

Bl 21 - 39 cm dark reddish brown (5YR3/3) moist, brown (7.5YR4/4) dry, coarse sandy loam; structureless; slightly hard dry, friable moist, very slightly sticky and non-plastic wet; common fine and medium roots; few termite nests (up to 10 cm in diam.); common fine and medium pores; smooth gradual boundary; (sample 3.20),

B21 39 - 62 cm reddish brown (5YR3.6/4) moist, yellowish red (5YR4/6) dry, sandy clay loam with about 20% coarse sand; structureless; few fine and medium roots; very hard dry, friable moist, sticky and slightly plastic wet; few patchy thin cutans often with reddish colour; and greyish spots of All material in root channels; smooth gradual boundary; (sample 3.21),

B2t 62 - 98 cm dark red (2.5YR3/6) moist, yellowish red (5YR4/8) dry, sandy clay with about 20% coarse sand; structureless: very hard dry, friable moist, sticky and plastic wet; few fine and medium roots; common fine and medium pores; common broken medium reddish cutans; increasing amount of coarse fragments with depth; smooth gradual boundary; (sample 3.22),

B23 98 - ] 18 cm reddish brown (5YR4/4) moist, brown (7.5YR5/4) dry, sandy clay; structureless; slightly hard dry, friable moist, slightly sticky and plastic wet; few fine and medium roots; common fine and medium and a few coarse red (2.5YR4/8-dry) mottles; few termite channels; common fine and medium pores; smooth gradual boundary; (sample 3.23),

B3 118-133 cm brown (10YR5/3) moist, pale brown (10YR6/3) dry, sandy clay loam; structureless; hard dry, friable moist, sticky and slightly plastic wet; common fine and medium yellowish red (5YR4/6) mottles; common fine and medium roots; common coarse sand; few fine roots; common fine and medium pores; abrupt smooth boundary; (sample 3.24),

(II)C 133+ cm blocked by coarse angular gravel.

Note: on the hard soil surface common coarse sand. 186 Laboratory data of profile No. 3

Particle size distribution (/i) in % wcight Sand Silt Clay Depth Hori- %>2 2000- 500- 200- 100- 50- 20- < 2 pM 1:5 No. in cmi. zon mm. 500 200 100 50 20 2 H2O KCI

3.19 0- 21 Al 0.5 32.4 24.9 12.9 9.0 5.6 4.3 10.9 6.6 5.2 3.20 21- 39 Bl 0.6 25.7 22.0 13.2 8.9 5.4 4.6 20.2 6.3 5.2 3.21 39- 62 B21 0.6 29.6 18.1 9.6 8.0 4.9 4.1 25.7 6.1 4.9 3.22 62- 98 B2t 1.0 26.0 14.2 8.0 6.5 3.9 3.3 38.1 5.8 4.6 3.23 98-118 B23 0.9 25.3 14.1 8.3 8.7 3.5 4.9 35.2 6.2 4.8 3.24 118-1133 B3 1.5 24.8 14.5 8.9 8.5 5.5 4.9 32.9 6.1 4.9

Exchangeable cations in meq/100 g Organic matter

Sample Ca Mg K Na Sum C.E.C. Base % C % N 1'2OS No. sat . (%) ppm

3.19 1.51 0.38 0.31 tr 2.20 3.95 56 0.43 0.05 3 3.20 1.77 0.63 0.41 tr 2.81 4.39 64 0.41 0.05 tr 3.21 2.03 0.97 0.42 tr 3.42 5.51 62 0.35 0.05 tr 3.22 3.06 1.61 0.42 tr 5.09 9.09 56 0.33 0.06 1 3.23 3.05 1.64 0.42 tr 5.11 7.35 70 0.19 0.04 1 3.24 2.80 1.64 0.42 tr 4.86 6.65 73 0.16 0.03 tr

Elemental composition of the fine earth (% by weight)

Sample SiO2 Al, O, Fe,l03 TiO, CaO MgO K,O Na2O P,O 5 Sum Loss on No. ignition %

3.19 85.9 7. 9 2.2 0.46 0.18 0.00 3.12 0.00 o.o;i 99.8 2.7 3.20 79.3 10. 1 2.7 0.55 0.18 1.31 3.01 0.55 0.0ci 97.7 4.0 3.21 79.4 13.8 3.7 0.69 0.18 0.57 2.85 3.58 O.Of( 104.9 5.6 3.22 76.8 15. 9 4.3 0.66 0.27 2.03 2.59 0.00 o.o:' 102.5 7.7 3.23 80.0 14. 3 3.8 0.63 0.16 0.56 2.61 0.99 .0.03 103.1 6.9 3.24 79.7 14. 1 3.9 0.64 0.15 0.25 2.66 0.00 0.0:1 101.4 6.2

Trace: element content of the fine earth (in ppm) S. O Si O Al, Mn Tu Zn Cr Co Ni Ba Sr 2 3 2 3 o3 No. A12O., R,O3 Fc2 o3 3.19 236 12 5 48 19 20 380 25 18.5 15.75 5.7 3.20 156 15 13 40 24 20 380 40 13.3 11.39 5.8 3.21 98 28 25 70 27 20 <100 17 9.8 8.32 5.8 3.22 66 12 25 59 12 20 <100 18 8.2 7.00 5.8 3.23 110 15 25 61 19 20 <100 25 9.5 8.13 5.8 3.24 92 15 21 85 24 24 <100 23 9.6 8.17 5.6

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO, CaO MgO K.2O Na2O P2O, No.

3.19 52.9 30.9 9.0 1.76 1.37 0.63 1.89 0.62 0.88 3.21 51.8 33.9 9.6 1.53 0.11 0.77 1.75 0.00 0.58 3.24 51.6 34.0 9.2 1.35 0.08 1.05 1.18 0.00 0.67

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi Q SiOj SiO2 Al2Oj

No. A12O3 R 2O3 Fe2O3

3.19 ++ + x 2.9 2. 45 5.4 3.20 ++ + X 3.21 ++ + x 2.6 2. 20 5.6 3.22 ++ + X 3.23 ++ + X 3.24 ++ + x 2.6 2..19 5.8

187 DESCRIPTION OF PROFILE NO. 4

Al 0-16 cm Dark brown (7.5YR3/2) moist, brown (7.5YR4/2) dry, coarse sandy loam; weak subangular blocky structure; hard dry, loose moist, non-sticky non-plastic wet; common very fine and fine (mainly grass) roots; common fine and medium tabular pores; few termite channels; smooth gradual boundary; (sample 4.12),

Bl 16— 43 cm dark reddish brown (5YR3/2) moist, dark brown (7.5YR3/2) dry, sandy clay loam with 25% coarse sand; weak medium subangular blocky structure; hard dry, friable moist, slightly sticky and slightly plastic wet; few fine, medium and coarse roots; few fine and medium tabular pores; rapid permeable; smooth gradual boundary (sample 4.13),

B21 43- JUrm dark reddish brown (5YR4/3) moist, (5YR3/4) dry, sandy clay loam with an appreciable amount of coarse sand; structureless massive; hard dry, friable moist, sticky and plastic wet; few thin broken cutans around sandgrains and along root-channels; few fine, medium and coarse roots; few termite nests (up to 5 cm in diam.); common fine tabular pores; smooth gradual boundary; (sample 4.14),

B22 61 - 78 cm dark reddish brown (5YR3/4) moist, reddish brown (5YR4/4) dry, sandy clay with an appreciable amount of coarse sand; very hard dry, friable moist, very sticky and plastic wet; structureless massive; common small thin broken cutans; few fine and medium pores; very few fine roots; few faint greyish and brownish mottling in the lower part of the horizon and common distinct yellowish red (5YR4/8—dry) mottles; smooth gradual boundary; (sample 4.15),

B2g 78 - 97 cm very dark grey (10YR3/1) moist, dark grey (10YR4/1) dry and dark brown (10YR4/3) moist, dark yellowish brown (10YR4/4) dry, sandy clay with common coarse sand; structureless massive; consistence as horizon above; common thin broken cutans; few distinct reddish mottles on boundary with B22; the grey colours in this horizon are coarse mottles in brown matrix; smooth clear boundary; (sample 4.16),

B2ca 97-112 cm very dark grey (7.5YR3/1) moist, dark grey (7.5YR4/1) dry, sandy clay; amount of coarse sand and structure as horizon above; very hard dry, firm moist, sticky and plastic wet; common broken cutans; few reddish brown mottles; very few fine roots; few fine pores; very few coarse hard calcrete nodules and quartz gravel and common soft and hard CaCO3 accumulations at the boundary to the underlying horizon; smooth clear boundary: (sample 4.17),

C 112 —125 cm yellowish brown (10YR5/6) moist, .brownish yellow (10YR6/6) dry, slightly gravelly loamy sand; common

dark red concretions; common large CaCO3 concretions; (sample 4.1 8),

R 125+ cm extremely hard granitic rock.

Note: On the very surface of the soil a thin (2—4 mm) layer of coarse sand occurs.

188 Laboratory data of profile No. 4

Particle size distribution (p) in% weight Sand Silt Clay pH 1:5 Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20 <2 No. in cm zon mm. 500 200 100 50 20 2 H2O KC1

4.12 0- 16 Al 0.9 37.1 22.5 11.2 8.7 5.3 4 5 10.7 6.8 5.8 4.13 16- 43 Bl 0.9 28.6 18.6 9.8 7.8 5.3 4 9 25.0 6.6 5.1 4.14 43- 61 B21 2.8 27.6 15.8 7.7 5.6 3.7 5 2 34.4 6.6 5.2 4.15 61- 78 B22 2.9 22.3 14.6 7.3 6.4 4.2 5 0 40.2 6.7 5.2 4.16 78- 97 B2g 3.9 23.1 11.3 6.4 5.7 4.2 5 8 43.5 7.2 5.6 4.17 97-112 B2ca 4.7 18.1 11.4 6.7 6.4 4.4 7 2 45.8 7.8 6.3 4.18 112-125 C 10.0 17.0 15 5 9.9 7.9 18.4 20.9 10.4 8.1 6.8

Exchangeable cations in meq/100g Organic matter

Sample Ca Mg K Na Sum C.E.C. Base P;OS % C % N No. sat. (%) ppm

4.12 2.52 0.60 0.39 0.09 3.60 4.39 82 4 0.44 0.05 4.13 3.56 1.82 0.73 tr 6.11 6.64 92 0.47 0.06 4.14 5.38 2.63 0.60 0.09 8.70 10.94 80 tr 0.39 0.06 4.15 7.20 3.08 0.69 tr 10.97 12.82 86 tr 0.31 0.05 4.16 8.79 3.71 0.74 0.09 13.33 14.25 94 tr 0.25 0.05 4.17 12.00 5.10 0.86 0.09 18.05 18.11 100 0.27 0.05 4.18 17.41 7.82 1.16 0.09 26.48 26.73 99 tr 0.11 0.02

Elementa compos tion of the fine earth (% by weight)

Sample SiO, Al2 O3 Fe2O3 TiO2 CaO MgO K2O Na,O P,OS Sum Loss on No. ignition %

4.12 85.0 6 1 1.9 0.31 0.20 0.89 2.85 0.00 0.11 97.6 3.0 4.13 80.9 9.2 3.1 0.54 0.30 0.65 2.52 0.00 0.05 97.3 5.2 4.14 77.3 12 8 4.3 0.61 0.28 0.73 2.48 0.00 0.06 98.6 7.1 4.15 73.7 13 8 4.6 0.60 0.32 1.76 2.69 2.40 0.12 99.9 8.1 4.16 73.1 14 9 4.9 0.64 0.37 2.24 1.61 0.17 0.13 98.1 8.6 4.17 74.0 15 8 5.2 0. 74 0.58 3.73 2.35 0.00 0.07 102.4 9.4 4.18 71.8 16 7 5.8 0. 79 0.73 1.80 2.53 0.00 0.03 100.2 11.2

Sample Trace element content of the fine earth (in ppm) Si2O5 Si2O3 AI2O3

No. Mn Cu Zn Cr Co Ni Ba Sr AI2Oj R;O3 Fe2O3

4.12 144 12 8 85 27 20 < 100 12 23.7 14.83 5.2 4.13 170 9 19 110 31 35 < 100 25 14.9 12.29 4.7 4.14 100 12 22 59 24 31 < 100 8 10.4 8.55 4.7 4.15 128 21 29 40 58 77 < 100 20 9.2 7.51 4.8 4.16 134 24 28 40 27 35 380 30 8.3 6.27 4.7 4.17 206 21 30 61 24 42 <100 32 8.1 6.57 4.8 4.18 850 31 31 35 29 35 380 28 7.3 5.96 4.5

Elementa composition of the clay fraction (% by weight K,0 Na,O P O Sample s.o2 AljO, Fe,0 3 TiO, CaO MgO 2 S No.

4.12 55.6 26.7 9.8 1.96 1.22 1.70 2.43 0.00 0.64 4.14 52.2 30.4 10.2 1.35 1.53 1.57 1.98 0.00 0.78 4.18 56.0 26.9 9.4 1.40 1.68 2.12 1.81 0.18 0.57

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi Q SiO2 SiO, A12O No. A12O R2O3 Fe2O 3

4.12 ++ + xx 3.5 2.87 4.3 4.13 ++ + X 4.14 ++ + tr x 2.9 2.40 4.7 4.15 ++ + tr X 4.16 ++ + tr X 4.17 ++ + tr X 4.18 ++ + tr xx 3.5 2.89 4.5

189 DESCRIPTION OF PROFILE NO. 5

Al 0-21 cm Dark brown (7.5YR3/2) moist, brown (7.5YR4/2) dry, coarse sandy loam; weak fine subangular blocky structure; firm dry, loose to friable moist, non-sticky non- plastic wet; abundant fine roots; smooth gradual boundary; (sample 5.31),

Bl 21 — 36 cm dark reddish brown (5YR3.5/3) moist, dark reddish grey (5YR4/2) dry, gravelly coarse sandy loam; structureless; consistence as horizon above; few fine and medium roots; common weathered rock fragments with presumebly Fe and Mg cementation increasing in the lower part of the horizon; abrupt wavy boundary; (sample 5.32),

C 36—55 cm weathered granitic rock of very gravelly coarse sandy ' loam texture; (sample 5.33).

190 Laboratory data of profile No. 5

Particle size idistribution (M) in % weight Sand Silt Clay pH 1:5 Depth Hori- %•>-> 2000- 500- 200- 100- 50- 20- <2 No. in cm zon mm. 500 200 100 50 20 2 H2O KC1

5.31 0-21 Al 2.7 29.7 20.2 17.5 11.2 8.0 5.2 8.2 6.8 5.9 5.32 21-36 Bl 52.9 31.9 22.3 13.6 11.1 6.9 4.0 10.2 6.7 5.0 5.33 36-55 C 46.4 40.3 19.5 14.6 4.9 6.2 4.8 9.7 6.6 5.3

Sample Exchangeable cations in meq/100 g Organic maltter Ba:îe No. Ca Mg K Na Sum C..E.C. sat . (%) %C %N P2O5

5.31 2.01 0.43 0.31 tr 2.75 3. 50 79 0.55 0 .05 2 5.32 1.11 0.43 0.26 tr 1.80 4.38 41 0.33 0.03 tr 5.33 0.91 0.49 0.28 tr 1.68 4.83 35 0.29 4

Sample Elemental composition of the Tine earth (%by weight) No. SiO2 A12O3 Fe2

5.31 89.0 8.2 2.0 0.56 0.33 0.31 2.91 0.00 0.05 103.4 3.3 5.32 90.4 8.7 2.6 0.49 0.26 0.49 3.03 0.56 •0.02 106.5 3.2 5.33 87.4 9.4 4.2 0.51 0.22 0.26 3.37 0.00 0.01 105.4 3.2

Sample Trace element content of the fine earth (in ppm) SiO2 SiOj A12O, No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2O3

5.31 274 5 2 21 15 < 2 1720 12 18.4 15.94 6.5 5.32 400 5 1 11 15 < 2 380 12 17.6 14.82 5.3 5.33 52 31 20 •»3 77 45 1260 13 15.9 12.35 3.5

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2O5 No.

5.31 52.7 29.4 1.44 2.89 0.55 1.79 0.00 2.48 5.32 53.9 30.8 9.1 1.55 0.09 1.11 2.14 0.59 0.72 5.33 53.1 30.5 9.1 1.36 1.62 0.75 1.64 0.72 1.26

Miner;»logy of the clay fraction Molar ratios

Sample K I Mt Mi V Chi Q SiO2 SiO2 A12O3 No. A12O3 R2O3 Fe2O3

5.31 ++ + XX 3.0 2.55 5.2 5.32 ++ + X 3.0 2.50 5.3 5.33 ++ + X 3.0 2.48 5.3

191 DESCRIPTION OF PROFILE NO. 6

Al 0-23 cm Dark brown (7.5YR3/2) moist, ,dark greyish brown (10YR4/2) dry, coarse sandy loam; very weak medium subangular blocky; hard when dry, slightly friable moist, slightly sticky non-plastic when wet; many fine and medium roots; few termite nests and channels; smooth gradual boundary; (sample 6.34),

Bl 23 - 43 cm dark reddish brown (5YR3/2.6) moist, brown (7.5YR4/3) dry, sandy clay loam; structureless massive; very hard dry, ,friable moist, sticky and plastic wet; common fine and medium roots; common fine and medium and few coarse pores; appreciable amount of coarse sand; few very fine gravel; few thin broken cutans; smooth gradual boundary; (sample 6.35),

B21 43 - 69 cm reddish brown (5YR4/3) moist, brown (7.5YR5/4) dry, sandy clay; structureless massive; very hard dry, friable moist very sticky and plastic when wet; common fine and medium roots; common faint small (but more distinct at lower part of horizon) dark red (2.5YR3/6) mottles; common fine and medium pores; amount of coarse .fragments increasing with depth; clear smooth boundary; (sample 6.36),

B2g 69 — 105 cm greyish brown (10YR5/2) moist, light brownish grey (10YR6/2) dry, sandy clay loam; structureless massive; many prominent medium and coarse dark red (2.5YR3/6) mottles; very hard dry, slightly friable moist, slightly sticky and plastic wet; few small prominent bluish mottles; few fine medium roots; few small medium cutans; common coarse fragments increasing with depth; smooth gradual boundary; (sample 6.37),

B2g 105 — 150 cm grey (10YR5/1) moist, ,slightly gravelly coarse sandy loam; massive; very few fine roots; many prominent coarse black mottles; increasing amount of coarse fragments, few small prominent dark red mottles; abrupt smooth boundary; (sample 6.38),

C 150+ cm extremely hard mottled granite.

192 Laboratory data of profile No. 6

Particle size distribution (M) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- < 2 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H 2O KC1

6.34 0- 23 Al 3.4 32..0 17.5 17,.1 4.1 6. 4 6.0 16.9 6. 2 4.6 6.35 23- 43 BI 0.5 27..4 15.1 13,.3 3.5 7. 1 3.5 30.1 6. 2 4.8 6.36 43- 69 B21 2.2 27,.2 12.1 10.4 4.8 5.,9 3.7 35.9 6. 4 4.7 6.37 69-105 B2g 3.3 25,.8 11.3 14.8 1.7 6. 9 4.5 35.0 6. 6 5.1 6.38 105-150 B2g 13.2 47.4 12.0 8.2 4.2 5.,2 3.7 19.3 7. 0 5.3

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 No. sat %) % C % N!i ppm

6.34 1.31 0.39 0.38 tr 2.08 5.27 40 0.51 0.05 1 6.35 2.54 1.14 0.45 tr 4.13 7.51 55 0.48 0.05 tr 6.36 3.15 1.47 0.50 tr 5.12 9.30 55 0.41 tr 6.37 2.75 1.87 0.57 tr 5.19 9.30 56 0.22 1 6.38 3.68 2.39 0.68 tr 6.75 9.77 69 0.18 tr

Elemental composition of the fine earth (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P,O,; Sum Loss on No. ignition %

6.34 89.1 9.4 2.6 0.59 0.19 0.43 2.77 0.00 0.07 105.1 4..18 6.35 83.6 13.0 3.5 0.63 0.19 0.45 2.46 0.15 0.04 104.0 6 .00 6.36 80.7 16.2 4.1 0.71 0.18 0.44 2.25 0.00 0.04 104.6 7,.42 6.37 78.0 17.6 4.8 0.77 0.19 0.67 2.34 0.00 0.05 104.4 7 .02 6.38 80.3 14.8 8.0 0.71 0.22 0.45 2.38 0.16 0.05 107.1 6 .69

SiC) SiO A1 O Sample Trace element content of the 1fine earth (in |ppm) 2 2 2 3 No. Mn Cu Zn Cr Co Ni Ba Sr Al; O3 R2O3 Fe2O3

6.34 2500 21 15 59 15 17 800 45 16. 1 13.67 5.8 6.35 108 24 18 50 12 20 800 22 10. 9 9.32 5.9 6.36 228 11 19 60 12 17 380 32 8,,5 7.28 6.2 6.37 128 34 25 110 27 31 380 40 7. 5 6.40 5.7 6.38 2508 41 21 114 51 58 <100 28 9.2 6.84 2.9

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2OS

6.34 53.0 31.9 8.1 1.70 1.52 0.89 1.59 0.16 1.20 6.36 52.1 35.4 8.4 1.28 0.08 0.81 1.24 0.00 0.63 6.38 49.4 31.8 12.0 1.02 1.32 1.76 1.92 0.00 0.77

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi Q SiO2 SiO2 No. A12O3 R :O3 Fe2O3

6.34 ++ + XX 2.8 2. 43 6.2 6.35 ++ + X 6.36 ++ + tr X 2.5 2. 17 6.6 6.37 ++ + tr X 6.38 ++ + tr X 2.5 2. 10 5.0

193 DESCRIPTION OF PROFILE NO. 7

Al 0 - 15 cm Dark brown (10YR3/3) moist and brown (10YR5/3) dry, loamy coarse sand; structureless, single grained; dry soft, moist friable, wet non-sticky and non-plastic; common fine and a few medium and thick roots; smooth gradual boundary; (sample 7.1),

Bl 15 - 34 cm dark brown (7.5YR3/4) moist, brown (7.5YR 5/4) dry, loamy coarse sand; structureless, single grained; dry slightly hard, moist friable, wet non-sticky and non- plastic; common fine, medium and thick roots; few fine tabular pores; smooth gradual boundary; (sample 7.2),

B21 34 - 55 cm brown (7.5YR4/4) moist, lightbrown (7.5YR6/4) dry, coarse sandy loam; structureless, single grained; dry hard, moist firm, wet slightly plastic; few fine, medium and thick roots; few fine and medium tabular pores; few small (1 cm diam.) greyish more consolidated soil fragments; smooth gradual boundary; (sample 7.3),

B3 55 - 69 cm brown (7.5YR5/4) moist, pinkish grey (7.5YR6/2) dry, slightly gravelly coarse sandy loam; structureless, single grained; dry very hard, moist firm, wet very slightly sticky and slightly plastic; few fine and medium roots; few fine pores; abrupt smooth boundary; (sample 7.4),

C 69+ cm weathered granitic rock with an appreciable amount of reddish and bluish mottling and of a very gravelly loamy coarse sand texture; (sample 7.5).

194 Laboratory data of profile No. 7

Particle size distribution (/i) in % weight Sand Silt Clay pH 1:5 Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- < 2 No. in cm. zon mm. 500 200 100 50 20 2 H2O KC1

7.1 0-15 Al 0.9 27..8 24.0 18. 8 13.1 6.8 2.9 6.6 6.2 5.1 7.2 15-34 Bl 1.1 27..7 21.3 19. 2 13.7 5.6 3.3 9.2 6.0 4.9 7.3 34-55 B21 1.7 26..3 22.3 15. 9 13.0 5.7 3.1 13.7 6.0 4.7 7.4 55-69 B3 9.4 32..4 25.5 12. 0 9.1 5.2 2.4 13.4 6.0 4.7 7.5 69+ C 75.0 33..3 , 24.3 13. 2 9.5 6.2 3.5 10.0 6.4 5.3

Exchangeable cations in meq/100 g Sample Ca Mg K Na Sum C.E.C. Base Organic matter P,O, No. sat. (%) %C %N ppm

7.1 1.51 0.26 0.72 0.26 2.75 3.07 90 0.46 0.04 3 7.2 1.01 0.38 0.49 tr 1.88 3.28 57 0.30 0.03 1 7.3 1.50 0.76 0.36 tr 2.62 4.79 55 0.20 0.04 tr 7.4 1.26 0.81 0.26 tr 2.33 3.73 63 0.20 0.03 1 7.5 1.26 0.80 0.36 tr 2.42 2.42 61 0.16 0.02 tr

Elemental composition of the fine earth (% by weight)

Sample SiO2* A12O3 Fe2

7.1 85.2 8.4 1.5 0.42 0.22 1..16 4. 24 0.14 0.05 101.3 2.4 7.2 85.9 8.9 1.5 0.29 0.20 0..49 4.62 0.56 0.07 102.5 2.4 7.3 84.8 9.4 1.8 0.36 0.17 0..35 4. 17 1.59 0.09 102.7 2.7 7.4 85.8 9.0 1.7 0.36 0.17 0..54 3. 81 0.47 0.08 101.8 2.9 7.5 78.9 11.0 5.9 0.39 0.17 0 .89 4. 33 0.82 0.08 102.5 3.8

Trace element content of the :fine earth (in ]ppm)

Sample Mn Cu Zn Cr Co Ni Ra Sr SiO, SiO, A12O3

No. A1;O3 R,O3 Fe2O3

7.1 188 9 3 19 19 6 800 49 17.1 15.35 8.7 7.2 120 21 5 46 15 <2 1260 55 16.4 14.80 9.6 7.3 22 24 4 63 <2 <2 2600 42 15.3 13.65 8.2 7.4 4 15 2 40 < 2 3 800 42 16.3 14.49 8.1 7.5 2830 31 3 50 56 35 1600 52 12.1 9.05 2.9

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A1,O3 Fe2O3 TiO2 CaO MgO K-.o Na2O Pj os No.

7.1 54.8 29.9 8.1. 2.07 0.33 1.19 C M •— < 32 0.92 35 7.3 54.4 31.8 7.6 1.61 0.09 1.14 20 0.46 67

7.5 53.9 31.1 9.1 1.56 0.83 1.31 81 0.00 po p 51

Mineralogy of the clay fraction Molar ratios

Sample K I Mt Mi V Chi Q SiO2 SiO2 A12O3 No. A12O3 R,O3 Fe2O3

7.1 3.1 2.65 5.8 7.2 x 7.3 tr X 2.9 2.52 6.5 7.4 tr XX 7.5 tr XX 2.5 2.48 5.4

195 DESCRIPTION OF PROFILE NO. 8

Ap 0-21 cm Dark brown (7.5YR3/2) moist, brown (7.5YR4/4) dry, coarse sandy loam; weak fine and medium subangular clods; in the upper part of the horizon slight horizontal bedding is visible; very hard dry, friable moist, slightly sticky, slightly plastic wet; common fine medium tubular pores; common very fine, fine and few medium roots; few termite nests 2 cm in diameter; smooth wavy boundary; (sample 8.53),

B21 21 — 47 cm dark reddish brown (5YR3/3) moist, reddish brown (5YR4/4) dry, sandy clay loam; structureless; slightly hard dry, friable moist, sticky and plastic wet; many fine and medium tubular pores; common coarse fragments; common fine termite channels; common fine and medium roots; thin cutans in root and termite channels; smooth gradual boundary; (sample 8.54),

B2(g) 47 — 76 cm dark reddish brown (5YR3/3) moist, yellowish red (5YR5/6) dry, sandy clay loam; structure and consistence as horizon above; coarse fragments increasing with depth; common faint dark grey (10YR4/1) and yellowish red (5YR4/8) mottles; few fine thin broken cutans; common fine termite nests and root channels; wavy gradual boundary; (sample 8.55),

B2g 76 — 104 cm dark brown (7.5YR3/2) moist, sandy clay loam with common distinct very dark grey (10YR3/1) and reddish brown (5YR/4/4) mottles; structureless; very hard dry, firm moist, sticky and plastic wet; common fine and medium tubular pores; appreciable amount of coarse fragments; common medium thin broken cutans; few small prominent reddish concretions in the lower part of the horizon; clear wavy boundary; (sample 8.56),

B3 104-129 cm brown (10YR5/3) moist, pale brown (10YR6/3) dry, slightly gravelly coarse sandy loam; common iron (?) concretions up to 1 cm in diameter; occasional angular rock fragments; soft dry, friable moist, sticky and plastic wet; common faint reddish and yellowish mottling; occasional very fine roots; clear wavy boundary; (sample 8.57),

C 129 - 144 cm greyish brown (10YR5/2) moist, light yellowish brown (2.5Y6/4) dry, weathered rock of coarse sandy loam texture; common distinct bluish black fine concretions.

196 Laboratory data of profile No. 8

Particle size distribution (M) in % weight Sand Silt Clay Sample Depthi Hori- %>2 2000- 500- 200- 100- 50- 20- < 2 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H 2O KC11

8.53 0- 21 Ap 3.2 28.1 17.0 16.7 9..4 6.3 3.7 18.8 6. 5 4.9 8.54 21- 47 B21 7.7 24.7 13.0 11.1 8.4 5.0 3.7 34.1 6. 6 4.9 8.55 47- 76 B2(g) 5.5 25.4 12.0 10.4 6..9 5.5 4.5 35.3 6.,8 5,.1 8.56 76-104 B2g 5.9 22.9 11.8 9.9 7.8 6.3 6.5 34.8 7..3 5..5 8.57 104-129 B3fl 18.6 27.6 12.8 10.5 8..5 3.2 9.6 27.8 7..6 5..5

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 ; No. sat. %c %N ppm

8.53 3.24 0.67 0.57 0.17 4.65 7.14 65 0.52 0.04 8 8.54 4.85 1.28 0.63 0.17 6.93 9.65 72 0.30 0.04 12 8.55 5.89 1.31 0.69 0.17 8.06 10.33 78 0.23 4 8.56 8.47 1.65 0.74 0.17 11.03 11.97 92 0.17 6 8.57 10.07 2.04 0.85 0.18 13.14 16.22 95 0.16 5

Elemental composition of the fine earth (% by weight)

Sample SiO2 A12O3 Fe2(33 TiO2 CaO MgO K2O Na2O P Sum Loss on No. ignition %

8.53 85.6 9.4 3.0 0. 49 0.24 0.44 3.06 0.32 0.11 102.6 4.6 8.54 79.8 12.7 4.0 0. 53 0.27 0.69 2.36 0.26 0.06 100.6 6.4 8.55 77.7 14.2 4.1 0.59 0.31 0.88 2.48 0.51 0.12 100.8 7.0 8.56 78.7 14.7 4.7 0. 68 0.39 0.62 2.77 0.26 0.06 103.0 8.2 8.57 83.7 15.1 5.9 0.69 0.44 1.08 2.31 0.00 0.08 99.3 8.3

Trace element content of the fine earth (in ppm) SiC SiO A1 O Sample >2 2 2 3 No. Mn Cu Zn Cr Co Ni Ba Sr Al2 o3 R2O3 Fe2O3 8.53 184 12 15 125 15 24 <100 <2 15. 5 12.90 5.0 8.54 176 12 17 86 19 27 <100 13 10. 7 8.91 5.0 8.55 274 21 33 127 23 35 800 12 9. 1 7.54 4.8 8.56 336 34 24 120 19 38 1260 19 9.3 7.84 5.5 8.57 1600 34 19 89 35 43 <100 26 8.3 6.63 4.0

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe,O, TiO; CaO MgO K,o Na2O P2OS No.

8.53 51.6 30.5 10.2 1.42 2.20 0.66 1.57 0.00 1.90 8.54 52.1 32.5 10.3 1.31 0.08 1.28 1.73 0.08 0.65 8.57 53.7 30.3 9.5 1.21 1.61 1.26 1.45 0.00 0.99

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi Chi SiO, SiO2 No. A12O3 R2O3

8.53 2.9 2.37 4.7 8.54 2.7 2.27 5.0 8.55 8.56 tr xx 8.57 tr XX 3.0 2.50 5.0

197 DESCRIPTION OF PROFILE NO. 9

Al 0—16 cm Very dark greyish brown (10YR3/1.6) moist, dark greyish brown (10YR4/1.7) dry, coarse sandy loam; moderate fine angular blocky structure; hard dry, firm moist, slightly sticky and non-plastic wet; many fine and medium roots; common coarse sand grains on the surface; few fine tubular pores; smooth gradual boundary; (sample 9.113),

Bl 16 — 34 cm very dark greyish brown (10YR3/2) moist, dark greyish brown (10YR4/2) dry, sandy clay loam; weak fine subangular blocky structure; slightly hard dry, friable moist, sligthly sticky non-plastic wet; common fine and medium roots; common coarse sand grains; common termite nests; smooth gradual boundary; (sample 9.114),

B22 34 - 56 cm dark brown (7.5YR3/1.7) moist, dark greyish brown (10YR4/2) dry, sandy clay; strong fine to medium angular blocky structure; very hard dry, firm moist, sticky and plastic wet; common medium broken cutans; common coarse sand grains; a little very fine gravel; few fine and medium roots; common termite nests up to 5^ cm in diameter; very few fine tubular pores; smooth gradual boundary; (sample 9.115),

B2g 56 - 86 cm very dark grey (10YR3/1) moist, dark grey (10YR4/1.4) dry, sandy clay; weak fine angular blocky structure; common fine distinct strong brown (7.5YR5/6-moist) mottles; few fine roots; few termite nests; common coarse sand; common moderately thick broken cutans; smooth gradual boundary; (sample 9.116),

B2g 86 — 112 cm dark grey (10YR4/1) moist, sandy clay; massive; very hard dry, firm moist, very sticky and plastic wet; common thin broken cutans; many medium and coarse prominent red mottles (5YR5/8-dry and 2.5YR4/8- moist); few medium prominent bluish mottles; (sample 9.117),

C 112 —140 cm dark grey (10YR4/1) moist and strong brown (7.5YR5/8) moist, ,slightly gravelly sandy clay; (sample 9.118),

R 140+ cm hard granitic rock.

198 Laboratory data of profile No. 9

Particle size distribution (JU) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1 5 No. in err . zon mm. 500 200 100 50 H,O KC1

9.113 0- 16 Al 0.8 22.8 20.4 18.6 11.3 6.7 3.4 16.8 6.7 5.0 9.114 16- 34 Bl 0.9 24.9 15.3 15.0 6.7 5.0 2.7^30.4 6.5 4.8 9.115 34- 56 B22 2.6 18.9 12.8 9.7 6.8 5.1 2<\ 0X2->6.6 5.0 9.116 56- 86 B2g 0.9 21.7 10.0 7.0 5.3 4.3/4.3 47.4 7.2 5.7 9.117 86-112 B2g 1.0 17.9 9.0 7.1 5.8 y.% 8.7 43.7 7.9 6.1 9.118 112-140 C 5.7 22.6 8.0 7.2 6.0 / 6.8 7.4 >8.0 6.2

Exchangeable cations in meq/100 g / Sample Ca Mg K Na Sum/ C.E.C. Base Organic matter P,O< sat. (%) ppm / %C % N

9.113 1.72 0.67 0.70 tr / 3.09 5.27 59 0.50 0.06 5 9.114 4.06 1.37 0.63 tr/ 6.06 9.00 67 0.38 0.06 9.115 5.11 1.95 0.89 tr' 7.95 du"!!3 59 0.39 tr >—. 9.116 6.66 2.46 1.21 / tr 10.33 14.27 73 0.27 2 9.117 6.67 2.53 1.36/ tr 10.56 1J..64 91 0.16 2 9.118 5.63 2.43 1.2-1' 0.17 9.44 ClZOß 79 0.05 1

Elementa composition of the fine earth (% by weight)

Sample SiO, Al O, ,F •,Oj TiO, CaO MgO K,0 Na,O P,OS Sum Loss on No. ignition % / 9.1 13 84.2 (9 0) 2 1 0.42 0.25 1.67 3.33 0.33 0.13 101.4 3.9 9.114 79.6 12 "4 3 1 0.45 0.23 0.42 3.19 0.00 0.04 99.5 6.1 9.115 74.1 16 9 4 0 0.61 0.29 1.88 2.63*0.00 0.19 100.6 8.3 9.116 69.1 20 1 4 8 0.69 0.39 2.15 2.73 0.21 0.17 100.4 9.0 9.117 62.3 20 2 5 9 0.71 0.34 1.12 2.3.5 0.42 0.07 93.3 9.5 9.118 71.7 18 8 6 3 0.66 0.29 0.18 (000^)0.00 0.13 98.6 8.3

Sample Trace element content of the fine earth (in ppm) SiO; SiO, A1,O, No. Mn Cu Zn Cr Co Ni Ba Sr A I,O3 R Fe,O3

9.113 100 24 7 288 6 20 640 28 15.8 13.78 6.8 9.114 130 36 36 228 32 40 460 24 10.9 9.39 6.2 9.115 114 36 45 240 32 40 320 24 7.5 6.47 6.5 9.116 114 30 37 230 32 29 440 28 5.8 5.06 6.5 9.117 212 46 37 300 26 54 540 28 5.2 4.40 5.3 9.118 280 54 34 230 32 44 480 22 6.5 5.34 4.7

Elemental composition of the clay fraction (% bv weight)

Sample SiO, A1,O, Fe,O3 TiOj CaO MgO K,0 Na,O P os No.

9.113 51.5 31.4 7.9 1.36 2.79 2.85 1.51 0.00 2 85 9.115 52.8 35.0 8.3 1.12 0.92 1.05 0.00 0.00 0.81 ~ 7 9.118 52.0 34.1 7.7 1.14 1.73 0.68 1.16 0.00 1 52

Mineralogy of the clay fraction Molar ratios Sample K I Mt Mi V Chi Q SiO, SiO, AljC No. Al,0 R,O, Fe,O3

9.113 ++ + x 2.8 2.40 6.3 9.114 ++ + X 9.115 ++ tr tr x 2.6 2.22 6.6 9.116 ++ + X 9.117 ++ + X 9.118 ++ + tr x 2.6 2.26 6.9

d JIJ) X, DESCRIPTION OF PROFILE NO. 10

Al 0-10 cm Dark reddish brown (5YR3.4/4) dry and (5YR3/2) moist, coarse sandy loam; moderate fine angular blocky structure; slightly hard dry, friable moist, non-sticky non-plastic wet; common very fine and fine (mainly grass) roots; few fine and medium tubular pores; smooth gradual boundary; (sample 10.6),

Bl 10 - 33 cm dusky red (2.5YR3/2) moist, dark reddish brown (5YR3.4/4) dry, coarse sandy loam; very ,weak fine angular blocky structure; slightly hard dry, friable moist, non-sticky very slightly plastic wet; few fine and medium roots; few fine and medium tubular pores; little termite activity; very fine and fine gravel increasing with depth; smooth gradual boundary; (sample 10.7),

B21 33 - 53 cm dark reddish brown (2.5YR2/4) moist, (2.5YR3/4) dry, sandy clay loam, structureless massive; hard dry, friable moist, slightly sticky and slightly plastic wet; very few fine and medium roots; few termite channels; smooth gradual boundary; (sample 10.8),

B22 53 - 72 cm dark reddish brown (2.5YR2/4) moist, (2.5YR3/4) dry, slightly gravelly sandy clay loam; structureless massive; hard dry, friable moist, slightly sticky and slightly plastic wet; very few fine roots; few fine tubular pores; few termite channels; clear wavy boundary; (sample 10.9),

B3 72 - 91 cm dark reddish brown (2.5YR2/4) moist, (2.5YR3/4) dry, gravelly sandy clay loam; structureless massive; hard dry, friable moist, very slightly sticky non-plastic wet; very few fine roots and a few medium roots; very few small termite nests; few fine soft CaCÛ3 concretions; clear wavy boundary; (sample 10.10),

(II)C 91+ cm dark reddish brown (5YR3/4) dry and pinkish white (5YR8/2) dry, very gravelly sandy clay loam; appearance of weathered calcrete rock with granitic matrix; very hard dry but in some parts soft; (sample 10.11).

200 Laboratory data of profile No. 10

Particle size distribution 1fl) in % weight Sand Sil Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1- 5 No. in cm. zon mm. 500 200 100 50 20 2 H:O KC1

10.6 0-10 Al 0.5 26 7 20.7 15.8 12.6 6.9 5.2 12.1 6.9 5.7 10.7 10-33 Bl 1.0 26 1 18 9 16.6 9.4 7.1 3.9 18.0 6.7 5.8 10.8 33-53 B21 8.8 25 2 17.6 13.4 11.0 5.9 3.3 23.6 6.9 5.5 10.9 53-72 B22 8.7 29 3 15 7 12.1 9.2 5.9 3.5 24.3 7.1 5.6 10.10 72-91 B3 37.2 29 2 15 3 10.5 8.4 5.3 4.6 26.7 7.7 6.6 10.11 91+ (II)C 57.6 21 3 12 1 10.7 10.5 6.8 4.5 34.1 8.3 7.1

Sample Exchangeable cations in meq/100 g Sample Ca Mg K Na Sum C.E.C. Base Organic matter P, sat. (%) %C % N ppm

10.6 4.81 0.82 0.57 tr 6 20 8.15 76 0.68 0.07 5 10.7 5.34 1.00 0.50 tr 6 84 7.96 86 0.37 0.05 tr 10.8 6.66 1.21 0.42 tr 8 29 9.36 89 0.39 0.05 tr 10.9 8.73 1.31 0.37 tr 10 41 10.91 96 0.36 0.05 2 10.10 12.81 1.47 0.42 tr 14 70 15.34 97 0.37 0.05 1 10.11 17.10 1.09 0.53 tr 18 72 17.77 100 0.33 0.06 1

Elemental composition of the fine earth (% by weight) Sample SiO, A1,O, Fe, 0, TiO, CaO MgO K,O Na,0 P,O Sum Loss on No. ignition %

10.6 83.8 8.7 2.4 0.39 0.44 0.33 3.49 1 73 0.10 101.4 4.3 10.7 82.8 10.6 3.6 0.60 0.45 0.75 3.30 0 00 0.06 101.5 4.9 10.8 80.5 12.4 3.9 0.57 0.46 0.79 3.36 1 14 0.11 99.9 5.6 10.9 77.6 12.6 4.3 0.59 0.50 0.32 3.21 0.00 0.03 99.1 6.1 10.10 77.1 13.4 4.0 0.52 0.70 0.62 4.00 0.81 0.04 101.1 7.0 10.11 64.2 11.5 3.9 0.58 13.24 0.68 2.71 0.33 0.10 97.2 16.1

Sample Trace element content of the "ine earth (in ppm) SiO, SiO, Al,0

No. Mn Cu Zn Cr Co Ni Ba Sr A1,O, R,O3 Fe,O 3

10.6 428 8 12 40 15 20 1720 42 16.2 13.84 5.6 10.7 393 18 24 36 20 35 380 49 13.2 10.81 4.6 10.8 344 18 28 36 15 31 1560 42 11.0 9.17 4.9 10.9 366 10 21 40 12 17 1560 12 10.5 8.60 4.8 10.10 334 17 28 35 8 20 800 42 9.8 8.21 5.3 10.11 238 24 18 33 51 73 800 80 9.5 7.84 4.7

Elemental composition of the :lay fraction (% by weight) Sample SiO, ALO, Fe,O, TiO, CaO MgO K,O Na,O P,O, No.

10.6 54.4 27.0 11.0 1.61 1.05 1.63 2.07 0.00 0.45 10.8 52.4 29.3 12.4 1.46 0.08 1.58 2.17 0.02 0.62 10.11 53.8 24.0 9.6 1.08 6.52 2.79 1.68 0.00 0.59

Mineralogy of the clay fraction Molar ratios

Sample K Mt Mi Chi SiO, SiO, A1,O3 No. Ai,O3 R,O, Fe,O,

10.6 3.4 2.67 3.6 10.7 10.8 3.0 2.39 3.7 10.9 tr 10.10 tr 10.11 3.8 3.04 3.9

201 DESCRIPTION OF PROFILE NO. 11

Al 0-16 cm Very dark greyish brown (10YR3/2) moist, brown (10YR5/3) dry, coarse sand; structureless, single grained; soft dry, slightly friable moist, non-sticky and non- plastic when wet; thin broken cutans; common fine tubular pores; frequent very fine and few medium and coarse roots; smooth gradual boundary; (sample 11.45),

Bl 16 - 45 cm dark brown (7.5YR4/4) moist, brown (7.5YR5/4) dry, loamy coarse sand; structureless, single grained; soft dry, slightly friable moist, non-sticky and non-plastic when wet; rapidly permeable; very few thin broken cutans; common fine, medium and coarse roots; common fine tubular pores; coarse fragments increasing with depth; smooth gradual boundary; (sample 11.46),

B21 45 - 82 cm yellowish red (5YR4/6) moist, reddish yelloI'W (7.5YR6/6) dry, slightly gravelly loamy coarse sand; structureless, single grained; soft dry, slightly friable moist, non-sticky and non-plastic when wet; rapidly permeable; few thin broken cutans; common fine and medium roots; common fine tubular pores; smooth gradual boundary; (sample 11.47),

B22 82 - 108 cm yellowish red (5YR4/6) moist, reddish yellow (5YR6/6) dry, slightly gravelly coarse sandy loam; structureless massive; soft dry, friable moist, non-sticky and non- plastic when wet; rapidly permeable; few thin broken cutans; common fine tabular pores; ,smooth gradual boundary; (sample 11.48),

B3 108 - 140 cm brown (7.5YR5/4) moist, light brown (7.5YR6/4) dry, slightly gravelly coarse sandy loam; structureless massive; soft dry, friable moist, non-sticky and non-plastic when wet; rapidly permeable; few thin broken cutans; few fine and medium roots; common medium distinct yellowish red (5YR4/6-moist) mottles, common fine tubular pores; smooth gradual boundary; (sample 11.49),

C 140 - 173 cm brown (10YR5/3) moist, pale brown (10YR6/3) dry, slightly gravelly coarse sandy loam; structureless massive; slightly hard dry, friable moist, slightly sticky and non- plastic when wet; rapidly permeable; few thin broken cutans; few fine tubular pores; common fine faint and sharp yellowish brown (10YR5/6-moist) mottles; few fine and medium roots; (sample 11.50),

(II)C 173+ cm coarse and very coarse angular gravel.

202 Laboratory data of profile No. 11

Particle size distribution (M) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20 <2 pH 1 :5 No. in cm. zon mm. 500 200 100 50 20 2 H2O KCI

11.45 0- 16 Al 2.4 38.9 21.7 27.5 1.8 4.0 0.9 5.2 7.0 5.0 11.46 16- 45 Bl 4.8 29.3 19.2 32.1 6.6 4.5 1.0 7.3 6.7 4.6 11.47 45- 82 B21 10.1 32.3 18.8 25.4 8.1 4.2 1.0 10.2 5.8 4.2 11.48 82-108 B22 8.3 33.6 19.8 18.6 9.7 4.7 1.4 12.2 5.5 4.0 11.49 108-140 B3 9.0 33.9 21.9 17.5 7.0 5.5 1.8 12.4 5.6 4.2 11.50 140-173 C 10.4 29.0 20.7 19.9 8.3 5.8 3.1 13.2 5.6 4.2

Exchangeable cations in meq/100 g Organic matter

Sample Ca Mg K Na Sum C.E.C Base % C % N P2OS No. sat. %) ppm

11.45 0.90 0.10 0.13 tr 1.13 2.19 52 0.23 0.03 4 11.46 0.50 tr 0.13 tr 0.63 1.75 36 0.22 0.02 1 11.47 0.50 tr 0.13 tr 0.63 2.19 29 0.19 5 11.48 0.50 tr 0.21 0.17 0 88 2.63 34 0.18 1 11.49 0.81 0.10 0.31 tr 1 22 2.63 46 0.24 5 11.50 0.91 0.20 0.31 tr 1 42 3.08 46 0.16 2

Elementa composition of the fine earth (% by weight

Sample SiO2 Al2 O3 Fe2 O3 TiO, CaO MgO KiO Na2O P,O, Sum Loss on No. 'gnition %

11.45 91.6 5.5 1.1 0.35 0.13 0.76 2.42 0.23 0.08 102.1 1 7 11.46 91.7 4.6 1.1 0.31 0.10 0.70 2.10 1.60 0.04 102.2 1 7 11.47 89.6 6.6 1.4 0.33 0.11 0.61 2.33 1.12 0.06 102.6 2 0 11.48 90.5 6.2 1.4 0.38 0.11 0.00 2.32 1.55 0.09 102.2 2 5 11.49 90.0 6.1 1.3 0.35 0.11 0.49 1.98 0.58 0.07 100.9 2 5 11.50 87.7 8.6 1.7 0.54 0.12 0.42 2.31 0.25 0.04 101.6 2 5

Trace element content of the fine earth (in ppm) SiOj SiOj A12O 3

Sample Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2C 3 No. 11.45 212 9 21 34 23 20 800 34 28.4 25.10 7.6 11.46 108 9 15 18 19 17 <100 32 33.8 29.52 6.9 11.47 8 12 6 24 19 14 <100 12 24.7 21.63 7.0 11.48 76 5 8 25 19 6 <100 2 22.9 20.14 7.2 11.49 80 15 16 21 19 24 <100 6 25.1 22.07 7.3 11.50 44 21 18 4 19 18 <100 20 17.4 15.44 7.8

Elemental composition of the clay fraction (% by weight)

Sample SiO, A12O3 Fe,O 3 TiO2 CaO MgO K Na:O P No.

11.45 51 .4 29. 7 6.9 1.46 3.77 0.59 1.82 0.00 4.28 11 .47 55.1 31. 2 7.2 1.84 0.13 0.78 2.61 0.68 0.45 11 .50 53.1 31. 9 7.2 1.36 1.83 .0.78 1.59 0.35 1.85

Mineralogy of the clay fraction Molar ratios Sample K I Mt Mi V Chi SiO, ALO, No.

11.45 2.9 2.56 6.7 11.46 11.47 3.0 2.62 6.8 11.48 11.49 11.50 2.8 2.47 7.0

203 DESCRIPTION OF PROFILE NO' 12

Ap 0-15 cm Dark brown (7.5YR3/2) moist, brown (7.5YR4/4) dry, slightly gravelly coarse sandy loam; moderate fine and medium angular clods; hard dry, friable moist, very slightly sticky non-plastic wet; common fine and a few medium roots; common medium root channels; few termite holes; clear smooth boundary; (sample 12.39),

B21 15 - 32 cm dark reddish brown (5YR3/2) moist and (5YR3/4) dry, fine gravelly sandy clay loam; massive; very hard dry, friable moist, sticky and slightly plastic wet; few fine and medium roots; appreciable amount of coarse sand; few small termite channels; smooth clear boundary; (sample 12.40),

B22 32 - 59 cm dark reddish brown (2.5YR2/4) moist and (2.5YR3/4) dry, sandy clay; massive; very hard dry, friable moist, sticky and plastic wet; few fine and medium roots; few termite channels greyish in colour; common medium broken cutans clearly visible on peds and around sand grains; appreciable amount of coarse sand and a little very fine gravel; clear smooth boundary; (sample 12.41),

B2t 59 - 87 cm dark reddish brown (5YR3/3) moist and (5YR3/4) dry with yellowish red (5YR4/6-dry) clay; massive; very hard dry, friable moist, sticky and plastic wet; very few fine, medium and coarse roots; common termite activity; appreciable amount of coarse sand and a little very fine angular gravel; occasionally medium and coarse angular quartz gravel is encountered on the boundary to the horizon below; smooth clear boundary; (sample 12.42),

B3 87 — 102 cm dark reddish brown (5YR3/4) moist, gravelly sandy clay; structureless; slightly hard dry, friable moist, very slightly sticky non-plastic wet; common very fine and fine angular gravel; increasing amount of decomposed rock fragments with depth; gradual wavy boundary; (sample 12.43),

C 102 — 125 cm gravelly clay with vivid bluish black and yellowish brown (10YR5/8) moist mottling; (sample 12.44),

R 125+ cm hard granitic rock of coarse grained texture.

204 Laboratory data of profile No. 1 2

Particle size distribution (/i) in % weight Sand Silt Clay Sample Deptr1 Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm zon mm. 500 200 100 50 20 2 H,O KCI

12.39 0- 15 Ap 5.2 30.7 19.9 15.1 4.1 7.4 5. 5 17.3 6.9 5.7 12.40 15- 32 B21 6.6 25.5 14.9 12.0 4.3 7.1 6.6 29.6 6.8 5.2 12.41 32- 59 B22 6.8 23.2 11.4 8.8 4.2 6.6 5.6 40.2 6.6 5.0 12.42 59- 87 B2t 7.7 23.0 9.8 7.5 4.5 5.5 6..7 43.0 6.8 5.3 12.43 87-102 B3 24.1 21.2 9.8 8.3 4.4 6.7 7.,8 41.8 7.3 5.8 12.44 102-125 C 45.0 19.1 6.1 4.4 2.9 6.9 10. 8 49.8 7.3 5.9

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P:O No. sat. % %N %C ppm

12.39 4.46 1.03 0.68 tr 6.17 8.81 70 0.64 0.07 10 12.40 5.92 1.88 0.68 tr 8.48 12.42 68 0.61 0.07 2 12.41 7.92 2.67 0.50 tr 11.12 15.66 71 0.45 4 12.42 8.97 2.80 0.32 tr 12.09 16.60 73 0.40 1 12.43 11.26 3.06 0.42 tr 14.74 17.08 86 0.37 4 12.44 13.48 4.19 0.51 tr 18.18 20.00 91 0.25 2

Elemental composition of the fine earth (% by weight)

Sample SiO, AU O3 Fe2Oj TiO, CaO MgO K, 0 Na,O P,O, Sum Loss on No. ignition %

12.39 76.9 12.8 3.4 0.52 0.62 0.57 3.47 2.21 0.08 100.6 10.4 12.40 74.0 15. 1 4.9 0.63 0.54 0.31 3.25 0.32 0.07 99.1 6.7 12.41 68.2 16. 2 5.4 0.64 0.54 1.06 3.03 2.54 0.08 97.7 8.3 12.42 68.5 18. 5 6.1 0.68 0.57 1.02 3.21 0.00 0.07 98.6 9.1 12.43 68.7 18. 9 6.6 0.67 0.66 0.97 3.34 0.17 0.10 100.1 9.2 12.44 61.3 24. 5 7.9 0.58 1.40 1.65 2.93 0.13 0.05 100.4 11.9

SiO, SiO, Sample Trace element content of the fine earth (in ppm) A1,O3 No. Mn Cu Zn Cr Co Ni Ba Sr A1,O3 R,O3 F^O,

12.39 388 28 28 43 31 27 <100 52 10.2 8.72 5.9 12.40 422 18 28 110 35 40 380 32 8.3 6.88 4.9 12.41 440 12 23 52 8 24 1000 12 7.2 5.89 4.7 12.42 454 15 33 40 15 45 1260 16 6.3 5.20 4.8 12.43 460 21 35 110 27 50 1280 20 6.2 5.05 4.5 12.44 292 24 86 14 51 85 380 19 4.2 3.52 4.9

Elemental composition of the clay fraction (% by weight)

Sample SiO, Fe,O3 TiO, CaO MgO O Na2 O P,O, No.

12.39 49.3 31. 1 12.0 1.09 1.53 1. 82 2.20 0.00 0.99 12.41 50.0 32. 12.2 1.07 0.07 1. 54 2.31 0.00 0.64 12.44 49.9 33. 6 10.5 0.84 1.35 1. 44 1.62 0.00 0.75

Mineralogy of the clay fraction Molar ratios Sample Mt Mi Chi SiO; SiO, A1,O, No. Al,Oj R,O,

12.39 2.7 2.16 4.1 12.40 12.41 2.6 2.12 4.2 12.42 12.43 12.44 2.5 2.10 5.0

205 DESCRIPTION OF PROFILE NO. 13

Al 0-21 cm Dark reddish brown (5YR3/3) moist, brown (7.5YR4/4) dry, slightly gravelly coarse sandy loam; very weak fine subangular blocky structure; soft dry, slightly friable moist, non-sticky, non-plastic wet; many fine and medium thick roots; many fine and medium tubular pores; smooth gradual boundary; (sample 13.59),

B21 21 - 44 cm dark reddish brown (5YR3/3) moist, reddish brown (5YR4/4) dry, gravelly coarse sandy loam; structureless, massive; hard dry, friable moist, slightly sticky and plastic wet; common fine and medium and occasional thick roots; many medium and coarse pores; coarse fragments increasing with depth; clear smooth boundary; (sample 13.60),

B22 44 - 76 cm dark reddish brown (2.5YR3/4) moist, yellowish red (5YR4/6) dry, gravelly coarse sandy loam; structureless, single grained; loose, dry and moist, non-sticky, non- plastic wet; many very fine and fine roots; coarse black, red and yellowish mottling in respectively 5YR and 7.5YR hues in some parts of the horizon; wavy gradual boundary; (sample 13.61),

B3 76 —118 cm reddish brown (5YR4/4) moist, strong brown (7.5YR5/6) dry, gravelly sandy clay loam; few fine and very fine roots; common fragments of partly decomposed granitic rock; gradual wavy boundary; (sample 13.62),

C 118 — 175+cm partly decomposed very hard granite with a high amount of quartz, weathering products have clayey texture, no roots; (sample 13.63).

206 Laboratory data of profile No. 13

Particle size distribution (ju) in '. > weight Sand Silt Clay Sample Depth Hori- 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm. zon 500 200 100 50 20 2 H,O KC1

13.59 0- 21 Al 16.7 35.5 19.5 15.7 8.3 8.0 4.3 8.7 6.6 5.1 13.60 21- 44 B21 24.2 36.9 17.8 13.0 7.7 5.6 4.1 14.9 6.2 4.5 13.61 44- 76 B22 58.1 38.8 16.1 8.6 6.2 4.7 4.3 21.3 6.0 4.4 13.62 76-118 B3 60.2 30.6 9.8 9.8 7.6 7.5 5.8 23.7 6.2 4.5 13.63 118-175 C 70.1 28.4 8.6 4.8 2.7 2.3 4.7 48.5 6.5 4.3

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2OS No. sat. % %C %N

13.59 2.27 0.49 0.26 0.17 3.19 15.69 20 0.43 0.05 13.60 2.53 1.16 0.26 0.17 4.12 6.70 62 0.41 0.05 13.61 3.05 1.58 0.21 0.09 4.93 8.28 60 0.41 13.62 3.56 2.15 0.32 0.17 6.20 9.38 66 0.26 13.63 9.71 10.45 0.43 0.55 21.14 26.59 79 0.24

Elemental composition of the fine earth (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2OS Sum Loss on No. ignition '

13.59 81.0 9.7 2.2 0.35 0.52 0.43 3.85 0.75 0.10 98.9 3.0 13.60 81.0 10.2 2.8 0.38 0.33 0.14 3.53 0.68 0.05 99.2 4.0 13.61 79.0 13.3 4.3 0.39 0.33 0.88 3.88 0.91 0.10 103.1 5.0 13.62 73.6 15.0 4.8 0.58 0.34 0.85 3.11 0.00 0.02 98.3 5.2 13.63 77.7 16.0 4.8 0.56 0.33 0.70 3.07 0.88 0.07 104.1 10.2

Trace element content of the fine earth (in ppm) SiO2 SiO2 A12O3

No. Mn Cu Zn Cr Co Ni Ba Sr Al2Oj R2O3 Fe2O3

13.59 200 9 11 35 12 17 1260 16 14.2 12.39 7.0 13.60 142 21 18 40 27 24 1260 32 13.4 11.42 5.7 13.61 202 28 21 35 31 45 1260 31 10.1 8.36 4.9 13.62 238 12 17 60 19 27 <100 38 8.3 6.91 4.9 13.63 84 18 27 140 27 40 1260 35 8.2 6.91 5.3

Elemental composition of the clay fraction (% by weight) Sample SiO A1 O K Na O P 2 2 3 Fe ,o3 TiO2 CaO MgO 2 No.

13.59 49.4 28.0 12.2 1.33 2.81 1.41 2.08 0.00 2.47 13.61 53.2 29.7 11.8 1.04 0.66 0.92 1.50 0.49 0.72 13.63 52.3 31.2 10.9 0.93 1.64 1.58 0.75 0.00 0.69

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi SiO2 SiO, A12O3 No. A12O3 R2O3 Fe2O3

13.59 xx 3.0 2.36 3.6 13.60 XX 13.61 4.0 tr X 3.0 2.43 13.62 tr 13.63 2.9 2.33 4.5

207 DESCRIPTION OF PROFILE NO. 14

Al 0 - 18 cm Dark brown (7.5YR3/2) moist, brown (7.5YR4/4) dry, slightly gravelly loamy coarse sand; structureless, single grained; slightly hard dry, slightly friable moist, non- sticky non-plastic wet; common fine and medium roots; many fine tubular pores; few termite channels; smooth gradual boundary; (sample 14.64),

B2 18 - 56 cm reddish brown (5YR4/5) moist, yellowish red (5YR4/8) dry, slightly gravelly coarse sandy loam; structureless, single grained; slightly hard dry, friable moist, slightly sticky, slightly plastic wet; common very fine and fine and few medium and coarse roots; common fine tubular pores; clear wavy boundary; (sample 14.65),

B3 56 - 90 cm yellowish red (5YR4/6) moist and (5YR5/6) dry, gravelly coarse sandy loam; loose dry and moist, non-sticky, non-plastic wet; common fragments of partly decomposed rock; common distinct black and reddish mottling; clear in some parts gradual wavy boundary; (sample 14.66),

C 90 — 110+cm hard, partly decomposed pink granite of gravelly coarse sandy loam texture; very few fine roots; (sample 14.67).

208 Laboratory data of profile No. 14

Particle size distribution (p) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20 <2 PH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H2(3 KC1

14.64 0- 18 Al 6.1 30,.1 19.3 21.4 13.3 6.4 2.7 6.8 6.3 4.8 14.65 18- 56 B2 12.6 30,.7 20.4 18.3 9.6 6.5 2.9 11.6 6.1 4.5 14.66 56- 90 B3 40.0 41,,6 17.8 9.7 7.3 5.7 4.3 13.6 6.0 4.4 14.76 90-110 C 48.4 34,,1 17.5 10.8 9.9 9.0 6.6 12.1 6.4 4.9

Exchange;ible cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 sat. % %C %N ppm

14.64 1.26 0.33 0.26 0.17 2.02 3.59 56 0.29 0.03 8 14.65 1.36 0.30 0.26 0.17 2.09 3.77 55 0.28 0.03 5 14.66 1.77 0.83 0.15 0.17 2.92 4.92 59 0.20 8 14.67 2.78 1.03 0.21 0.17 4.19 5.81 72 0.16 7

Elemental composition of the fine earth (% by weight)

Sample SiO2 Al2 O3 Fe2O3 TiO2 CaO MgO K 2O Na2O P2O5 Sum Loss on No. ignition %

14.64 77.0 15.5 4. 8 0.60 0.42 1.01 3.12 0.00 0.05 102.5 2.2 14.65 72.9 14.4 4,,6 0.95 1.83 1.66 1.44 0.00 0.12 97.8 2.8 14.66 77.7 16.1 8..4 1.00 1.90 1.82 1.64 0.00 0.06 108.6 3.9 14.67 75.1 15.6 7,,9 0.93 1.94 2. 28 1.55 0.00 0.09 105.3 3.9

Trace element content of the Ifine earth (in ppm) SiOj SiO Al2 Sample 2 O3 No. Mn Zn Cu Cr Co Ni Ba Sr A12O3 R2o3 Fe2 o3 14.64 310 7 5 25 19 10 380 32 8.4 7.04 5.1 14.65 160 14 15 17 27 6 100 30 8.6 7.16 4.9 14.66 328 22 28 5 19 18 100 51 8.2 6.16 3.0 14.67 864 8 9 37 15 10 380 20 8.2 6.19 3.1

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2O5 No.

14.64 50 .3 27 .6 11. 0 1.27 3.20 1.11 2.26 0.00 3.28 14 .65 51 .3 30 .9 12. 2 1.33 0.09 1.12 2.22 0.02 0.86 14.67 51 .4 29 .1 11. 7 1.13 1.52 1.08 2.00 0.94 1.16

Mineralogy of the clay fraction Molar ratios

Sample K Mt Mi Chi SiO, SiO2 A12O3 No. A12O3 R2O3 Fe2O3

14.64 XX 3.1 2.47 3.9 14.65 tr X 2.8 2.25 4.0 14.66 tr tr 14.67 tr tr 3.0 2.39 3.9

209 DESCRIPTION OF PROFILE NO. 15

All 0-2 cm Black (10YR2/1) moist, greyish brown (10YR5/2) dry, clay loam; weak medium platy structure; very hard dry, firm moist, slightly sticky and plastic wet; common distinct medium brown (7.5YR4/4) mottles, common very fine pores; abrupt wavy boundary; (sample 15.68),

A12 2—43 cm very dark grey (7.5YR3/1) moist, dark greyish brown (10YR4/2) dry, coarse sandy loam; structureless, massive; hard dry, friable moist, slightly sticky and plastic wet; little fine gravel; common medium tubular pores; common fine medium and few thick roots decreasing in number with depth; clear wavy boundary; (sample 15.69),

B2g 43 — 69 cm very dark grey (10YR3/1) moist, greyish brown (10YR5/2) dry, sandy clay loam; moderate coarse columnar structure; top of the columns have a light brownish grey (10YR6/2) colour; many fine prominent dark red (2.5YR3/6) mottles and a few faint brown (10YR5/3) mottles; common coarse sand grains; few fine pores; common very fine, fine and few medium roots; common thin broken cutans; the boundary with underlying horizon is clear and wavy; (sample 15.70),

B2g 69 - 91 cm dark grey (10YR4/1) dry and moist, slightly gravelly sandy clay with an appreciable amount of coarse sand; consistence as horizon above; structureless, massive; few fine and medium roots; common fine distinct dark red (2.5YR3/6) and strong brown (7.5YR5/6) mottles; common thick large cutans; slightly wavy gradual boundary; (sample 15.71),

B2g 91 - 127 cm grey (10YR5/1) moist and (10YR6/1) dry, slightly gravelly sandy clay, common coarse sand; very hard dry, firm moist, slightly sticky and plastic wet; prominent brownish yellow (10YR6/6) and yellowish brown (10YR5/6) medium and coarse mottles, and few small prominent bluish black mottles; very few very fine roots; common medium and large cutans and a few small slickensides in the lower part of the horizon; wavy gradual boundary; (sample 15.72),

B3 127 - 158 cm greyish brown (10YR5/2) moist and brown (10YR5/3) moist, slightly gravelly sandy clay loam; some yellowish and greyish mottling; calcareous; structureless, massive; common small cutans in the upper part of the horizon, and occasional fine roots; gradual wavy boundary; (sample 15.73),

C 158 — 180+cm greyish brown (10YR5/2) moist, strongly decomposed granite rock of sandy clay texture with prominent small dark bluish mottles; (sample 15.74).

210 Laboratory data of profile No. 15

Particle size distribution {ß) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20 <2 pH 1: 5 No. in cm zon mm. 500 200 100 50 20 2 H:O KCI

15.68 0- 2 All 1.1 19.5 6.6 6.3 7.1 11.7 19 4 29.4 6.5 5.2 15.69 2- 43 A12 4.4 39.5 17 4 8.3 5.9 4.4 8 9 15.6 6.2 4.6 15.70 43- 69 B2g 6.1 42.4 15 3 6.9 4.8 3.1 5 9 21.6 7.2 5.3 15.71 69- 91 B2g 10.0 34.7 11 4 6.7 3.8 4.4 4 0 35.0 8.5 6.6 15.72 91-127 B2g 10.4 31.2 12 1 7.3 5.1 4.6 4.2 35.5 8.8 6.8 15.73 127-158 B3 10.1 31.1 13 1 7.4 5.2 4.8 4.4 34.0 8.7 6.8 15.74 158-180 C 32.8 27.7 11 9 7.0 4.7 5.9 3.5 39.2 8.8 6.6

Exchangeable cations in meq/1 00 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P;O, No. sat. %• % C % N

15.68 7.72 2.42 1.26 0.17 11.57 15.65 74 1.84 0 17 16 15.69 2.79 0.96 0.42 0.17 4.34 7.15 61 0.80 0.05 7 15.70 3.82 2.21 0.21 0.68 6.92 8.96 77 0.35 5 15.71 6.95 4.57 0.42 3.14 15.08 15.33 98 0.17 1 15.72 7.27 4.24 0.47 3.68 15.66 15.78 99 0.17 1 15.73 7.30 4.77 0.48 4.24 16.79 16.13 100 0.11 3 15.74 7.03 5.82 0.58 5.16 18.59 18.81 99 0.15 3

Elemental composition of the fine earth (% by weight) Sample SiO, Al, Oj Fe, Oj TiO, CaO MgO K, O Na,O P,O, Sum Loss on No. ignition %

15.68 75.1 16 5 8.3 1 00 1.89 2.81 1.65 1.01 0.12 108.4 9.4 15.69 74.2 17.0 8.9 1 03 2.02 2.37 1.73 0.16 0.04 107.4 4.3 15.70 76.6 16.0 7.2 0.68 1.55 4.14 2.31 0.12 0.07 108.7 5.5 15.71 86.3 12 3 4.7 0.70 1.10 0.48 0.00 0.00 0.05 105.6 10.3 15.72 81.8 15 3 4.5 0 58 0.41 0.60 4. 8 0.89 0.05 108.3 7.4 X 15.73 73.0 21 0 5.8 0 49 0.74 1.92 2.64 0.88 0.08 106.6 4.2 15.74 86.1 7 5 1.5 0.43 0.24 0.87 3.62 0.34 0.14 100.8 7.7

Trace element content of the fine ear th (in ppm) SiO, SiO, A1,O 3

No. Mn Cu Zn Cr Co Ni Ba Sr Al.Oj R,O3 Fe,O 3

15.68 440 15 25 70 23 14 380 32 7.7 5.85 3.1 15.69 330 21 21 40 35 19 <100 30 7.4 5.56 3.0 15.70 230 28 26 60 15 10 800 20 8.1 6.31 3.5 15.71 176 21 34 127 19 14 380 6 11.9 9.60 4.0 1 15.72 120 5 16 32 <2 3 <100 6 9.1 7.67 5.3 15.73 176 <5 19 25 7 10 <100 6 5.9 5.02 5.7 I 15.74 320 12 18 27 19 18 <100 12 19.4 17.18 7.7 1

Elemental composition of the clay fraction (% ay weight)

Sample SiO, A1,O3 Fe,C3j TiO, CaO MgO K,O Na,0 o. i No.

15.68 54.4 29.3 9.4 1.44 1.31 1.36 2.21 0.00 0 57 J 15.70 54.4 27.8 10.6 1.83 0.09 1.73 2.95 0.00 0.72 j 15.74 55.6 27.3 9.9 1.06 1.85 1.82 1.73 0.00 0 74 I Mineralogy of the clay fraction Molar ratios Sample K I Mt Mi V Chi Q SiO, SiO, AI,O J No. Al,O R,O3 Fc,O i 15.68 ++ + XX 3.2 2.61 4.9 1 15.69 ++ + XX 15.70 + ++ + X 3.3 2.68 4.1 15.71 + ++ + X 15.72 ++ + + tr X 15.73 ++ + + tr tr XX 15.74 ++ + + tr tr XX 3.5 2.81 4.3

211 DESCRIPTION OF PROFILE NO. 16

Al 0-12 cm Dark brown (7.5YR3/2) moist, pinkish grey (7.5YR6/2) dry, slightly gravelly coarse sand; structureless, single grained; soft dry, loose moist, non-sticky non-plastic wet; many very fine and fine roots; smooth gradual boundary; (sample 16.131),

B21 12- 46 cm brown (7.5YRR4/4) moist, light brown (7.5YR6/4) dry, gravelly loamy coarse sand; consistence as horizon above; common fine medium and thick roots; common fine pores; coarse fragments increasing with depth; gradual wavy boundary; (sample 16.132),

B22 46 - 67 cm brown (7.5YR5/4) moist, light brown (7.5YR6/4) dry, gravelly loamy coarse to very coarse sand; structureless, single grained; slightly hard dry, loose moist, non-sticky, non-plastic wet; common fine and medium roots; strong wavy boundary varying between 60 and 95 cm depth; (sample 16.133),

B3 67 - 98 cm brown (7.5YR5/3) moist, pinkish grey (7.5YR7/2) dry, gravelly loamy coarse sand; with common prominent medium and coarse dark red (2.5YR3/6) and black (2.5YR2/0) concretions; few fine medium roots; gradual wavy boundary; (sample 16.134),

C 98 — 130+cm partly decomposed very hard, coarse grained granite rock of a very gravelly loamy coarse sand texture; (sample 16.135).

212 Laboratory data of profile No. 16

Particle size distribution (ß) in% weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1: 5 No. in cm zon mm. 500 200 100 50 20 2 H2O KC1

16.131 0- 12 Al 14.1 38.8 24.3 15.1 9.1 5.5 2.4 4.8 5.7 4.6 16.132 12- 46 B21 17.2 43.6 21.7 14.3 7.3 4.8 3.1 5.2 5.6 4.4 16.133 46- 67 B22 18.9 39.8 25.7 13.1 7.0 4.5 4.1 5.8 5.7 4.5 16.134 67- 98 B3 25.0 28.9 35.4 12.6 6.7 5.1 4.1 7.2 5.7 4.4 16.135 98130 C 86.7 52.7 23.8 4.7 3.8 4.3 4.3 6.4 5.7 4.4

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C. E.C. Base Organic matter P,OS No. sat.. 7o %C % N ppm

16.131 tr 0.12 0.08 tr 0.20 1.75 1 1 0.29 0.134 1 16.132 tr 0.13 0.08 tr 0.21 1.75 12 0.22 0.132 tr 16.133 tr 0.20 0.08 tr 0.28 1.31 21 0.14 1 16.134 tr 0.20 0.08 tr 0.28 1.31 21 0.17 tr 16.135 tr 0.26 0.13 tr 0.39 1.75 22 0.11 tr

Elemental composition of the fine eartrl (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K,o Na2O P2O:; Sum Loss on No. ignition %

16.131 86.5 8.4 0.8 0.18 0.14 0. 22 4.94 1.53 0.05 102.8 1.6 16.132 85.7 8.4 0.9 0.20 0.13 0. 29 4.93 0.00 0.05 100.6 1.5 16.133 86.0 9.1 0.9 0.19 0.15 0.46 4. 56 0.00 0.10 101.2 1.6 16.134 83.6 9.0 1.2 0.27 0.12 0.00 5. 16 0.66 0.03 100.1 2.2 16.135 79.9 11.5 2.7 0.31 0.23 0.,42 5. 22 2.96 0.02 102.4 2.0

Trace element content of the fine earth (in ppm) Sample SiO2 SiO2 A12O 3 No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R:O3 Fe,O 3

16.131 66 < 5 <5 76 <2 12 760 3 17.5 16.54 16.5 16.132 30 <5 <5 <5 18 34 720 16 17.3 16.25 15.3 16.133 <10 <5 <5 60 20 38 720 <2 16.1 15.19 16.4 16.134 276 <5 <5 52 16 <2 720 10 15.7 14.50 11.9 16.135 280 20 8 20 50 14 720 19 11.7 10.15 6.8

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe 2O3 TiO2 CaO MgO K, O Na2O P, os No.

16.135 47.0 26.5 6.8 1.30 6.65 0.53 2.44 0.29 8. 50

Mineralogy of the clay fraction Molar ratios

Sample KI Mt Mi V Chi Q SiO2 SiO, A12O 3 No. A1 O O Fe O 2 3 R2 3 2 3

16.131 XX 16.132 XX 16.133 XX 16.134 XX 16.135 + ++ tr XX 3.0 2.!i9 6.2

213 DESCRIPTION OF PROFILE NO. 17

All 0 - 15 cm Very dark greyish brown (10YR3/2) moist, greyish brown (10YR5/2) dry, loamy coarse sand; structureless, single grained; soft dry, friable moist, non-sticky and non-plastic when wet; common fine pores; many very fine and fine and medium roots; common coarse fragments of gravel; smooth gradual boundary; (sample 17.151),

A12 15 — 34 cm very dark greyish brown (10YR3/2) moist, brown (10YR5/3) dry, slightly gravelly loamy coarse sand; structureless, single grained; non-sticky and non-plastic when wet; common fine pores; many very fine, fine and few medium and coarse roots; abrupt wavy boundary; (sample 17.152),

(II)C 34— 45+cm coarse fragments of granite and quartz gravel.

214 Laboratory data of profile No. 17

Particle size distribution (M) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1: 5 No. in cm zon mm. 500 200 100 50 20 2 H2O KC1

17.51 0-15 All 5.4 34.9 23.4 18.5 9,,8 5.9 2.5 5.0 6.1. 4.8 17.52 15-34 A12 11.8 28.5 25.0 21.1 6.6 8.4 3.3 7.1 6.3 5.1

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 No. sat. % %C %N ppm

17.51 1.05 0.07 0.13 0.17 1.42 3.14 45 0.34 0.04 9 17.52 1.26 0.12 0.21 0.17 1.76 3.14 56 0.29 0.03 7

Elemental composition of the fine earth (% by weight)

Sample SiO2 A12O, Fe2 O3 TiO, CaO MgO K2O Na2O P2OS Sum Loss on No. ignition %

17.51 84.9 8.5 1.0 0.25 0.20 0.66 4.71 0.49 0.08 100.8 1.7 17.52 85.3 10.7 1.2 0.40 0.24 0.04 5.23 0.89 0.10 104.1 2.0

Trace element content of the fine earth (in ppm) Sample SiO2 SiO2 A12O 3 No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2CP3 17.51 108 <5 2 18 15 6 <100 6 16.9 15.78 14.1 17.52 24 9 6 40 15 24 <100 6 13.5 12.60 14.2

Elemental composiltion of the clay fraction (% by weight)

Sample SiO2 A12O3 FCJOJ TiO2 CaO MgO K2O Na2(3 P. No.

17.52 51.4 26.9 7.3 1.31 4.48 0.58 2.71 0.54 4..78

Mineralogy of the clay fraction Molar ratios

Sample K I Mt Mi V Chi Q SiO2 SiO2 A!2O3 No. A12O,, R2O3 Fe,(

17.51 ++ + XX 17.52 ++ + XX 3.2 2.76 5.7

215 DESCRIPTION OF PROFILE NO. 18

Ap 0-15 cm Dark reddish brown (7.5YR3/2) moist, greyish brown (10YR5/3) dry, coarse sandy loam; structureless, massive; very hard dry, slightly friable moist, non-sticky, nonplastic wet; common fine tubular pores; many very fine and fine roots; common ant activity; smooth gradual boundary; (sample 18.136),

B21 15- 36 cm dark brown (7.5YR3/2) moist, brown (7.5YR4.5/2) dry, coarse sandy loam; structureless massive; very hard dry, friable moist, slightly sticky and slightly plastic wet; common fine and medium roots; common fine and medium tubular pores; common ant activity; smooth clear boundary; (sample 18.137),

B22 36 — 55 cm brown (7.5YR4.5/4) moist and dry sandy clay loam; structureless, massive; very hard dry, firm moist, slightly sticky and plastic wet; common distinct fine and medium dark red (2.5YR3/6) mottling in the lower part of the horizon and a few bluish black mottles; common coarse fragments; common pores; few fine and medium roots; clear wavy boundary; (sample 18.138),

B2g 55 — 104 cm greyish brown (10YR5/2) moist, light brownish grey (10YR6/2) dry, sandy clay; moderate to weak medium columnar structure; extremely hard dry, firm moist, slightly sticky and plastic wet; common fine distinct dark red (2.5YR3/6), medium yellowish red (5YR5/6) mottles; many fine and medium strong brown (7.5YR5/6) mottles; few fine bluish black mottles; common large thin cutans; very few fine roots; gradual in some parts clear boundary; (sample 18.139),

B3 104 - J43 cm brown (10YR5/3) moist and grey (10YR5/1) dry, slightly gravelly sandy clay; common distinct medium yellowish red (5YR4/6) and strong brown (7.5YR5/6) mottles; occasionally bluish black mottling; common medium and large thick cutans; few pores; clear in some parts gradual wavy boundary; (sample 18.140),

C 143 — 160+cm partly decomposed hard, coarse grained granitic rock of very gravelly sandy clay loam texture; (sample 18.141).

216 Laboratory data of profile No. 18

Particle size distribution (M) in % weight) Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200 100- 50- 20- <2 pH 1: 5

' H,0 KC1

18.136 0- 15 An 1.4 33.2 20.7 13.3 8.3 6.2 7. 0 11.3 6.2 5.2 18.137 15- 36 B21 0.6 33.7 18.2 10.6 6.0 5.2 6. 6 19.7 6.1 4.9 18.138 36- 55 B22 3.6 30.8 16.4 11.0 6.2 2.5 7. 2 25.9 6.2 4.7 18.139 55- 104 B2g 4.1 23.0 12.4 8.9 5.9 4.0 5. 9 39.9 6.9 5.4 18.140 104-143 B3 3.2 22.5 11.9 8.5 5.0 4.0 6. 7 41.4 7.5 6.4 18.141 143- 160 C 57.8 26.4 12.2 7.3 5.4 3.2 6. 1 40.4 7.3 6.3

Exchangeablc cations in ineq/1 00 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P,O5 No. sat. "/.b %C %N ppm

18.136 1.41 0.67 0.44 tr 2.52 5.26 48 0.58 0.05 1 18.137 1.66 1.67 0.25 tr 3.58 6.62 54 0.38 0.04 tr 18.138 2.44 2.21 0.24 tr 4.89 7.53 65 0.13 tr 18.139 6.91 4.75 0.45 0.14 12.25 14.81 83 0.30 tr 18.140 7.43 5.98 0.45 0.18 14.04 16.62 85 0.17 tr 18.141 8.50 6.69 0.48 0.18 15.85 16.70 95 0.12 tr

Elemental composition of the fine earth (% by weight)

Sample SiO, A12O3 Fc,<0, TiO; CaO MgO K,O Na,O P,O, Sum Loss on No. ignition %

18.136 86.9 7.7 1.9 0.39 0.25 1.79 3.59 0.00 0.10 102.6 3.4 18.137 81.5 11.1 3.1 0. 57 0.30 2.09 3.55 0.00 0.13 102.4 4.2 18.138 81.9 11.8 3.7 0.55 0.25 0.45 3.27 0.53 0.06 102.4 4.9 18.139 73.4 15.1 4.8 0. 59 0.36 2.32 3.05 0.47 0.10 100.2 7.5 18.140 74.4 15.6 5.0 0.62 0.46 2.68 3.00 0.33 0.13 102.3 7.9 18.141 74.8 14.7 4.9 0. 56 0.46 1.78 3.04 0.00 0.03 99.7 7.7

SiO, AljO Sample Trace element content of the fine earth {in ppm) SiO, 3

No. Mn Cu Zn Cr Co Ni Ba Sr R,O3 R2O3 Fe,0 3

18.136 216 <5 <5 46 20 4 560 11 19.2 16.56 6.3 18.137 150 28 6 96 26 10 600 6 12.4 10.52 5.5 18.138 124 38 21 352 18 104 600 13 11.8 9.86 5.1 18.139 86 26 23 228 26 64 520 13 8.2 6.86 4.9 18.140 194 20 20 52 18 36 400 <2 8.1 6.71 4.9 18.141 280 26 11 120 16 40 560 11 8.6 7.13 4.8

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A1,O3 Fe,O3 TiO, CaO MgO Na,O P,OS No.

18. 136 51.4 24.8 9.5 1.45 4.73 0.94 2.29 0.00 4.93 18. 138 52.6 29.0 10.6 1.34 1.55 1.48 1.97 0.00 1.45 18. 141 54.5 28.0 10.1 1.03 2.25 1.61 1.45 0.03 0.97

Mineralogy of the ctay fraction Molar ratios

Sample K 1 Mt Mi Chi SiO, SiO AI,O3 No. AI,O3 Fe,O3

18.136 3.5 2.83 4.1 18.137 18.138 3.1 2.50 4.3 18.139 18.140 18.141 3.3 2.68 4.3

217 DESCRIPTION OF PROFILE NO. 19

Al 0- 15 cm Dark reddish brown (5YR3/4) moist, brown (7.5YR5/4) • dry, clay loam; apedal; soft dry, friable moist, sticky and plastic wet; common fine roots; (sample 19.109),

R 15+ cm blocked by dolerite.

DESCRIPTION OF PROFILE NO. 20

All 0- 30 cm Dark reddish brown (5YR3/4) moist and dry, ;fine gravelly coarse sandy loam; loose, soft, non-sticky non-plastic; common fine roots; gradual boundary; (sample 20.107),

A12 30 - 65 cm dark reddish brown (5YR3/3) moist and (5YR3/4) dry, gravelly coarse sandy loam; consistence as above; increase of fine angular gravel with depth; (sample 20.108),

(II)C 65+ cm blocked by gravel.

218 Laboratory data of profile No. 19 and No. 20

Particle size distribution (ß) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <7 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H2O KC1

19. 109 0-15 Al tr 2.4 6.5 13 .0 7. 9 10. 5 19.8 39.9 6.7 5.4 20. 107 0-30 All 34.7 35 .3 21.5 13 .1 6. 5 3. 2 5.1 15.3 7.2 5.6 20. 108 30-68 A12 43.8 43 .0 19.5 9 .5 4. 3 3. 4 5.0 15.3 7.1 5.3

Exchangeable cations in meq/100 g Sample Ca Mg K Na Sum C.E.C. Base Organic matter No. sat.% ^ ^J- ppm

19.109 13.00 2.74 2.93 tr 18.67 27.13 69 1.28 0.22 235 20.107 5.57 1.53 0.41 tr 7.51 9.64 78 0.45 0.06 25 20.108 5.07 1.70 0.31 tr 7.08 8.10 87 0.34 0.04 7

Elemental composition of the fine earth (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2O5 Sum Los on No. ignition '

19.109 63.0 20. 1 10..9 1..24 1.32 3..38 2.04 0.28 0.42 102.7 12.9 20.107 68.0 15.4 8..1 0..94 1.97 2..32 3.86 1.55 0. 20 102.4 4.4 20.108 73.9 17.7 8..2 1..06 2.02 1..32 4.29 0.58 0. 12 109.1 4.6

Sample Trace element content of the fine earthi (in ppm) SiO SiO2 A12O3 No. Mn Cu Zn Cr Co Ni Ba Sr Al2 R2O3 Fe2O3

19:109 1580 61 125 100 18 164 200 10 5.3 3.94 2.9 20.107 560 31 48 112 18 20 760 250 7.5 5.60 3.0 20.108 450 20 34 156 4 38 760 155 7.1 5.48 3.4

Elemental composition ol•the clay fraction (% by weight)

Sample SiOj Al.tO3 Fe2O3 TiO2 CaO MgO K2O Na2O P2OS No.

19.109 51.0 28..4 14.7 0.77 1.65 1.45 1.17 0.00 0.89 20.107 46.8 26..7 15.9 1.79' 2.36 3.14 2.24 0.00 2.21

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi Chi Q SiO2 SiO2 No. A12O3 R2O3 Fe,O3

19.109 ++ + tr X 3.1 2.29 3.0 20.107 + + + tr X 3.0 2.16 2.6 20.108 + + + tr X

219 DESCRIPTION OF PROFILE NO. 21

Al 0-33 cm Reddish brown (5YR4/3) moist and (5YR4/4) dry, coarse sand; structureless, single grained; soft dry, loose moist, non-sticky, non-plastic wet; common very fine, fine and few medium roots; few termite holes; smooth gradual boundary; (sample 21.96),

B21 33 — 80 cm yellowish red (5YR4/6) moist and dry, loamy coarse sand; structureless, single ,grained; common fine and medium tubular pores; consistence as horizon above; few very fine, fine and occasional medium roots; smooth gradual boundary; (sample 21.97),

B22 80 - 129 cm dark reddish brown (2.5YR3/4) moist, yellowish red (5YR4/8) dry, coarse sandy loam; structureless, massive; slightly hard dry, friable moist, non-sticky, non-plastic wet; common very fine, fine and few medium roots; common fine tubular pores; smooth gradual boundary; (sample 21.98),

B3 129 - 170 cm reddish brown (2.5YR3/6) moist, yellowish red (5YR5/6) dry, coarse sandy loam; structure and consistence as horizon above; coarse fragments increasing with depth; very few fine roots; common fine and medium tubular pores; abrupt smooth boundary; (sample 21.99),

(II)C 170+ cm extremely hard mottled granite.

220 Laboratory data of Profile No. 21

Particle size distribution (M) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm zon mm. 500 200 100 50 20 2 H2O KC1

21.96 0- 33 Al 1.1 36.3 22.5 20.8 9.8 2.5 0.6 7.5 6.3 4.7 21.97 33- 80 B21 1.1 33.4 26.9 16.8 7.0 2.4 1.2 12.3 6.3 4.7 21.98 90-129 B22 2.2 29.8 22.3 16.4 9.2 3.3 2.1 16.9 6.3 4.7 21.99 129-170 B3 3.3 33.6 20.0 15.6 8.7 3.9 1.9 16.3 6.4 4.8

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2OS No. sat. "A° % C % N ppm

21.96 1.26 0.07 0.26 tr 1.59 3.91 41 0.16 0.03 6 21.97 1.26 0.03 0.31 tr 1.60 4.35 37 0.18 0.03 3 21.98 1.26 0.23 0.31 0.18 1.98 4.78 41 0.05 1 21.99 1.26 0.20 0.25 tr 1.71 4.78 36 0.15 2

Elemental composition of the fine earth (% by weight)

Sample SiO2 Al: O3 Fe2<0, TiO2 CaO MgO K 2O Na2O PjOs Sum Loss on No. ignition %

21.96 90.8 5.9 1.9 0-25 0.13 0.19 3.29 0.96 0.02 103.5 2.1 21.97 87.9 9. 1 2.8 0.56 0.14 0.55 3.31 0.00 0.00 104.3 3.1 21.98 82.2 10. 1 2.0 0.51 0.16 1.12 3.53 0.95 0.10 100.7 3.5 21.99 82.7 9.2 2.9 0.57 0.17 0.65 2.83 0.64 0.08 99.7 3.2

Trace element content of the fine earth (in ppm) SiC) SiO Sample 2 2 Al, o3 Sr Al No. Mn Cu Zn Cr Co Ni Ba 2 O3 R2O3 Fe2 o3 21.96 212 24 6 150 6 22 900 14 26. 6 21.66 4.8 21.97 184 30 13 156 6 29 720 11 16. 5 13.81 5.1 21.98 156 37 37 136 14 24 540 13 13. 8 12.25 7.8 21.99 166 30 9 150 <2 4 540 <2 15.3 12.79 5.0

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2OS No.

21.96 48.5 30.7 10.5 1.42 3.06 0.74 1.81 0.00 3.32 21.97 49.5 32.9 11.0 1.36 1.23 0.80 1.92 0.00 1.21 21.99 48.4 32.5 10.1 1.25 2.61 1.10 1.39 0.00 2.66

Mineralogy of the clay fraction Molar ratios

Sample K I Mt Mi V Chi Q SiO2 SiO2 A12O;> No. A12O3 R2O3 Fe2O 3

21.96 X 2.7 2.21 4.6 21.97 X 2.6 2.10 4.7 21.98 X 21.99 H : tr X 2.5 2.11 5.0

221 DESCRIPTION OF PROFILE NO. 22

All 0—2 cm Very dark greyish brown (10YR3/2) moist, sandy clay; thin brittle crust; the material has a weak fine crumb structure; soft dry, friable moist, sticky and plastic wet; abrupt wavy boundary; (sample 22.90),

A12 2- 28 cm very dark grey (10YR3/1) moist and dry, clay with some coarse fragments; largest structural elements are weak coarse prisms which break down into weak coarse subangular blocky; very hard dry, firm moist, slightly sticky, slightly plastic wet; common fine and medium roots; few tubular pores; common vertical cracks up to 2.5 cm wide; cracks take 12% of the volume; few fine calcium carbonate concretions; wavy gradual boundary; (sample 22.91),

A13 28 — 64 cm very dark grey (10YR3/1) moist and dry, clay with an appreciable amount of coarse sand and fine grit; structureless, massive; in some parts however, fine and medium wedge shaped elements; very hard dry, firm moist, slightly sticky, slightly plastic wet; common cracks, some are 1 cm wide at 50 cm depth; common fine calcium carbonate concretions; common very fine, fine and few medium and thick roots; gradual smooth boundary; (sample 22.92),

Aca 64 — 97 cm very dark grey (10YR3/1) moist and dry, clay; common fine and medium pressure faces; consistence and coarse fragments as horizon above; few fine and very fine roots; common fine cracks up to 0.5 cm wide; common fine calcium carbonate concretions; very few fine pores; smooth gradual boundary; (sample 22.93),

Aca 97 — 127 cm very dark grey (10YR3/1) moist and dry, clay; massive, structureless; very hard dry, firm moist, slightly sticky, slightly plastic wet; very few fine roots; calcareous; common pressure faces; few small slickensides; smooth gradual boundary; (sample 22.94),

IIC 127 — 170 cm dark reddish brown (5YR3/4) moist, clay; structureless, maassive; hard dry, friable moist, slightly sticky and plastic wet; highly calcareous, many medium soft calcium carbonate accumulations; common fine distinct bluish mottling; common shiny pressure faces and coarse fragments; occasional fine roots; (sample 22.95),

170+ cm blocked by coarse gravel.

222 Laboratory data of profile No. 22

Particle size distribution (ß) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 1 pH 1: 5 No. in cm zon mm. 500 ZUU 1UO 5U 20 H,0 KC1

22.90 0- 2 All 0.9 14.5 7.3 9.6 6.0 8.5 10.6 43. 5 8.2 6.6 22.91 2- 28 A12 1.6 9.3 7.8 11.2 6.1 7.6 10. 5 47..5 8.2 6.8 22.92 28- 64 A13 1.9 11.0 7.8 8.8 6.7 7.6 10.9 47..2 8.4 6.9 22.93 64- 97 Aca 2.0 14. 1 8.3 8.6 5.9 6.6 10.,5 46.0 8.2 6.9 22.94 97-127 Aca 2.6 9.3 7.4 10.5 6.2 8.0 14.,3 44..3 8.5 7.2 22.95 127-170 IIC 3.2 10.0 7.0 9.7 4.3 6.6 11.,2 51 .2 8.3 7.1

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2OS CaCOj sat.% %C %N %

22.90 22.24 9. 30 1.34 0.09 32.97 35.48 93 0.60 0.09 17 0.64 22.91 23.51 11. 37 0.81 0.18 35.87 39.47 91 0.50 0.09 3 0.52 22.92 19.85 12. 89 0.65 1.11 34.50 37.32 92 0.55 4 0.69 22.93 17.50 14. 18 0.60 1.29 33.57 35.91 94 0.53 3 0.83 22.94 15.37 15. 41 0.66 2.22 33.66 32.87 100 0.16 tr 2.95 22.95 16.15 17. 08 0.66 2.22 36.11 38.50 • 94 0.41 2 0.99

Elemental composition of the fine earth (% by weight)

Sample SiO, AI,O3 A1,O3 TiO, C;aO MgO K,O Na,O P,O, Sum Loss on No. ignition %

22.90 70.0 15.2 6,.3 0.78 1.60 1.70 2.90 1.37 0.08 100.0 10.7 22.91 71.2 16.5 6 .8 0.77 1. 70 1.91 2.87 0.00 0.05 101.5 11.7 22.92 71.5 15.4 6.6 0.72 1. 58 2.48 2.81 1.94 0.05 103.1 11.8 22.93 71.0 15.0 6,.3 0.70 1. 51 1.67 2.69 1.02 0.03 100.0 11.4 22.94 69.0 15.0 6.6 0.71 2. 37 2.92 2.59 1.25 0.09 100.5 12.1 22.95 68.4 15.9 6,.8 0.73 1. 96 2.58 2.82 1.42 0.11 100.7 12.3

Trace element content of the fine earth (in ppm) SiO, Sample SiO, Al,0 3

No. Mn Cu Zn Cr Co Ni Ba Sr A1,O, R,O3 Fe,O 3

22.90 540 31 40 50 27 47 800 35 7.8 6.18 3.8 22.91 590 55 52 60 35 50 <100 32 7.5 5.90 3.7 22.92 650 42 60 180 58 40 540 23 7.9 6.21 3.7 22.93 670 42 40 180 44 44 720 24 8.0 6.33 3.7 22.94 786 38 41 136 20 55 540 24 7.8 6.10 3.6 22.95 640 58 52 224 30 68 720 36 7.3 5.74 3.7

Elemental composition of the

22.90 55.5 24.3 12.0 0.76 2.65 2.76 1.23 0.00 0.73 22.92 55.7 24 2 12.2 0.78 2.39 2.48 1.63 0.00 0.66 22.95 56.1 23.4 12.0 0.75 2.68 2.98 1.27 0.00 0.70

Mineralogy of the clay fraction Molar ratios Sample K 1 Mt Mi V Chi SiO, SiO, AI,O, No. A1,O, R,O, Fe,O,

22.90 3.9 2.94 3.2 22.91 22.92 3.9 2.95 3.1 22.93 22.94 22.95 4.1 3.06 3.1

223 DESCRIPTION OF PROFILE NO. 23

Al 0-12 cm Dusky red (2.5YR3/2) moist, dark reddish brown (5YR3/3) dry, sandy clay; weak medium subangular blocky structure; hard dry, friable, slightly sticky and plastic wet; common fine and medium roots; few fine pores; common very fine cracks 1 mm wide; wavy gradual boundary; (sample 23.85),

B21 12- 40 cm dark reddish brown (2.5YR2/4) moist and dry, clay; apedal; extremely hard dry, firm moist, slightly sticky and plastic wet; common fine, medium and few thick roots; few very fine cracks; common small broken cutans; very few fine tubular pores; appreciable amount of coarse fragments; smooth gradual boundary; (sample 23.86),

B2t 40 - 76 cm dusky red (10R3/4) moist, dark reddish brown (2.5YR3/4) dry, clay with common coarse fragments; structureless, massive; few fine medium and thick roots; consistence as horizon above; very few very fine cracks; few medium tubular pores; common fine thin broken cutans; smooth gradual boundary; (sample 23.87),

B23 76 - 122 cm dusky red (10R3/4) moist, dark reddish brown (2.5YR3/4) dry, clay; amount of very fine gravel and coarse sand increasing with depth; structureless, massive; hard dry, slightly friable moist, very slightly sticky and slightly plastic wet; few fine and medium roots; few fine and medium tubular pores; smooth clear boundary; (sample 23.88),

B3 122 — 160 cm dark red (2.5YR3/6) moist, fine gravelly sandy clay; structureless, massive; hard dry, firm moist, slightly sticky and slightly plastic wet; very few fine, medium and thick roots; (sample 23.89),

B3 160 — 175 cm as horizon above,

175+ cm blockage by extremely hard calcrete.

224 Laboratory data of profile No. 23

Particle size distribution (»i) in % weight Sand Silt Clay Sample Depthi Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1: 5 r3U No. in cm. zon mm. 500 200 100 20 2 H2O KCL

23.85 0- 12 Al 0.8 21..0 9.9 10.9 5..4 4.9 8.1 39.8 6.9 5.2 23.86 12- 40 B21 3.0 15.3 8.7 10.6 5.,6 5.3 5.4 49.1 6.4 4.9 23.87 4a 76 B2t 3.0 17..6 8.1 9.4 5.6 5.1 4.6 49.6 6.4 4.8 23.88 76-122 B23 3.8 19..1 7.3 10.3 5. 8 6.1 4.5 46.9 6.6 4.9 23.89 122-160 B3 40.0 22..0 8.5 10.1 5. 1 6.2 5.0 43.1 7.0 5.3 Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 No. sat.9! %C %N

23.85 10.85 3.81 1.41 0.09 16.16 21.18 76 1.26 0.14 11 23.86 10.06 3,.77 1.02 0.09 14.94 19.50 77 0.64 0.10 1 23.87 9.65 3.47 0.75 tr 13.87 19.40 71 0.49 2 23.88 9.13 2.95 0.70 tr 12.78 18.11 71 0.35 tr 23.89 12.18 2.73 0.80 0.09 15.80 18.94 83 0.37 tr

Elemental composition of the fine earth (% by weight)

Sample SiO2 Al,,C»3 ? i, TiOj CaO MgO K,O Na,O P,O,t Sum Loss on No. ignition %

23.85 70.2 14. 9 6.0 0.73 0.61 1.41 2.91 0.27 0.12 101.0 10.3 23.86 74.1 18. 3 7.3 0.79 0.50 0.00 2.91 1.48 0.08 101.5 10.9 23.87 70.1 19. 1 7.4 0.76 0.48 0.87 2.80 2.08 0.03 103.7 11.0 23.88 75.3 18..2 6. 9 0.74 0.46 0.50 3.04 0.00 0.06 105.1 10.0 23.89 73.2 16..2 5..8 0.66 0.54 0.84 3.31 0.00 0.03 100.6 8.5

fine earth (in ppm) Sample Trace element content of the SiOj SiO, A12O3 No. Mn Cu Zn Cr Co Ni Ba Sr A1,O3 R3O3 Fe,O 3

23.85 590 18 40 41 37 67 <100 12 8.4 6.71 3.9 23.86 490 34 43 41 48 73 <100 12 6.5 5.20 3.9 23.87 480 31 32 70 19 50 <100 19 6.2 4.99 4.0 23.88 450 24 19 60 15 35 <100 6 7.0 5.67 4.2 23.89 472 38 31 60 31 54 380 16 7.7 6.23 4.4

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe,O3 TiO, CaO MgO K,O Na,O P2C No.

23. 85 51.3 28.5 13.8 1.20 1.48 1.51 1.58 0.00 0.62 23. 87 49.5 31.0 13.5 0.93 1.19 1.63 1.48 0.00 0.80 23. 89 50.4 30.2 13.4 0.96 1.64 1.35 1.17 0.00 0.90

Mineralogy of the clay fraction Molar ratios

Sample K I Mt Mi V Chi Q SiO2 SiO, A12O3 No - ÄÜÖ", R^Ö"3 Fe,O3

23.85 ++ + + x 3.1 2.33 3.2 23.86 ++ + + x 23.87 ++ + + x 2.7 2.12 3.6 23.88 ++ + + x 23.89 ++ + + x 2.8 2.20 3.5

225 DESCRIPTION OF PROFILE NO. 24

All 0 — 19 cm Dark brown (7.5YR3/2) moist and dry, sandy clay loam: very weak subangular blocky structure; slightly hard dry, firm moist, slightly sticky and slightly plastic wet; many fine, medium and a few very coarse horizontal roots at the base of the horizon; common very fine cracks; common fine pores; clear wavy boundary; (sample 24.81),

A12 19 — 45 cm dark brown (7.5YR3/2) moist and dry, sandy clay loam with an appreciable amount of coarse sand and a little fine gravel; medium coarse prismatic structure; very hard dry, firm moist, slightly sticky and slightly plastic wet; common cutans on the vertical prismatic faces; common cracks often 1 cm wide; common fine hard calcium carbonate concretions; common very fine and few fine medium roots; few coarse tubular pores; clear wavy boundary; (sample 24.82),

ACca 45 — 76 cm very dark greyish brown (10YR3/2) moist and dry, slightly gravelly sandy clay loam; weak coarse angular blocky structure; common medium broken cutans on the ped faces; extremely hard dry, firm moist, slightly sticky and slightly plastic wet; very few very fine roots; very few medium pores; few cracks, some 1 cm wide at 50 cm depth; many fine and medium calcium carbonate concretions; abrupt clear boundary; (sample 24.83),

ACca 76 — 170 cm brown (7.5YR5/4) moist, slightly gravelly coarse sandy loam; highly calcareous; fairly hard dry, friable moist, non-sticky, non-plastic wet; few fine roots; abundant medium and coarse subangular calcrete fragments; (sample 24.84),

170+ cm blockage by extremely hard calcrete.

226 Laboratory data of profile No. 24

Particle size distribution (p) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H2O KC1

24.81 0- 19 All 2.6 28.5 10.4 11.2 8.0 6.7 7.0 28.2 8.2 6.8 24.82 19- 45 A12 3.9 28.2 8.0 10.8 6.5 6.9 7.1 32.5 8.6 7.2 24.83 45- 76 ACca 4.4 22.2 7.8 10.4 5.9 7.6 11.8 34.3 8.7 7.3 24.84 76-170 ACca 8.3 30.0 17.4 12.8 5.6 9.5 8.7 16.0 9.0 7.5

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O, CaCo3 No. sat. % %C %N ppm

24.81 20.72 7.25 0.75 0.18 28.90 32.94 88 0.58 0.11 2 24.82 21.40 11.12 0.38 0.18 33.08 33.11 100 0.43 0.07 3 2.70 24.83 21.41 14.21 0.43 0.18 36.23 35.88 100 0.35 tr 5.10 24.84 12.85 13.11 0.43 0.37 26.76 25.10 100 0.16 2 14.07

Elemental composition of the fine earth {% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2O5 Sum Loss on No. ignition %

24.81 79.3 .11.7 3.8 0.57 0.26 0.60 3.24 0.00 0.05 99.5 10.1 24.82 77.0 11.5 4.6 0.66 2.32 1.66 2.07 0.78 0.09 100.6 11.1 24.83 75.9 lt.8 4.9 0.71 4.13 1.31 2.01 0.00 0.03 100.8 12.7 24.84 69.3 11.6 4.0 0.52 8.93 1.89 2.68 2.29 0.12 101.3 14.1

Sample Trace element content of the fine earth (in ppm) SiOj SiO, A12O3 No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2O3

24.81 432 18 25 120 31 18 <100 18 11.5 9.53 4.8 24.82 458 9 12 32 12 20 <100 3 11.4 9.09 3.9 24.83 464 24 23 29 31 54 <100 26 10.9 8.60 3.8 24.84 400 31 27 50 17 40 1720 53 10.2 8.31 4.5

Elemental composition of the clay fraction (% by weight) Sample SiO2 A1,O3 Fe2O3 TiO, CaO MgO KjO Na2O o No. 5

24.81 57.1 23.8 11.1 0.84 3.01 2.85 1.02 0.00 0.39 24.82 58.4 23.1 10.5 1.02 2.54 2.50 1.16 0.22 0.57 24.84 56.8 19.5 10.0 0.68 4.52 4.24 0.95 0.82 2.52

Mineralogy of the clay fraction Molar ratios

Sample I Mt Mi Chi SiO2 No. A12O3 Fe2O3

24.81 tr tr xx 4.1 3.14 3.4 24.82 tr tr XX 4.3 3.32 3.4 24.83 tr tr XX 24.84 tr tr 4.9 3.72 . 3.1

227 DESCRIPTION OF PROFILE NO. 25

All 0- 3 cm Very dark grey (10YR3/1) moist, clay; soft dry, friable moist, sticky and plastic wet; very thin brittle crust which overlies fine granular mulch; common coarse sand grains; wavy abrupt boundary; (sample 25.75),

A12 3 — 33 cm very dark grey (10YR3/1) moist and dry, clay loam; largest structural elements are coarse prisms determined by the cracks; cracks are 1 cm wide at the base of the horizon; moderate medium angular blocky structure, with a few wedged shaped elements in the lower part of the horizon; very hard dry, firm moist, sticky and plastic wet; common fine and medium roots; very few fine pores; cracks take 10% of the volume; smooth gradual boundary; (sample 25.76),

A13 33 — 67 cm very dark grey (10YR3/1) moist and dry, clay; common coarse sand grains; very weak fine wedged shaped structure; few fine pressure faces; consistence as horizon above; few very fine and fine roots; few medium hard calcium carbonate nodules; common fine cracks of 0.5 cm wide; smooth gradual boundary; (sample 25.77),

ACca 67 — 96 cm black (10YR2/1) moist and dry, clay loam; with some coarse fragments in some parts of the horizon; massive , apedal structure; few very fine roots; common fine cracks less than 0.5 cm wide; common small pressure faces; very few small and medium calcium carbonate concretions; smooth gradual boundary; (sample 25.78),

ACca 96 — 142 cm very dark grey (10YR3/1) moist and dry, silty clay loam with occasional coarse fragments; massive structure; common pressure faces; few small intersecting slickensides; very few very fine roots; common very fine cracks; coarse fragments of calcium carbonate in lower part of the horizon; smooth gradual boundary; (sample 25.79),

(II)C 142 - 190 cm red (2.5YR4/6) moist and very dark grey (2.5YR3/0) moist, weathered calcrete of very gravelly coarse sandy loam texture; common coarse and very coarse subangular fragments of calcrete of a pinkish white colour (7.5YR8/2) moist; the red material is non to slightly calcareous; blocked by very hard calcrete at the base of the horizon; (sample 25.80).

228 Laboratory data of profile No. 25

Particle size distribution (M) in % weight; Sand Silt Clay Sample Deptr Hori- %>2 2000- 500- 200- 100- 50- 20 <2 pH 1 5 H,O KC1

25.75 0- 3 All 1.6 9.3 3.2 6.7 7.4 9.3 12 5 51.6 8.2 6.5 25.76 3 33 A12 0.7 7.8 2.9 5.5 4.7 13.0 27 0 39.1 8.7 6.7 25.77 33- 67 A13 0.8 10.1 3.4 5.2 5.7 7.3 12.9 55.4 8.8 6.8 25.78 67- 96 AC 1.4 7.4 3.2 5.0 5.3 15.5 30.6 33.0 8.6 6.8 25.79 96-142 ACca 1.3 4.9 2.2 4.0 5.4 17.7 36 1 29.7 8.5 6.7 25.80 142-190 (II)C 69.0 41.8 12.0 6.2 3.9 4.7 12.0 19.4 8.6 7.0

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P,O, CaCo3 sat '° %C %N

25.75 31.77 10 64 1.97 0.19 44.57 52.28 85 0.83 0.12 25 ' Ó.91 25.76 35.63 11 45 0.95 1.51 49.54 60.61 82 0.78 0.10 10 0.45 25.77 33.45 11 45 0.95 3.69 49.54 58.18 85 0.44 9 0.64 25.78 32.48 11 89 0.84 5.42 50.63 60.79 83 0.74 11 0.82 25.79 35.83 13 31 1.01 5.62 55.77 77.63 72 0.65 10 0.62 25.80 24.71 9 29 0.61 4.35 38.96 45.38 86 0.07 1 1.13

Elemental composition of the fine earth (% by weight)

Sample SiO, A1,C j Fe, D3 TiO, CaO MgO K.,0 Na,0 P,O, Sum Loss on No. ignition %

25.75 85.8 8.6 2.0 0.47 0.24 0.51 3.43 1.64 0.07 102.8 13.1 25.76 79.5 11.6 3.0 0.40 0.19 0.57 4.89 0.00 0.08 100.3 15.2 25.77 78.0 12.0 3.8 0 58 0.28 1.07 4.12 1.46 0.12 101.4 15.1 25.78 78.5 13.3 3.9 0.75 0.47 0.53 3.68 0.38 0.05 101.5 15.3 25.79 83.7 9.6 2.8 0 47 0.29 0.15 3.66 2.28 0.04 102.9 15.9 25.80 78.6 14.4 4.6 0 59 0.35 0.86 3.11 0.33 0.06 102.8 14.2

Trace element content of the fine earth (in ppm) SiO, SiO, Al,0 3

Sample Mn Cu Zn Cr Co Ni Ba Sr AI,O3 R,O, Fe;O 3

25.75 830 28 35 86 35 10 <100 59 17.0 14.79 6.6 25.76 1160 18 29 140 35 28 <100 32 11.6 9.96 6.0 25.77 1024 28 17 147 12 20 <100 38 11.0 9.18 5.0 25.78 1210 15 28 152 19 38 <100 26 10.0 8.44 5.4 25.79 1250 15 32 140 27 45 100 31 14.9 12.58 5.4 25.80 666 24 29 86 19 54 100 19 9.3 7.74 4.9

Elemental composition of the clay fraction (% by weight) P Sample SiO, A1,O, Fe,O3 TiO, CaO MgO K,O Na,O o, No.

25.75 56.4 23.4 12.2 0.80 2.96 2.75 1.01 0.00 0.48 25.77 57.1 22.6 12.6 0.88 2.60 2.13 1.36 0.00 0.81 25.80 57.9 21.4 12.2 0.68 2.43 4.11 1.00 0.00 0 36

Mineralogy of the clay fra ction Molar ratios

Sample K I Mt Mi V Chi Q SiO, SiO, A1,O3 No. A1,O3 R,O3 Fe,O3

25.75 + + ++ xx 4.1 3.07 3.0 25.7.6 + + ++ XX 25.77 + + ++ xx 4.3 3.17 2.8 25.78 + + ++ XX 25.79 + + ++ X 25.80 + + x 4.6 3.37 2.8

229 DESCRIPTION OF PROFILE NO. 26

All 0 — 2 cm Coarse and medium granitic sand, loose dry, on hard smooth surface, abrupt boundary; (sample 26.01),

A12 2 — 24 cm dark reddish brown (5YR3/2) moist, sandy loam; weak medium subangular blocky structure; hard, firm, slightly sticky and plastic; common fine and medium roots; common coarse sand; gradual boundary; (sample 26.02),

B21 24 - 48 cm dark reddish brown (5YR3/3) moist (5YR3/4) dry, sandy clay loam; weak medium subangular blocky structure; hard, firm, slightly sticky and slightly plastic; roots decreasing with depth; coarse sand grains and coarse fragments increasing with depth; gradual boundary; (sample 26.03),

B22 48 - 80 cm dark reddish brown (5YR3/3) moist, reddish brown (5YR4/4) dry, slightly gravelly sandy clay loam; apedal; common coarse sand; common fine calcium carbonate and some hard concretions; soft, friable, sticky and plastic; (sample 26.04),

B2ca 80 - 120 cm dark reddish brown (5YR3/4) moist, yellowish red (5YR4/6) dry, gravelly sandy clay loam; apedal; highly calcareous; common hard fine calcium carbonate concretions; soft, friable, slightly sticky and plastic; (sample 26.05),

(II)C 120 cm blockage by coarse gravel.

230 Laboratory data of profile No. 26

Particle size distribution (ji) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2! pH 1:5 No. in cm zon mm. 50 200 100 50 20 2 H2O KC1

26.01 0- 2 All 12.3 43.7 26.7 16.2 6.9 4.5 0.0 2.0 7.2 6.2 26.02 2- 24 A12 3.9 19.5 18.4 19.5 11.5 6.6 5.6 18.9 7.2 6.0 26.03 24- 48 B21 3.0 17.9 15.4 16.7 12.8 5.7 5.7 25.8 7.7 6.2 26.04 48- 80 B22 6.9 17.8 14.5 16.7 10.6 7.0 6.0 27.4 8.5 7.2 26.05 80-120 B2ca 20.1 19.2 13.5 14.8 10.4 5.8 7.6 28.7 8.6 7.3

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O No. sat. 9!' %C %N

26.01 1.26 0.53 0.23 tr 2.0:! 2.14 94 0.08 0.01 16 26.02 9.74 2.35 0.84 tr 12.9^^ 12.55 100 0.76 0.08 80 26.03 14.50 3.74 0.52 tr 18.7fi 17.72 100 0.45 0.07 41 26.04 17.10 2.93 0.48 0.18 20.6<> 18.06 100 0.44 6 26.05 18.79 3.45 0.55 tr 22.7<) 20.94 100 0.39 9

Elemental composition of the fine earth (% by weight)

Sample SiO2 Al3:O3 Fe2(0, TiO2 CaO MgO K 2O Na2O P2O;, Sum Loss on No. ignition %

26.01 74.4 10.6 5.3 0.84 2.52 2..22 3.53 1.86 0.12 101.4 1.3 26.02 71.4 12.8 7.1 1.28 2.31 2..06 2.65 2.15 0.22 101.9 6.3 26.03 70.8 14.0 7.3 1.14 2.33 1. 68 2.64 0.28 0.14 100.3 7.1 26.04 70.0 14.3 7.8 1.23 2.46 3..35 2.51 0.76 0.13 102.5 7.6 26.05 70.6 13.6 7.0 1.11 3.22 1,.65 2.78 0.00 0.05 99.9 8.2

Sample Trace element content of the :fine earthi (in ppm) SiO2 SiO2 A12O,) No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2O 3

26.01 420 34 26 150 32 40 700 35 11.9 9.01 3.2 26.02 886 22 36 184 24 48 460 32 9.5 7.00 2.8 26.03 880 24 46 180 26 55 400 32 8.6 6.43 3.0 26.04 670 42 46 92 26 26 360 48 8.3 6.17 2.9 26.05 670 42 44 136 20 10 400 48 8.8 6.63 3.0

Elemental1 composition of theclay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO O Na 2O P2 No.

26.01 52.3 19.4 9. 6 0.62 7. 15 3. 56 0.81 0.08 6. 54 26.03 51.6 25.5 15. 1 0.70 2. 00 2. 37 0.73 0.99 1. 15 26.05 51.0 24.4 14. 1 0.63 4. 97 2. 13 0.43 0.00 2. 48

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi SiO2 SiO2 A12O3 No. R2O3 Fe2O3

26.01 + + 4.6 3.48 3.2 26.02 + + 26.03 + tr 3.4 2.49 2.6 26.04 + tr 26.05 + rr 3.6 2.60 2.7

231 DESCRIPTION OF PROFILE NO. 27

Al 0—20 cm Dark reddish brown (5YR3/3) moist and yellowish red (5YR4/6) dry, clay; structureless; soft dry, friable moist, sticky and plastic wet; common very fine roots; (sample 27.106),

20 cm blocked by dolerite.

DESCRIPTION OF PROFILE NO. 28

Al 0 — 38 cm Black (5YR2/1) moist and dry, clay; structureless; very hard dry, slightly friable moist, sticky and plastic wet; common very fine and fine calcium carbonate concretions; (sample 28.105),

38 cm blocked by dolerite.

232 Laboratory data of profile No. 27 and No. 28

Particle size distribution (ß) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pHl:5 No. in cm. zon mm. 500 200 100 50 20 2 H2O KC1

17. 107 0-20 Al tr 2.4 3.0 6.9 8.7 8. 9 21. 5 48.6 7.1 5. 8 28. 105 0-38 Al tr 7.4 2.8 4.2 6.4 5. 2 15. 5 58.5 8.9 7. 2

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 No. ppm sat.% %C %N

27.107 18.4 6.23 1.60 tr 26.23 33.15 79 1.20 0.25 276 28.105 37.6 18.80 0.39 1.13 57.92 46.27 100 0.94 0.10 Elemental composition of the fine earth (% by weight)

Sample SiO2 A12O3 Fe3O3 TiO2 CaO MgO K2O Na,O P2O, Sum Loss on No. ignition %

27.107 65.6 18.2 10.8 1.06 1.80 2.75 1. 13 0.00 0.54 101.9 13.9 28.105 63.8 17.8 10.7 1.07 5.31 3.23 0.48 0.00 0,.04 102.5 16.8

element content of the fine earth l2 Sampl Trace (in ppm) SiC SiO2 Al, o3 No. Mn Cu Zn Cr Co Ni Ba Sr Al, o3 R2O3 Fe,;O3 27.106 754 26 67 16 38 22 300 15 6.1 4.44 2.6 28.105 680 26 34 86 50 62 200 32 6.1 4.40 2.6

Elemental composition of the clay fraction (% by weight) Al, Fe Sample SiO2 :O3 2o3 TiO2 CaO MgO K2O Na, O P2OS No.

27.106 50.9 26. 3 15.1 0.72 3.06 1.35 0.46 0.00 2.21 28.105 54.4 23, 5 13.8 0.71 3.89 2.93 0.00 0.00 0.83

Mineralogy of the clay fraction Molar ratios

Sample K I Mt Mi Chi SiO2 SiO2 No. Fe2O3

27.106 ++ 3.3 2.40 2.7 28.105 + 3.9 2.86 2.7

233 DESCRIPTION OF PROFILE NO. 29

Al 0-22 cm Brown (7.5YR4/3) moist, light brown (7.5YR6/4) dry, loamy sand; weak fine subangular blocky structure; slightly hard dry, loose moist, non-sticky, non-plastic wet; common fine and medium tubular pores; many very fine, fine and medium roots; smooth gradual boundary; (sample 29.119),

B21 22 — 36 cm reddish brown (5YR4/4) moist; reddish yellow (7.5YR6/6) dry, sandy loam; structureless; slightly hard dry, friable moist, slightly sticky and slightly plastic wet; common fine pores; common very fine, fine and medium roots; faint reddish mottling in the lowest part of the horizon; smooth gradual boundary; (sample 29.120),

B2 36 - 50 cm yellowish red (5YR4/6) moist (5YR5/6) dry, sandy clay loam; structureless; hard dry, friable moist, sticky and plastic wet; common fine tubular pores; common very fine, fine and medium roots; few fine thin reddish broken cutans increasing in size and number with depth; occasional coarse fragments; smooth gradual boundary; (sample 29.121),

B2t 50 - 80 cm yellowish red (5YR4/8) moist (5YR 5/8) dry, sandy clay loam; structure and consistence as horizon above; common fine and medium pores, rapidly permeable; common medium fairly thick broken cutans of a dark red (2.5YR3/6) coulor; occasional coarse fragments; few very fine and fine roots; smooth gradual boundary; (sample 29.122),

B3 80 - 95 cm yellowish red (5YR4/6) moist, reddish yellow (5YR6/6) dry, gravelly sandy clay loam; structureless; very hard dry, friable moist, sticky and plastic wet; pores and permeability as horizon above; common fine prominent dark red (2.5YR3/6) mottles; few fine pinkish grey (7.5YR6/2) mottles; few fine and medium roots; few termite channels filled with grey material; abrupt wavy boundary; (sample 29.123),

C 95 — 113 cm partly weathered schist of very gravelly sandy clay loam texture in horizontal bedding with occasional coarse fragments of finely grained quartzite; black and reddish and yellowish colouring common; occasional fine roots; (sample 29.124).

234 Laboratory data of profile No. 29

Particle size distribution (ß) in % weight Sand Sil Clay Sample Depth Hori %>2 2000- 500- 200- 100- 50- 20- < 2 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H,O KC1

29.119 0- 22 A tr 12.3 31.4 36 4 7.5 0.4 3.7 8.3 7.1 6.3 29.120 !2- 36 B21 tr 9.1 39.0 22 2 3.5 0.8 3.8 21.6 6.2 4.4 29.121 36- 50 B2 2.1 8.3 27.5 22 7 5.0 1.4 4.1 31.0 6.2 4.6 29.122 )0- 80 B2t 2.5 9.7 23.4 22.9 5.7 1.2 4.5 32.6 6.0 4.4 29.123 80- 95 B3 18.2 8.5 23.7 24 4 7.8 2.1 5.7 27.8 5.7 4.3 29.124 95-113 C 65.5 20.3 23.1 19 5 5.8 3.7 4.8 22.8 5.6 4.4

Exchange^ ble cations in meq/100 g Sample Ca Mg K Na Sum C.E.C. Base Organic matter P,O, No. sat. % % C % N ppm

29.119 .25 0.20 0.13 tr 1.58 3.23 49 0.27 0.04 29.120 .26 0.23 0.21 tr 1.70 3.24 53 0.25 0.04 29.121 .51 0.64 0.21 tr 2.36 5.44 43 0.27 tr 29.122 .26 0.57 0.13 tr 1.96 5.23 38 0.13 tr 29.123 .26 0.43 0.13 tr 1.82 4.34 42 0.20 tr 29.124 .26 0.43 0.15 tr 1.84 4.78 39 0.10 tr

Elemental composition of the fine earth (% by weight) Sample SiO, Al, o, Fe,O, TiO, CaO MgO K,O Na,O P,O Sum Loss on No. lgn tion %

29.119 95.2 4.5 1.0 0.41 0.16 0.98 0 51 0.00 0.06 102.9 2.4 29.120 87.4 9.8 2.0 0.59 0.11 0.06 0 55 0.00 0.01 100.5 4.5 29.121 85.3 12.5 2.3 0.70 0.14 0.58 0 50 0.30 0.11 102.4 5.7 29.122 82.5 13. 6 2.6 0.74 0.15 1.09 0.59 0.00 0.15 101.4 5.9 29.123 82.2 13.7 2.6 0.76 0.12 0.21 0.66 0.27 0.00 100.6 5.6 29.124 73.8 21.6 2.1 0.77 0.13 1.28 0.34 0.00 0.10 100.1 8.2

Trace element content of the fine earth (in ppm) SiO, SiO, A1,O,

No. Mn Cu Zn Cr Co Ni Ba Sr A1,O, R,O, Fe,Os

29.119 66 24 <5 <5 18 4 <100 7 35.9 31.31 6.9 29.120 24 42 17 112 16 <2 <100 <2 15.2 13.43 7.7 29.121 <10 24 9 126 6 14 <100 7 11.6 10.34 8.6 29.122 14 24 6 96 8 30 240 8 10.3 9.20 8.2 29.123 60 22 <5 172 4 20 140 <2 10.2 9.09 8.2 29.124 60 26 4 146 18 30 200 7 5.8 5.46 15.8

Elemental composition of the clay fraction (% by weight)

Sample SiO, Al Fe,O,i TiO, CaO MgO K,O Na, 0 P,OS No.

29.119 49.6 32.7 5.6 1.39 4.10 0.48 0.61 0.74 4.79 29.121 50.6 37.9 7.1 1.50 0.82 0.62 0.62 0.00 0.84 29.124 49.1 36.7 6.7 1.54 2.20 2.65 0.53 0.39 2.65

Mineralogy of the clay fraction Molar ratios Sample K I Mt Mi Chi SiO, Al.O, No. A1,O, Fe,O,

29.119 2.6 2.32 9.2 29.120 29.121 2.3 2.03 8.4 29.122 29.123 29.124 2.3 2.03 8.6

235 DESCRIPTION OF PROFILE NO. 30

All 0- 23 cm Very dark greyish brown (10YR3/1.6) moist, greyish brown (10YR4/2) dry, sand; very fine subangular blocky; soft dry, loose moist, non-sticky, non-plastic wet; many fine medium and occasional coarse roots; few ant holes; smooth gradual boundary; (sample 30.125),

A12 23 - 52 cm brown (7.5YR4/3) moist and (1OYR5/3) dry, sand; structureless; slightly hard dry, loose moist, non-sticky, non-plastic wet; common fine, medium and occasional coarse roots; few ant holes; smooth gradual boundary; (sample 30.126),

A13 52 - 80 cm brown (7.5YR4/4) moist, light brown (7.5YR5.6/4) dry, sand; structure, consistence and permeability as horizon above; common fine, medium and occasional coarse roots; smooth gradual boundary; (sample 30.127),

A14 80- 120 cm brown (7.5YR4/4) moist, light brown (7.5YR6/4) dry, sand; structure, consistence and permeability as horizon above; few fine and medium roots; smooth gradual boundary; (sample 30.128), (

A3 120 — 165 cm strong brown (7.5YR5/5.6) moist, reddish yellow (7.5YR6/6) dry, sand; structureless; hard dry, loose moist, non-sticky non-plastic wet; common medium • sand grains; very few fine medium and coarse roots; j smooth gradual boundary; (sample 30.129), ,

C 165 — 220 cm strong brown (7.5YR5/6) moist, reddish yellow j (7.5YR6/6) dry, sand; structure, consistence and permeability as horizon above; occasional fine and medium roots; few fine yellowish red (5YR5/8) mottles; coarse fragments increasing with depth; (sample 30.130).

236 A

Laboratory data of profile No. 30

~~"— Particle size distribution (M) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm. zon mm. 50 200 100 50 20 2 H,O KC1

30.125 0- 23 All tr 7 9 34.3 42.1 11.1 0.2 0.4 4.0 6.5 6.0 30.126 23- 52 A12 tr 7 3 29.1 49.8 9.5 0.4 0.6 3.3 6.3 5.8 30.127 52- 80 A13 tr 7 7 29.5 49.9 8.4 0.4 0.6 3.5 6.1 5.2 30.128 80-120 A14 tr 9 2 29.1 48.6 7.9 1.2 0.6 3.5 6.5 5.3 30.129 120-165 A3 tr 11 3 37.2 41.3 5.3 0.6 1.4 2.9 5.8 5.3 30.130 165-220 C tr 11 6 34.6 37.2 9.9 0.8 0.8 5.1 5.4 4.6

Exchangeable cations in meq/1 00 g

Sample Ca Mg K Na Sum C.E.C. Base Orf anic matter P,OS sat '° %C: %N C/N ppm

30.125 1.20 0.26 0.13 tr 1.59 2.19 73 0.35 0.04 9 12 30.126 0.20 0.13 0.08 tr 0.41 1.31 31 0.15 0.02 8 1 30.127 tr 0.07 0.08 tr 0.15 0.87 17 0.10 2 30.128 tr 0.07 0.05 tr 0.12 0.87 14 0.06 2 30.129 tr 0.07 0.05 tr 0.12 0.87 14 0.05 3 30.130 tr 0.10 0.05 tr 0.15 0.87 17 0.05 3

Elemental composition of the fine earth (% by weight)

Sample SiO, A1,O3 Fe, O3 TiO, CaO MgO K,O Na2O P,O, Sum Loss on No. ignition %

30.125 98.9 2-6 1.0 0.31 0.15 0.43 0.49 0.02 0.06 103.9 1.9 30.126 101.7 !-7 0.8 0.31 0.10 0.35 0.39 0.00 0.00 / 105.4 1.2 30.127 97.8 1.1 0.5 0.20 0.10 1.81 0.27 0.22 0.08 102.0 0.9 30.128 97.7 15 0.6 0.25 0.11 1.96 0.35 0.00 0.10 102.5 0.8 30.129 98.4 !-3 0.6 0.17 0.09 0.05 0.36 1.43 0.02 102.3 0.8 16 30.130 95.0 0.7 0.22 0.09 0.85 0.23 0.27 0.08 / 99.1 1.1

SiO Sample Trace element content of the fine earth (in ppm) SiOj : A12O No. Mn Cu Zn Cr Co Ni Ba Sr A1,OS R,O3 Fe,O 3

30.125 212 <5 <5 50 18 10 <100 <2 65.39 52.75 4.2 30.126 34 <5 <5 <5 4 <2 <100 <2 103.8 80.03 3.4 30.127 10 10 <5 20 16 4 140 <2 >100 >100 3.2 30.128 20 <5 <5 46 18 4 <100 <2 >100 89.77 3.8 30.129 24 <5 <5 76 16 10 <100 <2 >100 >100 3.5 30.130 20 <5 <5 76 <2 4 <100 <2 100.7 77.82 3.4

Elemental composition of the clay fraction (% by weight)

Sample SiOj A1:O3 Fe,O3 TiO, CaO MgO K:O Na3O P, o5 No.

30.126 42.1 22.3 7.3 1.31 11.68 "" 0.06 0.75 0.00 14 .47 ' 30.130 44.2 25.5 9.0 1.44 8.28 0.51 0.69 0.00 10.31

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi V Chi Q SiOj SiO, A1,O3 No. A1,O3 R2O3 Fe,O3

30.125 ++ + XX 30.126 ++ + xx 3.2 2.65 4.8 30.127 ++ + XX 30.128 ++ + XX 30.129 ++ + XX 30.130 ++ + xx 2.9 2.40 4.5 DESCRIPTION OF PROFILE NO. 31

All 0- 15 Dark greyish brown (10YR4/2) moist and dry, sandy loam; moderate medium subangular blocky structure; hard dry, friable moist, slightly sticky and slightly plastic wet; many fine, medium and a few thick roots; common fine cracks up to 0.5 cm wide; highly calcareous; wavy gradual boundary; (sample 31.142),

Allca 15- 39 cm dark greyish brown (10YR4/2) moist, greyish brown (10YR5/2) dry, sandy clay; moderate medium prisms breaking into coarse angular blocky; very hard dry, slightly friable moist, slightly sticky and slightly plastic wet; cracks up to 1,5 cm wide; few pores; faint thin broken cutans; many fine and medium roots; highly calcereous; a little termite activity; few coarse sand grains and fine gravel; smooth gradual boundary; (sample 31.143),

A12ca 39 - 67 greyish brown (10YR5/2) moist, light brownish grey (10YR6/2) dry, slightly gravelly sandy clay loam; moderate medium and coarse prisms breaking into moderate coarse angular blocky structure; extremely hard dry, firm friable, slightly sticky and slightly plastic wet; common thick cutans along the ped surfaces; few fine and medium tubular pores; CaCO3 as horizon above; few very fine and fine roots; some cracks 1 cm wide at 50 cm depth; smooth gradual boundary; (sample 31.144),

A13ca 67 -116 cm greyish brown (10YR5/2) moist and dry, slightly gravelly sandy clay loam; weak coarse blocky structure; extremely hard dry, friable moist, slightly sticky and slightly plastic wet; amount of soft and hard CaCO3 concretions increasing with depth; highly calcereous; few thin broken cutans; very few fine and occasional medium roots; coarse fragments increasing with depth; few fine cracks up to 0.5 cm wide; smooth gradual boundary; (sample 31.145),

ACca 116 - 176 cm brown (1OYR5/3) moist, pale brown (10YR6/3) dry, slightly gravelly sandy loam; structureless, massive; hard dry, friable moist, non-sticky, non-plastic wet; no roots; (sample 31.146),

(II)C 176 cm blockage by calcrete.

238 Laboratory data of profile No. 31

Particle size distribution (M) in % weight Sand Silt Clay Sample Depth Hori- 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm. 500 200 100 20 2 zon 50 H,O KC1

31.142 0- 15 All 2.3 7.0 10.7 31.0 6.7 7.2 22.2 15.2 7.9 7.5 31.143 15- 39 Allca 4.6 8.0 12.0 25.2 8.3 7.7 1.4 37.4 7.8 7.5 31.144 39- 67 A12ca 5.1 9.3 10.4 24.8 9.0 7.2 6.4 32.9 7.8 7.5 31.145 67-116 A13ca 7.7 8.0 11.8 24.2 6.0 7.2 19.2 23.6 7.8 7.5 31.146 116-176 ACca 7.1 7.2 9.3 23.8 8.6 5.9 23.6 21.6 7.8 7.4

Exchangeable cations in meq/100 g Sample Ca Mg K Na Sum C.E.C. Base Organic matter P,O, CaCOj No. sat.% % C % N C/N ppm %

31.142 19.83 1.16 0.48 tr 21.47 20.67 100 0.80 0.11 10.28 31.143 25.64 1.51 0.27 0.09 27.51 23.03 100 0.51 0.08 13.06 31.144 22.07 1.75 0.27 0.05 24.14 23.55 100 0.50 14.63 31.145 23.68 2.23 0.29 0.05 26.25 25.41 100 0.32 13.23 31.146 20.74 2.84 0.35 0.05 23.98 23.12 100 0.23 13.62 Elemental composition of the fine earth (% by weight)

Sample SiO, A1,O3 FeaO3 TiO, CaO MgO K,O Na2O P,O, Sum Loss on No. ignition l.

31.142 80.6 7.2 2.8 0.59 7.50 0.00 \0.86 0.00 0.10 99.7 11.7 31.143 77.5 8.0 3.1 0.57 9.49 0.00 \0.67 1.06 0.12 100.5 13.7 31.144 77.5 8.2 3.4 0.57 9.66 0.00 0.85 0.72 0.11 101.1 13.4 31.145 76.6 8.2 3.4 0.60 9.47 0.00 io.68 0.00 0.11 99.0 13.7 31.146 77.1 8.6 3.3 0.58 8.76 0.00 /0.97 0.03 0.12 99.5 13.1

Sample Trace element content of the fine earth (in ppm) SiO, SiO, A1,O3 No. Mn Cu Zn Cr Co Ni Ba Sr Al,Oj RjO3 Fe,O3

31.142 376 10 <5 <5 16 10 300 6 18.9 15.17 4.0 31.143 460 <5 9 26 30 20 260 10 16.5 13.19 4.0 31.144 468 <5 13 52 44 32 220 2 16.0 12.68 3.8 31.145 554 42 13 20 44 40 540 11 15.9 12.59 3.8 31.146 660 29 40 18 680 6 15.2 12.20 4.0

Elemental composition of the clay fraction (% by weight) K O P O Sample SiO2 Al, o3 Fe,O3 TiO, CaO MgO 3 Na,O 2 S No.

31.142 56.0 20.3 7.8 0.82 11.29 •' I.SS^ 0.71 0.28 1.19 31.144 62.0 21. 9 8.9 0.95 2.35' 2.11 ; 0.86 0.30 0.65 31.146 60.0 20.0 8.0 0.82 6.61 1.90 0.72 0.00 1.94

Mineralogy of the clay fraction Molar ratios

Sample K 1 Mt Mi Chi SiO, SiO, A1,O3 No. A1,O3 R,O3 Fe,O3

31.142 + + xx 4.7 3.76 4.1 31.143 + + XX 31.144 + tr XX 4.8 3.81 3.9 31.145 + tr XX 31.146 + rr XX 5.1 4.06 4.0

239 DESCRIPTION OF PROFILE NO. 32

A 0 - 30 cm Dark brown (10YR3/3) moist, brown (10YR5/3) dry, coarse sandy loam; structureless, massive; hard dry, friable moist, non sticky, non plastic wet; common fine and medium pores; horizon looks grey in appearance when compared with the underlying redder horizons; smooth gradual boundary; (sample 32.147),

B21 30 - 61 cm reddish brown (5YR4/4) moist, yellowish red (5YR5/6) dry, clay, structureless, massive; hard dry, friable moist, slightly sticky and slightly plastic wet; many distinct medium red (2.5YR4/6) mottles increasing in prominence with depth; common fine and medium thin cutans, slightly darker than the soil matrix; little coarse fragments and some coarse sand; common fine roots; a little biological activity; smooth gradual boundary; (sample 32.148),

B22 61 - 88 cm yellowish red (5YR4/6) moist, brown (7.5YR5/4) dry, slightly gravelly clay; structure and consistence as above; common coarse and medium dark red (2.5YR3/6) mottles; common coarse fragments; very few fine and medium roots; few tubular pores; smooth gradual boundary; (sample 32.149),

B3 88 -110 cm strong brown (7.5YR4/6) moist and (7.5YR5/6) dry, slightly gravelly clay ;^ structureless, massive; hard dry, friable moist, slightly sticky and plastic wet; common prominent medium and coarse dark red (2.5YR3/6) mottles; few fine and coarse bluish black mottles; occasional fine roots; common fine tubular pores; coarse fragments increasing with depth; clear, in some parts wavy boundary; (sample 32.150),

C 110 — 125 cm strong brown (7.5YR4/6) moist matrix, weathered granitic rock of a gravelly clay texture; prominent red, black and some yellowish mottling; hardness increasing with depth; no roots; (sample 32.151),

R 125+ cm hard granite.

240 Laboratory data of profile No. 32

Particle size distribution (ß) in % weight Sand Silt Clay Sample Deptrl Hori- 2000- 500- 200- 100- 50- 20- < 2 pH 1: 5 No. in cm zon mm. 500 200 100 50 20 2 H,O KC1

32.147 0- 30 A 1.2 26.0 19.9 23.4 6.0 4.3 6.0 14.4 6.1 5.0 32.148 30- 61 B21 1.6 15.6 9.2 10.7 6.0 4.2 5.0 49.3 5.8 4.6 32.149 61- 88 B22 8.3 14.5 9.1 11.3 3.9 3.5 5.5 52.2 5.8 4.5 32.150 88-110 B3 9.7 13.3 8.3 10.9 6.1 3.9 7.6 49.9 6.1 4.8 32.151 110-125 C 24.3 16.2 9.0 10.5 6.1 5.1 9.0 44.1 5.9 4.9

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2O5 No. sat.% % C % N C/N ppm

32.147 2.11 0.39 0.18 tr 2.68 3.94 68 0.51 0.04 13 1 32.148 3.26 1.44 0.18 tr 4.88 9.32 52 0.39 0.06 7 tr 32.149 3.07 1.58 0.18 tr 4.83 9.34 52 0.36 tr 32.150 3.69 1.69 0.21 tr 5.59 9.81 57 0.23 tr 32.151 2.75 1.51 0.24 tr 4.50 8.44 53 0.31 1

Elemental composition of the fine earth (% by weight)

Sample SiOj Al, >3 Fe2 O3 TiO2 CaO MgO K2O NajC) P2O,, Sum Loss on No. ignition %

32.147 86.9 8.6 2.4 0. 53 0.32 0.27 1.04 0.00 0.00 100.1 3.9 32.148 73.6 19.6 4.8 0.64 0.24 0.62 1.10 0.00 0.11 100.7 9.2 32.149 71.6 21.7 5.4 0.69 0.26 1.03 1.21 0.79 0.12 102.8 9.9 32.150 63.2 24.4 6.5 Q.78 0.30 0.42 1.25 2.80 0.12 99.8 10.2 32.151 70.8 20.6 5.9 0.74 0.27 0.56 1.21 0.79 0.06 100.9 8.6

Trace element content of the fine earth (in ppm) SiO SiO A1 O Sample 2 2 2 No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2O 3

32.147 220 34 7 52 34 12 120 <2 17.1 14.50 5.6 32.148 52 34 6 128 <2 <2 120 3 6.4 5.50 6.4 32.149 54 38 10 66 <2 36 <100 <2 5.6 4.83 6.3 32.150 100 42 3 128 <2 34 <100 <2 4.4 3.76 5.9 32.151 150 42 <5 66 <2 34 <100 5 5.8 4.94 5.5

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2O Na2O P2O, No.

32.147 49.6 32.9 7.4 0.97 3.52 0.69 0.93 0.00 3.99 32.148 50.2 36.8 8.7 0.89 0.81 0.69 1.03 0.00 0.75 32.151 49.7 36.5 9.0 0.89 1.20 0.70 0.90 0.00 1.13

Mineralogy of the clay fraction Molar ratios

Sample K. 1 Mt Mi V Chi SiO2 SiO2 Al, No. A12O3 R2O3 Fe2 o,

32.147 ++ 2.6 2.24 7.0 32.148 ++ X 2.01 6.6 32.149 ++ tr tr 32.150 ++ tr tr 32.151 ++ tr tr 2.3 2.00 6.4

241 DESCRIPTION OF PROFILE NO. 33

A 0 - 30 cm Dark brown (10YR3/3) moist, greyish brown (10YR5/2) dry, coarse sandy loam; structureless, single grained; slightly hard dry, loose moist, non-sticky, non-plastic wet; common fine pores; common very fine, fine and medium roots; smooth gradual boundary; (sample 33.152),

B21 30 - 58 cm dark brown (10YR4/3) moist, brown (10YR5/3) dry, coarse sandy loam; structure as above; hard dry, friable moist, slightly sticky and very slightly plastic wet; little termite activity; common fine and medium pores; few fine and medium roots; very faint brownish mottling in the lower part of the horizon; smooth gradual boundary; (sample 33.153),

B22 58 - 99 cm dark brown (10YR4/3) moist, light brownish grey (10YR6/2) dry, slightly gravelly coarse sandy loam; amount of coarse fragments increasing with depth; apedal; very hard dry, friable moist and slightly sticky and plastic wet; common prominent small and medium reddish brown (5YR4/4) mottles in which few black prominent mottles; few faint thin broken cutans; common fine and medium tubular pores; occasional coarse roots; smooth clear boundary; (sample 33.154),

C 99 — 130 cm hard, partly weathered granular granitic rock with common red and black mottling of very gravelly sandy clay loam texture; in some parts the orginal coarse granitic rock structure is still visible; occasional pink feldspars; no roots; (sample 33.155).

242 Laboratory data of profile No. 33

Particle size distribution ()i) in % weight Sand Silt Clay Sample Depth Hori- %>2 2000- 500- 200- 100- 50- 20- <2 pH 1:5 No. in cm. zon mm. 500 200 100 50 20 2 H2 O KC1

33.152 0- 30 A 2.1 28..7 22..8 19.3 7.9 6.2 6.0 9.4 6.1 5.1 33.153 30- 58 B 5.9 29,,2 16..7 16.9 7.4 8.9 5.4 15.5 6.1 4.9 33.154 58- 99 B 13.2 31..2 17..0 15.0 8.0 5.6 4.5 18.7 6.1 4.9 33.155 99-130 C 77.0 30..3 13.,7 13.5 5.8 6.7 5.9 24.1 6.3 5.1

Exchangeable cations in meq/100 g

Sample Ca Mg K Na Sum C.E.C. Base Organic matter P2OS No. sat. % % C % N C/N ppm

33.152 1.21 0.41 0.23 tr 1.85 4. 38 42 0.48 0.05 10 2 33.153 1.72 0.87 0.26 tr 2.85 4..39 65 0.29 0.03 10 1 33.154 2.23 1.34 0.29 tr 3.86 5..28 73 0.22 tr 33.155 2.43 1.97 0.39 tr 4.79 7..06 68 0.15 1

Elemental composition of the fine earth (% by weight)

Sample SiO2 Al, O3 Fe,,O3 TiO2 CaO MgO K Na2O P2O,[ Sum Loss on No. "° ignition %

33.152 84.1 9.1 1.7 0.42 0.47 0.82 4.00 4.49 0.15 105.2 2.8 33.153 80.6 11.5 2.6 0.58 0.45 1.59 4. 14 1.25 0.13 102.8 3.5 33.154 80.4 12.4 2.9 0.54 0.47 0.15 3.98 1.14 0.11 102.1 3.4 33.155 86.1 14.0 3.7 0.65 0.34 0.47 4. 19 0.57 0.04 109.9 4.3

Trace element content of the :fine earth (in ppm) Sample SiO2 SiO2 A12O3

No. Mn Cu Zn Cr Co Ni Ba Sr A12O3 R2O3 Fe2O3

33.152 150 34 <5 56 16 24 760 27 15.8 14.09 8.5 33.153 120 34 <5 <5 16 10 820 27 11.9 10.40 7.1 33.154 380 46 7 52 38 28 860 36 11.0 9.58 6.7 33.155 114 50 3 100 38 72 760 31 10.5 8.95 6.0

Elemental composition of the clay fraction (% by weight)

Sample SiO2 A12O3 Fe2O3 TiO2 CaO MgO K2 O Na2O P2OS No.

33.152 49.9 25.4 8.3 1.39 5.51 1.08 2.29 0.00 6.11 33.153 52.1 29.5 9.3 1.42 1.98 1.37 2.26 0.00 2.06 33.155 51.2 30.5 9.6 1.39 2.28 0. 99 1.84 0.00 2.20

Mineralogy of the clay fraction Molar ratios

Sample K Mt Mi Chi SiO2 SiO2 No. A12O3 R2O3 Fe2O3

33.152 3.3 2.76 4.8 33.153 3.0 2.49 5.0 33.154 tr 33.155 tr 2.9 2.37 5.0

243 SUMMARY

This research deals with the development of soils in the semi-arid environment of central East Botswana, Africa. The material for this study was collected from the catchment areas of two tributaries of the Limpopo rivier, i.e. the Mahalapshwe and Bonwapitse. The physical environment reflects the variations in climate, the contrasting parent material, the soil-vegetation relationships and the landscapes on which the soils are encountered. The soil temperature and moisture regimes, notably the alternating wet and dry seasons, proved significant to the development of the soils. Granite and dolerite are the main suppliers for the parent material of the soils. The soil texture has a major influence on the formation of vegetation patterns of which three were recognized. Slight differences in topography are responsible for remarkable variations in soil profile development, especially in the granitic region. Base exchange phenomena are almost entirely dependent on the clay fraction, as the amount of organic matter is very low. Coarse sand was found to be a major component of the sand fraction, whereas the distribution of clay in the soils gives rise to the recognition of four clay curves, which were correlated with various soil-forming processes. Good correlations were found between a number of elements (SiO2, Al2O3 and Fe2O3) and some grain size fractions. The amount of trace elements is low. Zinc showed a high correlation with a group of bivalent trace elements (Co, Cu and Ni); their occurrence is mainly confined to the finer soil fractions. Mineralogical studies point to the advanced stage of weathering in the soils, disclosing that only the more persistent mineral species are retained. In addition the mineral composition of the sand fraction indicates the variation in origin of the parent materials. Five heavy mineral suites were recognized, the light mineral composition being closely associated with the heavy mineral composition. Micromorphological observations indicated the presence of "pedorelicts" as well as the limited occurrence of more recent clay translocation and accumulation in most soils. Plasmic fabrics could partly be correlated with the various soils. No uniform pattern emerged relative to the B-horizon in Alfisols. The Vertisols are similar in their development as is known from other parts of the world, although the distinct animal activity is a remarkable

245 feature. The sandy soil of the Kalahari shows little profile development. Enrichment of iron is observed in the C-horizons of the granitic soils on the peneplain. This phenomenon is considered a paleo-feature. Redistribu- tion of iron takes place in some hydromorphic Alfisols. The soils were classified according to the USDA 7th Approximation (1970) and correlated with the FAO/UNESCO system (1968, 1970). Four orders are recognized: Entisols, Vertisols, Inceptisols and Alfisols. The presence of the large number of Haplustalfs is typical in the transition zone from the dry to the wet tropics. Land use is aimed at beef production, relatively small areas are cropped. There is a tendency that, especially around population centres, less suitable soils are taken into cultivation.

246 SAMENVATTING

Onderwerp van deze studie vormt de bodemgenese in het semi-aride, oostelijk deel van Centraal Botswana, Afrika. Het materiaal voor dit onderzoek werd verzameld uit de stroomgebieden van twee zijrivieren van de Limpopo, t.w. de Mahalapshwe en de Bonwa- pitse. De plaatsgehadhebbende klimaatsveranderingen, de sterke verschillen in moedergesteente, de relatie tussen bodem en vegetatie en de landschaps- eenheden waarin de verschillende bodems werden aangetroffen, zien zich weerspiegeld in het totale fysische milieu. De bodemtemperatuur en het vochtigheidsregime, in het bijzonder de afwisselende natte en droge seizoenen, zijn belangrijke factoren in de bodemontwikkeling. Graniet en doleriet vormen de voornaamste gesteenten waarvan het moedermateriaal afkomstig is. De bodemtextuur heeft een grote invloed op de vorming van vegetatie- patronen, waarvan er drie werden onderscheiden. Speciaal in het granietgebied blijken kleine verschillen in de topografie verantwoordelijk te zijn voor opmerkelijke variaties in profielontwikke- ling. Grof zand is het voornaamste bestanddeel van de zandfractie. De variatie in kleigehalten was zodanig, dat vier kleicurven konden worden aangetoond, die gecorreleerd werden met verschillende bodemvormende proces- sen. De uitwisseling van basen geschiedt voornamelijk via de kleifractie aange- zien het organische stofgehalte bijzonder laag is. Goede correlaties werden gevonden tussen een aantal elementen (SiO2, Al2O3 en Fe2 O3 ) en enige korrelgrootten. De hoeveelheid sporenelementen is laag. Zink vertoonde een goede correlatie met een groep tweewaardige sporenelementen (Co, Cu en Ni); hun voorkomen is voornamelijk beperkt tot de klei- en siltfractie. Dé hoge mate van verwering in de meeste bodems werd mineralogisch aangetoond. Hierbij bleek dat slechts de meest weerstandskrachtige mineralen behouden bleven. Tevens duidde de mineralogische samenstelling van de zandfractie op de verscheidenheid van oorsprong van het moedermateriaal. Vijf zware-mineraalgroepen werden onderscheiden. De samenstelling der

247 lichte mineralen is nauw verbonden mee die der zware. Micromorfologische waarnemingen toonden de aanwezigheid van „pedorelicten" aan, alsmede het beperkt voorkomen van recent kleitransport en -accumulatie. Plasmic fabrics konden slechts gedeeltelijk worden gecorreleerd met de verschillen in bodemvorming. Het fabric van de B-horizonten van de Alfisolen bleek niet uniform te zijn. De ontwikkeling van de Vertisolen onderscheidt zich van die in andere gelijksoortige gebieden van de wereld door de opmerkelijke dierlijke activiteit. Aan de zandbodem van de Kalahari kon geen noemenswaardige profielont- wikkeling worden onderkend. Aanrijking van ijzer werd waargenomen in C-horizonten van granietbodems op de peneplain, waarvan het ontstaan als een paleoverschijnsel wordt opgevat. In sommige hydromorfe Alfisols vindt een redistributie van ijzer plaats. De bodems werden geclassificeerd volgens de USDA 7th Approximation (1970) en gecorreleerd met het FAO/UNESCO systeem (1968, 1970). Vier orders werden onderscheiden: Entisols, Vertisols, Inceptisols en Al- fisols. Typisch voor de overgangszone van droge naar natte tropen vormt de aanwezigheid van een groot aantal Haplustalfs. Landgebruik is voornamelijk gericht op veeteelt (vleesproductie), betrek- kelijk kleine arealen worden voor de verbouw van gewassen gebruikt. Er bestaat een neiging om speciaal rond de bevolkingscentra minder geschikte gronden in cultuur te brengen.

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259 CURRICULUM VITAE

De auteur werd geboren in 1940 te Baarn en behaalde het H.B.S.-b diplo- ma in 1957 aan het Baarns Lyceum aldaar. In datzelfde jaar ving hij aan met de studie fysische geografie aan de Rijksuniversiteit te Utrecht. Hij specialiseerde zich in de bodemkunde en legde in 1964 het doctoraal examen af. Gedurende meer dan drie jaar (1965—1968) was hij werkzaam als bodemkundige voor de FAO in het kader van een trainings- en karteringsproject te Wad-Medani, in de Sudan. In de loop van 1968 volgde overplaatsing naar Mahalapye en vervolgens Gaborone in Botswana, waar hij als bodemkundige verbonden was aan een FAO/UNDP-SF multidisciplinair project voor landontwikkeling. In september 1971 werd aangevangen met een voortgezet onderzoek aangaande de bodemgenese in Oost Botswana, aan het Bodemkundig Instituut der Rijksuniversiteit te Utrecht.

260 W. Siderius - Soil Transitions in Central East Botswana (Africa)

ERRATA

pp. 5, 107 and 251 read: Doeglas instead of: Douglas or Dougles p. 6, line 2 from bottom read: Botswana instead of: Boswana p. 7, line 5 from top read: 15 instead of: 16 p. 10, on small scale map read: 30 instead of: 15 and p. 11 read: Bonwapitse instead of: Bonwapiste p. 14, line 8 from top read: is instead of: in p. 17, caption of Table 2 read: cals instead of: calc p. 20, line 8 from top read: 57 instead of: 47 p. 22, bottom line read: Mueller instead of: Mueeler p. 28, delete: line 20 from top pp. 28, 30 and 39 read: Boocock instead of: Boockock p. 35, Table 12, (column 2) read: Lanthanum instead of: Lathanum p. 36, bottom line read: Na20 instead of: MgO and line 3 from bottom read: vertical instead of: certical p. 38, line 13 from bottom read: Si0 instead of: 2 Sio2 p. 43, line 15 from top read: C instead of: read: E p. 45, in Key to Fig. 7 and p. 28 Archaean instead of: Archaen and line 13 from top read: are instead of: read: is 61, Table 18 (column 6) metadolerite instead of: meta-doerite and (column 5) read: channel instead of: read: channal p. 81, line 21 from top 39 instead of: 36 p. 85, line 10 from top etc. read: CEC instead of: read: C.E.C. p. 91, line 2 from bottom margalitic instead of: read: margalithic p. 96, line 2 from top phosphorus instead of: read: phosphate and line 4 from bottom ferric instead of: read: ferri p. 99, Table 29, line 6 from top 0.915 instead of: read: -0.915 p. 102, line 7 from bottom Sr read: instead of: S p. 105, legend of Fig. 32 read: tourmaline instead of: toermaline p. 107, line 4 from bottom read: Pettijohn instead of: PettijJohn p. 118, line 5 from top read: Harmsen, 1959 instead of: Harmse, 1961 p. 1 19, Table 33 read: EC instead of: p. 122, caption of Fig. 35 e A "•e read: crossed instead of: p. 130, line 3 from top crosed read: extinction instead of: distinction p. 135, line 18 from top Rhoads instead of: Roads p 136, caption of Fig. 42 read: circumference instead of: circumpherence p. 137, line 18 from top read: situ instead of: sity p. 141, line 4 from bottom instead of: widess read: widens instead of: Mohr et al. p. 147, line 2 from bottom read: Mohr and Van Baren 148, caption of Table 35 read: instead of: radius ratio ratio radius and line 11 from bottom read: instead of: SiO2 149, line 7 from bottom read: too instead of: to 153, line 7 from bottom read: outlined instead of ourlined and line 5 from bottom, delete: oilier, 1959 155, line 4 from top read: Burridge instead of Barridge 157, Table 40, insert headings as in Table 39 159, Table 42 read: Al203 instead of: AI2O3 Fe2°3 162, caption of Fig. 48 read: AI2O3 instead of: Ae20j 163, Table 45, insert:fraction lines in Molar ratios 167, line 13 from bottom read: criticism instead of: critisism 169, line 9 from top read: integrated instead of: intergrated and line 10 from top read: FAO/UNESCO instead of: UNESCO 175, bottom line, delete: 500 183, insert: subordinated) , dominant(++) ; moderate amount(x), large amount(xx) 249., insert: Barshad, I., 1969. Chemistry of soil development. In: Bear (ed.), pp.1-70 249, insert: Bawden, M.G., 1965. Some soils of Northern Bechuanaland. D.O.S. England, 256, line 4 from bottom read: Rooij, N.M. de instead of: Rooij, N.M. p.256, line 11 from bottom read: 1965 instead of: 1963 p. 258, insert: Tiurin, I.V., 1965. The system of soil classification in the USSR. Pédologie, Spec. No. 3, pp. 7-24. Stellingen

1. In tegenstelling tot de invloed van Kalahari zand op de bodemvorming in Transvaal (Zuid-Afrika), is deze gering te noemen voor wat betreft de huidige bodemgenese in centraal oost Botswana. (Harmse, H. J. von M., 1967, proefschrift Utrecht)

2. De aanwezigheid van "pedorelicten" in bodemmateriaal is niet zonder meer een aanwijzing voor policyclische bodemvorming, zoals vaak wordt aangenomen. (Ruellan, A., 1971 in Paleopedology (ed. Yaalon), ISSS and ïsr. Univ. Press, Jeruzalem)

3. Standarisatie van geomorfologische begrippen kan slechts gerealiseerd worden door de oprichting van een internationaal overlegorgaan, naar analogie van de thans bijna 50 jaar bestaande ISSS. (International Society of Soil Science, opgericht 1924)

4. Een theoretische benadering van de bodemsamenstelling uit de totaal- chemische analyse resultaten is dan zinvol, indien de mineralogische compositie van het bodemmateriaal bekend is.

5. De bestudering van micro-sedimentologische verschijnselen in de bodem verdient meer aandacht. (dit proefschrift)

6. Bij het waarderen van de invloed van het moedermateriaal op de bodemvorming is een grove indeling van gesteenten zoals die in "zuur, inter- mediair of basisch" vaak onvoldoende om verschillen in bodems ver- oorzaakt door variaties binnen een bepaald type uitgangsgesteente te te begrijpen. 7. De invloed van het werk van E. W. Hilgard op de moderne begrips- vorming in de pédologie wordt nog te weinig onderkend. (Jenny, H., 1961, E. W. Hilgard and the birth of modern soil science, Collana Delia Vista "Agrochemica", Pisa) 8. Enkele richtingen in de aardwetenschappen, waaronder de bodemkunde, zijn bij uitstek geschikt voor toegepast onderwijs in ontwikkelings- landen.

9. Op vele kaarten is de begrenzing van de Kalahari woestijn foutief aangegeven. (Meulenhof Atlas, 1959; Edinburgh World Atlas, 1967; Grote Bosatlas, 1968)

10. De klassifikatie van ongekonsolideerd oppervlaktemateriaal van de maan als "lunar soil" (maanbodem of maangrond) is voorbarig gezien de huidige fragmentarische kennis omtrent de bodemvormende faktoren die op dit materiaal hebben ingewerkt. (Proceedings Apollo 11 Lunar Science Conference, 1970, Vol.'s 1-3, Pergamon Press, Inc. ; NASA Preliminary Science Report Apollo 14,1971, Washington)

11. De tijd is nabij dat het schrijven van een proefschrift korter zal duren dan het vormen van een kabinet.

W. SIDERIUS 2 mei 1973 W.Siderius - Soil Transitions in Central East Botswana (Africa)

ERRATA

pp. 5,107 and 251 read: Doeglas instead of: '• Douglas p.6, line 2 from bottom, read: Botswana instead of: Boswana p.7, line 5 from top, read: 15 instead of: 16 p.10, on small scale map, read: 30 instead of: 15 p.14, line 8 from top, read: is instead of: in p.17, caption of Table 2, read: cals instead of: calc p.20, line 8 from top, read: 57 instead of: 47 p.22, bottom line, read: Mueller instead of: Mueeler p.28, line 16 from top and p.30, line 6 from top read: Boocock instead of: Boockock p.36, bottom line, read: Na2O instead of: MgO p.38, line 13 from bottom, read: SiO2 instead of: Sioo p.43, line 15 from top, read : C instead of: E 2 p.45, in Key to Fig.7, read: Archaean instead of: Archaen p.61, Table 18, read: metadolerite instead of: meta-doerite p.85, line 10 from top etc. .read: CEC instead of: C.E.C. p.96, line 2 from top, read: phosphorus instead of: phosphate p.102,line 7 from bottom, read: Sr instead of: S p.107,line 4 from bottom, read: Pettijohn instead of: Pettij john p.118,line 5 from top, read: Harmsen,1959 instead of: Harmse,1961 p.119,Table 33, read: ECg instead of: Ece p.122,caption of Fig.35, read: crossed instead of: crosed p.147,line 2 from bottom, read: Mohr and Van Baren instead of: Mohr et al. p.149,line 7 from bottom, read: too instead of: to p.153,line 5 from bottom, delete: oilier,1959 p.155,line 4 from top, read: Burridge instead of: Barridge p. 159,Table 42 read: AI2O3 instead of: A12O3

Fe2O3 A12°3 p.162,caption of Fig.48, read: A1.0, instead of: Ae2°3 p.163,Table 45, insert: fraction lines in Molar ratios p.167,line 13 from bottom, read: criticism instead of: critisism p.169,line 10 from top, read: FAO/UNESCO instead of: UNESCO p. 249, insert :Barshad, I., 1969. Chemistry of soil development. In : Bear (ed.) pp.1-70. p.256,line 4 from bottom, read: Rooij.N.M.de instead of: Rooij.N.M. p.258,insert:Tiurin,I.V.,1965.The system of soil classification in the USSR. Pédologie, Spec.No.3,pp.7-24.