168 JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND Maataloustieteellinen Aikakauskirja Vol. }): 168-209, 1981 Agriculture in northern Namibia, Owambo and Kawango 1965 1970 SYLVI SOINI Agricultural Research Centre, 51600 Jokioinen Preface In 1964, the Evangelical-Lutheran Owambo-Kawango Church asked the Lutheran World Federation for an agriculturist and so, by the Finnish Missionary Society I was invited to take up this work. For three years, from May 1965 to June 1968, I worked for the ’’CDS project 18, Agricultural Survey of Owambo and Kawango”. Subsequently, I served as a teacher at the Finnish Mission’s private High School of Oshigambo and gave lessons weekly at the Engela Parish Institute. I would like to warmly thank all the authorities mentioned above, for the opportunity to have worked in these areas. I am grateful to the Neudam College of Agriculture in Windhoek, for analysing soil samples with South African method; to the Agricultural Research Centre, Department of Soil Science in Helsinki, for making Finnish soil tests and other analyses; to the Herbarium in Windhoek and to Prof. H. Roivainen, University of Helsinki, Department of Botany, for identifying plant samples (ROIVAINEN 1974); to Miss Marjatta Elonheimo for her geographical studies which were in close connection with my work and to Dr. Stengel from the Water Affaires Office in the South West African Administration, who granted us an opportunity to study some aeriel photographs of Owambo. During the first 6 months of my work and some shorter periods later, I received inspiration and guidance about the country and the problems of its people from my interpreter and assistant Mr. Obed T. Embula. My thanks also to the ministers, church members and students of the Engcla Parish Institute and the Oshigambo High School, for their information and questions. In presenting this report I wish to thank Prof. L. Kettunen, agr. R. Hänninen, Mrs Eva Saarela, Miss Merja Manninen, Miss Allison Moore, Mrs. Rauha Kallio and the Agricultural Economics Research Institute for their help in making this publishing possible. I am grateful to the Scientific Agricultural Society of Finland for including this study in their series of publications. CONTENTS Abstract 1 Introduction 2 General description 21 location 2 2 climate 2 3 soils https://www.c-info.fi/en/info/?token=7_Wu2YlIC8ajSPV9.BPyDCianIG7B6K8POsycIA.OVomySGvwxOKpotMJO0e_Yp2BnsVmEDOsZ3xVDuAEiyv2DUwfLOvXBjFnt8bbyq4vV8zvyFMv3Ua9DBC_7-725CWskg45WnNQ7vi83_pzTEfOoE9Y8a6g27xe12Bn-7XiVRgG30wkK2q26wXGosBp5nQPstQb5YakQ 169 24 waters 2 5 vegetation 26 population 2 7 economy 3 Soil studies 31 purpose and method 32 terraines and soil types 3 3 texture 34 soil organic matter 3 5 soil reaction .... 36 specific conductivity 37 macronutrients .. . 371 calcium 372 potassium 373 phosphorus 374 magnesium 38 micronutrients . . . 381 manganese 382 iron and zinc 383 other trace element levels 4 Observations and questions concerning farming in the working areas of the Owambo—Kawango Church 1965-1970 41 water supply 411 storage and irrigation 412 prevention of runoff 41 3 prevention of seepage 414 limiting evaporation 42 plant nutrient supply . 421 organic fertilizers 422 artificial fertilizers 4 3soil conservation in the veldt 44 farming 441 agronomy 442 gardening 443 nutrive value of some products 444 forestry 44 5 animal husbandry 45 domestic economy 46 markets 47 human factors 5 Recommendations 6 Summary References Selostus Abstract. The soils ofOwambo and Kawango plateau in Northern Namibia between logitudes 14°—21°E and latitudes 17° 23”—18°30” S arc studied applying some methods of the Finnish agricultural soil map work. Soil samples of 120 sites, 76 from 3 depths are analysed, the results are connected with the descriptions of terraines and presented as averages and figures. This basic knowledge is connected with the facts of references, observations during the period, results of agricultural observation trials, qucstionaircs and discussions with the farmers. According to these the descriptions and suggestions are made concerning the agriculture in the area. Water and plant nutrient supplies, soil concervation and the most possible different branches of the farming life in the area arc taken into consideration and a list of these is presented. 170 1. Introduction In Owambo, when the first missionaries came about 100 years ago, they existed not only on salaries from Finland, but on the result of their farming. They had to introduce all their own agricultural knowledge and putit into practice along with those customes they were able to accept from the inhabitants. For the new Christians, adjustment to a systematic form of agriculture was fairly easy. When set free of heathen taboos in general, they could learn for example, how to use kraal manure for fertilizing and how to plough with oxen. Kalle Koivu (work period: 1904—47) was a very active farmer to follow as a teacher. When the Government took over the responsibility for primary school education, there were no separate vocational schools to assume the responsibility of education in agriculture. Thus agricultural education did not proceed at the same pace as at the time when the mission organised it and when teachers of the Church had to take care of their own living partly by cultivating the land. Now the agricultural education could mainly be received from what was included in the government schools study programs. At the project’s beginning, some questions and problems were exposed by Mr. Smith, the Government Officer, some were put by the inhabitants and some came from my studies during the five year period. This work is mainly a preliminary study of the soils, vegetations and farming in the area, connecting theoretical agricultural knowledge to local reality, and some suggestions are made for further investigations of farming in these areas. The original report on the agricultural survey of Northern Namibia, CDS 18 project of the Lutheran World Federation 1965—68 (—1970) was given 1971 as dubblicates to the Owambo—Kawamgo Church, Lutheran World Federation, Finnish Missionaries Society and the South West African authorities. This version is revised, shortened concerning original analyse numbers and citations and extended in nutritional aspects. 2. General description 2.1. Location The working area of the Owambo—Kawango Church is situated between longitudes 14°—21° E and latitudes 17° 23’—18° 30’ Sin Northern Namibia (Map I and II). This is between the border of Angola in the north and Etoshapan in the south and from Ruacana Falls on the Kunene in the west, to somewhere east of Rundu. In the west, Owambo is 4 201 000 ha (approximately 12 5 X 340 km) and the Kawango is 3 299 617 ha in area. These areas, however, should be increased to an aggregate of 9 777 250 ha, according to the recommendations stated in the Commission of Enquiry Report, in the South-West African Affairs 1962—1963. The altitude of the main are is 1090—1150 m. In Owambo, the watercourses run south to the Etoshapan and east to the Kawango river, from where they turn south at Andara. 3 Maataloustieteellinen aikakauskirja 3 171 2.2 Climate It has been described by BARNARD 1964, that the climate of this plateau is more subtropical than what is expected at that altitude. The average temperature in January is about +25.5° C (the highest temperatures are in the middle and northern parts of Owambo) and in July between +1 5°—I-17° (the highest temperature on the Kawango riverside). The average annual precipitation is 300—500 mm in western and south-eastern Owambo, 500—600 mm in the middle and north-east areas and above 600 mm, only in a small area on the Kawango riverside. The average variability of precipitation is about 30 %, being somewhat lower than in the west. The average duration of the rainy season (number of months with more than 50 mm of average precipitation) is 4 months in the west and 5 on the Kawango. The average annual number of rainy days, vary from 30—59 in the west to 60 on the Kawango and there may be thunderstorms between 30—40 of these days. Approximately 90 % of the average annual precipitation occurs from October Map I. NAMIBIA. 172 to March. According to these figures the climate can be classified as a sub-humid climate in the main area and semiarid climates in the west and south-west. Marginal dry cultivation is possible in the main area where the grazing area for one stock unit is approximately 6—B ha. The considerable altitude and daytime temperatures cause evaporation, consequently, dry times can often occur. For example in a period of 20 years, there has been 3 very dry, 3 dry, 9 normal, 1 good and 4 very rainy years. In some years, low night temperatures have caused damages to subtropical and tropical fruit trees and to other cultivated plants, when at a sensitive growing stage. This information is comparable with that of other South African districts by COOKE (1964) 2.3. Soils The soils of the project area belong geologically to the Kalahari system (200KE 1964). They are sands which may primarily be Pliocene, redistributed during the Quarternary (Pleistocene), comprising chalcedonic limestones, silicified sandstones and ochreous sands (HAMILTON andCOOKE 1960,AN0N. 1964). The sandlayers are usually several tenths of meters deep. Original rocks can be seen only several tenths of meters deep. Original rocks can be seen only near the Kunene river. Precipitated calcerous concretes, known as ’’white stones” are found for example under the wild fig tree (Omukuyu gwemanya = stone fig tree) on the Oshigambo river (Ondonga, Fig. 1 a), in the middle field subsoil of Nkongo (Uukuanyama) and in Ombafi (North Uukuambi) under more than 10 m of loose sand and in some other sites. In earlier dry ages, under the influence of continuous winds from the north-east, these sands have obviously risen from the Kalahari area to the east, forming in the Kawango high longitudinal ridges and later in the east Map 11. NORTHERN NAMIBIA. and middle of the Owambo transverse and barchan dunes, almost completely vanishing to the west. (Fig. 1 b). Also these sands have been redistributed by rain and by water from the north of Angola, such as the Guvelai delta. Owing to the moderate precipitation of later years, these formations have turned into uneven plateaus where rain water sometimes covers large valleys (oshanas) between consolidated sand hills. One description of tropical ’’plain soils” of East Africa 1966), when used to describe the Owambo soils, is as follows: calcareous or non-calcareous light- coloured (pale grey to pale brown) pedocals, usually forming catenary sequences with black calcareous clays in the broad depression in some areas interrupted by red earth ”. VINE (1966) describes pedocals as being dry region soils, in which CaCO, and possibly CaS0 4 tends to accumulate in the upper layers of the subsoil, while the leaching action of the rain is restricted to the top layers. These belong mainly to the Zonal Soils where effects of climate and vegetation arc acting over long periods and dominate over those of parent rock and drainage factors. Anyhow Owambo— Fig. 1. Different descriptions of Owambo-Kawango area. 173 174 Kawango area is not calculated as dry but semiarid and subhumid and the lime layers are usually deeper in the subsoil and exceptionally in subsurface. According to PAPADAKIS (1969), the soils west of Owambo are arid brown kaolisols and in east Owambo and the Kawango area, the soils are eutrophic kaolisols. The descriptions of salina or solonized soils with abundat Na + or solonchak soils with Ca++ in connection with solid soils with abundant leaching of soluble salts (BRIDGES 1970) may be suitable in description of some varieties of different valley soils in the area. 2.4. Waters Two permanent rivers form borders to the area; The Kunene in the northwest corner and the Okavango along the northern border of the Kawango area and in the middle of Owambo there are temporary rain water systems between the oshanas. In the west it is the Oshana Etaka, in the middle the Cuvelai delta-system and in the mid-east the Oshigambo river. In some years, water from the Angola side (efundja) will occasionally flow through the oshanas of the Cuvelai delta to the Etosha Pan (BARNARD 1966). During the dry season, water is taken for domestic purposes by digging holes often more than ten meters deep to the underground water table. The South-West African Govenment has built earth dams, in soils which are impermeable and boreholes, where the ground-water is not too brackish. Mr. H. W. Stengel of the Water Affairs Office, suggests that there is a ’’bitter sea” in the areas of Ombalantu, Mbunda, Uukolankadhi, Enhana, Ohandjwumbali and Omboloka. The government has made plans for canal from the Kunene river to the middle of Owambo to irrigate about 10 000 ha and provide water for cattle over 430 000 ha (totalling approximately one tenth of Owambo), riverside irrigation using water from the Kawango and if possible, a diversion of water from the Kawango into the Cuvelai in the northern parts of Angola for regular water supplies to the northern parts of Owambo (ANON. 1961,ANON. 1962—63). 2.5. Vegetation There are four different natural types of vegetation (Fig. 1 c) apart from gardenlike or nearly open inahabited areas. From the northwest, along the northern border and norheast to east of Owambo and Kawango, there are forest savannas with Baikiaea plurijuga (Rhodesian kiaat, ’’omupapa”), Guihourtia coleosperma (Rhodesian mahogany, ’’uusivi”), Sclerocarya birrea (murula, ’’ongongo”) and others, mosdy decidous trees. Even though the rainfall is only 600 mm in the main forest area from east Owambo to the Kawango, the forest is often the habitat of the Miombo woodland and savanna, which is the driest type of broadleaved woodland and derived savanna formation. In the middle and in most of the western areas of Owambo, there is a mopane (Colophospermum mopane) forest savanna, but the very typical mopane grass savanna can be seen in the western middle part of the country. As the settlements spread makalani palms (Hyphene ventiricosa) have parts of the mopane forests, especially in the Uukuambi tribe area. In the south close to the Etosha Pan, there are ordinary grasslands. The Baikiaea forest savanna moves occasionally to the Combertaceae—Acacia thickets in the southeast, to the northeast side of Etosha and to the southern parts of the Kawango area. The flora of the 175 whole area is still quite rich even in herbs and grasses in spite of overgrassing in many inhabited areas. 2.6. Population The population, according to the census of 1960, was 234 363 persons in the Owambo and 27 871 persons in the Kawango, i.e. 45.5 %+5.3 % which represents more than half of the whole South West African population. The population is quite heavily concentrated near the waters of the Cuvelai system in middle Owambo (over 8 persons per km 2 ) and near the Kawango riverside (4—B persons per km 2 , BARNARD 1964). 2.7. Economy Each family supports itself on its own cultivated fields. The fields arc commonly about 2—lo ha per family (Fig. 2—5) and the method of cultivation is by plough and hoe. The main crop is ’’omahangu” millet (Pennisetum typhoides), while others are ’’iilyalyaka” (Sorghum sp.J, beans, pumpkins, watermelons, legumes, various groundnuts etc. Many native plants are also used as vegetables: onions, leaves, flowers, tuberous roots and water lilies. Some trees and shrubs have been saved near the family’s dwelling, as common cultivated fruit trees, decoratives or shadows. Travelling around the countryside and talking with the inhabitants in 1965—70 it was easy to observe how the hoe was giving way to the plough. A ’’taboo”, expressed in the old religion, demanded that women only hoe fields because of the fertility. With Christianity however such taboos gradually disappeared and the first Christian native to follow the mission workers’ example of ploughing the field with oxen, is still alive. The skill of ploughing spread so rapidly, that over half of the families had a plough of their own. In some districts, possibly only s—lo % of the families prefered to make exclusive use of the hoc in tilling the soil. Initially oxen were used for ploughing, but donkeys were introduced from the south and were used by half of the ploughers. In a few cases, tractors were also used by the inhabitants of Owambo. A large majority of all cases used crop stubble for feeding the cattle and the very best straw for building purposes. However, ploughing-in the stubble is not yet common although burning had become quite rare. Fertilizing is with kraal manure but insufficient in most cases, since when applied in September and ploughed after the first rains of November—December, it loses much nutrient value. Because of the land tenure system, in which the land belongs to the tribe with only those fields in sight being granted for new cultivation, the main tribal areas have become densely populated. In addition, the forests have been cut down and common pastures between fields are overgrazed. Some tribes however, have spared certain fruit trees to provide shade and these trees have given the tribal area a special individuality. Only in Ongandjera, the fruit trees have not been spread, the reason being that not only their fruit but also the surrounding fields may belong to the headmen. In the peaceful times, people have been able to acquire new fields from forests, near larger grazing areas or from districts bordering other tribes and even within the areas of other tribes. The government has also made such migrations easier by providing dams and boreholes in those districts. 176 The livestock population of 828 930 head (large and small livestock) represents a stocking rate of 6.7 ha per head (ANON. 1962—1963), although the carrying capacity of the fields is 6—B ha per head (large livestock). Cows, goats and hens are the most common domestic animals together with donkeys and pigs. Sheep are seen only in the west and horses are most uncommon. Animal husbandry based solely on natural grazing has always been the practice of the inhabitants and government has for many years attempted to develop this kind of farming by providing water supplies, veterinary help and organizing the grazing customs and markets. In addition income can be earned from sale of handicrafts since many homemade household articles have become marketable and sales could be increasing in the special articles for men and women made from wood, palm leaves or clay. The possibilities for agriculture are considerably better than in other parts of South West Africa (apart from Tsumeb and the Grootfontcin districts). However other natural resources seem to be limited to various kinds of valuable trees, to possible coal findings near Etosha and salts in Etosha. As part of its policy of support and development, the government has begun to execute industry and marketing plans for the homelands (ANON. 1962—1963). As a result, Owambo home transport and trade has been developing rapidly with income entering the area from contract workers, working outside the homeland even though their salaries were not high. Money used by the government for area development is also in some cases used to pay the wages of the inhabitants. 3. Soil studies 3.1. Purpose and method This study aims to supply some basic details on the soils of Owambo and Kawango. To determine the textures and fertilities of soils, 283 samples were collected from 120 sites. 1 Seventysix samples represented the surface (o—2o cm), subsurface (20—40 cm) and subsoils (40—60 cm) and were examples of different types of terrain from each main tribe area (Fig. 1 a). The particle size distribution was determined from 64 samples by wet and dry sieving, as well as by the pipette method. The results are presented in table 1. The names of the soil types follow the system presented by AALTONEN et al. (1949), which is based on texture. The exchangeable Ca and K, as well as the readily soluble P were determined from acid ammonium acetate (pH 4.65) by a method used by VUORINEN and MÄKITIE (1955). The soils’ pH and specific conductivity were determined from a 1: 2.5 soil/water suspension and the organic materials were determined by the bichromate method. The results are presented in tables 2—4. Since the Finnish soil testing method has been developed for acid soils 114 samples were analysed with the South African methods. Nitrogen was analysed by the Kjeldahl Method, phosphorus and potassium extracted, with a 1.0 % citric acid solution and then determined: P colorimetrically, K by a flame-photometer. Map of soil sample sites and data of samples are obtainable from the author. 177 Some drawings were made of soil profiles in averages and are included in this study. The Finnish interpretation table of the soil testing results is also presented in table 5 with the total number of analyses of different soils distributed in these fertility classes presented in table 6. The intake of other plant nutrients have recently been found to be important to human health, especially considering sandy soils with intensive cultivation and macronutrient fertilizers (ROSE 1968, MARJANEN 1969). Some other nutrients were consequently analysed from 59 samples: Mg, Mn, Fe and Zn, extractable in acid ammonium acetate (pH 4.65) with atomic absorption. The results are presented in table 7. Some total microelement contents were analysed; Co, Cu, Mn, Mo, Ni, Pb, Sr, V, Zn and Sn. The results as mg/kg of dry soil are presented in table 8. 3.2. Terraines and soil types The author suggests that Owambo soils have been redistributed by winds since the beginning of the Cuvelai delta formation. Ancient dune formations seem to be observable in the landscape (Fig. 1 b and d) especially in aerial photographs, such as those taking in the rainy season of 1963 from which four small drawings are Fig. 2. Ombalantu. 178 presented. Higher places are not visible in western Ombalantu (Fig. 2), but the water valleys follow the direction of possible transverse dunes. The distinct heights of the ancient barchan dunes can be seen surrounded by cultivated fields near Ogongo (Fig. 3). In northeastern Uukuambi (Fig. 4) the heights of transverse formations can be seen more clearly with their surrounding fields. The rainwaters easily sink into the loose sand at the top of the heights, with calcareous concrete layers consequently appearing deep under the surface. This could be seen in Ombafi, where sand was removed for road work. The concrete layers may expel the water from the sands near the lower edges of the heights and usually, the cultivation is on the edges of these ridges and near the valleys. Near Ondangwa (Fig. 5), the ancient formations arc not visible, but the fields are spotted with new erosion hollows or future water dongas or plantless ’’iipale”. The ’’iipale” extends when wind erosion occurs during the dry season. These formations are connected with a water- rcpellence phenomenon in dry sandy soils (McGHIE 1979) and ovegrazing. In Uukuanyama, the heights and valleys are more definite towards the east and north. In the Kawango area, there are quite high and large longitudinal ridges, with large deep intervening valleys. Fig. 3. Ogongo. Fig. 4. Uukuambi, north cast. Fig. 5. Ondangwa. The most common altitude level for cultivated fields is above the rainwater and may therefore be called uplands. The highest tops of the ancient dunes or uplands can be cultivated, but usually they are uncultivated deep, loose or slightly cemented sands. If they are quite loose, they are called ’’ehekevi”. A little lower than the cultivated level is the very typical mopane forest. It is found on the barely rising (east) sides of the shallow western oshanas. In the very far west, there are large bush savannas with indistinct variations in height. The oshanas and rivers are at the lowest levels and are called valley soils. They may vary from good grass-growing to quite plantless soils and from loose sand to heavy clay, mixed with organogenic mud and can be both often or seldom covered with running or standing water. 3.3. Texture There is only a slight difference between loose sands and other hight soils. Cultivated and virgin upland soils do not differ, but from west to east they resemble more and more closely ’’ehekevi ”, which are sands (Table 1). More than 50 % of them contain sands in amounts above 60 %. All of them contain more than 60 % coarse-fine sand to finer-coarse sand mixtures. Nearly half of them contain more than 90 % of this mixture (coarser fine sand triangle Fig. 6). This kind of mixture is closely similar to the particle size distributions analysed in Finland on the soil catena between dunes and alluvial fine sands in the Liminka district. The analyses of loose sands are not similar to analyses of young dune soils, which are 85—95 % finer coarse sands at the top of the dunes and 60—80 % finer coarse sands between heights. According to the South African texture triangle (Fig. 6), the 64 soil samples included 4 clay, 8 sandy clay, 2 loam and 50 sands. Table 1. The average particle size distribution of analysed soils (Fig. 6 and 7). Terrain types Samples Clay (Cl) Silt (SI) Fine sand (Fs) Sand (S) and districts 0.002 0.002-0.006-0.02 0.02-0.06-0.2 0.2-0.6-2 mm fine coarse fine coarse fine coarse Upland soils cultivated west 9 1.3 0.0 0.1 6.1 29.8 47.2 15.5 east (average) 10 5.0 35.9 5 5.9 3.1 Ondonga 5 3.7 36.1 56.4 3.8 Uukuanyama 9 5.8 35.3 56.1 2.8 Kawango 6 5.2 36.6 5 5.0 3.1 virgin west 4 6.7 33.4 45.0 14.9 east 12 5.0 37.0 53.7 4.3 loose sand soils 6 3.6 33.2 56.2 7.0 farwest savanna 2 5.3 0.3 0.8 5.0 5 5.4 31.6 1.1 mopaneforest 3 13.7 0.7 0.8 5.3 22.7 35.6 21.2 Valley soils west 5 22.5 4.2 8.3 9.2 19.5 25.4 10.9 east 6 24.1 4.2 3.9 1.8 25.6 36.1 4.3 bottle clay, Owambo 2 44.9 5.7 4.6 1.6 19.9 17.8 5.5 riverbed, Kawango 2 46.2 8.6 10.5 13.4 19.2 2.1 180 In comparison of eastern and western soils and some special formations (Fig. 7) the sorting out of the particle sizes seams to have been stronger in the East than in the West. 3.4. Soil organic matter Humus content determined in topsoils from 72 sites are quite low (Table 2). In high soils the humus contens are always less than 1 % and differences about 0,5 %. In valley soils, the percentages are less than 5 % and the differences are obvious, for the valley may be quite plantless or covered with different amounts and kinds of plants. The highest humus percentage (0.91) in cultivated uplands was determined at the Nkongo mission station. The 0.80 % is from a teacher’s field in Ogongo. The Table 2. Humus content of different soils in average. Samples Upland soils Samples Valley soils Humus % Humus % average (low-high) average (low-high) Cultivated Owambo 17 0.42(0.17-0,91) 4 1.59(0.98-3.40) Kawango 6 0.44(0.28-0.57) 1 0.86 Virgin Owambo 21 0.45 (0.28-0.71) 13 1.11 (0.90-3.90) Kawango 7 0.53 (0,30-0.65) 3 2.22 (0.80-4.05) 181 Fig. 6. Distribution of Ovambo. Kavango soils in two different texture triangcls. 182 virgin upland soils contain slightly more humus than the cultivated soils. There was no difference however in the humus content between the forest and the grassland types of the virgin soils. Nitrogen content, often connected closely with the amounts of soil organic matters, were also determined in South West Africa. They were found sufficient for gardening purposes only in 5 of 32 valley soil samples, but not in the 82 upland samples. 3.5. Soil reaction The soil reaction appeared, on average, to be near neutral (Table 3 and Fig. 8). The pH values were in Kawango, where there is higher rainfall than elsewhere, a little lower in uplands and river, but higher in valleys. The same is slightly observable in Uukuanyama soils when compared with Ondonga and virgin west soils. The low pH values in western cultivated upland surfaces are exceptional and Fig. 7. Some average particle size distributions. 183 Table 3. Average soil pH and specific conductivity (10 X mmho/cm 20° C). Specific conductivity Terrain type Samples pH surface subsurface subsoil o—2o cm 20—40 cm 40—60 cm 12 3 12 3 Upland soils: cultivated west 10 6.33 7.00 7.50 0.59 0.71 1.47 Ondonga 6 7.29 7,16 7.26 0.73 0.63 0.65 Uukuanyama 7 7.09 7.10 7.07 0.66 0.55 0.78 Kawango 5 6.33 6.36 6.39 1.80 0.49 0.49 virgin west mopane forest 4 7.06 7,42 7.67 7.40 13.06 19.30 west, others 6 6,57 6.54 6.40 0.62 0.68 1.13 Ondonga 6 6.61 6.97 7.22 0.61 0.79 1.66 Uukuanyama 4 6.35 6.17 6.39 0.49 0.49 0.49 Kawango 5 6.35 5.93 5.92 1.47 1.56 0.86 Deep loose sands 4 6.27 5.92 6.25 0.49 0.49 0.49 Valley soils: cultivated Uukuanyama 4 7.24 7.62 7.71 0,98 1.25 1.21 Kawango 1 2 6,87 6.77 6,60 1.33 1.06 0.88 virgin west 6 7.13 7.47 7.79 6.52 5.88 3.13 Ondonga 5 7.08 7.44 7.68 2.79 2.79 3.73 grassland 2 9.40 9.47 9.20 14.63 20.46 6.60 Uukuanyama 1 2 6.95 6.98 7.05 0.93 0.50 0.49 Kawango 2 7.12 7.90 7.97 2.35 1.00 0.98 1 temporary river Fig. 8. Average soil pH in various soil groups and districts. 184 may be connected with their low calcium and high phosphorus contents and very slight height differences. The loose sand soils have a slightly lower pH, because rainwater is absorbed more easily than in other uplands. Subsoils seem to turn to weak alkaline, especially in the valleys and low western soils. The highest pH values (pH 9.85) were determined in the Ondonga low grasslands, close to Etosha and in the deep valley soil of Oshigambo. The lowest pH (4.90) was in the Ondonga grasslands in dune top formation and in the Oshango deep, loose sands of the forest savanna. Tables 5 and 6 show that cultivated fields registered a reaction between 5 and 7.50. Virgin soils had greater variability and valley soils greater alkalinity. The same variabilities have been stated in samples analysed in South West Africa. 3.6. Specific conductivity Specific conductivities in millimho/cm/20oC usually proved to be too low (Tables 3, 5 and 6). But values, that are too high have also been found in virgin and valley soils. In particular, a too high brack content has been stated in plandess ’’Oshana” in Tsandi. Table 4. Average nutrient content in soils according to terrain types and districts Terrain types Ammonium acetate extractable (pH 4.65) and district Ca mg/1 K mg/1 P mg/1 Samples 1 2 3 1 2 3 1 2 3 surface sub- subsoil o—2o cm surface 40—60 20-40 cm cm Upland soils: cultivated west 10 417 617 947 106 122 173 5.9 5.9 4.8 Ondonga 6 762 800 975 116 146 167 5.9 3.9 3.4 Uukuanyama 7 951 1204 2607 133 101 99 3.1 0.6 0.7 Kawango 5 355 545 565 72 71 63 3.4 1.1 0.6 virgin west mopanc forest 4 475 820 750 158 192 267 0.8 1.1 0.7 west, others 6 2850 2779 967 232 218 197 1.1 1.2 0.7 Ondonga 6 625 4121 12121 110 109 142 1.2 1.3 2.2 Uukuanyama 4 331 275 219 51 24 21 1.8 0.8 0.6 Kawango 5 5 508 310 283 53 41 3 2.1 1.0 0.7 Deep loose sands 4 150 83 67 32 1 3 15 1.8 1.1 1.1 Valley soils: cultivated Uukuanyama 4 17981 42831 53106 424 305 255 11.1 7.8 8.4 Kawango 2 1300 1363 1687 280 72 42 5.7 1.9 1.1 virgin west 6 3087 3429 11025 676 508 387 1.1 3.0 3.8 Ondonga 5 4521 45 50 4500 634 586 541 6.9 4.4 3.8 grassland 2 5050 8050 100 315 340 150 2.8 3.2 1.1 Uukuanyama 1 2 1550 2450 3850 92 95 105 0,3 0.4 0.2 Kawango 2 14687 13995 5150 445 185 165 9.9 4.3 3.2 temporary river 3.7. Macronutrients 3.7.1. Calcium Deposits of calcium in Owambo and Kawango are quite apparent in some profiles. White lime layers have been found in many places, in various depths, and in various forms. Just under the topsoil in Omangundu, there arc loose lime layers and in Engela, concrete lime layers. There are lime concrete under the subsurface in Nkongo and more than 10 m deep under sand layers in Ombafi. In Uusathima, water has been extracted from lime concrete layers. Lime layers seem to be more common near valleys (such as ’’iihenene”) and at river banks, such as those found in Oshigambo, Onguediva and east of Mupini in the Kawango area. The exchangeable calcium amounts in the analysed soils are variable. Generally (Tables 4—6 and Fig. 9), the cultivated soil surfaces have a low calcium content, the virgin soil surfaces seem to have still less calcium and the loose sands least of all. Many valley soils are rich in calsium however, for example, some cultivated valleys in the Uukuanyama have very high Ca-contents. This may even be the reason for the cultivability of those soils. It seems (Table 6), that cultivated fields usually have somewhat higher Ca-contents than virgin upland soils. Some virgin soil samples with high Ca-contents were taken from the above lime profiles, from low grasslands in Southern Ondonga and close to one plantless valley in the west. Thus, all of them seem to be exceptional sites. Table 5. Interpretation table of soil testing results for mineral soils (KURKI, TAKANEN et al. 1965). Fertility class pH Specific conductivity Coarse Clay lOx millimho/cm (20° C) soils soils Too high to high 7 7.4 < 7.4 < 10 Very good 6 6,6-7.3 6.6-7.3 Good 5 6.2-6.5 6.2-6.5 Satisfactory 4 3.8—6.1 5.8—6.1 4 Rather low 3 5.4-5.7 5.4-5.7 Low 2 5.0-5.3 5 0-5,3 2 Very low 1 5.0 > 5.0 > mg/litre of soil Calcium, Ca Potassium, K Phosphorus, P Coarse Clay Coarse Clay Coarse Clay soils soils soils soils soils soils 7 4 000 5 600 800 1 000 200 200 6 2 600 J 600 400 500 70 40 5 2 000 2 600 250 300 25 15 4 1 400 2 000 150 200 10 6 3 800 1 500 100 150 4 3 2 400 1 000 50 100 2 1.5 1 <4OO < 1 000 <5O