Doctoral Degrees (Soil Science)

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Application of soil indigenous knowledge in rural communities of eastern South Africa.
(2018) Buthelezi, Nkosinomusa Nomfundo.; Hughes, Jeffrey Charles.; Muchaonyerwa, Pardon.; Modi, Albert Thembinkosi.; Caister, Karen Fern.
This study investigated ethnopedological knowledge related to classification, fertility and non-agricultural uses of soil in four villages in KwaZulu-Natal and the Eastern Cape, South Africa. Ethnographic methods elicited general soil indigenous knowledge. Ethnopedologic techniques gathered understanding of soil taxonomy, mapping and fertility, and selection and use of healing, cosmetic and geophagic soils. Local assessments of soil fertility and mapping were compared to scientific approaches. Soil samples were analysed for physicochemical properties. Soils used for non-agricultural purposes were analysed by X-ray diffraction and X-ray fluorescence spectrometry. Local classifications were based on observable soil morphological properties. Soil maps produced by farmers in areas with distinct geomorphic units closely correlated with scientific maps; on a floodplain the correlation was poor. Farmers assessed soil fertility using both crop and soil variables. There was poor correlation between farmers’ fertility classes and laboratory data. Farmers understood soil-crop associations which formed the basis for their soil suitability assessment and have developed specific soil use and management practices. Two soil types were identified for non-agricultural uses. Ukhethe, used for agriculture, was also used for geophagy; ibomvu for sun protection, healing and cosmetics. Geophagic soils were mainly saprolite from Leptosols. They were mostly fine-grained, had bright Munsell hues, contained mica, kaolinite, quartz and iron oxides, and elements such as Cu, Zn, Co and Pb. Ibomvu occurred in Ferralsols and was red to dark-red. Despite low sun protection factors, critical wavelengths >370 nm, the presence of TiO2 and high Fe2O3 explained its sun protection ability. The soil was fine grained, had low pH and exchangeable bases, and contained kaolinite that possibly explained its healing role. These communities applied their pedological knowledge to soil use and management. There were diverse non-agricultural uses and possible land use conflicts where a soil has more than one use. Farmers classified soils at levels that could be incorporated as higher categories in the current South African system. Farmer fertility assessment could benefit from laboratory data. Soil suitability classification systems should be used to assess both agricultural and non- agricultural uses. Valuing all local uses of soil will ensure fair and relevant land use planning.
Bioremediation of Atrazine- and BTX-contaminated soils : insights through molecular/physiological characterization.
(2001) Ralebitso, Theresia Komang.; Van Verseveld, Henk W.
Most natural products and xenobiotic molecules, irrespective of their molecular or structural complexity, are degradable by some microbial species/associations within particular environments. Atrazine- and selected petroleum hydrocarbon (benzene, toluen~ and 0-, m- and p-xylene (BTX))-degrading associations were enriched and isolated"trom atrazine- and petroleum hydrocarbon (PHC)-contaminated KwaZuluNatal loamy and sandy soils, respectively. In total, eight pesticide- and forty BTXcatabolizing associations were isolated. Electron microscopy revealed that, numerically, rods constituted the majority of the populations responsible for both atrazine and PHC catabolism. Cocci and, possibly, spores or fungal reproductive bodies were observed also. For the BTX-catabolizing associations, the population profiles appeared to be dependent on the enrichment pH and the molecule concentration. After combining selected associations, to ensure that all the isolated species were present, batch cultures were made to determine the optimum pH and temperature for growth; With an atrazine concentration of 30 mgr1, the highest specific growth rates, as determined by biomass (OD) changes, were recorded at 30DC and pH 4 although the rate§ at 25DC and pH 5 were comparable. For the BTX (50 mgr1)-catabolizing associations, the highest growth rates were recorded at pH 4 for the four temperatures (15, 20, 25 and 30DC) examined. The sole exception was p-xylene with the highest specific growth rate recorded at pH 5 and 30De. Batch and continuous (retentostat) cultivations in the presence/absence of methanol and under C- and N-limited conditions were used to investigate the impacts of the solvent and the catabolic potentials of a combined atrazine-catabolizing culture (KRA30). In general, different degradation rates were recorded for the culture in response to element limitation. Addition of citrate as the primary carbon source / effected atrazine (100 mg!"l) degradation rates comparable to that of Pseudomonas sp. strain ADP while succinate addition effected herbicide co-metabolism. Carbon supplementation may, therefore, be considered for site amelioration practices. To complement conventional culture-based microbiological procedures, molecular techniques were employed to explore the diversities and analyze the structures of the microbial communities. In parallel, anaerobic microbial associations which targeted atrazine were also characterized. The soil DNA isolation/characterization protocol adopted consisted of a clean-up step followed by the polymerase chain reaction (peR) and 16S rDNA fingerprinting by denaturing-gradient gel electrophoresis (DGGE). The preliminary results suggested that despite different, but chemically similar, petroleum hydrocarbon molecules, the common selection pressures of the primary enrichments effected the isolation of similar and complex aerobic microbial associations. Some similar numerically-dominant bands characterized the aerobic and anaerobic atrazine-catabolizing associations although distinct differences were also recorded on the basis of the enrichment/isolation pH value and the concentration of the herbicide. Cloning and sequencing were then used to identify some of the numerically-dominant and non-dominant association members. Community-level physiological profiling (CLPP) for physiological fingerprinting was made with Biolog EcoPlates and highlighted the differences in the isolated aerobic atrazine-catabolizing associations depending on the enrichment pH and molecule concentration. Logarithmic-phase cultures of the combined atrazine- and BTX-catabolizing associations were used to explore the association profiles following pH and temperaiure optImIzation. Although some common numerically-dominant components were maintained, differences in numerical and, possibly, activity dominance were observed in the 16S rDNA profiles in response to changes in pH and temperature. This indicated that environmental parameter optimization and characterization of catabolic association structure must precede bioaugmentation so that control of key variables will facilitate maintenance of the dominant site-specific species. Following KRA30 cultivation in the presence/absence of methanol and under carbon and nitrogen-limited conditions, the population fingerprints showed that the presence of methanol effected shifts in species numerical dominance and, possibly, changes in atrazine catabolic capacity. Also, Coulter counter results, optical density readings and 16S rDNA characterization by DGGE indicated that degradation rate changes were accompanied by shifts in species numerical/activity dominance within the association. Although N-limitation effected the highest rates of herbicide catabolism, a potential versatility of the combined association for bioaugmented and/or biosupplemented remediation with acceptable rates regardless of any elemental limitation was recorded. To determine if the contaminated and pristine source soils contained comparable catabolic populations and, thus, offered potential for intrinsic bioremediation, PCRDGGE was used to characterize the populations in comparison with the enriched/isolated associations. Some similar dominant bands characterized the contaminated soils and the enriched/isolated associations. The significance of this, in relation to a possible correlation between numerical and activity dominance in the component species, is discussed with respect to the use of PCR-DGGE to identify natural attenuation potential and monitor sustained intrinsic and enhanced (bioaugmented and biosupplemented) bioremediation.
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.
Comparative characteristics of biochar types from human faecal wastes and pine-bark and sorption of selected heavy metals from effluent and their mobility in an amended loam soil.
(2018) Koetlisi, Koetlisi Andreas.; Muchaonyerwa, Pardon.
Heavy metals from industrial effluents poses risks to the environment and human health. Pyrolysis of locally available organic wastes could address solid organic waste management and produce a biochar that could immobilise heavy metals in industrial effluents, at source, and in amended soils. Limited research work on characteristics and effectiveness, in addressing environmental challenges, of biochar from latrine waste, sewage sludge and pine bark which are ubiquitous organic wastes in South Africa. The aim of this study were to determine effects of pyrolysis temperature on yield, characteristics and sorption capacities of selected metals from solutions and effluents on biochar from latrine wastes, sewage sludge and pine-bark and on metal mobility in amended soil. The three materials were pyrolysed under limited oxygen at 350, 550 and 650°C. Proximate and ultimate analysis, surface area, porosity and functional groups were analysed on the biochar produced. Batch sorption studies were conducted to determine biochar sorption capacity with Cd, Zn, Cu and Cr in single metal solutions and for Zn, Cu and Cr from a multiple metal solution. A leaching column study was conducted using a loam soil amended with sewage sludge biochar at equivalent rates of 0, 50 and 100 kg ha-1 and the columns leached with industrial effluent while others were leached with distilled water, measuring pH, electrical conductivity, Zn, Cu and Cr in the leachate at each event and in three equal sections of the soil at the end of the experiment. A pot trial was conducted with spinach grown on a loam soil amended at 0, 25, 50 and 100t ha-1 of sewage sludge and latrine waste biochar pyrolysed at 350°C biochars and irrigated with 25% industrial effluent for some and tap water for others. Drymatter, tissue water content, Zn and Cu, and soil pH, EC, Zn and Cu were determined at the end of the trial. Latrine waste had higher biochar yield, ash content, surface area and pore volume, and lower fixed C and volatile matter than sewage sludge. Biochar yield, volatile matter, total C, N and H decreased with pyrolysis temperature, while ash content, surface area and porosity increased. Surface functional groups of the biochar also varied with feedstock and pyrolysis temperature. The Cd sorption capacities were higher for latrine waste biochar than from sewage sludge. Mixtures of pine bark biochar with latrine waste (1:1) or sewage sludge (1:3) biochar showed synergistic effects on Cd sorption. Sorption capacities of latrine waste, sewage sludge and pine- vi bark biochar (350°C) were, respectively, 312.5, 400 and 232.6 mg kg-1 for Zn, 102, 98.0 and 33.3 mg kg-1 for Cu, and 18.9, 13.8 and 67.1 mg kg-1 for Cr from industrial effluent. Conversely, sorption capacities biochar from latrine waste, sewage sludge and pine-bark, respectively, were 278, 227 and 357 mg Zn kg-1, 97.1, 137 and 21.3 mg Cu kg-1, and 122, 106.4 and 147.06 mg Cr kg-1 for single metal solutions. Addition of biochar did not affect shoot drymatter but affected root drymatter and tissue Zn and Cu, with higher Cu than Zn in the tissue. The additions of sewage sludge biochar to neutral, loam soil did not significantly reduce leaching of Cu and Zn from the applied effluent. Moreover, the application of biochar from both latrine waste and sewage sludge increased metal uptake by spinach in the same soil. The findings of this study imply that the characteristics of biochar from latrine waste, sewage sludge and pine bark are different and that faecal waste biochars show positive metal immobilization potential in batch equilibrium studies, but have little or negative effects when added to neutral soils even at extremely high application rates.
Composting performance of vermiculite-cattle manure composts and their effects on selected soil properties and maize (zea mays L.) production on sandy loam soils in Zimbabwe.
(2021) Pisa, Charity.; Muchaonyerwa, Pardon.
Abstract available in PDF.
Effect of potassium, nitrogen and silicon fertilisation on sugarcane growth and quality, nutrient uptake dynamics and soil chemistry in two contrasting soils of KwaZulu-Natal, South Africa.
(2020) Rhodes, Ruth.; Hughes, Jeffrey Charles.; Miles, Neil.
Abstract available in pdf.
The effect of various crop residue management practices under sugarcane production on soil quality.
(2003) Graham, Martha Helena.; Haynes, Richard John.; Wallis, Frederick Michael.
This study examined the influence of different management practices under sugarcane production on soil chemical, biological and physical properties on a long-term (59yr) field experiment in KwaZulu-Natal. These management practices included conventional post-harvest burning of crop residues, with the tops either left on the soil surface or with tops removed, and green cane harvesting with the retention of crop residues on the soil surface as a trash blanket. Each of these treatments were either fertilized or did not receive fertilizer. The data collected was used to evaluate the effect of crop residue management on soil quality under sugarcane production. Soil organic matter content increased from 39 g C kg¯¹ soil, under conventional burning to 55 g C kg¯¹ soil in the surface 10 cm under green cane harvesting where crop residues are returned to the soil. It also resulted in greater recycling of nutrients and increases in exchangeable K and Ca and extractable P. Fertilizer application resulted in a build-up of soil nutrients in combination with trash retention. Fertilizer application induced increases in exchangeable P and also some accumulation in soil organic P. Exchangeable and non-exchangeable K concentrations were also higher in fertilized than non-fertilized treatments. However, nitrogen fertilizer application and, to a lesser degree, organic matter mineralization, resulted in soil acidification to a depth of 30 cm. Acidification in the fertilized treatments resulted in a concomitant increase in exchangeable acidity and exchangeable Al, due to the increase in H⁺ ions and solubilized Al species on exchange sites. Base cations moved into soil solution and were leaching to lower soil layers. The decrease in soil pH resulted in the surface charge conferred on the variable charge surfaces on soil colloids becoming less negative and as a result there was a decrease in ECEC. Acidification in fertilized treatment not only increased exchangeable Al but also the buffering reserve of non-exchangeable al; both that complexed with soil organic matter (CuCl₂- extractable) and that present as hydroxy - Al associated with mineral colloids (ammonium acetate - extractable). The increased organic matter content under trash retention resulted in an increase in ECEC. This enabled the soil to retain greater amounts of Ca²⁺, Mg²⁺ and K⁺ which were returned to the soil in the trash. Both residue retention and fertilizer application had a positive effect on the microbial biomass C and N and the microbial quotient increased from 0.39% to 0.86% as organic C increased from 39 g C kg¯¹ soil under burnt treatments to 55 g C kg¯¹ soil under trashed, fertilized treatments. This increase was associated with increased concentrations of labile organic material (K₂S0₄₋extractable) present as well as increased amounts of nutrients being cycled through the plant-soil system. The light fraction organic matter also increased with increasing returns of organic residues. However, the large active microbial biomass under the trashed, fertilized treatment resulted in an increased turnover rate of this fraction and consequently resulted in lower LF dry matter, C and N than in the unfertilized treatment. Aggregate stability increased with increasing amounts of organic material returned due to trash retention. Nevertheless, fertilized treatments induced a lower aggregate stability than unfertilized ones, despite the tendancy for the latter to have higher organic C and microbial biomass values. This was attributed to an increase in the proportion of exchangeable cations present in monovalent form (due to application of fertilizer K and leaching of Ca and Mg) favouring dispersion and a decline in aggregate stability. Green cane harvesting resulted in an increase in microbial activity (basal respiration, FDA hydrolytic activity, arginine ammonification rate and dehydrogenase activity) and in the activity of specific soil enzymes involved in turnover of C, N, P and S to a depth of 30 cm. Increased activities of these enzymes reflect a higher rate of turnover of C, N, P and S. The metabolic quotient decreased with increasing residue return, indicating a more metabolically efficient microbial community. Fertilizer application resulted in a variable effect on enzyme activity. Long-term fertilizer application resulted in an increase in invertase and acid phosphatase, a decrease in L-histidase and arylsulphatase and had little effect on protease and alkaline phosphatase. These variable effects were explained in terms of an interaction between fertilizer - induced increases in Corg and soil nutrient status and fertilizer - induced soil acidification. The size and activity of the soil microbial biomass was studied in the plant row and in the inter-row of a sugarcane field under burning or green cane harvesting. Soils were sampled to 30 cm depth in (i) the centre of the plant row, (ii) 30 cm out from the row centre and (iii) 60 cm out from the row centre (i.e. the middle of the inter-row area). Under burning, the only substantial input of organic matter to the soil was from root turnover in the row area where the root biomass was concentrated. As a consequence, the size (microbial biomass C) and activity (basal respiration of the soil microbial community were concentrated in the row. However, under green cane harvesting there was a large input of organic matter in the inter-row area in the form of the trash blanket itself and through turnover of crop roots that were concentrated in the surface 10 cm of the soil below the blanket. As a result, soil microbial activity was considerably higher in the interrow area under green cane harvesting than under burning. Phospholipids are essential membrane components of microorganisms and a good correlation was found between the total PLFA's extracted from soils and the microbial biomass C, indicating that phospholipids are an accurate measurement of living biomass. Mutivariate statistical analysis (PCA) was used to separate different PLFA profiles under burning versus trash retention and under different land uses (sugarcane, maize, annual and perennial pasture and undisturbed veld). Soil organic matter content contributed the greatest variance in the data along the first axis. That is increasing soil organic matter return not only increased the size of the microbial biomass, but also affected the composition of the microbial community. There was a shift in the different sub-fractions under different management practices. MUFA's are general biomarkers of Gram negative bacteria and were found to be a sensitive indicator of higher substrate availability (i.e they increased under green cane harvesting). Fungal biomarkers indicated an increased fungal biomass associated with surface application of residues. Soil physical conditions were considered to be a contributing factor to the shift in microbial community structure. Increased organic matter content improved soil physical conditions and preferentially stimulated the growth of aerobic microorganisms. In addition to this, the proportion of SATFA (gram positive bacteria) was found to increase in response to burning. This increase was attributed to the survival mechanisms of these microorganisms (i.e. endospore formation). It was found that the conversion from burning to trash management changes the composition of the soil microbial community. The effect of management practices on soil functional diversity was also evaluated using two methods (i.e. Biolog plates and substrate induced respiration (SIR)). Biolog plates are a selective technique that stimulate growth of a small proportion of the soil microbial community whereas the SIR technique measures the activity of the metabolically active microbial community in situ. As a result the SIR method separated treatments more effectively than Biolog plates (i.e. annually tilled treatments, permanent grassland sites and fertilized and unfertilized treatments). The quantity and the quality of organic C supply influenced the catabolic diversity. Conversion from burning to green cane harvesting greatly increased catabolic evenness and richness and therefore presumably also tended to increase the resilience of the soil to stress and disturbance particularly in relation to decomposition functions. It was concluded that conversion from preharvest burning to green cane harvesting results in an increase in soil organic matter content, an improvement in soil structure and soil nutrient status, an increase in the size, activity, taxonomic and functional diversity of the soil microbial community. The practice should therefore be promoted to the South African sugar industry.
The effects of land use and management practices on soil microbial diversity as determined by PCR-DGGE and CLPP.
(2011) Wallis, Patricia Dawn.; Titshall, Louis William.; Hunter, Charles Haig.; Morris, Craig Duncan.
The environmental impact of anthropogenic disturbances such as agriculture, on the soil ecosystem, and particularly on soil microbial structural and functional diversity, is of great importance to soil health, conservation and remediation. Therefore, this study assessed the effects of various land use and management practices on both the structural (genetic) and functional (catabolic) diversity of the soil bacterial and fungal communities, at two long-term sites in KwaZulu-Natal. The first site is situated at Baynesfield Estate, and the second at Mount Edgecombe Sugarcane Research Institute. At site 1, the land uses investigated included soils under pre-harvest burnt sugarcane (Saccharum officinarum, Linn.) (SC); maize (Zea mays, Linn.) under conventional tillage (M); permanent kikuyu (Pennisetum clandestinum, Chiov) pasture (KIK); pine (Pinus patula, Schiede) plantation (PF); and wattle (Acacia mearnsii, De Wild) plantation (W), all fertilized; and undisturbed native grassland (NAT) that had never been cultivated or fertilized. At site 2, a sugarcane (Saccharum officinarum × S. spontaneum var. N27) pre-harvest burning and crop residue retention trial was investigated. The treatments studied included conventional pre-harvest burning of sugarcane with the tops removed (Bto), and green cane harvesting with retention of crop residues on the soil surface as a trash blanket (T). Each of these treatments was either fertilized (F) or unfertilized (Fo). The polymerase chain reaction (PCR), followed by denaturing gradient gel electrophoresis (DGGE) were used to determine the structural diversity, and community level physiological profiling (CLPP) using BIOLOG plates, the catabolic diversity. In addition, the soils were analysed with respect to selected physicochemical variables, and the effects of these on the soil microbial communities were determined. Replicate soil samples (0–5 cm) were randomly collected from three independent locations within each land use and management, at both sites. Soil suspensions for the CLPP analyses were prepared from fresh soil subsamples (within 24 h of collection) for the bacterial community analyses, and from 8-day-old soil subsamples (incubated at 4°C to allow for spore germination) for the fungal community analyses. BIOLOG EcoPlates™ were used for the bacterial CLPP study and SF-N2 MicroPlates™ for the fungal analysis, the protocols being adapted and optimized for local conditions. This data was log [X+1]-transformed and analysed by principal component analysis (PCA) and redundancy analysis (RDA). For PCRDGGE, total genomic DNA was isolated directly from each soil subsample, and purified using the MO BIO UltraClean™ soil DNA Isolation kit. Protocols were developed and optimized, and fragments of 16S rDNA from soil bacterial communities were PCR-amplified, using the universal bacterial primer pair 341fGC/534r. Different size 18S rDNA sequences were amplified from soil fungal communities, using the universal fungus-specific primer pairs NS1/FR1GC and FF390/FR1GC. Amplicons from both the bacterial and fungal communities were fingerprinted by DGGE, and bands in the fungal DGGE gels were excised and sequenced. The DGGE profiles were analysed by Bio-Rad Quantity One™ Image analysis software, with respect to band number, position, and relative intensity. Statistical analyses of this data then followed. Soil properties [organic C; pH (KCl); exchangeable acidity; total cations (ECEC); exchangeable K, Ca and Mg; and extractable P] were determined by PCA and were shown to have affected the structural and catabolic diversity of the resident microbial communities. At Baynesfield, canonical correspondence analysis (CCA) relating the selected soil variables to bacterial community structural diversity, indicated that ECEC, K, P and acidity were correlated with CCA1, accounting for 33.3% of the variance, whereas Mg and organic C were correlated with CCA2 and accounted for 22.9% of the variance. In the fungal structural diversity study, pH was correlated with CCA1, accounting for 43.8% of the variance, whereas P, ECEC and organic C were correlated with CCA2, and accounted for 30.4% of the variance. The RDA of the catabolic diversity data showed that the same soil variables affecting fungal structural diversity (organic C, P, ECEC and pH) had influenced both the bacterial and fungal catabolic diversity. In both the bacterial and fungal RDAs, organic C, P and ECEC were aligned with RDA1, and pH with RDA2. However in the bacterial analysis, RDA1 accounted for 46.0%, and RDA2 for 27.5% of the variance, whereas in the fungal RDA, RDA1 accounted for only 21.7%, and RDA2 for only 15.0% of the variance. The higher extractable P and exchangeable K concentrations under SC and M, were important in differentiating the structural diversity of these soil bacterial and fungal communities from those under the other land uses. High P concentrations under M were also associated with bacterial catabolic diversity and to a lesser extent with that of the soil fungal communities under M. Similarly, the higher organic C and exchangeable Mg concentrations under KIK and NAT, possibly contributed to the differentiation of these soil bacterial and fungal communities from those under the other land uses, whereas under PF, the high exchangeable acidity and low pH were possibly influencing factors. Under W, low concentrations of P and K were noted. Other factors, such as the presence/absence and frequency of tillage and irrigation, and the diversity of organic inputs due to the diversity of the above-ground plant community, (in NAT, for example) were considered potentially important influences on the nature and diversity of the various land use bacterial and fungal communities. At Mount Edgecombe, CCA showed that organic C and Mg had a significant effect on soil bacterial structural diversity. Organic C was closely correlated with CCA1, accounting for 58.7% of the variance, whereas Mg was associated with CCA2, and accounted for 41.3% of the variance. In the fungal structural diversity study, ECEC and pH were strongly correlated with CCA1 and accounted for 49.1% of the variance, while organic C was associated with CCA2, accounting for 29.6% of the variance. In the functional diversity studies, RDA showed that both bacterial and fungal community catabolic diversity was influenced by soil organic C, pH, and ECEC. In the bacterial analysis, RDA1 was associated with organic C and pH, and accounted for 43.1% of the variance, whereas ECEC was correlated with RDA2, accounting for 36.9% of the variance. In the fungal analysis, RDA1 was correlated with ECEC and accounted for 47.1% of the variance, while RDA2 was associated with pH and organic C, accounting for 35.8% of the variance. The retention of sugarcane harvest residues on the soil surface in the trashed treatments caused an accumulation of organic matter in the surface soil, which did not occur in the pre-harvest burnt sugarcane. This difference in organic C content was a factor in differentiating both bacterial and fungal communities between the trashed and the burnt treatments. Soil acidification under long-term N fertilizer applications caused an increase in exchangeable acidity and a loss of exchangeable Mg and Ca. Thus, as shown by CCA, a considerably lower exchangeable Mg concentration under F compared to Fo plots resulted, which was influential in differentiating the bacterial and fungal communities under these two treatments. In the structural diversity study at Baynesfield, differences were found in bacterial community species richness and diversity but not in evenness, whereas in the fungal analysis, differences in community species richness, evenness and diversity were shown. The soil bacterial and fungal communities associated with each land use were clearly differentiated. Trends for bacterial and fungal diversity followed the same order, namely: M < SC < KIK < NAT < PF < W. At Mount Edgecombe, no significant difference (p > 0.05) in bacterial structural diversity was found with oneway analysis of variance (ANOVA), but two-way ANOVA showed a slight significant difference in bacterial community species richness (p = 0.05), as an effect of fertilizer applications. A significant difference in fungal species richness (p = 0.02) as a result of management effects was detected, with the highest values recorded for the burnt/fertilized plots and the lowest for the burnt/unfertilized treatments. No significant difference was shown in species evenness, or diversity (p > 0.05), in either the bacterial or the fungal communities. In the catabolic diversity study at site 1, the non-parametric Kruskal-Wallis ANOVA showed that land use had not affected bacterial catabolic richness, evenness, or diversity. In contrast, while fungal catabolic richness had not been affected by land use, the soil fungal community catabolic evenness and diversity had. At site 2, the land treatments had a significant effect on soil bacterial community catabolic richness (p = 0.046), but not on evenness (p = 0.74) or diversity (p = 0.135). In the fungal study, land management had no significant effect on the catabolic richness (p = 0.706), evenness (p = 0.536) or diversity (p = 0.826). It was concluded, that the microbial communities under the different land use and trash management regimes had been successfully differentiated, using the optimized protocols for the PCR-DGGE of 16S rDNA (bacteria) and 18S rDNA (fungi). Sequencing bands produced in the 18S rDNA DGGE, enabled some of the soil fungal communities to be identified. CLPP of the soil microbial communities using BIOLOG plates showed that, on the basis of C substrate utilization, the soil bacterial and fungal communities’ catabolic profiles differed markedly. Thus, it was shown that the different land use and management practices had indeed influenced the structural and catabolic diversity of both the bacterial and fungal populations in the soil.
Effects of the land disposal of water treatment sludge on soil physical quality.
(2001) Moodley, Magandaran.; Johnston, M. A.
An essential step in producing "drinking" water is to precipitate the suspended and dissolved colloids through the addition of flocculents such as lime, ferric chloride, aluminium sulphate and/or poly-electrolytes. The by-product of this process is termed water treatment sludge (WTS) and contains mainly silt, clay and some organic matter. Previously this material was disposed of in landfill but more recently, alternative methods for its disposal are being evaluated. A potential disposal option is land treatment. In this system of waste disposal the inherent properties of the soil are used to assimilate the waste. Although the effect of the land disposal of WTS on soil chemical quality is gaining increasing research attention, few studies have investigated the effects on soil physical quality. This study was originally commissioned by a local water utility to evaluate the effects of the land disposal of sludge produced at their works, on soil quality. At this plant organic polymers are used to both flocculate the material and to thicken the sludge in the water recovery process. Fresh sludge has a consistence approaching that of slurry but dries to angular shaped aggregates of extremely high strength. Nevertheless, sludge aggregates comprise a network of micro-pores and channels and are therefore porous. Because of these properties, the potential use of WTS as a soil conditioner was considered.. Since lime, gypsum and polyacrylamide are wellrecognised soil conditioners, these were included as reference treatments in the study. Two field trials (Brookdale and Ukulinga) and laboratory experiments were designed to investigate the influence of WTS on soil in terms of water retention, hydraulic conductivity, evaporation, aeration, aggregation and strength. Seven rates of WTS are represented at the . Brookdale trial but research efforts were concentrated on the 0, 80, 320 and 1280 Mg ha' treatments. WTS was also applied as a mulch (without incorporation into the soil) at the 320, 640 and 1280 Mg ha" level. Gypsum was applied at rates of 5 and 10 Mg ha", lime at 2 and 10 Mg ha' and anionic polyacrylamide at 15 and 30 kg ha'. At the Ukulinga trial, WTS was mixed with the upper 0.2 m of the soil at rates of 0, 80, 320 and 1280 Mgha'. Only the high rates of gypsum, lime and anionic polyacrylamide being tested at the Brookdale trial are represented at the Ukulinga trial. All treatments in this study were maintained fallow. The laboratory study features an additional two soils to those from the field experiments, chosen to produce a range in clay contents. WTS influenced several soil physical properties. Soil bulk density decreased following the addition of sludge to soil. This caused an increase in porosity (particularly macro-porosity) and therefore water retained at saturation, but only of statistical significance at the 1280 Mg ha" level. Equally an increase in water retention at the wilting point (-1500 kPa matric potential) also occurred, owing to the high microporosity of sludge aggregates. Despite these effects very little change in both the plant available and readily available water content occurred. Neither, gypsum nor lime caused any significant change in water retention. Aslight improvement was noted on the polyacrylamide treatment at the Brookdale site but this effect did not persist for very long after the trial was established. Although in situ field measurements were influenced strongly by natural spatial variability, WTScaused a marked increase in the saturated hydraulic conductivity (Ks). The reasons for this relate to the higher porosity and the inherently stable nature of the sludge aggregates, which imparts a more open structure to the soil and reduces the extent of pore blockage. This finding was corroborated in a laboratory study in which strong positive correlations between sludge content and Ks was found. The water retention curve and saturated hydraulic conductivity was used to predict the unsaturated hydraulic conductivity function (Kw)using the RETe computer model of van Genuchten et al., 1991. The results showed a decrease in Kw on the sludgeamended treatments the extent of which increased with sludge content. This finding was tested in an evaporation study conducted under controlled environmental conditions. More water was conserved on the sludge-amended treatments than the control, because of its lower Kw. The application of the sludge as a mulch was more effective in conserving water than incorporating the sludge with soil. The air-filled porosity at field capacity (-10 kPa matric potential) of the sludge-amended soil remained within a favourable aeration range of 10-15%, which suggests that aeration should not be a limiting factor for plant growth. Air-permeability nevertheless improved substantially. Attempts at using the size distribution of dry soil aggregates to evaluate the influence of the sludge on aggregation proved unsuccessful. Saturated soil paste extracts for selected soil depths beneath the mulch layers at the Brookdale trial, nevertheless, showed significant increases in Ca2+ and Mt+ concentrations, which is encouraging from a soil stability perspective. Due to the inherently strongly aggregated nature of this soil, no meaningful change in aggregate stability, however, was measured. Significant improvements in soil stability were, nevertheless, found when fresh sludge was mixed with soil. If the sludge is not allowed to dry fully beforehand the polymer that it contains remains active and available for bonding of the soil particles together. Upon drying, these polymers become irreversibly attached to the soil substrate and win not become reactivated even upon re-wetting of the soil. This also explains why sludge aggregates found below only a few centimetres of the soil surface maintained their strongly aggregated nature. This suggests that although WTS consists of mainly silt and clay, the risk of this constituent fraction becoming released and clogging water conductive soil pores are, at present, low. Despite the high strength of the sludge aggregates the penetrometer soil . strength (PSS)within the tilled layer was non-significantly different from the control treatment. Below the tilled layer, however, the PSS on the sludge-amended treatments were lower owing mainly to wetter soil conditions. The research completed to date suggests that land treatment as an environmentally acceptable disposal option for water treatment sludge shows promise since soil conditions tend to be improved.
Estimation of hydrological properties of South African soils.
(1983) Hutson, John Leslie.; Cass, A.
A computer simulation model of the soil water regime can be a useful research, planning and management tool, providing that the data required by the model are available. Finite difference solutions of the general flow equation can be applied to complex field situations if soil profile characteristics are reflected by appropriate retentivity (B( Ψ)) and hydraulic conductivity (K(Ψ)) functions. The validity of a flow simulation model depends upon the degree to which simulated flow corresponds to the flow pattern in real soils. Macroscopic flow in apedal soils is likely to obey Darcy's law but in structured or swe~ling soils, macro-pores and shrinkage voids lead to non-Darcian flow. Physical composition and structural stability properties of a wide range of South African soils were used to assess swelling behaviour and depth-related textural changes. The applicability of a one-dimensional Darcian flow model to various soil types was evaluated. Core retentivity data for South African soils were used to derive regression equations for predicting B (Ψ) from textural criteria and bulk density. A sigmoidal, non-hysteretic two-part retentivity function having only two constants in addition to porosity was developed for use in water flow simulation models. Values of the constants, shapes of the retentivity curves and soil textural properties were related by fitting the retentivity function to retentivity data generated using regression equations~ Hydraulically inhomogeneous soils may be modelled by varying the values of the retentivity constants through the profile to reflect changing soil properties. Equations for calculating K(B) or K(Ψ) from retentivity data were derived by applying each of three capillary models to both exponential and two-part retentivity functions. Comparison of these equations showed that the definition and value of semi-empirical constants in the capillary models were as important as the choice of model in determining K(B). K(Ψ) was calculated using retentivity constants corresponding to a range of bulk density, clay and silt content combinations. Three retentivity constant-soil property systems were evaluated. These were derived from retentivity data for South African soils between 1) -10 and -1500 kPa, 2) 0 and -50 kPa and 3) from published retentivity data for British soils. Only that derived from retentivity data accurate in the 0 to -50 kPa range led to K(Ψ) relationships in which saturated K and the slope sK/sΨ decreased as bulk density, clay or silt content increased. Absolute values of K were unreliable and measured values are essential for matching purposes. A method for evaluating the constants in a K(Ψ) or K(B) function from the rate of outflow or inflow of water after a step change in potential at the base of a soil core was described. Simple exponential g (Ψ) and K(Ψ) functions were assumed to apply to each pressure potential range. Retentivity parameters were obtained by fitting the 8(Ψ) function to the measured retentivity curve. A value for K[s] , the remaining unknown parameter in the K(Ψ) function, was obtained by matching measured outflow and inflow data to a family of simulated curves. These were computed using measured retentivity parameters, core dimensions and ceramic plate conductivity, and a range of K[s] values. An advantage of this method is that there are no limitations on core length, plate impedance or pressure potential range which cannot be ascertained by prior simulation. Regression equations relating texture to retentivity, and a conductivity model were applied in a simulation study of the water regime in a weighing lysimeter in which gains and losses of water were measured accurately. Active root distribution was assumed proportional to root mass distribution. Relative K(Ψ) curves for each node were computed using one of the conductivity equations derived earlier. Daily water potentials for a month were simulated using three conductivity matching factors. By matching simulated Ψ values to tensiometer potentials measured at five depths an appropriate matching factor was chosen. The effects of an over- or underestimate of K(Ψ) were demonstrated. This work simplifies the prediction and use of retentivity and conductivity relationships in soil water flow simulation models. These models can be used for assessing the water regime in both irrigated and dry-land crop production. Other applications include catchment modelling, effluent disposal and nutrient and solute transport in soil.
Evaluation of extraction based fertilizer recommendations.
(2015) Nongqwenga, Nqaba.; Modi, Albert Thembinkosi.
There is a need to improve methods by which nitrogen, phosphorus and potassium are currently recommended. There is a considerable lack of mechanistical justifications for the methods used to recommend these nutrients. Lack of mechanistical justification can be attributed mainly to the disregard of nutrient (N, P and K) dynamics. Also the difficulty in incorporating these dynamics on fertilizer recommendation programs has compromised the mechanistical basis of extraction based approaches. The aim of the study was to evaluate these conventional (extraction based fertilizer recommendations) methods used to recommend these nutrients, by comparing their performance to the alternative approaches provided in this study. This evaluation was carried out through several studies, and a review of literature. From literature review it was apparent that there is indeed a need for revision of these methods. Their lack in mechanistical, technical and practical justification was considered and critically analyzed. It was proposed that alternative P and K recommendations can be achieved through quantity/intensity (Q/I) relations (amount of a respective nutrient in solution relative to the amount of nutrient adsorbed). It was also proposed that N recommendations can be improved by integrating mineralizable N. It was also concluded that these alternative approaches can routinely in a cost effective manner be determined. The first chapter evaluated P and K Q/I relations in several South African soils. Parameters of K dynamics were derived from activity ratio diagrams and these were used to explain K dynamics. Phosphorus sorption curves were linearized by Langmuir equation, and parameters derived therefrom were used to evaluate P dynamics. It was found that pH measured in water had a correlation coefficient (R2) of 0.71 with P sorption maxima. It was also found that electrical conductivity could account for 76% variance in K intensity parameter. It was suggested that these correlations could be exploited further to empirically model these crucial parameters. Thus, these correlations provide a possibility of determining these parameters routinely. Pot trials were also conducted to evaluate the crop response, when P or K was made with the alternative approaches using maize and potato as test crops. Conventional extraction approach recommended higher P rates, and the P uptake between the two methods was not significantly improved. The extraction based approach recommended lesser K rates and K uptake was significantly higher under the alternative approach. The impact of integrating mineralizable N on N recommendations was also evaluated under control conditions. It was found that although alternative N recommendation approach recommended lesser N rates the N uptake was not significantly reduced. In fact the non-significant trend was that N uptake was higher when N recommendations were made with an alternative approach. From these initial pot trials only one nutrient was allowed to vary and the rest were kept constant at optimum levels. The second set of pot trials were carried out (parallel to the previous one), and on this set, all three nutrients were allowed to vary per experimental units. On these NPK was recommended with alternative approach and compared to the conventional approach. The results obtained were similar to those obtained when N, P or K were allowed to vary individually. It was also suggested that total carbon can be used to assess the validity of these approaches. This was based on the consistent inverse correlation that was obtained between total carbon and P or K. Field trials were also conducted at Ukulinga research farm Pietermaritzburg and Wartburg, using maize and potato as test crops. The lack of concurrent response from nutrient uptake was also observed here similar to the observations already made in pot trials. These were characterized by conventional method recommending higher rates of N and N uptake not concurrent with the rates. It was also found that there was a poor correlation between applied fertilizer and extraction based intensity parameters, with R2 ranging between 0.005 – 0.011, compared to R2 of Q/I parameter which was 0.98 for both P and K. This poor correlation was evident between nutrient uptake and total biomass. Yield of both maize and potato at both sites was higher when recommendations were made by alternative approaches, and yield grade of potatoes was also improved when the recommendations were made by alternative approach. Total biomass of maize was also significantly improved when the recommendations were made by the alternative approach. Earlier, observation with regards to correlation of total carbon and nutrients was also observed under field conditions. This suggested that this is an important parameter to evaluate fertilizer recommendation program. It was concluded that recommending P and K with Q/I relations, and integrating mineralizable N on N recommendations is more mechanistically, technically, theoretically and practically justified compared to the conventional method.
An evaluation of the fertilizer requirements of Chicory (Cichorium intybus var. sativum) in KwaZulu-Natal, South Africa.
(2018) Gordon, Douglas Hamilton.; Hughes, Jeffrey Colin.; Manson, Alan David.
Abstract available in PDF file.
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.
Fertiliser value of biogas slurry for maize and dry bean production and its effect on soil quality and carbon dioxide emissions.
(2019) Mdlambuzi, Thandile.; Muchaonyerwa, Pardon.; Tsubo, Mitsuru.
Abstract available in pdf.
Grassland degradation and rehabilitation of soil organic carbon and nitrogen stocks.
(2014) Dlamini, Phesheya.; Chaplot, Vincent A. M.; Chivenge, Pauline.
Land degradation is widely considered to adversely affect soil fertility, soil quality, constrain productivity, subsequently leading to a decline in soil organic carbon (SOC) and nutrients in soils, yet little is known about the stocks, environmental controls, destabilization mechanisms and carbon sequestration potential of degraded grassland soils. The aim of this dissertation was to evaluate (1) the impact of land degradation on SOC and nitrogen (N) stocks, distribution and SOC quality, to elucidate the environmental controls, in a communal rangeland with varying intensities of degradation, (2) to examine the rehabilitation potential of the same rangeland (3) to assess the spatial variability and replenishment potential of SOC and N stocks in a typically degraded grassland catchment. A meta-analysis was conducted to provide a quantitative review of the impact of land degradation on SOC stocks in grassland soils, worldwide. Subsequently, the impact of degradation on SOC and N stocks and organic matter quality was investigated in a communal rangeland in the KwaZulu-Natal province, South Africa with varying intensities of degradation. Thereafter, different rehabilitation techniques were applied in the same communal rangeland to replenish SOC and N stocks. Advantage was also taken of 23 ha degraded grassland catchment to assess the spatial variability, carbon replenishment potential of SOC and N and to elucidate the main environmental controls. Degradation resulted in a significant depletion of SOC stocks in grassland soils, both in the meta-analysis and field experiment. The meta-analysis indicated that the depletion of SOC stocks as a result of degradation was more pronounced in sandy acidic soils under dry climate than clayey soils under wet climate. The field experiment showed that degradation significantly depleted SOC stocks by 89% and N stocks by 76% in sandy acidic soils at the study site. The reduction of the stocks due to degradation was accompanied by an increase in soil bulk density, a decrease in soil aggregate stability and concomitant decrease of macro and micronutrients (e.g, Ca by 67%; Mn, 77%; Cu, 66% and Zn, 82%). SOC and N stocks decreased sigmodially with a linear decrease in grass aerial cover. After two years, the “Savory and fertilization techniques increased SOC stocks by 6.5% and 3.9%, respectively. At catchment level, degradation led to high spatial variability of SOC and N stocks controlled primarily by soil surface characteristics, including grass cover, soil surface crusting and secondarily by topography. The carbon replenishment potential of degraded grassland catchment was estimated to be 4.6 t C ha-1, with clay-rich Acrisols having a greater capacity to replenish SOC stocks than sandy Luvisols and Gleysols. In conclusion, the results of this dissertation indicate that degradation results in high depletion of SOC and N stocks. However, rehabilitation has the potential for carbon sequestration and can lead to more sustainable grassland ecosystems.
Investigation of 2:1 layer silicate clays in selected southern African soils.
(1986) Buhmann, Christl.; Fey, Martin Venn.
As very little detailed X-ray diffraction investigations have been carried out in South Africa on 2:1 phyllosi1icates in soils, the aim of the present study was to contribute to the knowledge of soil genesis, as well as K-fixation and swelling, by investigation of the clay fraction of selected soils known to be rich in these minerals. X-ray diffraction analysis has been used almost exclusively as the investigative technique. In Chapter 1 a literature review is presented on the reasons for X-ray diffraction peak broadening and the problems encountered in the identification of swelling clay minerals. For interstratifications, the concept of an ABAB layer sequence, considered as having suggested an abab that the inter1ayer space, X-ray diffraction is questioned. data from which It is the ABAB arrangement is inferred can as well be explained in terms of an alternative AAAB layer sequence, having an aabb interlayer arrangement. Chapters 2, 3 and 4 deal with layer silicate formation/alteration in the course of soil development in dolerite and shale-derived profiles. Dolerite-derived pedons could· be characterized by one of the following layer silicate suites : suite i : discrete smectite (Fe-containing beidellite-montmorillonite) with or without traces of kaolinite and talc (Vertisol) suite ii : smectite-kaolinite interstratification (Vertisol) suite iii : 14 ft minerals (vermiculite, beidellite, montmorillonite, chlorite) and 7 ft minerals (halloysite, kaolinite ) in about equal proportions (Vertisol and Mollisol) suite iv : kaolinite with subordinate chlorite and traces of talc (Oxisol, Ultisol). Eccashale-derived Vertisols are dominated by mica-smectite interstratifications. The occurrence of an iron-rich pedogenic talc is discussed in Chapter 4. X-ray and chemical data suggest 30 - 50 mole percent substitutions of iron for magnesium. The mineralogical basis for K-fixation has been established in Chapter 5. Two K-fixing components could be identified : dioctahedral high-charge vermiculite as a discrete mineral and random mica-smectite interstratifications with 20 - 60% mica. In Chapter 6, some of the most expansive soils in South Africa have been investigated. They can be subdivided into two groups denoted by the swelling component as follows : (a) smectite-dominated (the smectite species involved being most probably beidellite with a heterogeneous charge distribution); (b) mica-smectite interstratification with random or ordered stacking arrangement.
An investigation, using synchrotron radiation and other techniques, of the composition of San rock art paints and excavated pigments from Maqonqu shelter, and comparative paint data from three other sites in KwaZulu-Natal, South Africa.
(2011) Escott, Boyd John.; Hughes, Jeffrey Colin.
This study aimed to: 1) characterise the individual San parietal art rock art paint colours; 2) relate paint compositions to erosion susceptibility; 3) determine if paint pigments can be related to pigment samples excavated from a Shelter deposit, and/or a variety of field samples; and 4) determine if paint samples from geographically distinct sites can be distinguished on their composition. A combination of mineralogical (X-ray diffraction (XRD), synchrotron micro-XRD (μ-XRD)) and chemical (energy dispersive X-ray micro-analysis (EDX), X-ray fluorescence spectrometry (XRF), and synchrotron micro-XRF (μ-XRF)) analytical techniques were used. Maqonqo Shelter (MQ), 35 km south-east of Dundee, KwaZulu-Natal, South Africa, was the primary study site chosen as it contained both a large number of paintings, as well as a large deposit. Thirty paint (of various colours) and 3 blank wall samples were collected using Silver Mylar tape and analysed using a combination of EDX, μ-XRD and μ-XRF techniques. Sixty two large (> 2.5 g) ‘ochre’ pieces were selected from the upper three layers of the deposit and analysed using XRD, XRF and EDX. A further 63 small pieces (< 2.5 g) were analysed using μ-XRD and μ-XRF techniques. To compare the MQ paint samples with potential source materials, three distinct sample sets were collected. The first included samples of the Shelter wall and surface rocks located near the painted panel (analysed by XRD, XRF and EDX). A second sample set of 17 samples was collected from the surrounding landscape (± 3 km radius of MQ; analysed by XRD and XRF). Their selection was based on ease of accessibility, degree of pulverulence, and perceived Fe content i.e., red and/or yellow colouration. No white sources were found. A third set of 11 samples (obtained from six sites, analysed using XRD and XRF) was collected within ± 50 km distance of the Shelter. Their selection was based on old mining survey reports that detailed the location of Fe ore outcrops. Paint samples from three additional shelters i.e., Fergies Cave (FC), Giants Castle Game Reserve, central Drakensberg; Sheltered Vale (SV), Mount Currie District, south-western KwaZulu-Natal; and Twagwa Shelter (TW), Izingolweni District, southern KwaZulu-Natal, were collected to compare paint composition over distance. Site selection was determined according to the following criteria: 1) the shelters had to reside a significant distance away from the primary site so as to minimise any possible interaction that might have existed between the authors of the respective artworks (each site is at least 100 km distant from the other); 2) each had to be located upon a distinct geological formation so that external influences from different regions, and their possible affects on the paint samples, could be noted; and 3) the climatic regimes of each of the shelters should be relatively distinct. Fifteen paint and nine blank wall samples were collected from the three shelters (three each of red, white and blank samples; analysed using EDX, μ-XRD and μ-XRF), with the exception that no white samples were collected from FC. In total, 673 EDX, 212 μ-XRD, 378 μ-XRF, 98 XRD, 98 XRF and 6 ICP-MS traces were produced and analysed. Due to the extremely heterogeneous nature of the paint samples at the microii scale, the more generalised EDX reduced window scans were used as the basis of the paint samples’ characterisation, with the data obtained from the more precise μ-XRD and μ-XRF techniques providing additional supportive information. Irrespective of colour, almost all of the MQ paint samples had elevated Ca contents that tended to increase in the order of black < orange £ red and yellow < pink < white. The predominant Ca-based mineral was gypsum, although Ca-oxalates, whewellite and weddellite, were also present. The blank samples collected from MQ also had high gypsum content, but no Ca-oxalate. It is thus proposed that the Ca-oxalates formed after the painting event and were derived from the original paint constituents. The white pigments consisted of gypsum (dominant), anhydrite, bassanite and whewellite, or a combination thereof. Whewellite increased within increasing paint depth, while gypsum showed the reverse trend. This indicates that, whilst both gypsum and whewellite were originally present within the original paint pigment, additional gypsum has been added via secondary evaporite deposition. Although initially considered to be sourced along with the gypsum, another potential whewellite source is organic additives. The most likely source for the white pigments would be precipitates found on sandstone walls of shelters near MQ. Of more immediate importance, however, is that the pigments, being gypsum based, are water-soluble and thus susceptible to erosion. Most of the orange paints had an elevated Al content and contained gibbsite, suggesting bauxitic material associated with locally sourced dolerite within the Ecca Series within KwaZulu-Natal (as evidenced by their respective Ti levels). Two samples were so similar that it is likely that the same pigment was utilised in the creation of both images. Two samples did not contain high Al contents, however, indicating that they were probably sourced from the soft, ochreous material found within local Fe nodules. A consistent combination of goethite and haematite, together with a low Al and elevated Ti content, indicate that the yellow and red samples were probably sourced from Fe nodules found locally, the red samples differing from the yellow pigments primarily in their higher haematite content. A low Si and relatively low Fe content discounts red sands/clays and Fe-ores as sources of the red pigments. The red samples were ‘thinner’ than the other samples with quartz contents comparable to those of the blank samples. The thin nature of the red paints, the erratic distribution of whewellite upon the paint surfaces, the dominance of gypsum and, to a certain extent quartz, all strongly suggest that the red paints are at least partly absorbed into the surface of the Shelter wall. This, together with the strong staining ability of haematite, is probably the most important reason that the red pigments have outlasted images painted in other colours. It may also account for the high degree of variability found within the red paint dataset, though age differences between the sampled images could also be a contributing factor. The single dark red paint sample, except for an elevated Mn content, was very similar in many ways to the red paint samples analysed. The only readily available pigment source identified that had both low Al and high Fe and Mn contents, was plinthite. The pink samples represented the ‘middleiii ground’ between the red and white paints, suggesting that this colour was the result of a blending of the two. The black paint sample had the highest recorded Fe content of the entire paint dataset. A high Mn and relatively low Al content suggest that a soft inner core of an Fe nodule was used in its manufacture. The presence of maghemite and a dark colouration strongly suggest that the manufacture also involved calcination. The initial distinction between the paint and excavated samples was that the former all exhibited elevated Ca and S values due to the deposition of secondary evaporite minerals. Even when taking these additional deposits into account, however, the two datasets still remained distinct indicating that the excavated materials sampled were not utilised in the manufacture of the MQ paints. A potential exception concerned the orange paint samples, which were similar in composition to both doleritic samples from deeper excavated layers and the local (weathered doleritic samples) and distant (bauxite samples) field samples. Whilst weathered dolerite/bauxitic material was clearly the source of the orange pigments, a more detailed investigation is needed to find a precise location. No other relationships between the paint pigments and the excavated pigments and field samples were established. A comparison of the blank samples from all four study sites showed that the techniques used could distinguish between different sites despite sampling the smallest and, relatively speaking, poorest quality samples. The FC blank samples had elevated C and Ca contents (associated with Caoxalates). The conditions within this Shelter favour the formation of weddellite and whewellite, the former not typically found at the other three sites. In addition, low K, Si and Al contents (often associated with sandstone matrix minerals) indicate that the surface of the relatively dense, compact Cave sandstone is more resistant to physical erosion compared to the other sites, and/or FC shelter experiences a high amount of secondary deposition, with the result that a majority of the samples are composed of evaporite minerals. The SV samples were composed primarily of the evaporite-type minerals, with only minor sandstone ‘contamination’ indicated by quartz and kaolinite. The quartz content, whilst not always high, was present in most of the samples analysed, possibly indicating a greater amount of more uniform surface erosion (relative to the other sites). The TW blank samples were distinct from the other shelters’ as they contained no Ca-based minerals but did contain the very rare mineral schlossmacherite. A comparison of the paint colours also revealed differences between the different shelters. Whilst the white samples from SV and MQ are dominated by whewellite and gypsum (minerals probably present within the pigments when they were applied), the presence of quartz, sanidine and apatite in the SV samples indicated a degree of shelter wall ‘contamination’, with anhydrite, bassanite and glushinskite suggesting climatic variations that favoured various evaporite depositional regimes. The TW white paint contained minimal secondary deposited minerals common in the other shelters. The one mineral that is dominant within the TW samples is minamiite. As this mineral was not identified in any of the blank samples, it is likely that this mineral originates from the original pigment source. The TW white paints also contained 10 to 40 times more Zn than those recorded for any of the other paint samples. This was possibly present within the structure of greigite. The red SV samples could be distinguished from MQ red samples by the presence of wall ‘contaminants’ in a manner similar to that described for the white samples. The TW samples indicate a change in pigment source and/or manner of paint manufacturing technique, for these red samples contained minamiite. This mineral is white and thus its selection could not have been based on colour but rather it must represent a paint additive. With the exception of only one sample from TW, no goethite was found within any of the red samples collected from the three additional sites indicating a different haematite source to that of MQ. An interesting facet of this study, although not directly addressed, concerns what the results do not show with respect to the compositional nature of the pigments analysed. Most texts available today list a number of pigment sources stated to have been utilised in the manufacture of the San parietal rock art. This study has shown that very few of these potential sources were utilised within the four shelters investigated. In addition, this study has also highlighted the presence of minerals about which little is known, yet which appear to be commonly associated with parietal rock art.
Investigations into aluminium toxicity and resistance in cynodon dactylon using invitro techniques.
(2004) Ramgareeb, Sumita.; Cooke, John Anthony.; Watt, Maria Paula Mousaco Deoliveira.
Aluminium toxicity is a significant limiting factor to agricultural crop production globally, promoting the need for plants that are resistant to low pH and high Al3 +, Current literature suggests that Al3 + inhibits plant growth by stopping root elongation. Although considerable research has been directed towards Al3+-inhibited root growth, the initial cellular targets and primary mechanisms of Al3+ toxicity still remain unclear. The present study, therefore, considered an alternate approach to investigating Al3 + toxicity and Al3 + resistance. Callus, a group of actively dividing meristematic cells, was exposed to Al3 + and the influence of Al3 + on callus growth was investigated. In South Africa, gold mining results in the production of wastes that require vegetation cover resistant to low pH and high Al3+, in order to promote stabilisation and prevent erosion. Cynodon dactylon was considered a key species for such a purpose since small populations of this grass were found growing on the acidic gold tailings. Different C. dactylon genotypes were exposed to Al3 + and the feasibility of using differences in callus growth to identify potential Al3 +-resistant individuals was assessed. An in vitro method for indirect somatic embryogenesis was concurrently established to regenerate whole plants from such calli. Embryogenic calli were initiated from young leaf segments, using 2,4-D. Somatic embryo maturation and plant regeneration were achieved on a hormone-free Murashige ~d Skoog (MS) nutrient medium. In addition to this protocol for micropropagation via indirect somatic embryogenesis, nodal cuttings, on a single hormone-free MS nutrient medium, were shown to be suitable explants for micropropagation via direct organogenesis, albeit resulting in low plantlet yields (1 plant/explant). In the investigation of Al3 + resistance, each of the three parameters tested (genotype, Al3+ concentration and exposure time) had a significant influence on callus growth rate. The nutrient medium supporting callus growth was modified in order to ensure known concentrations of free Al3 + ions (0.08-2.3 mM). This was achieved through the use of a chemical speclatlOn model (MINTEQA2). Fresh callus mass measurements for three genotypes were recorded at two-weekly intervals for a total of 8 weeks. Significant differences in callus growth rate were used to identify the genotypes as Al3+-sensitive (AlS), moderately Al3+-resistant and Al3+-resistant (Al-R), suggesting that it is feasible to use undifferentiated meristematic callus cells to screen for resistance to Al3+. In addition to callus growth rate, it was also possible to differentiate between the Al-S and the Al-R genotype using differences in cell numbers. Exposure to 0.8 mM AI3+ for 2 weeks resulted in an 88% reduction in the Al-S meristematic cell number whereas no Al3 + concentration tested had a significant inhibitory effect on the Al-R cell number. Aluminium was detected inside the callus cells, with the Al-S cells accumulating three times more Al in the nucleus than did the Al-R cells. It is suggested, therefore, that Al3 + inhibited meristematic cell number in the Al-S genotype by interfering with cell division. Two possible mechanisms by which the Al-R genotype was able to exclude Al3+ from its cells were investigated. The Al-R callus was able to maintain a higher extracellular pH (4.34 in Al-R and 4.08 in Al-S) and immobilise more Al in the cell wall (33% more in the Al-R) than the Al-S genotype. The present study has developed a valuable tool for investigating the physiological effects of Al3 + on actively dividing meristematic cells. In addition, the somatic embryogenesis route allows for the concurrent in vitro selection and plantlet regeneration of genotypes of interest. Future work is necessary to confirm that the properties of undifferentiated cells in culture are maintained by the ex vitro whole mature plants.
A laboratory and glasshouse evaluation of an anaerobic baffled reactor effluent as a nutrient and irrigation source for maize in soils of KwaZulu-Natal, South Africa.
(2012) Bame, Irene Bongsiysi.; Hughes, Jeffrey Colin.
Scarcity of water for irrigation is a serious hindrance for small-scale farmers in sub-Saharan Africa. The use of good quality water for irrigation has resulted in increasing pressure on such water which has prompted sourcing of wastewater as an alternative. One possibility, being investigated by eThekwini Water and Sanitation (Durban, South Africa), is to install anaerobic baffled reactors within local communities to treat wastewater to allow its use for agriculture. The success of wastewater irrigation depends on the ability of the soil to assimilate the water, nutrients and any other contaminants that are applied to it. The aim of this project was to investigate the potential of an anaerobic baffled reactor (ABR) effluent as both an irrigation and nutrient source for use in peri-urban agriculture. The effluent was slightly alkaline (pH 7.40–7.60) and in class C2S1 (medium-salinity/low sodicity water) according to the United States Soil Salinity Laboratory classification for irrigation waters. It was very low in heavy metals, values being below permissible levels according to the Food and Agricultural Organisation (FAO) of the United Nations and the South African Department of Water Affairs and Forestry (DWAF) guidelines for water use in agriculture. The total solids were low thus particulate matter was minimal with a greater concentration of the major elements found in solution. An investigation was carried out to ascertain the behaviour of the effluent when applied to soil and how the soil was able to adsorb plant nutrients from it. A soil column study was undertaken in the laboratory with three contrasting soil types namely a sandy soil (Longlands, E horizon), an organic soil (Inanda, A horizon) and a clayey soil (Sepane, A horizon). The effluent was leached through the soil while distilled water was concurrently used as a control. Results indicated that after application of 16 pore volumes, leachates from the columns contained concentrations of Na, equal to that in the incoming effluent for all soils. The concentrations of Ca and Mg were lower in the leachates than in the original effluent indicating adsorption in the soils. Phosphorus was the element that was most strongly adsorbed in all soils. While its adsorption in the Ia could be attributed to organic matter and the presence of iron oxides and oxyhydroxides, the clay type and amount in the Sepane was likely to have been responsible for P adsorption. The NO₃-N, which was initially low in the effluent, increased as leaching progressed, while the NH₄-N decreased. In the water-leached columns, elements were leached out of soil because none were added with the water. At the end of leaching, columns were allowed to drain and then sectioned into 2 cm segments. The 0-2 cm, 8-10 cm and 14-16 cm segments representing the top, middle and bottom parts of the column were analysed for inorganic-N, phosphorus and potassium. The elemental content of the 0-2 cm segment was significantly higher (p<0.05) than the lower segments in all columns for soluble P in all soils. This reflects the immobile nature of P in soils and confirmed the high amounts of P retained by the soils. There were significant differences between the effluent and the water-leached soils in terms of P retention. The amount of inorganic-N and K in the top layer was not significantly different from the other layers. In the Ia 0–2 cm segment, a pH increase of about 1.3 pH units was recorded in the effluent-leached columns when compared to the equivalent segment in the water-leached columns. A glasshouse study was undertaken to assess the availability to maize of nutrients from the effluent. Maize was grown for 6 weeks in pots filled with the same soil types used in the columns study except that a similar sandy soil, Cartref (Cf, E horizon), replaced the Lo due to inadequate availability of the latter. Fertilizer (N, P and K) was applied at the full recommended rate, half the recommended rate and zero fertilizer for each of the three soils used. This corresponded to 0, 100, 200 kg N ha⁻¹ for all soils; 0, 40, 80 kg P ha⁻¹ and 0, 50, 100 kg K ha⁻¹ for the Cf; 0, 10, 20 kg P ha⁻¹ and 0, 102.5, 205 kg K ha⁻¹ for Ia; and 0, 30, 60 kg P ha⁻¹ and 0, 5, 10 kg K ha⁻¹ for Se. Lime was applied to the Ia soil at the rate of 10 t ha⁻¹. Plants were watered with either effluent or tap water. Dry matter yield and nutrient concentrations for effluent-irrigated maize were significantly higher (p<0.05) than for all equivalent fertilizer applications in the water-irrigated plants. The unfertilized effluent-irrigated plants were not significantly different from the fertilized water-irrigated plants, but performed as well as the water-irrigated plants at half fertilization irrespective of soil type. Phosphorus deficiency was observed in the Ia and Se soils but not in the Cf soil, irrespective of fertilizer treatment. Plants grown on the Cf soil irrigated with effluent and fully fertilized had the highest above-ground dry matter yield (4.9 g pot⁻¹) and accumulated the most nutrients namely N, P, K, Ca and Mg than all other treatments. After harvest the most marked changes had occurred in the Cf soil for P as the effluent-irrigated soils were significantly higher (p<0.05) than the water-irrigated soils reflecting the P input from the effluent. The effect of effluent on soil and plants was further investigated by planting maize on the Ia soil without lime application. Plants that received effluent irrigation and no lime had significantly higher (p<0.05) dry matter yields and accumulated more N, P and K than the water-irrigated with no lime as well as the equivalent limed treatments. This suggests an interaction effect between the lime and the effluent with its effects obvious on above-ground dry matter yield and plant N, P and Mg. A soil column experiment using the Cf, Ia and Se soils and planted with maize was conducted to assess the ability of plants to take up nutrients with concurrent leaching. Plants from the Cf soil recorded the lowest above-ground dry matter yield which was observed from the less vigorous growth as compared to plants in the Ia and Se soils. This growth pattern could also be explained by the low N accumulation in the plants from the Cf soil. Unlike N, P in plants grown on the Cf soil was significantly higher (p<0.05) than in the plants on the Ia and Se soils, despite having the least P gain from the effluent. The readily available P triggered both more uptake and also greater losses through leaching. The rate at which P was being supplied from the effluent was greater than its uptake by the plants and with limited capacity to hold onto P in this sandy soil there was inevitably loss though leaching. A pot experiment was conducted to investigate the interaction effects between lime and effluent. Lime type (calcium hydroxide or dolomite) was applied to two acidic top soils namely Inanda and Avalon at 0%, 25%, 50%, 75% and 100% of the recommended rates for these soils. Maize was planted and after 6 weeks it was harvested and evaluated for above-ground dry matter yields and plant nutrient concentrations. Non-significant effects were recorded for above-ground dry matter, N, P and K as a result of altering the liming rate and type within each soil. The effects of lime application were apparent in the soils after harvest as increasing the lime rate caused an increase in pH and an inverse relationship with the exchangeable acidity and acid saturation in soils, as expected. Although the unlimed treatments did not impact on the acidity as much as the limed treatments, effluent irrigation was shown to reduce soil acidity after harvest when compared to the soils at the beginning of the experiment. Phosphorus accumulation in plants was also unaffected by either lime rate or type which showed that effluent irrigation could influence P availability and further liming would not accrue benefits to the soil so as to influence plant P uptake. Based on these data, ABR effluent could be perceived as a resource rather than a waste product. It could conveniently be used for irrigation provided there is soil and plant monitoring to assess build-up of elements especially in the long term. Further investigations have to be carried out on other crop types both in the field and glasshouse to ascertain nutrient uptake and effect on different soil types.
Land use and land management impact on CO2 emissions from soils in selected smallholder farming systems.
(2016) Adam, El-Khatab Mohamed Abdalla.; Chivenge, Pauline.; Chaplot, Vincent A. M.; Everson, Colin.
Abstract available in PDF file.

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