Please read the abstract in the section 00front of this document / Thesis (PhD (Agronomy))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science, Johannesburg, South Africa 2017. / Fuelwood is still heavily relied upon by rural communities as a source of energy. The current levels of wood harvesting have been deemed unsustainable, with models predicting the local exhaustion of wood resources in most cases. However, wood depletion has generally not happened to the level of severity predicted by the models. This may partially due to under-accounting for coppice regeneration. Many savanna species that are harvested for fuelwood demonstrate strong coppicing ability, which allows for regrowth after a disturbance. This ability to regrow or coppice is a key functional trait which allows species to persist and survive in frequently disturbed environments. There is surprisingly limited knowledge about coppice dynamics in savanna trees and how managerial actions might influence the coppice response and production of savanna species. To address this problem, this study investigated the influence of four post-harvest treatments on various aspects of the coppice response of Terminalia sericea and Dichrostachys cinerea – two important savanna fuelwood species – in a field experiment. A total of 108 felled trees per species were exposed to one of four treatments, which were applied monthly for 12 months. The treatments were (1) Control – no coppice shoots were removed for 12 months, (2) Harvest – all coppice shots were removed monthly, (3) Single prune – the coppice shoot with the widest diameter was left on the stump, and (4) Usable – coppice shoots that reached a diameter of 2 cm were removed. The effect that these treatments had on the average diameter, length and cumulative number of coppice shoots produced per stump was compared. The measurements of diameter and length were used in developing allometric equations for the prediction of coppice shoot biomass. The predicted biomass produced through the study was compared across treatments to gain an understanding of how productivity could be influenced by management of coppice shoots. The mean shoot diameter, length, as well as cumulative number of coppice shoots produced per stump was higher in the single prune treatment for both species while the harvest treatment resulted in high numbers of coppice shoots but with low average diameter and length. Applying the growth rates of coppice shoots found in this study it can be assumed that unmanaged coppice shoots will take approximately 5.5 years to reach a preferred harvestable diameter of 4 cm, while single prune coppice shoots would take 3.3 years to reach the preferred harvestable diameter. Diameter had more of an influence on the predicted coppice biomass production of T. sericea while D. cinerea biomass prediction was more influenced by shoot length. However, only diameter was used to compare the prediction of coppice biomass with previously developed equations as these equations did not consider length for predicting biomass of different components of trees. From the derived models, the calculated biomass at the end of the study period as well as the calculated biomass produced through the year was greatest for the control treatment. The predicted dry shoot stem biomass at the harvestable diameter of 4 cm was 114.60 g for T. sericea and 95.88 g for D. cinerea. From the findings of this study it is clear that post-harvest management can be utilised to manipulate coppice response and biomass production. Keywords: Fuelwood; Coppice shoot; Post-harvest treatment; Diameter; Length; Biomass / LG2018

With the high rate of human population growth in Africa, it is imperative that food production be increased through improving yields and bringing more land under cultivation. Nitrogen is a key element required for plant growth and with the low input of fertilizers into African farming-systems, it is necessary to harness biological nitrogen fixation (BNF) to its fullest extent. To maximize nitrogen fixation in crop and pasture legumes under various conditions and cropping systems requires intensified research. In this study the diversity of root nodule bacteria associated with Lotononis species in South Africa was investigated. To our knowledge, no past attempts have been made to investigate the diversity of rootnodule-bacteria associated with the genus Lotonollis. Eighty nodulated plants representing thirty-two Lotononis spp. were collected from all the main geographical and climatological regions in South Africa. Isolates obtained from rootnodules were purified and characterized with sodium dodecyl-sulphate gel polyacrylamide gel electrophoresis (SDS-PAGE), supplemented at the genomic level with 16S rDNA sequence data of selected strains. Initial screening (SDS-PAGE) showed that most isolates obtained from the same plant species, grouped into various clusters within the dendrogram. A few of the isolates from similar host plants seemed to cluster with high similarity. It is thus reasonable to conclude that host specificity in the symbiotic interaction is less applicable for most species of Lotononis. When considering the geographical origins of the isolates, their diverse nature was clearly illustrated. It was showed that isolates from similar geographical regions were evenly distributed throughout the dendrogram. Some of the isolates obtained from arid environments formed closely related electrophoretic groups. It was subsequently shown that root-nodule bacteria associated with Lotononis species are not restricted to a particular rhizobial genus, but that heterogeneity is evident. Some of the isolates were also related to genera outside the Rhizobiaceae, namely Methylobacterium and Burkholderia. / Dissertation (MSc (Microbiology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

Thesis (PhD(Agric) (Agronomy))--University of Stellenbosch, 2007 / A selection of species suitable for cover crop management in the different wine grape regions is required to enable more producers to apply this environment friendly practice in a sustainable manner as part of an integrated production strategy. The correct management practice(s) to be applied to these species over both the short and long term in a cooler and warmer wine grape region needed clarification. The effect of seeding date on the dry matter production (DMP) and weed control efficacy of seven grasses and sixteen legumes, as well as varieties of three of these species, was determined during 1991 and 1992. The decomposition rate of the mulches was determined. In the cooler climate of Stellenbosch (33o55'S, 18o52'E), the Medicago species, subterranean clovers, pink Seradella and three Vicia species did not compete effectively with the winter weeds if the weekly precipitation from mid-March to mid-May (autumn) exceeded 18 mm. The two oat species, as well as rye and triticale produced more than five t/ha of dry matter if the precipitation exceeded 18 mm per week. The DMP of the above-mentioned species indicated that these species could be considered for cover crop management in Lutzville (31o35'S, 18o52'E), if full surface irrigation of 18 mm per week could be applied for 10 weeks directly after sowing, followed by 18 mm fortnightly. Seeding date had a significant effect on DMP in both regions. A highly significant correlation (r = 0.85, p ≤ 0.0001) existed between the decomposition rate of the mulches and the initial amount of dry matter present on the soil surface.

Winter rotational cover crops (WRCC) are often used to boost soil fertility and plant nutrition. However, selection and use of WRCC for soil physical improvement is usually overlooked. The objective of this study was to determine the effects of WRCC on soil strength, aggregate stability and water conservation of a hardsetting soil. The soil physical properties were determined after four rotations of growing monocultures of vetch (Vicia dasycarpa cv. Max), lupin (Lupinus angustifolius cv. Tanjil) and oats (Avena sativa cv. Sederberg) and after two rotations of growing bicultures of oats (Avena sativa cv. Pallinup) and vetch (Vicia dasycarpa cv. Max) across two soil layers, 0 to 15 cm and 15 to 30 cm. The individual WRCC and a weedy fallow constituted the treatments in the monoculture study whilst in the biculture study the various combinations of WRCC namely; 90% oat plus 10% vetch (O90V10); 70% oat plus 30% vetch (O70V30) and 50% oat plus 50% vetch (O50V50) and a weedy fallow constituted the treatments. After four rotations with cover crop monocultures, oats significantly (P ≤ 0.05) reduced penetration resistance (PR) whilst vetch increased PR in both soil layers compared to the weedy fallow control. The effect of the biculture treatments was only experienced within the 15 to 30 cm depth. The treatments O50V50 and O70V30 increased the PR compared to the control. The WRCC in monoculture significantly increased the soil aggregate stability relative to the control in both soil layers. Vetch, lupin and oats resulted in a 41.7%; 20.4% and 15.7% increase in MWD in the 0 to 15 cm soil layer and 47.2%; 44.2% and 39.7% in the 15 to 30 cm depth, respectively. An increase in aggregate stability was associated with increased macro-aggregation. Under the biculture, WRCC slightly increased, non- significantly, the aggregate stability. Both hot water and dilute acid extractable polysaccharides showed no significant correlation with aggregate stability in the two studies. Oats monoculture resulted in a significant difference (P ≤ 0.05) on cumulative infiltration compared to the control. However, after 2 h vetch and lupin showed no significant difference from the control on cumulative infiltration. Oats resulted in a 7.8% increase in final infiltration rate (FIR) whilst vetch and lupin reduced FIR by 9% and 16.7% respectively, compared to the control. Bicultures of oats and vetch significantly (P ≤ 0.05) increased cumulative infiltration compared to the weedy fallow control. A similar significant increase in FIR was also observed under bicultures. The treatments O50V50; O90V10 and O70V30 resulted in a 163.3%; 113.3% and 105.4% increase in FIR respectively, compared to the control. Cover crop monocultures significantly (P ≤ 0.05) increased plant available water (PAW) compared to the weedy fallow, with vetch, oats and lupin resulting in a 28.3%; 22% and 23.9% increase respectively, in PAW. However, no significant differences were observed on PAW after two rotations with bicultures. Compared with winter weedy fallow, WRCC improved most of the soil physical properties under study, with the most suitable results expected under bicultures compared to monocultures. Under CA, selection of WRCC like oats, vetch and lupin, one should therefore take into consideration their effects on soil physical properties as a selection criterion and not biomass and fertility alone.

Thesis (MScAgric (Agricultural Economics)--University of Stellenbosch, 2009. / The growing scarcity of fossil energy, expressed by rising real prices, justifies an investigation into the viability of utilising alternative, sustainable energy sources. Another motivation is to mitigate CO2 pollution resulting from using fossil fuels, causing climate change. Biomass has the potential to become a major global primary energy source during the next century. In South Africa, a limited amount of land is suitable for high‐potential biomass energy sources like sugar cane or grain. Large areas of South Africa are, however, dry and more suitable for woody biomass production. Cultivating trees in short‐rotation‐system plantations provides a sustainable and effective way of producing biomass. The first part of this study investigated the physical capacity of the Cape Winelands District Municipality (CWDM) for woody biomass production in short‐rotation systems, based on a land availability assessment using Geographic Information Systems (GIS). The CWDM comprises about 2.3 million hectares, of which about 175 000 ha with a slope of less than 35% have been identified as suitable for woody biomass production. Within the CWDM, the following land use classes were excluded: nonagricultural land, such as urban areas, bare rock and mines; ecologically sensitive areas; as well as areas with slope gradients that are too steep for biomass production, due to limited accessibility and trafficability. This was followed by an assessment of suitable tree species and their productivity rates – also using GIS with climate data (i.e. temperature extremes, frost and mean annual precipitation) and terrain data. By combining the identified biomass production sites with the productivity rates of the identified species, an annual supply of woody biomass for energy generation at a medium productivity of about 1 412 000 tonnes of fresh biomass is expected, using exotic species like Eucalyptus claducalyx ( and about 1 306 000 tonnes, using indigenous species like Acacia karoo).

The cellulosome is a multimeric enzyme complex that has the ability to metabolise a wide variety of carbonaceous compounds. Cellulosomal composition may vary according to the microbe’s nutritional requirement and allows for the anaerobic degradation of complex substrates. The complex substrates of interest in this research study were sugarcane bagasse and pineapple fibre waste, as they represent two important lignocellulosic, South African agricultural crops. The effective degradation of complex plant biomass wastes may present a valuable source of renewable compounds for the production of a variety of biofuels, for example bioethanol, and a variety of biocomposites of industrial importance. The identification of renewable energy sources for the production of biofuels is becoming increasingly important, as a result of the rapid depletion of the fossil fuels that are traditionally used as energy sources. An effective means of completely degrading lignocellulose biomass still remains elusive due to the complex heterogeneity of the substrate structure, and the fact that the effective degradation of the substrate requires a consortium of enzymes. The cellulosome not only provides a variety of enzymes with varying specificities, but also promote a close proximity between the catalytic components (enzymes). The close proximity between the enzymes promotes the synergistic degradation of complex plant biomass for the production of valuable energy products. Previous synergy studies have focused predominantly on the synergistic associations between cellulases; however, the synergy between hemicellulases has occasionally been documented. This research project established the synergistic associations between two Clostridium cellulovorans hemicellulases that may be incorporated into the cellulosome and a cellulosomal endoglucanase that is conserved in all cellulosomes. This research study indicated that there was indeed a synergistic degradation of the complex plant biomass (sugarcane bagasse and pineapple fibre). The degrees of synergy and the ratio of the enzymes varied between the two complex substrates. The initial degradation of the bagasse required the presence of all the enzymes and proceeded at an enhanced rate under sulphidogenic conditions; however, there was a low production of fermentable sugars. The low quantity of fermentable sugars produced by the degradation of the bagasse may be related to the chemical composition of the substrate. The sugarcane contains a high percentage of lignin forming a protective layer around the holocellulose, thus the glycosidic bonds are shielded extensively from enzymatic attack. In comparison, the initial degradation of the pineapple fibre required the action of hemicellulases, and proceeded at an enhanced rate under sulphidogenic conditions. The initial degradation of the pineapple fibre produced a substantially larger quantity of fermentable sugars in comparison to the bagasse. The higher production of fermentable sugars from the degradation of the pineapple fibre may be explained by the fact that this substrate may have a lower percentage of lignin than the bagasse, thus allowing a larger percentage of the glycosidic bonds to be exposed to enzymatic attack. The data obtained also indicated that the glycosidic bonds from the hemicellulosic components of the pineapple fibre shielded the glycosidic bonds of the cellulose component. The identification of the chemical components of the different substrates may allow for the initial development of an ideal enzyme complex (designer cellulosome) with enzymes in an ideal ratio with optimal synergy that will effectively degrade the complex plant biomass substrate.

Community food gardens are regarded as a means through which rural households can improve their livelihoods. This study explores the contribution of community food gardens (CFG) to livelihoods in the Lepelle-Nkumpi local municipality in the Limpopo province. The objectives of this study are, firstly to explore the reason behind CFG participation and the reasons behind the participating possibility. Secondly, the study seeks to identify the socio-economic factors influencing the participation of households in CFG and lastly to determine the influence of CFG and other socio-economic variables on household food security status (HFSS). Descriptive statistical analysis was used to describe the socio-economic characteristics and the reasons behind CFG participation and the reasons behind the participating possibility. The binary logistic regression model was used to analyse the determinants of household participation in community food gardens as well as the contribution of CFG to HFSS on Statistical Package for Social Science (SPSS) software version 21. Through a structured questionnaire, data was collected from a sample of 180 households which was obtained using multistage sampling. Descriptive results on the characteristics of sampled households revealed that there are high levels of food security in the area with 70% being food secure of which around 42.2% are CFG participants and 30% are food insecure. Furthermore the descriptive statistical analysis indicated that participation of households in CFG is mainly to obtain a source of food among the CFG participants and to generate income amongst the non-participants. On the basis of descriptive analysis, this study concludes that source of food and income generation respectively are the main reasons behind CFG participation and the possibilities of becoming a participant. Therefore the study accepts the research hypothesis stating that “There are social and economic reasons behind household participation and the possibilities of participating in CFG”. Binary results for the determinants of CFG participation revealed that socio-economic variables such as household size, farm income, household monthly income, land size, household perception, marital status, agricultural training and homestead gardening significantly influence household decisions to participate in CFG. This is an implication that socio-economic variables tested in this study are significantly influential to the household decision to participate in CFG, leading to the acceptance of the first hypothesis which states that “Socioeconomic factors determine the community food garden ownership or participation”. The results of the contribution made by CFG to HFSS showed that socioeconomic variables such as gender, age, household size, farm income, educational level, household monthly income, marital status, information access, formal employment status and CFG involvement significantly affect household food security status in the study area. The result indicates a positive contribution to HFSS and implies that socio-economic variables tested in this study have a significant influence on HFSS, leading to the acceptance of the second hypothesis which states that “Community food gardens have a positive effect on food security status of household in Lepelle-Nkumpi Local Municipality Limpopo province.” Therefore it is relevant to concluded that in the area of Lepelle-Nkumpi local municipality, social economic factors plays a vital role in the participation of households in CFG as well as improving the state household food security status.

MSc (Plant Production) / Department of Plant Production / See the attached abstract below

MSCAGR (Soil Science) / Department of Soil Science / Maize (Zea mays L.) is widely grown in the semi-arid regions of South Africa mainly for its grain that is used for direct human consumption, feed for animals and raw materials for the industries. The challenges of soil infertility, water supply, and availability of high yielding cultivars remain a major constraint for its production in this environment. These constraints are a major threat to sustainable crop production and food security. Maize/lablab Zea mays L.\ L. purpureus) intercropping system could thus become an option for food security among small scale maize producers in dry environments. Preliminary studies show the huge potential of maize/lablab intercropping in the semi-arid environments of the North-Eastern South Africa. Therefore, this study aimed to assess the effects of maize/lablab intercropping on soil water content, nitrogen dynamics and crop productivity based field experiments and crop simulation modeling using the model APSIM. The trials were conducted at two sites (Univen and Syferkuil) in Limpopo province, South Africa, for two seasons (2015/2016) and 2016/2017). The treatments consisted of; (i) sole maize (ii) sole lablab (iii) maize and lablab planted at the same time (Maize+lablab-ST) and (iv) maize with lablab planted 28 days after maize (Maize+lablab-28).The treatments were laid out in an RCBD replicated 4 times, with individual plots size measuring 4.5 m × 4 m (18 m2) and the layout of the field as consisting of 4 plots per block giving a total of 16 plots in 4 blocks. The following parameters were determined: soil water content, soil NO3--N and NH4+-N levels, dry matter and grain yield. The APSIM-model (version 7.7) was then used to simulate maize grain yield and dry matter production to assess risks associated with the production of maize/lablab intercropping. The results obtained from this study showed that maize/lablab intercropping had significant effects on measured parameters (grain, biomass yield soil water content, and N-minerals). Maize+lablab-28 produced 46 % higher grain yield than sole cropping (24%) and maize+lablab-ST) (30%). The results also showed variation in soil water content at different depths among the treatments. The soil water content was increased with depth. The intercropped plots and lablab sole had significantly higher soil water content than the sole maize. At all depths, the highest soil water content was obtained under sole lablab followed by maize+lablab-ST and maize+lablab-28. It was notable however that maize/lablab intercropping showed a higher NO3--N and NH4+-N levels at all depths. At both sites, the soil NO3--N showed a sharp drop at V7 sampling time. The results showed the benefits of intercropping in comparison to sole cropping as demonstrated by positive land equivalent ratios of >1 for both cropping systems in both years and sites. Modelling exercises showed that APSIM was able to simulate the results sufficiently. In the simulation experiment, a stronger negative effect of planting lablab with maize simultaneously was found. Hence, delayed planting of lablab should be a standard practice / NRF