School of Agricultural, Earth and Environmental Sciences

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An experiment in land use mapping in the Three Rivers District, Natal.
(1965) Christopher, Anthony John.; Davies, Ronald John.; Biesheuvel, H.
No abstract available.
Natal : a study in colonial land settlement.
(1969) Christopher, Anthony John.; Davies, Ronald John.
No abstract available.
Tissue culture studies on the genus Rosa with special reference to the shoot tip.
(1969) Jacobs, Gerard.; Allan, P.; Bornman, Chris H.
A modified Berthelot (1934)-Knop (1865) solution was found to support the growth of rose pith segments while Murashige and Skoog's (1962) medium did not. Possibly the NH(4)+ content of the latter medium is toxic to rose tissue. The best callus growth was obtained with indolebutyric acid (IBA), which was superior to naphthaleneacetic acid (NAA), indoleacetic acid (IAA) and 2,4 dichlorophenoxybutyric acid (2,4-DB) at the concentrations tested, while gibberellic acid (GA) greatly enhanced callus formation in the presence of both IBA and kinetin. Occasional differentiation of shoots was observed both in cultured pith segments and in callus formed at the basal cut surface of the shoot tips. However, the precise culture conditions required for differentiating rose pith and callus tissue remain unknown. An interaction was found between NAA and kinetin with regard to root and leaf development in shoot tips. Root formation took place only in the absence of kinetin and in the NAA range of 0.5 to 2.0 mg/l, while normal leaf development occurred only in the absence of NAA and in the presence of 4.0 to 18.0 mg/l kinetin. Neither any combination of NAA and kinetin nor the sequential application of growth substances induced both root and shoot growth. Furthermore, shoot tips sampled in late summer formed roots much more readily than tips sampled in late winter. GA reduced the favourable effect of high kinetin treatments on leaf development. Different species of auxin affected growth of the shoot tip in different ways. IAA did not inhibit growth of the shoot tip in the same manner as was observed for NAA, IBA and 2,4 dichlorophenoxybutyric acid (2,4-D). It is concluded that further experimentation with different ratios of various species of auxin and cytokinin, as well as the sequential administration of growth substances, may lead to the successful culture of intact plantlets from rose shoot tips and shoot apical meristems, and ultimately to possibly virus-free rose plants.
Potassium studies on an Avalon medium sandy loam.
(1970) Farina, Martin Patrick Warner.; Hulme, Sampie A.; Sumner, Malcolm E.
Abstract available in pdf file.
Soil acidity and liming in Natal.
(1970) Reeve, Neville George.; Sumner, Malcolm E.; Orchard, Edwin Retief.
1. Effects of Aluminium Toxicity and Phosphorus Fixation on Crop Growth on Oxisols in Natal Simple, routine methods for estimating exchangeable Al and P fixing capacity of acid soils are described. A glass-house study on eight Oxisols revealed marked growth response of 'trudan' (Sorghum sudanense) to amelioration by lime, gypsum and Ca silicate which is ascribed to elimination of A1 toxicity rather than to improved P availability. Growth response to amelia rants took place up to the point of elimination of exchangeable Al after which a significant reduction in yield occurred. P fixation is shown to be a major fertility limitation in the soils studied. Since no apparent relationship between P fixing capacity and exchangeable A1 existed and since lime did not decrease P fixation despite its ability to eliminate soluble A1, it is concluded that P fixation is an adsorption reaction rather than a precipitation reaction. Although the soils studied are all capable of fixing large quantities of P considerable variation exists between them. Fertilizer recommendations based only on an estimate of the available P in the soil per se could thus be in serious error. 2. Lime Requirements of Natal Oxisols based on Exchangeable Aluminium The exchangeable Al status of eight Natal Oxisols is a suitable criterion for the measurement of lime requirement defined as the amount of lime necessary for maximum crop production. The principal function of lime in these soils is to eliminate A1 toxicity; it has little or no effect on P availability. A "critical value" for exchangeable A1 below which 'trudan' did not respond to lime application was found. On the average the amount of lime necessary for maximum growth and exchangeable Al control was approximately one sixth the amount required to raise the soil pH to 6.5. 3. Cation Exchange Capacity and Exchangeable Aluminium in Natal Oxisols Positive charges in acid soils reduce CEC at low electrolyte concentration probably by double layer interaction. The resultant net CEC (determined by washing soil free of salt with water) is the effective CEC under field conditions and the difference between net CEC and exchangeable bases is accordingly a convenient measure of exchangeable A1. A reaction scheme is proposed which relates the large pool of non-exchangeable Al (extractable with N NH[4]0Ac-pH4) in these soils to the relatively small amounts of exchangeable AI; this reaction scheme is governed primarily by net CEC and exchangeable bases rather than by pH. 4. Amelioration of Subsoil Acidity in Natal Oxisols, The large pH dependent CEC in Natal Oxisols effectively limits the downward movement of lime. Although heavy fertilisation, particularly with acid forming nitrogenous fertilizers increases the rate of movement, relatively small amounts of Ca salts having little ability to neutralise subsoil exchangeable Al could be leached from limed topsoil. In contrast, bases equivalent to 80% of that applied leached rapidly from gypsum treated topsoil. Although gypsum did not eliminate subsoil exchangeable A1, it was considerably more efficient than lime in this respect. However, gypsum caused severe loss of exchangeable Mg which could have serious nutritional consequences if not corrected.
An economic analysis of the demand for resources and the supply of output in South African agriculture.
(1970) Nieuwoudt, Wilhelmus Liberté.; Behrmann, Herbert Ian.
No abstract available.
Local atmospheric circulations and the mesoclimate of Durban.
(1970) Preston-Whyte, Robert Arthur.; Davies, Ronald John.
Rapid urban and industrial growth along the Natal coast has occurred with little concern for characteristics of local climate. In general, industrial growth has taken place without taking into account the potential for pollution transportation during the winter season; urban areas have developed without consideration for the vital need in sub-tropical latitudes to maintain adequate mixing of the lower atmosphere. The apparent inadequacy in planning for climate has partly been due to a lack of understanding of the nature and characteristics of local wind systems. The motivation for this study stems , therefore, from the need to evaluate the influence of land-sea and topographically-induced wind systems upon certain aspects of weather and climate on the Natal coast. During summer, moist and relatively cool air is advected almost daily over the Natal coast by the sea breeze . Observations of spatial and temporal variations of these winds were made in the period 1963-69 from recording stations in the Durban area and along a 40-mile transect approximately normal to the coast at Durban. Comparable observations have not as yet been made in South Africa nor have there been a ttempts to examine the influence of sea breezes upon selected climate and weather phenomenon. In this latter connection the role of the sea br eeze is examined in two separate fields in this study, namely urban climatology and thunderstorm development. Climatic discomfort caused by the combined effect of high temperatures and humidities on the Natal coast, is at a maximum in urban areas . Since these areas are also highly populated , a need exists to evaluate the ability of the sea breeze to reduce urban temperatures by advection of cooler air over the area, by eddy diffusion of heat or by displacement of urban temperatures aw~ from poorly ventilated areas. Thus climatic discomfort in these areas may also be reduced. Detailed observations of the influence of the sea breeze, in particular, and wind in general, upon the spatial variation of temperature , humidity and human comfort were, therefore, undertaken in the Durban area. It is believed that this i s the first time an attempt has been made to describe the spatial distribution of a comfort index in an urban area. The results should be of interest to the a rchitect and town planner. The sea breeze, strengthened by gradient and valley Vlinds, is shown to penetrate at least 40 miles inland. In accordance with this , it is suggested that the inland invasion of marine air takes place in response to lowered pressure in adjacent inland areas in southern Natal and provides the moisture required to feed thunderstorms which develop in this area. These storms subsequently move towards the coast following the retreating convergence zone between winds with an onshore and offshore component of motion and reach Durban after sunset. Land breezes are best developed in winter. Observational techniques were similar to those employed in the sea breeze study and provide the only detailed examination of spatial and temporal variations of land breezes in South Africa. Until recently the nature and characteristics of topographically-induced winds in Natal were also a relatively unexplored feature of local atmospheric circulations. However, Tyson (1967) has examined local winds in certain Natal valleys and his prediction that mountain- plain winds reach the coast during the night is also examined in this study. While the relatively weak. and shallow land breeze may be of secondary importance when compared with the sea breeze, it would be a mistake to underestimate the importance of these winds upon certain aspects of coastal climate. In p~rticular the tendency for land breezes to initiate cloud and precipitation at night is examined while the potential for the transportation of atmospheric pollution by these winds is also briefly discussed. A study of the diurnal variation of precipitation at Durban reveals a high frequency of low intensi~ precipitation at night. The nature of this precipitation differs in both frequency and" amount from high intensity rainfall which is the product of thunderstorm and frontal activity. It is suggested in this study that the land breeze plays a dominant role in providing the buoyancy necessary to cause nocturnal drizzle precipitation from shallow stratus cloud. The thesis is divided into four parts. Part I examines details of the physiography, weather, climate, observati ~nal methods and analysis techniques. Because of the variability of weather on the coast of Natal that section is dealt with in more detail than would have been deemed necessary for a similar study inland. Without knowledge of the characteristics of the atmospheric circulation, the behaviour of local wind systems in relation to large scale systems could not be adequately discussed. In Part II land and sea breezes and topographically-induced wind systems are examined in detail. Emphasis is placed not only on the observational characteristics of these winds such as onset, depth, velocity gradient, surging, relation to gradient winds and dissipation but also on their relation to theoretical models of the relevant wind system. The influence of local wind systems upon selected climatic elements is dealt with in Part Ill. Characteristics of the diurnal variation of precipitation are examined in Chapter 6. Rainfall frequencies and amounts are shown to be highest in the first half of the night and a model is developed to explain the influence of land breezes and mountain-plain winds upon low intensity but high frequency nocturnal rainfall. High intensity but low frequency rainfall produced by thunderstorms also occurs soon after sunset and a further model is advanced to explain this phenomenon in relation to the sea breeze. The effect of air movement upon the spatial variation of temperature, humidity and a discomfort index in both summer and winter is examined in Chapters 7 and 8. The relationship between these elements has permitted the development of an empirical model to predict values across the city of mean midday summer and winter temperatures as well as discomfort index values. In Part IV the most significant aspeots relating to the study as a whole are summarised. In conclusion the potential f or the transport of pollutants by land breezes and topographically induced winds is briefly discussed as an aid to planning and siaple spatial models are given showing generalised air movement and ventilation characteristics in the Durban area and along the Natal coast.
The mineralogy and related geology of the Albert Silver Mine, Bronkhorstspruit, Transvaal
(1970) Champion, Alfred Timothy.
The Albert Silver mine is situated on the farm Roodepoortjie, 32 kilometres north of Brorikhorstspruit in the Transvaal. The deposit forms the largest of a number of sub-parallel quartzhematite lodes accompanied by sulphide mineralization and is accompanied by an extensive alteration zone along its northern flank.
Soils and land-use planning in the Howick Extension Area.
(1970) Scotney, Derek Michael.; Scott, J. D.
No abstract available.
Nutritional restriction of the growth rate of broiler breeder replacement pullets.
(1971) Gous, Robert Mervyn.; Stielau, Werner Johannes.
No abstract available.
The use of climatic data for maize grain yield predictions.
(1972) Mallett, John Bertram.; De Jager, James M.
The development and testing of a mathematical model for maize grain yield predictions is described. The model is based upon daily considerations of soil moisture, atmospheric evaporative demand and stage of crop development. Final yield predictions depend upon a knowledge of yield decrement due to moisture stress and the number of occasions that stress is recorded. This information was determined in the following manner:- (i) Stress imposed in lysimeters before and after anthesis was found to reduce grain yields by 3,2% and 4,2% per stress day respectively. (ii) A stress day was identified with the aid of mass-measuring lysimeters and a U.S. Weather Bureau Class A evaporation pan for measuring atmospheric evaporative demand. A nomogram constructed in terms of evaporative demand and available soil moisture, which discriminates between stress and non-stress days, was obtained for the Doveton soil used in the lysimeters. The model was applied to Cedara rainfall and evaporation data and yield probability patterns for three planting dates were obtained. It was found that highest yields (8,5 Mg ha(-1)) and least seasonal yield variation, may be expected from the earliest planting data 15/10. The Cedara : Doveton yield prediction model was also applied to climatic records for two other Natal stations (Estcourt and Newcastle) and six stations outside Natal (Bethlehem, Potchefstroom, Hoopstad, Standerton, Ermelo and Krugersdorp). Interesting comparison of the suitability of their respective climates for maize production was obtained. A method which uses the predicted number of stress days and the resultant yield decrement to determine the most effective and economic irrigation scheduling is developed and described. The effect of moisture holding characteristics of various soils upon the shape of the discriminating curve is discussed, and a method of obtaining discriminating curves for other soils by modifying the Doveton curve is described.
The influence of variations in the level of nutrition on reproduction in the ewe.
(1972) Lishman, Arthur William.; Stielau, Werner Johannes.
No abstract available.
Factors affecting nitrogen utilization by sugarcane in South Africa.
(1972) Wood, Richard Anthony.; Orchard, Edwin Retief.
TIhe response of sugarcane to applied N in South Africa varies considerably from one soil to another, particularly in the plant crop. Responses to fertilizer N by ratoon cane are generally much greater than those given by plant cane. Where irrigation is practised yield response per unit of N is significantly higher than that obtained under rain grown conditions. Response of cane to N can be influenced by various factors, some of which are able to bring about differences in yield as great or greater than those obtained from the N fertilizer itself. These include seasonal effects, time and method of N application, the form of N applied, and the nature of the soil . The N cycle in relation to sugarcane has been examined, as several factors affecting response of cane to N are concerned with the transformations which N undergoes in the soil - plant system. The potential of different soil series within the sugar belt to mineralize N, greatly influences the response of plant cane to applied N. The N supplying power of sugar belt soils is also dependent upon how recently they were opened for cultivation, and the length of time they remain dry prior to replanting. However, accurate assessment of soil N available to cane remains difficult, and it is probable that N recommendations will continue to be made largely on an empirical basis of management and yield. Incorporation of cane trash in the soil, and the C/N ratio of cane roots may affect efficiency of N fertilizer usage by the crop, particularly in the sandier soils of the industry low in N, due to the immobilization of applied N. Apart from the soil pH effect as such, specific N carriers are able to influence r ates of nitrification and thus susceptibility to leaching, especially in the more weakly buffered soils which constitute over 30% of the industry. It appears likely that utilization of N by cane grown in these soils, could be enhanced by the use of the nitrification inhibitor N-Serve. Application of all the N to the furrow at time of planting can cause severe leaching losses even in heavily textured soils. Top-dressing some weeks after planting, results in more efficient recovery of fertilizer N. Even so, only 25%-30% of N applied in the widely used ammonium form is recovered by the above ground parts of the cane crop.
The late cenozoic carnivora of the south-western Cape Province.
(1972) Hendey, Quinton Brett.; King, Lester Charles.
Abstract available in PDF file.
Nutritional studies with a spanish-type groundnut on an avalon medium sandy loam soil.
(1972) Snyman, Jacobus Wilhelmus.; Nathanson, Karl.
Calcium requirements of a Spanish-type groundnut cultivar on an Avalon medium sandy loam soil. The effect of different levels of application of agricultural lime, dolomitic lime and gypsum on yield and quality of the Nelson Spanish groundnut cultivar was studied in a field experiment. The effect of the applied treatments was studied by means of detailed soil and plant analyses. The results reported were obtained in a season with below normal rainfall. The so-called "typical drought damage" symptoms were found to be largely due to nutritional deficiency conditions. A linear increase in kernel yield was obtained as a result of increased levels of exchangeable calcium in the soil. Calcium uptake by the fruit proceeded more efficiently where gypsum was used as calcium carrier. The calcium content of the fruit was increased as a result of increases in the level of exchangeable calcium in the soil. The gypsum treatments resulted in a marked increase in shelling percentage, percentage ovarian cavities filled and increased kernel yield. The mechanism of action of the gypsum treatments was not solely improved calcium nutritional conditions. A poor correlation between calcium content of the soil and the groundnut fruit, and shelling percentage and percentage ovarian cavities filled was obtained in the case of agricultural lime and dolomitic lime treatments. The level of exchangeable soil calcium and soil pH on the majority of groundnut fields investigated was found to be low enough to expect considerable increases in yield following on applications of agricultural lime. Such an increase in pH would result in an improved nitrogen status of the plants as a result of more efficient nitrogen fixation. Applications of agricultural lime should be supplemented with a supply of calcium in a more soluble form, such as gypsum. The more soluble calcium carrier would provide a supply of readily available calcium for uptake over periods of moisture stress. The relationship between chemical composition of the soil and plant, and yield and quality factors were studied. The occurrence, cause and control of hollow heart and black plumule damage in groundnut kernels Hollow heart and black plumule are symptoms of nutritional abnormalities in groundnut kernels. Although the occurrence of these symptoms are associated with the occurrence of drought conditions, the calcium and boron status of the Avalon medium sandy loam is low enough to result in the occurrence of these symptoms on a small scale under normal rainfall conditions. The supply of available boron in the soil is decreased as a result of fixation into an unavailable form during dry periods. Decreased boron concentrations in the plant under these conditions results in the occurrence of boron deficiency symptoms in the kernels (hollow heart damage). At the same time, it is suggested, that due to the nutritional association between calcium and boron in the plant, the decreased levels of boron in the plant results in a decreased metabolic activity of calcium indicated by the occurrence of black plumule damage (a calcium deficiency symptom). The critical level of boron in the kernel as far as both hollow heart and black plumule damage is concerned, appears to be between 10,2 and 13,9 ppm. Applications of gypsum resulted in a marked decrease in hollow heart and black plumule damage. This treatment resulted not only in increased levels of calcium in the kernel, but at the same time appears to prevent the fixation of boron thus allowing normal uptake of boron by the plant. Applications of agricultural and dolomitic lime had no effect on the occurrence of either form of damage. These treatments were associated with a marked increase in calcium content and a decrease in boron content of the kernels. The ratio Ca content of the kernel (ppm)/K content x Mg content of the kernel was found to be fairly closely correlated with the occurrence of black plumule damage. The calcium, potassium and magnesium status of the soil was of little value for the purpose of predicting hollow heart damage. The intensity of hollow heart and black plumule damage was increased by applications of urea. Cultivars differed in their susceptibility to hollow heart and black plumule damage. An application of 26 kg/ha borax virtually eliminated both forms of damage.
The effect of diluent on the bacterial reaction to disinfectants.
(1973) Hathorn, Fergus Ask Shuldham.; Abbott, C. W.
No abstract available.
Some effects of environment, age and growth regulating compounds on the growth, yield and quality of sugarcane in southern Africa.
(1974) Rostron, Harold.; Nathanson, Karl.; Thompson, G. D.
An assessment has been made of the potential for increasing yields of well grown irrigated sugarcane crops beyond their present maxima. The effects of age at harvest and artificial growth regulators on yield have also been investigated. Measurement of the apparent maximum yield of cane fresh weight (tc/ha) and total dry matter (t.dm/ha) of three varieties grown on a specially prepared site, indicated that actual cane yields were 63-70% of the estimated potential maximum. Differences in morphology between two extreme varieties, NCo 376 and CB 36/14, were insufficient to affect growth and yield under good growing conditions. The average productivity over a period of one year of plant and first ratoon crops of three varieties was 65 t.dm/ha and 150 tc/ha. This is a crop growth rate of 17,0 g/m(2)/dy, representing an average conversion into plant dry matter of 1,9% of total incident radiation (ri.) or 4,3% of visible ri. This level of productivity is equivalent to rates reported for sugarcane growing in more favourable parts of the world and for other highly productive crops. In an experiment in which a series of crops were ratooned at different times of the year and harvested at ages ranging from 32 to 72 weeks, sugar yield and all measures of cane quality were closely correlated with cane yield for crops of all ages. Sugar yield varied with age at harvest, according to the cycle of weather conditions experienced by the crop. Crops ratooned in January and February produced the highest yields of 23 tons estimated recoverable sugar per hectare ( ters/ha) at 64-72 weeks of age. The average rate of sugar production at this time ranged from 1,3-1,5 ters/ha/month. At 12 months of age crops ratooned in July and September had the highest yields of 17,2 ters/ha, but they then made little further growth. High rates of sugar production of 1,4-1,6 ters/ha/month were obtained from crops ratooned between June and September and harvested between May and. August at 40-56 weeks of age. Considering data for all crops, cane yield was correlated with weather conditions only up to 40 weeks of age. After this, increments of cane yield were correlated better with the amount of growth already made than with either crop age or the average weather conditions experienced. Artificial chemical ripening was successful on young immature crops harvested in May at the beginning of the milling season, but there was only a small response under less favourable growing conditions and when the crop was older and more mature. Ethrel and Polaris were the most successful of several ripeners tested, Ethrel being more active than Polaris. Cane quality was improved and sucrose storage was increased despite reductions in rates of photosynthesis and sheath and lamina size. The ripening response varied with variety, condition of the crop at the time of spraying, rate of chemical application and the time interval between spraying and harvesting. From this work it is concluded that it will probably be easier to raise the sugar yield of existing high yielding varieties by altering the proportioning of photosynthate in favour of sucrose storage, rather than by increasing cane yield.
Characteristics of sesquioxidic soils.
(1974) Fey, Martin Venn.; Le Roux, J.
Sesquioxidic soil clays from Oxisols in South Africa, Australia and Brazil, and two clays from Andosols in Japan and New Zealand, were investigated by XRD, OTA, IR, EM and quantitative mineralogical analysis. The volcanic-ash soil clays are dominated by allophane; clays from Natal are dominated by kaolin (30 - 45%) and free iron oxides (20 - 25%), with smaller amounts of gibbsite (0 - 12%) and pedogenic chlorite (less than 20%); Oxisol clays from Australia and Brazil contain free iron oxides (40 - 50%), gibbsite and kaolin (both about 25%). Acid ammonium oxalate (pH 3) was found to be superior to currently popular alkaline reagents for extracting amorphous aluminosilicates and alumina from these clays. Boiling 0,5- NaOH dissolved large amounts of finely-divided kaolinite and halloysite, while hot 5% Na[2]CO[3] reaction was too slow (partial dissolution of synthetic amorphous aluminosilicates with one extraction) and insufficiently selective (gibbsite and kaolin of poor crystallinity dissolve to a variable extent). On the other hand, synthetic gels (molar Si0[2]/A1[2]O[3] ranging from 0,91 to 2,55) dissolved completely after 2h shaking in the dark with 0,2tM acid ammonium oxalate (0,2 ml/mg). Specificity of oxalate for natural allophane was indicated by removal of similar quantities of silica and alumina using different clay: solution ratios. Oxalate extraction data indicated that allophane is absent in Oxisol clays, which are characterized by small quantities of amorphous, A1-rich sesquioxide (1,5 to 7%), some of which may originate in interlayers of 2: l phyllosilicate structures. Allophane was determined quantitatively in volcanic-ash soil clays by allocating hydroxyl water content to oxalate-soluble silica plus alumina on the basis of an ignition weight loss/chemical composition function for synthetic amorphous aluminosilicates. Both Si02/A1[2]O[3] ratios and quantities of allophane were found to be lower than those obtained using boiling 0,5N NaOH, in agreement with the interpretation that the latter treatment attacks crystalline aluminosilicates. Parameters of chemical reactivity and distribution of electric charges following various chemical pretreatments of allophane were found to correspond closely to those predicted on the basis of synthetic gel behaviour. Results for Oxisol clays suggested that the role of amorphous (oxalate-soluble) alumina in governing physicochemical properties is generally subdorninant to that of the poorly-crystalline, A1-substituted iron oxide component which is removed by deferration with citrate-dithionite-bicarbonate reagent. Hysteretic pH-dependent net negative exchange charge was shown to arise from hysteresis of positive exchange charge, while CEC is fully reversible by titration with strong acid. A mechanism is postulated to account for this observation. Levels of silica in the soil solution of Natal Oxisols are higher than those of more strongly-weathered soils from Australia and Brazil, and may be sufficiently high to exert a favourable effect on plant-available P following phosphate fertilization. Although soluble silica levels are also relatively high in volcanic-ash soils, a similar effect is not likely to manifest itself significantly owing to the very high P adsorption capacity of allophane. A study of soil solution equilibria indicated that in terms of silica and aluminium hydroxide potentials, kaolinite is the most stable mineral in all the soils. Allophane persists as a partial metastable equilibrium state in volcanicash soils while gibbsite formation in Oxisols is contingent upon periodic, nonequilibrium leaching conditions. The role of clay mineral suite in governing levels of exchangeable aluminium in acid soils is examined. A revised model system for allophane is proposed in which tetrahedral substitution of Al for Si may reach a maximum of 1 : 1 in an aluminosilicate phase. Additional alumina takes the form of discreet amorphous or crystalline material. The composition of allophane corresponding to maximum A1 for Si substitution will depend upon the availability of basic cations for charge balancing during neogenesis of the amorphous aluminosilicate.
The hydrogeology of Botswana.
(1974) Jennings, Christopher Mark Hubert.
Botswana covers an area of 570 000 km and has a population of about 600 000. It is estimated that three-quarters of the human and livestock populations are dependent on ground water, with an estimated 26 x 10 m of water from this source being used annually. Details of the physiography, climate, denudational and depositional surfaces and geology are given: Ground water occurs in both primary and secondary aquifers under both water-table and artesian conditions at varying depths from less than 1m to over 300m. The water-bearing properties of the various aquifers are described with the basalt/Cave sandstone contact providing the greatest number of successful boreholes and the sedimentary rocks of the Pretoria Group providing the highest yields (208,45 litres/minute). The shallowest water is found in the Kalahari Beds and the deepest in the Ecca Group. Detailed descriptions are given of the hydrogeology of the Central Kalahari, Lobatse, Orapa and Serowe. In the Lobatse area, estimates of the average monthly recharge rate have been made as well as estimates of the total storage capacity of the various ground-water basins. The percentage of annual rainfall contributing to ground water has also been calculated. An annual recharge rate has also been calculated for Serowe while the total amount of water in storage in the important Cave sandstone aquifer has been estimated. Hydrogeological details of the Kalahari Beds, basalt/Cave sandstone aquifer and Middle Ecca aquifers are given following core drilling programmes. ERTS photography was used to assist in obtaining a figure of 56 x 10 m of extractable water present in storage in the "sand rivers" of eastern Botswana. Detailed aquifer tests on a variety of aquifers are described and show that the secondary aquifers generally present often behave in a similar fashion to primary aquifer. Approximately 5 000 boreholes are presumed to be present in Botswana. It is estimated that 17% of the successful boreholes have yields in excess of 150 1/min. The siting of boreholes using geological/geophysical aids has resulted in an increase in the success rate of nearly 25%. New geophysical techniques for the location of ground water have been investigated and ground geophysical methods used include electrical resistivity, inductive and conductive electromagnetic, Afmag, self-potential and seismic reflection and refraction methods. The well-tried resistivity method remains the most successful technique but self-potential, Afmag and seismic methods have given encouraging results. Extremely detailed studies using environmental isotopes are described. These have enabled quantitative estimates of ground-water storage and turnover times to be made; have given round-water flow rates; have outlined areas of recharge; have enabled permeabilities to be calculated; have enabled a clearer picture of recharge mechanisms through the unsaturated zone to be built-up; and have provided important evidence of areas in which recent recharge has contributed to ground-water supplies. The studies have shown that measurable amounts of tritium are present over far wider areas than originally anticipated and thus more recharge is taking place than thought earlier from laboratory tests and hydrogeological considerations. In Lobatse a water balance model is proposed and calculations based on this model indicate that some leakage, hitherto unsuspected, between several of the ground-water basins, take place. The carbon-14 method has, in addition, helped outline areas of recharge (Central Basin, Lobatse) which tritium had failed to do and has shown by using combined 3H and l4C data that mixing of young and old waters takes place. In the Kalahari, radiocarbon has been used to calculate ground-water flow rates, permeability and transmissivity. The oldest ground water in Botswana has an age of 33 700 years. Isotopic studies in the unsaturated zone have shown that water moves given rates downward at a rate of between 31 and 41 cm per year. Studies of water levels in boreholes have shown that nearly all boreholes show responses which can be directly correlated with seasonal recharge and hence the nature and frequency of recharge can be estimated. In addition, storage capacity and safe yield have been estimated using long term water level changes and knowing the amount abstracted from the basin. The rapid responses shown in some boreholes indicates surprisingly rapid recharge. Two boreholes in Botswana showed effects of the Tulbagh earthquake on 29th September 1969. The disturbance of semi-diurnal fluctuations in boreholes could possibly be used as an early warning device to predict catastrophic earthquakes. A prelimlinary annual safe yield for ground-water supplies in Botswana is estimated to be 4 x 10 9 m3 per annum. Tree roots have been found in boreholes at depths greater than 68m. This emphasises the role vegetation can have in causing transpirational losses from ground-water supplies. Irrigation from boreholes is unlikely to be profitable unless exceptionally large supplies are obtained or water be present at very shallow depth. Underutilised boreholes, e.g. boreholes drilled specifically for cattle ranching, could also be profitably used for irrigation. Details of ground-water chemistry and examples of fresh water overlying saline, saline water overlying fresh, chemical stratification with depth and changes in quality with time are given. The distribution of fluoride rich waters in Botswana is also given. This thesis has therefore attempted to outline the current status of hydrogeological research in Botswana and it is hoped that this will lay the foundation for later, more detailed and quantitative, studies. These will become even more vital than at present, as it is estimated that all readily available surface water resources in eastern Botswana will be fully utilised by the late 1980's and the country will rely even more heavily on ground water than at present.
Soil amelioration and boron nutrition effects on the growth of sunflowers (Helianthus annuus L.) on an Avalon medium sandy loam.
(1975) Blamey, Frederick Paxton Cardell.; Nathanson, Karl.
Studies with sunflowers (Helianthus annuus) on an Avalon medium sandy loam, both in pots and in the field, indicated that the poor growth of this crop on this soil was largely due to soil acidity. Marked improvements in plant growth were brought about by liming as shown by measurements of emergence, seedling mass, population, plant heights, leaf areas and yield. Based largely on soil and plant analyses, it was concluded that improved growth with soil amelioration resulted from reduced aluminium toxicity and, since lime was more efficient than gypsum in neutralizing toxic Al, lime was markedly superior to the latter in improving plant growth. An annual application of 2 400 kg agricultural lime/ha increased seed yields >5 fold in the first and >10 fold in the second season in which the field experiment was carried out. In the pot experiment, no benefit of liming above the level required to neutralize toxic Al (-pH (N KCl) 4.5) was recorded and, on the contrary, yields tended to be depressed above this level. Highly significant linear relationships between yield and exch. Al (meq100g) were recorded in the pot and field experiements and, averaged over two seasons, seed yields in the field were increased 12% for each 0,1 meq/100g reduction in exch. Al. Another factor which decreased sunflower seed yields on this soil was boron deficiency and symptoms of B deficiency in the field were identified and described. At the levels of boron in the unfertilized soil, this deficiency affected the reproductive, rather than the vegetative stage of growth and correction of B deficiency by applying 10 kg borax/ha per annum increased seed yields by 38% and 18% in the two seasons, respectively. Soil amelioration had only a slight effect on the boron nutrition of sunflowers in this study. The chemical composition of the plant tissue was found to be a suitable means of quantifying B deficiency in sunflowers, the B concentration being a slightly superior method in most cases to the Ca:B ratio in plant tissue. Using field data, critical B concentrations in (i) month-old seedlings, (ii) the topmost, fully-mature leaf at flowering and (iii) in the seed were determined. The relationships were established between the amount of borax applied to the soil and the B concentration in plant tissues and these relationships could be used as a basis for recommending corrective B fertilization.

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