Tesi sul tema "Soil erosion – South Africa – Eastern Cape"

Aggregate stability and aggregate size distribution on soil surface that is impacted by rain drops affect soil erosion yet little is known about less weathered coarse textured soils. The objectives of the current study were to determine (i) the aggregate stability and associated aggregate fraction size distribution and (ii) the impact of the initial aggregate size on the aggregate stability and the resulting sediment fraction size distribution following rain drop impact in some quartz dominated coarse textured soils in the Eastern Cape Province. Soil samples for this experiment were collected from 14 ecotopes on the surface with a natural slope between 7.5 to 11% and at the depth between 0 to 0.2 m in the Eastern Cape Province. In each ecotope, twenty-five different spots were sampled using a spade at depth 0 to 0.2 m in other to eradicate biasness and ensure homogeneity. Thereafter, the soil samples were mixed to make a composite sample. The composited soil samples were then placed in rigid containers and taken to the soil science laboratory of the University of Fort Hare, Alice Campus where analyses were carried out. The soil properties were determined by passing the < 5 mm soil sample through a 2 mm sieve. The total Na, Ca and Mg contents in the soil samples were also determined using the wet digestion with sulphuric acid method. The total Soil organic matter content (SOM) was determined by the process known as weight loss on ignition. Thereafter, the fraction size distribution and aggregate stability was done by passing < 5 mm soil samples through a 3 mm sieve. The obtained calibrated aggregates between 3 and 5 mm were oven dried at 40o C. Thereafter, five gram (5g) of oven dried calibrated aggregates was immersed in a 50 mL deionized water in a 250 mL beaker for 10 minutes. The soil material left was transferred to a 0.053 mm sieve already immersed in ethanol and moved five times in the ethanol to separate < 0.053 mm from > 0.053 mm fragments. The remaining > 0.053 mm was re-immersed in ethanol and further oven dried at 40o C for 5 minutes. Thereafter, the > 0.053 mm fraction was transferred from 0.053 mm sieve, oven dried at 40o C, dry sieved using Digital Electromagnetic Shaker on a six column of sieves: 2 mm, 1 mm, 0.5 mm, 0.25 mm, 0.106 mm, and 0.053 mm. The aggregate stability was determined using the resulting size distribution in seven classes by calculating the mean weight diameter (MWD, mm). The soils were very stable, moderately stable or unstable. The presence of smectite and cultivation as opposed to pasture lowered aggregate stability. The studied soils showed three different aggregate size distributions. Unstable soils were dominated by 0.106 – 0.25 mm aggregate size and showed a positively skewed aggregate fraction size distribution. Aggregates finer than 0.106 mm were limited because of the coarse nature of the soil texture. Moderately stable soils broke down to both micro aggregates, 0.106 – 0.25 mm and macro aggregates, 2 – 5 mm giving a bimodal distribution. The aggregate size distribution in the very stable soils was dominated by the aggregate fraction size 2 – 5 mm and a negatively skewed aggregate fraction size distribution. The smaller the initial aggregate size the higher was the aggregate stability but the reverse was true for splash erosion. It was thought that the short 5 minutes duration of the rainfall might not have been enough to cause a total breakdown of the aggregates. Alternatively, ecotopes that were dominated by primary soil minerals such as quartz showed different breakdown behaviour compared to those containing secondary minerals such as kaolinite or smectite.

Accelerated soil erosion holds strong links to excessive land degradation, socioeconomic problems and accelerated climate change, particularly in developing countries such as South Africa. An analysis of the properties of severely eroded soils is undertaken to determine which characteristic properties influence the erodibility of the soils at several gully and badland sites in three catchments of the Ngqushwa rural municipality, which is tagged as one of the area’s most severely affected by soil erosion and degradation in the Eastern Cape. Physical, biological and chemical properties of the soils were analysed, including aggregate stability, soil texture, organic matter- and carbon content, clay mineralogy, sesquioxide content as Fe2O3 and cation composition. The distribution of a number of these properties was also determined, particularly between erosion sites, along hillslope profiles and with depth. The study area comprises three catchments, namely Mgwalana, Bira and Gqora which share common soil parent materials, land use history, exhibit similar topography and advanced degree of erosion. A total of 63 soil samples were strategically collected from identified erosion zones and site controls devoid of active erosion; where stability was evident by means of vegetation cover and soil surface condition. Surface samples were collected above 30cm depth and subsurface samples at depths greater than 30cm. To determine the fate of carbon additional samples were collected from runon and sink zones at the Mgwalana catchment along a transect from top to bottom slope. Laboratory analyses was performed to determine the soil properties, whereby C content was measured by the dry combustion method, Fe2O3- and cation content by Atomic Absorption (AA) Spectrometer, texture by the separation method described by Schlichting, Blume & Stahr (1995), clay mineralogy by X-Ray Diffraction and organic matter content by conversion of total C. In addition to these properties being used to infer aggregate stability, the wet sieving method was also used for this purpose and for validation of the other soil properties. The results revealed that no one soil property has a greater influence on aggregate stability than the others, but rather that the stability of the soil is dependent on the combinations of these properties in the soil and the interactions that occur between them. Based on this, the results indicated greater stability for runon, sink and control samples, mainly in the topsoil, which were characterised by a relatively higher C- and organic matter content, loam texture and higher concentrations of Ca2+. Furthermore, the less stable eroded samples were characterised by a more clay rich texture particularly in the subsoil, relatively lower C- and organic matter contents and a greater sodicity due to higher concentrations of Na+. The least stable soils belonged to the Gqora catchment, which were found to consist of higher silt content in the topsoil and a higher Fe2O3 content in the subsoil. The clay mineralogy was relatively uniform across all catchments, comprising of primarily illite and secondly kaolinite. The sample with the highest sodicity in terms of ESP contained smectite clay in addition to illite and kaolinite which is assumed to contribute to this increased Na+ concentration. These findings aid in the conclusion that the chemical characteristics of the soils, in association with biological and, to a less extent, physical properties of the soil exacerbate the erosion problem initiated by the extrinsic contributors, such as climate and topography. Investigation into the fate of carbon on eroded lands revealed a topographically driven dynamic whereby the total carbon content was found to be greater at the top and middle slope positions as well as in the sink zone. These hillslope sections were found to have a lower slope gradient and slightly more pronounced concave shape to those sections with lower C values. These topographic variables influence the degree of gully erosion taking place at different hillslope sections, which tends to be greater where slope angle is increased and convexity exists, resulting in the removal of soil C at these positions and its deposition in areas of accumulation, namely the runon and sink zones of low angle concave slope sections. The findings of this research may be used to develop restoration and management strategies with the ultimate goal to reduce the soils vulnerability to erosion by enhancing those soil properties conducive to greater aggregate stability as determined in the present study.

Soil organic matter (SOM) plays a primary role in aggregation and stabilization of soils, hence reducing their susceptibility to erosion. In South Africa (SA), most soils have low (< 4 percent) soil organic matte (SOM) contents, making them susceptible to soil erosion. Little is known about SOM quality effects in soil stabilization in the SA context, it is therefore difficult to advocate specific organic matter sources in order to stabilize a particular soil. This study evaluated effects of different litter quality sources (Vachellia karoo (sweet thorn) leaf litter and Zea mays (maize) stover) on soil aggregate stabilization at a soil micro-level (soil aggregate), guided by the following specific objectives; (i) to characterize soil properties that influence the erodibility of soils in the Ntabelanga area, Eastern Cape (EC) Province, SA (ii) to assess fractionation of organic carbon during decomposition of different litter sources (iii) to determine rate of soil macroaggregate re-formation under different litter amendments (iv) to determine the influence of different litter quality on splash soil erosion and (v) to delineate the Ntabelanga area into different soil erosion sensitivity zones. Soil samples collected from a proposed Ntabelanga dam site, EC Province, SA, were characterized for factors influencing erodibility. Soil physical and chemical properties were analyzed, soil erodibility (K-factor) estimated using SOC content and surface properties and soil loss rates by splashing determined under rainfall simulations at 360 mm h-1 rainfall intensity. Soil loss was then correlated with the chemical and physical soil properties. SOC showed significant (P< 0.05) inverse relationship with soil loss. Soils samples were bulked to seven composite samples according to major soil horizons (orthic A, melanic A, pedocutanic B, red apedal B, saprolite, G horizon and prismacutanic B) in the areas of soil associations, macroaggregate (> 0.250 mm) were removed by passing through a 0.250 mm sieve. The remaining soil microaggregates (< 0.250 mm) were then mixed with high quality Vachellia karoo leaf litter (C/N = 23.8) and low quality Zea mays stover (C/N = 37.4) and incubated at 23oC for 30 weeks. Jars were arranged as a 7 × 3 factorial laid in completely randomized design (CRD) with three replicates. Data was repeatedly measured at 1, 3, 8, 14, 23 and 30 weeks after incubation: to determine the stabilization of SOM by fractionating the soil particulate organic matter (POM), rate of soil macroaggregate re-formation and influence of litter quality on splash soil erosion along a decomposition continuum. Free light fractions (Free LF), coarse particulate organic matter (CoPOM) and fine particulate organic matter (FiPOM) within macroaggregates (> 250 μm) decreased exponentially from week 1 to 30 and were significantly (p < 0.05) influenced by litter quality × soil horizon × time interactions. A similar trend for FiPOM fractions in macroaggregates was observed in the 53-250 μm microaggregates (p < 0.05). The greatest influence on changes in POM fractions occurred within the first 3 weeks of incorporation. Both V. karroo leaf litter and Z. mays stover significantly stabilized the macroaggregates within the first 3 weeks after incubation. Cumulative macroaggregates yields, mean weight diameter (MWD), percentage water stable aggregates (%WSA) and whole soil stability index (WSSI) in litter amended soils increased up to week 8 of incubation and thereafter gradually declined in all soils. An increase in macroaggregation resulted in increased MWD, WSSI values and large and small aggregates distribution. Aggregation was significantly higher in soils with higher clay content than sand content, suggesting that soil texture was highly influential in litter decomposition. Rate of litter decomposition was influenced by soil type × time interactions which determined extent and macroaggregation dynamics along a decomposition continuum. The amount of splashed sediments was determined from each soil horizon at 360 mm h-1 simulated rainfall intensity applied as either single 8minute rainstorm (SR) or 4 × 2minute intermittent rainstorms (IR) separated by a 72 h drying period. Results showed a reduction in splashed sediments under IR and SR storms in litter-amended soils during the first 8 weeks of incubation with gradual increase thereafter. More sediments were splashed under IR than SR and litter quality had no influence on splashed sediments per soil horizon. Soil horizons profile with more clay than sand particles enhanced the litter effects on the soil resistance against detachment. The amount of SOC loss was influenced by primary particle size distribution and initial SOC content of the soil. Rainfall pattern and the initial SOC content were the main factors by which different soils influenced SOC loss. More rainstorm patterns should be investigated on these soils.

Due to the particular nature of accelerated soil erosion, its impact on food security is usually very intense. The impact starts first on the farmer, and then to his/ her environment. This is why soil erosion, when unchecked, is very devastating. Therefore this study was set to evaluate the perceived impact of soil erosion on food security in the Upper and Lower Areas of Didimana, Eastern Cape of South Africa, and the role farmers’ adoption behaviours play in the interaction. Three specific objectives were put forward by the study, vis-à-vis: (1) to establish farmers’ perceptions on the impact of soil erosion on food security of the study area; (2) to establish farmers’ innovation adoption behaviour with respect to soil erosion control in the study area; and (3) to establish farmers’ perceptions on the impact of extension activities with respect to soil erosion-control in the study area. The central argument of discussion is that soil erosion like every other agricultural problem, is the result of farmers’ non-adoption or inappropriate adoption of improved and recommended soil management technologies in the study area. The survey method of research was adopted for the study, where data were collected, using a well structured questionnaire, from a total of 60 farmers in the study area, through a simple random sampling process. Farmers’ perception suggested that the impact of soil erosion in their area is severe. This severity is demonstrated firstly in the form of climate change, as the time of rain in their area is gradually changing, and thus changing their time of cropping. Similarly the livelihoods of farmers are being negatively affected, as farmers’ crops, livestock, and even household feeding are being affected. More so, findings indicate that most farmers now plant fewer crops and there is an estimation of crop loss by most farmers of well between 21-60 percent of crops every year. Farmers’ perception further revealed that due to soil erosion, over 50 percent of farmers are unsustainable and a total of 71.7 percent of farmers’ population admitted that the amount of food available for their households is being severely affected. In virtually every sphere of human endeavours improved technologies have been developed to solve human problems, but the main reason problems like soil erosion is still very evident is the fact of farmers’ non-adoption or inappropriate adoption of specific recommended technologies. In the study area, the role of farmers’ adoption behaviour in the interaction of the impact of soil erosion on food security was very prominent. Findings indicate that despite the presence of certain recommended soil management technologies in the study area, majority of farmers do not use them neither extension advices. Moreover their satisfaction with those technologies was found to be low, which could be an explanation why they do not use them. For innovation to be adopted, rejected or utilized inappropriately, the effectiveness and performance of agricultural extension, as well as farmers’ perception play a great role. Thus in the study area, farmers’ perception on extension effectiveness indicates that extension hardly talk about soil erosion and its control during times of their visit. Similarly, farmers’ rating for extension services and advices was as well very low (23.4 percent). In fact, a comparison of farmers’ traditional methods of soil erosion control with extension recommendations (53.4 percent) indicated that farmers perceive their local methods of more importance than extension methods. In the same vein, majority of farmers in the area indicated that extension officers are inadequate in their jobs. Reasons offered range from issues of unreliability, lack of regular visits, communication problems, less attention for crop farming, and other reasons such as extension being unconcerned for subsistence farmers, as well as the fact that they focus more on cooperatives. In all, the findings of the descriptive statistics reveal that the impact of soil erosion on food security in the study area is very significant, and the results of the linear regression model of relationships in the study reveal that soil erosion relates positively with age of farmers, their product quality, and their sustainability. In a similar note, the innovation adoption behaviours of farmers was also found to be positively related to farm yield and food accessibility. Thus showing that innovation adoption behaviour of farmers in the interaction of soil erosion and food security in the study area is significant. Therefore, efforts should be geared toward improving factors that increases yield and accessibility of farmers to serve as boosters of farmers’ motivation towards the adoption of appropriate soil management technologies in their area.

The study examines the effect of ridged pineapple cultivation on factors influencing the soil erodibility of Glenrosa and Oakleaf soil forms in the Bathurst district of South Africa. A number of physical and chemical variables influencing soil erodibility are investigated, namely soil moisture, bulk density, porosity, infiltration rate, aggregate stability, shear strength, soil texture, soil structure, penetrability, organic carbon, pH and cation exchange capacity. These soil characteristics are examined in undisturbed soils under natural vegetation and compared to those on adjacent traffic areas, pineapple ridges and pineapple furrows. The results of the analyses between the four sample sites indicate that ridged cultivation of pineapples has a negative effect on factors influencing soil erodibility on the areas studied. The results of the analysis within each of the sample sites do not illustrate any clear relationships and thus depict the complexity and multiplicity of the soil erodibility phenomenon. A further study, augmenting the soil erodibility data with actual soil loss data, is recommended

This study originated from an evaluation of the performance of a commercially available high concentration point focus concentrator PV system. The effect of module design flaws was studied by using current-voltage (I-V) curves obtained from each module in the array. The position of reverse bias steps revealed the severity of mismatch in a string of series-connected cells. By understanding the effects of the various types of mismatch, power losses and damage to the solar cells resulting from hot spot formation can be minimized and several recommendations for improving the basic performance of similar systems were made. Concern over the extent and type of defect failure of the concentrator photovoltaic (CPV) cells prompted an investigation into the use of a light beam induced current (LBIC) technique to investigate the spatial distribution of defects. An overview of current and developing LBIC techniques revealed that the original standard LBIC techniques have found widespread application, and that far-reaching and important developments of the technique have taken place over the years. These developments are driven by natural progression as well as the availability of newly developed advanced measurement equipment. Several techniques such as Lock-in Thermography and the use of infrared cameras have developed as complementary techniques to advanced LBIC techniques. As an accurate contactless evaluation tool that is able to image spatially distributed defects in cell material, the basis of this method seemed promising for the evaluation of concentrator cells.

[Portion of abstract]: Sediment dynamics are influenced by transformed landscape connectivity in catchments worldwide. The upper Thina catchment, an important high rainfall resource in the northern Eastern Cape, South Africa, is an example of where ongoing subsistence farming on communal land has led to overgrazing and trampling that has initiated large erosive features (e.g. gullies) and river incision. The formation of gullies led to increased hillslope-channel connectivity and the resultant river incision decreased the channel-valley fill connectivity. These two changes in connectivity led to increased sediment export from the catchment that has various down-stream ecological and socio-economic impacts. This study investigates how the change in hillslope-channel and channel-valley fill connectivity has altered the sediment dynamics in the Vuvu catchment, a headwater tributary of the Thina River. A combination of methods were used to assess the changes in hillslope-channel and channel-valley fill connectivity. High resolution aerial images were used to map source features, such as fields, gullies, sheet erosion, landslides, roads and livestock tracks. Topographic and geological characteristics of the source features were extracted using a Geographic Information System. Furthermore, hillslope-channel pathways, such as the natural drainage network, continuous gullies, discontinuous gullies, roads and livestock tracks were mapped and analysed in terms of topographic and geological characteristics. Historic aerial images were assessed to calculate the date the larger gullies began forming. Recent aerial photos and cross sectional surveys of the valley fill were combined to map the various sediment sinks. Particle size and organic content were analysed for flood bench cores and terrace samples. The chronology of the flood benches was determined using unsupported Pb-210 and Cs-137 dating, and determined for the terraces using Optically Stimulated Luminescence dating. Quantitative and qualitative sediment tracing approaches, using mineral magnetic properties, were used to trace the origin of suspended sediment (collected during flood events), sediment stored in the flood benches and sediment stored in the terraces. Hydrological monitoring was used to assess the potential to store sediment on flood benches along the valley fill through flood bench inundation frequency. Hydrological and hydraulic modelling extended the measured inundation frequencies to a 73 year period and other cross sections along the valley fill. Furthermore, a future scenario of an increased vegetation cover and reduced hillslope-channel connectivity was assessed in terms of channel-valley fill inundation frequency.

The invasion of Acacia mearnsii in the Kouga catchment, Eastern Cape, South Africa, has various negative impacts on the ecosystem. These impacts include: reduced species richness, increased water use, increased nutrients and increased N cycling rates. The native shrubby fynbos vegetation has adapted to the acidic nutrient poor soils and Mediterranean climate of the Kouga Mountains. Fynbos, however, is currently being out competed by the much taller Acacia mearnsii trees, due to their competitive nature and ability to fix nitrogen, thereby enriching the soil. The invaded sections of the valley bottoms and lower hill slopes are characterised by an almost complete monoculture of Acacia mearnsii, with very few fynbos species still present. The Department of Water and Environmental Affairs sponsored Working for Water programme started clearing Acacia mearnsii in 1996 in the Kouga Mountains. Cleared sites have remained bare for long periods, indicating that soil properties are not favourable for indigenous propagule re-establishment. The aim of this research was to assess how A. mearnsii invasion and clearing affect fynbos recovery through its impact on soils. This was done by characterising vegetation and soil properties on fynbos, infested and cleared slopes. Vegetation cover for various growth forms was determined and a species list was compiled for each plot. The slope angle, surface hardness, litter cover, bare ground cover and soil depth were measured in the field, whereas water repellency, particle size and the chemical composition were measured in the laboratory. Furthermore, the plant establishment capacity of soils from fynbos, infested and cleared slopes was calculated. This was done by germinating fynbos seeds and growing fynbos plants in soils from the various slopes. The effect that invasion and clearing has on soil erosion was quantified using erosion plots on fynbos, infested and cleared slopes. The invasion and clearing of Acacia mearnsii led to an increase in soil nutrients, especially nitrogen, phosphorus, potassium, carbon and manganese. Furthermore, soils became more acidic, with increased water repellency and reduced surface hardness. The vegetation changed to a tree-dominated structure, replacing the native species. Native plant germination was relatively unaffected by invasion and clearing, with an increase in germination just after clearing. Plant growth of a native grass, Themeda triandra, and herb, Helichrysum umbraculigerum, has increased on soils from cleared slopes. This study showed that soil movement increased on slopes which are invaded and cleared of Acacia mearnsii, with erosion rates doubling on invaded slopes

A history of land degradation is reconstructed in a part of the dividing ridge between the Great Fish and Keiskamma rivers, in Peddie District, former Ciskei. The study entails a comparative investigation of the progressive changes in land use, vegetation and soil erosion in three tenure units, namely: former commercial farms, traditional and betterment villages. Analysis of the sequential aerial photography of the area for 1938,1954, 1965, 1975 and 1988 is employed. This is backed by groundtruthing exercises. Data thus obtained are quantified, and linkages between degradation, anthropogenic and physical factors are derived using PC ARC/INFO GIS. Differences in land tenure systems emerge as the main controlling factor to variations in land degradation. Confinement of vegetation diminution and erosion to traditional and betterment villages is observed at all dates. Scantily vegetated surfaces and riparian vegetation removal are a characteristic feature of both areas throughout the study period. 'Betterment,' introduced in the early 1960s to curb land degradation is, instead observed to exacerbate it, particularly soil erosion. Trends in land use change are characterised by the abandonment of cultivated land, which is noted to coincide with a sharp rise in population. Erosion intensification into severe forms particularly between 1965 and 1975, coincident with a period of extreme rainfall events, emerges as the most significant degradation trend. A close spatial correlation between abandoned cultivated land and intricate gullies is identified. So is the case between grazing land and severe sheet erosion. Within the grazing lands, an examination of erosion and categories of vegetated surfaces reveals that erosion occurs predominantly on the scanty vegetation category. Such erosion-vegetation interaction largely explains the non-recovery of the scanty vegetation category, even during periods of intense rainfall. Extensive channel degradation is evident along stream courses with scanty riparian vegetation. Physical factors are noted to have a significant bearing on erosion. The high prevalence of erosion on the Ecca group of rocks confirms its erosion-prone nature. Pockets of colluvium and alluvium accumulation in the steep bottomlands are identified as the sites of the most severe gully erosion. Field surveys at some of the sites indicate that a dolerite sill through the area forms a boundary of colluvium accumulation and the upslope limit to gully incision. That these sites are recognised as formerly cultivated land, portrays the interaction between physical and anthropogenic variables with regard to inducing degradation in the area.

Effective microorganisms (EM), a commercial concoction of microbes that includes yeasts, fungi, bacteria and actinomycetes, have been found to be effective in enhancing crop growth by a number of scholars. It is registered in South Africa, but it had not been thoroughly investigated. The present study investigated the effects of EM on growth, yield and quality of tomato (Lycopersicon esculentum Mill), butternut (Curcurbita moschata) and Swiss chard (Beta vulgaris), along with selected soil properties. In field-grown tomato it was observed that the application of EM caused a significant increase in the number of fruits at seven weeks after transplanting. However, plants treated with EM alone, or EM in combination with other amendments, subsequently produced lower yields owing to an outbreak of early and late blights which affected them the most severely. Combined applications of EM with organic amendments improved plant N content and increased soil N content above initial levels. The application of compost resulted in soil N and P concentrations higher than those of the control presumably due to nutrients being slowly released from the compost material. In a follow up greenhouse trial EM application had a negative effect on tomato leaf dry matter yield, number of leaves, number of trusses, fruit yield and number of fruits. The negative effects of EM were ascribed to N immobilization by the EM that could have resulted in reduced N availability to plants. The lower number of fruits associated with EM application resulted in improved average fruit weight of tomatoes grown in the greenhouse, possibly as a result of more assimilates being partitioned to the few fruits EM application also had a negative effect on field grown butternut as reflected by lower total yield, lower marketable yield and lower first grade yield. The results were attributed to immobilization of N induced by application of EM, and to the inability of EM to control pumpkin fly that attacked very young fruit, resulting in their failure to develop or resulting in the down grading of mature fruits. The application of EM alone had a positive but non significant effect on the yields of both the first and second harvests of Swiss chard. However, when applied with compost or goat manure, a non significant negative effect on yield was observed. When applied with inorganic fertilizer, EM had no effect on yield but tended to increase the uptake of nitrogen by Swiss chard. Though goat manure had a narrower C: N ratio than compost, it did not result in greater EM effectiveness as had been hoped. However, goat manure had a more positive effect on soil properties than compost. It increased the N, P, and K contents of the soil and resulted in a narrower C: N ratio of the soil compared to compost. Generally, the results of the four trials conducted with three different crops indicated that EM had inconsistent effects on crop performance.

Low cover crop biomass production is a major obstacle to the success of conservation agriculture currently promoted as panacea to the inherent problem of soil erosion and loss of soil productivity in the Eastern Cape (EC). Therefore, this study evaluated cover crop management strategies for optimizing biomass production for better soil cover, soil nitrogen (N) and phosphorus (P) fertility, weed control and maize yields. The strategies tested are cover crop bicultures, selection of an adapted lupin cultivar and seeding rate, and the feasibility of rain fed winter cover cropping. The cover crop experiments were carried in rotation with summer maize between the winter of 2009 and summer of 2010/2011. Biculture trial was carried out by seeding oat (Avena sativa) and vetch (Vicia dasycarpa) at three mixture ratios and as sole crops under irrigation. On a separate irrigated trial, two lupin cultivars (Lupinus angustifolius var Mandelup & Qualinock) were seeded to a range of seeding rate, 40 to 220 kg ha-1. To study the feasibility of rain fed winter cover cropping, oat, vetch, rye (Lolium multiflorum), barley (Hordeum vulgare), radish (Raphanus sativa) and triticale (Triticale secale) were relayed into a maize crop in February, March and April of 2010. The irrigated trials were followed with SC701 maize cultivar, whilst the rain fed trial was followed with DKC61-25 maize cultivar. Bicultures gave higher cover crop biomass than sole vetch, increasing with an increase in the oat component of the mixture. Increased N and P uptake was observed with bicultures compared to sole oat, however, the levels were comparable to sole vetch. Sole vetch increased soil inorganic N and P at maize planting, whilst the slow decomposition by sole oat residue resulted in mineral lock up. Bicultured cover crop residues had intermediate decomposition rates and resulted in optimum levels of inorganic N and P for prolonged periods compared to sole crops. Weed suppression by the bicultures was comparable to sole cover crops. Biculturing technology significantly (P<0.05) increased maize grain yield compared to sole oat and the yields were comparable to those from sole vetch. For lupins, 206 kg ha-1 seeding rate gave the optimum biomass yield. Weed dry weights in both cover crop and maize crop decreased with an increase in lupin biomass. Comparable soil total N and inorganic P values at maize planting, were observed from plots planted to 120, 180 and 220 kg ha-1. Maize grain yield increased with an increase in lupin seeding rate. The study on rain fed winter cover cropping had most cover crop species’ biomass decreasing with each delay in planting except for radish, which increased. Vetch produced the highest amounts of biomass from February and March planting whilst radish had the highest biomass in April planting. The two species resulted in the greatest N improvement compared to the other species. Regardless of the grazing, the grass specie residues managed to persist to the next cropping season and the residue remaining were comparable to that of radish and vetch. Late-planted cover crops had the greatest residue remaining than early-planted, as a result, April planted cover crops provided better weed suppression than March and April planted. Vetch provided the highest maize grain yield (4005 kg ha-1) whilst all other species tested had comparable grain yields. The results suggested that bicultures could be grown to give sufficient biomass for both weed suppression and soil fertility improvement. Furthermore, increasing lupin plant densities improve its function as a cover crop with respect to weed suppression, soil fertility improvement and maize yields. The study also showed that for dry land systems, February and March planted vetch and April planted radish can provide the greatest biomass and maize yield improvement.

Soil structure and its associated physical properties are essential soil components. Soil texture and mineralogy are inherent soil properties that influence soil management. This study assessed the implication of tillage, texture and mineralogy on soil sieving, aggregate stability indices and physical fractions of organic matter in soils of Eastern Cape Province of South Africa. An Iris FTLVH – 0200 digital electromagnetic sieve shaker (Filtra Vibraciόn SL Spain), was used to determine settings for sieving efficiency. Mean weight diameter (MWD), water stable aggregate (WSA), state of aggregation (SA), dispersion ratio (DR), water dispersible clay (WDC), clay dispersion ratio (CDR), clay flocculation index (CFI), and potential structural deformation index (PSDI) were aggregate stability indices evaluated to check for sensitivity in evaluating aggregate stability of soils under two tillage systems and physical fractions of carbon and nitrogen in soils of Eastern Cape Province. The T4I3P2 and T4I4P3 settings were sensitive under tillage and T4I1P4, T3I4P3 and T4I4P3 were sensitive under mineralogical considerations for sieving efficiency. The total carbon in soils under conventional tillage (CT) was 17.7 g/kg and in soils under no tillage (NT) it was 15.8 g/kg. The total carbon content in the clay fraction of soils under CT was 24.1 percent higher than the total carbon content in the clay fraction of soils under NT. The total nitrogen content in the clay fraction of soils under CT was 5.4 percent higher than the total nitrogen content in the soils under NT. The total carbon in the sandy loam (SL) textured soils was 17.4 g/kg and in the sandy clay loam (SCL) textured soils it was 17.1 g/kg. The total nitrogen in SL soils was 3.7 g/kg and in SCL soils it was 3.7 g/kg. The clay fraction had higher total carbon than other fractions in Sl and SCL soils. The higher values of nitrogen were observed in the silt fraction for SL soils and clay fraction for SCL soils. The total carbon in the soils dominated with kaolinite was 17.3 g/kg and in quartz dominated soils the value was 16.9 g/kg. The total nitrogen in the soils dominated with kaolinite was 3.7 g/kg and in the soils dominated with quartz the value was 3.7 g/kg. For soils under NT the WDC was 135.8 g/kg and for soils under CT it was 139.7 g/kg. The ASC was 72.5 for soils under NT and 92.0for soils under CT. The DR was 0.9 for soils under NT and 0.8 for soils under CT. The CFI was 0.5 for soils under NT and 0.5 for soils under CT. The CDR was 0.5 for soils under NT and 0.5 for soils under CT. The MWDw was 1.6 mm for soils under NT and 1.4 mm for soils under CT. The MWDd was 4.0 mm for soils under NT and 4.0 for soils under CT. The percent WSA > 0.25 mm was 61.7 percent for soils under NT and 56.2 percent for soils under CT. The PSDI was 55.2 percent for soils under NT and 61.15 percent for soils under CT. The SA was 43.2 percent for soils under NT and 37.89 percent for soils under CT. The WDC was 125.7 g/kg for SCL soils and 151.4 g/kg for SL soils. The CDR was 0.5 for both SCL and SL soils. The DR was 0.9 for SCL soils and 0.8 for SL soils. The CFI was 0.5 for both SCL and SL soils. The ASC was 56.2 g/kg for SCL soils and 115 g/kg for SL soils. The MWDw was 1.5 mm for SCL soils and 1.4 mm for SL soils. The MWDd was 3.6 mm for SCL soils and 3.6 mm for SL soils. The percent WSA > 0.25 mm was 53.0 percent for SCL soils and 62.5 percent for SL soils. The PSDI was 59.2 percent for SCL soils and 59.7 percent for SL soils. The SA was 33.6 percent for SCL soils and 45.2 percent for SL soils. The WDC was 313.3 g/kg for kaolinitic soils and 120.7 g/kg for quartz dominated soils. The CDR was 0.5 for kaolinitic soils and 0.5 for quartz dominated soils. The DR was 0.9 for kaolinitic soils and 0.8 for quartz dominated soils. The CFI was 0.5 for kaolinitic soils and 0.5 for quartz dominated soils. The ASC was 110.0 g/kg for kaolinitic soils and 101.7 g/kg for quartz dominated soils. The WSA > 0.25 mm was 57.3 percent for quartz dominated soils and 68.4 percent for kaolinitic soils. The MWDw was 1.6 mm for quartz dominated soils and 0.8 mm for kaolinitic soils. The MWDd was 3.6 mm for quartz dominated soils and 3.4 mm for kaolinitic soils. The PSDI was 56.3 for quartz dominated soils and 76.0 for kaolinitic soils.

Thesis (MSc)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Arid and semi-arid rangelands of the Nama-Karoo Biome are believed to have changed considerably since the arrival of domestic livestock in the veld. Severe grazing pressure is considered to be one of the prime factors responsible for the perceived degradation of vegetation and concurrent soil degradation. To understand the process of degradation and to make further recommendations for future veld restoration, a large-scale project was undertaken in the Eastern Cape. This project focused on the role that landscape heterogeneity plays in providing refuges for plant species. The key question asked in this project was: What role do these hypothetically less grazed mesas play in the conservation of rangelands in the Nama-Karoo of the Eastern Cape? This study, a component of the larger project, investigated grazing and soil landscape gradients on- and off- the three mesas (Tafelberg, Folminkskop and Buffelskop) in the Middelburg District of the Eastern Cape, South Africa and the possible influences that they might have on the veld. The flats surrounding the mesas were mostly used as grazing camps in contrast to the plateaux of the mesas, which had varied levels of accessibility. In the absence of direct observations, the primary objective of the study was to test the differential dung pellet abundance and impact of animals on different parts of the landscape. As such, dung pellet counts in this study were correlated with surrogates of soil physical properties including bare ground, trampling and litter cover. Variation in dung pellet density was found at the different habitats (flats, slopes and plateaux) of all mesas. The flats to the north-eastern and south-western of Tafelberg mesa were found to be more heavily utilized by livestock and herbivores, while the plateaux and southeastern slopes of Folminkskop and Buffelskop were also utilized by grazers. The Tafelberg mesa was the only study site that was consistent with the hypothesis which stated that grazers would be less concentrated on the plateau compared to the surrounding flats due to its inaccessibility, whilst the high mean dung pellet density on the plateaux of the smaller Folminkskop and Buffelskop mesas due to easier access contradicted the original hypothesis. It appeared that dung pellet density did not clearly turn out to be an indicator of habitat use in this study, but showed where slopes and plateaux were accessible to herbivores, as in the case for the Buffelskop mesa, a higher abundance of dung pellets were found suggesting that higher intensities of habitat use took place. During this study a strong pattern was observed of bare soil patches on the flats surrounding the mesas. There was a decrease in percentage of bare soil along the gradient of the three mesas with a high percentage of bare soil on the plateaux of the mesas. A significant correlation was found between bare soil and dung pellet density. However, the plateaux of Folminkskop and Buffelskop had a high percentage of bare soil compared to the plateau of Tafelberg mesa. Farmers mainly used these smaller mesas as grazing camps for their livestock and herbivores. A positive correlation between bare soil and litter cover of the different habitats was evident in this study. A lower percentage of litter cover at these sites was associated with a high percentage of bare soil. Litter is very important in a healthy vegetation community in terms of nutrient cycling and fertile patches. A detailed assessment of soil chemical and physical properties would reveal, firstly, if vegetation change is better explained by soil or grazing effects and, secondly, if changes in soil have resulted from land use. Differences in macro- and micro-site variations between open-canopy (between shrubs) and closed-canopy (under shrubs) sites for each habitat were determined to differentiate between local scales due to land use and landscape scales due to geomorphology. The results suggested that carbon, phosphorus, calcium, magnesium, copper and manganese levels in soils at landscape scale better explain vegetation changes between habitats. At a local scale (open- and closed-canopy sites) land use was responsible for little changes in soils. Changes in only soil potassium, zinc and boron elements were actually a consequence of local scales due to land use. The soil nutrient content on the slopes appeared to be intermediate between the flats and plateaux of all three mesas. It appeared that dolerite capped Tafelberg and Folminkskop mesas had high silt and clay content, while Buffelskop (sandstone) mesa had a lower silt and clay content. Consequently, the texture and parent material of the soils contributed to the variations in soil nutrient composition between these mesas. High infiltration rate together with low nutrient content on the flats clearly showed that these flats, surrounding the mesas were degraded. The high infiltration rates were caused by high activity by livestock and other indigenous animals on the flats which breaks the surface crusting of bare soil and improve infiltration. It was concluded that high levels of grazing at these sites have also altered the textural and soil properties. Endozoochory dispersal and the deposition of dung pellets in areas of small patch disturbances play an important role in veld regeneration in degraded areas. Dung pellets collected from permanent study sites on the southeastern and northwestern flats and slopes, and all the study sites on the plateau of Tafelberg mesa, was sown in seedling trays, watered and monitored for seedling germination. Species list were then compared to below-ground soil seed bank data and above-ground vegetation data collected by other researchers at the same permanent study sites. Higher seedling percentages were recorded from dung pellets collected on the flats than on the plateau. A total of sixteen species were found to germinate in dung pellets collected on the flats compared to ten species germinating in dung pellets collected on the slopes and two species on the plateau of Tafelberg mesa. The seeds that germinated represent a variety of palatable grasses and shrub species. Aristida sp., Eragrostis bicolor, Eragrostis ch/orome/as and Eragrostis obtusa were palatable grasses recorded for dung pellets collected on the flats. Of the species recorded, Aristida sp., Chenopodium sp. and Pentzia sp. were found in dung pellets but were not recorded in parallel soil seedbank and vegetation studies. Successful restoration of veld conditions requires strict grazing management practices. Germination of seed in dung pellets might be considered to be a valuable means of indicating restoration potential and rangeland conditions for the identification of both degraded and conservation worthy areas. With appropriate land management skills and restoration measures, these challenges can be constructively and creatively faced.
AFRIKAANSE OPSOMMING: Daar word geglo dat die ariede en sernl-arlede weivelde van die Nama-Karoo bioom aansienlik verander het sedert die aankoms van mak lewende hawe in die veld. Swaar weidingsdruk word beskou as een van die vernaamste faktore verantwoordelik vir die waarneembare oorbeweiding van plantegroei en die gelyktydige grond agteruitgang (degradasie). Ten einde die proses van degradasie beter te verstaan, en om verdere aanbevelings te kan maak vir toekomstige veld herstel, is huidiglik 'n grootskaalse projek in die Oos-Kaap aan die gang oor die rol wat landskap ongelyksoortigheid speel in die voorsiening van skuiling aan plant spesies. Hierdie studie ondersoek weiding en grondlandskap gradiënte (op en af) van die drie mesas (Tafelberg, Folminkskop en Buffelskop) in die Middelburg streek van die Oos- Kaap, Suid-Afrika en die moontlike invloed wat hierdie gradiënte op die veld het. Die vlaktes was meestal gebruik vir weidingskampe in teenstelling met die kruin van die mesas. Hierdie studie het duidelike patrone vir habitat-gebruik op die vlaktes, hange en kruine van al die mesas aangetoon. Die vraag wat gestel was, was watter rol speel hierdie hipoteties minder beweide mesas in die bewaring van weivelde in die Nama- Karoo van die Oos-Kaap? Hierdie studie toets nie direk vir mis verspreiding as 'n plaasvervanger vir dier verspreiding in die landskap sedert werklike dier getalle nie oorweeg was nie. In die awesigheid van direkte waarneming, die primêre doelwit was om te toets die differensiaal misdigtheid en die impak van diere op verskillende dele van die landskap. Mis getalle in hierdie studie was gekorreleer met plaasvervangers van fisiese eienskappe insluitent onbedekte grond, vertrapping en droë plant material decking. Variasie in misdigtheid was gevind by die verskillende habitate (vlaktes, hange en kruine) van all die mesas. Die vlaktes aan die noord-oostelike en suid-westelike kante van die Tafelberg mesa was meer hewig benut deur lewende hawe en hêrbivore, terwyl die kruine en suid-oostelike hange van Folminkskop en Buffelskop ook gebruik was deur weidende diere. Die Tafelberg mesa was die enigste studie area wat konsekwent was met die hipotese, terwyl die hoë gemiddeld misdigtheid op die kruine van die kleiner Folminkskop en Buffelskop mesas, as gevolg van makliker toegang weerspreek die oorspronklike hipotese. Dit blyk dat misdigtheid duidelik opkom as 'n nie aanwyser habitat-gebruik in hierdie studie, maar wys well waar hange en kruine toeganklik was vir herbivore, soos in die geval van Buffelskop mesa, oorvloed van mis was gevind wat voorstel dat hoer intensiteit van habitat-gebruik voorgekom het. 'n Duidelike patroon is waargeneem tydens hierdie studie van onbedekte grond areas op die vlaktes rondom mesas. Daar was 'n afname in persentasie onbedekte grond langs die gradiënt van die drie mesas. Die kruine van Folminkskop en Buffelskop toon hoër persentasies onbedekte grond in vergelyking met die kruin van die Tafelberg mesa. Daar is 'n betekenisvolle korrelasie tussen onbedekte grond en misdigtheid gevind. Boere gebruik hierdie kleiner mesas hoofsaaklik as weidingskampe vir hulle lewende hawe en hêrbivore. In hierdie studie is daar 'n positiewe korrelasie gevind tussen onbedekte grond en droë plant material decking van die verskillende habitatte. Droë plantmateriaal bedekking speel 'n baie belangrik rol in 'n gesonde plant gemeenskap in terme van voedingsirkulering en vrugbare kolle. 'n Breedvoerige skatting van grond chemise en fisiese eienskappe wou openbaar eerstens of plantegroei verandering beter verklaar word deur grond of weiding effekte en tweedens, of verandering in grond veroorsaak was deur land-gebruik. Verskille in makro- en mikroterrein-wisseling tussen oop-blaredak (tussenplantruimtes) en toeblaredak (onderplantdekking) terreine vir elke habitat was bepaal om te onderskei tussen lokaal effek as gevolg van land-gebruik en landskap effek as gevolg van geomorfologie. Die resultate stel voor dat koolstof, fosfor, kalsium, magnesium, koper en mangaan vlakke in die grond by landskap effek beter plantegroei verandering tussen habitate verduidelik. By 'n lokaal effek (oop-en toe-blaredak terreine) land-gebruik was verantwoordelik vir min veranderinge in grond. Verandering in grond kalium, sink en baron elemente was werklik 'n gevolg van lokaal effek as gevolg van land-gebruik. Die nutrient inhoud van grond op die hange blyk intermediêr te wees tussen die van die vlaktes en kruine van al drie mesas. Hierdie studie toon ook dat die geologie en topografie van hierdie mesas die grond tekstuur en nutrient samestelling op en af van die mesas beinvloed. Dit wil voorkom asof die dolerite bedekte Tafelberg en Folminkskop mesas, hoë slik en klei materiaal bevat, terwyl Buffelskop (sandsteen) mesa 'n laer slik en klei inhoud het. Gevolglik, tekstueel en ouer materiaal grond dra by tot die variasie in grond nutrient samestelling tussen hierdie mesas. Hoë infiltrasie tempo tesame met lae voedingstof van die vlaktes dui daarop dat die vlaktes rondom die mesas oorbewei was. Hierdie hoë infiltrasie tempo word veroorsaak deur hoë dierlike aktiwieteite op die vlaktes deur lewende hawe en ander inheemse diere wat die oppervlakke van onbedekte grond versteur en infiltrasie verbeter. Die gevolgtrekking word gemaak dat die hoë weidingsvlakke van hierdie terreine ook die tekstuur en ander grond eienskappe verander het. Endozoochoreeuse verspreiding en die mis-afsetting in gebiede van klein areaversteurings, speel 'n belangrike rol in veld herlewing in oorbeweide gebiede. Mis versamel by permanente studie terreine op die SO en NW vlaktes en hange, as ook al die studie terreine op die kruin van die Tafelberg mesa, is gesaai in saailing bakke, besproei en gekontroleer vir saailing ontkieming. 'n Lys van spesies is vergelyk met onder-grondse saadbank gegewens en bo-grondse plantegroei gegewens wat deur ander navorsers by dieselfde studie terreine versamel was. Hoër saailing persentasies is gevind vir mis wat op die vlaktes versamel is as op die kruine. 'n Totaal van sestien geidentifiseerde spesies het uit die mis op die vlaktes ontkiem in vergelyking met die tien spesies wat ontkiem het uit die mis van die hange en twee spesies iut die mis van die kruin van Tafelberg mesa. Die ontkiemde saad verteenwoordig 'n verskeidenheid van vreetbare gras en struik spesies. Aristide sp., Eragrostis bicolor, Eragrostis chloromelas en Eragrostis obtusa is vreetbare grasse wat gevind was in die mis versamelop die vlaktes. Die spesies opname wys dat Aristida sp., Chenopodium sp. en Pentzia sp. Gevind was in die mis, maar nie in die parallelle grond saadbank en plantegroei studies nie. Die suksesvolle herstel van veldtoestande vereis "n streng weidingsbestuur toepassing. Die ontkieming van saad in mis kan beskou word as "n bekostigbare manier om veld herstel potentiaal te bepaal, asook weiveld toestande vir die indentifiseering van beide degradasie en bewaring van waardevolle areas. Met gepaste veldbestuur vaardighede en herstel maatreels, kan hierdie uitdagings konstruktief en kreatief aangespreek word.

South African rangelands in combination with their surrounding homesteads occupy 13% of the entire land surface in South Africa. These rangelands are a source of forage for communal livestock. The rangelands in communal tenure system are degraded due to high human population and livestock numbers. The rangeland of Peddie was never evaluated since the introduction of Nguni Cattle Empowerment Project. Therefore, socio-ecological evaluation was conducted in order to interlink farmer‟s perceptions and scientific data to recommend appropriate rangeland management and restoration programme. Two structured questionnaires consisting of close and open ended questions were used to investigate farmer‟s perceptions on rangeland condition, dynamics, and their causes. Sixty households were randomly selected on the bases of livestock ownership and the membership in Nguni Cattle Project. In each household, any respondent of 20 years or greater, and a key informant of age greater than 40 years were selected. For scientific assessment of range condition, three homogenous vegetation units namely grassland, scattered and dense bushland were demarcated into four 100m x 50m replicates. In each replicate, two 100m transects were laid parallel to each other with 30m equidistant apart. The step point and harvesting method along each transect were employed for herbaceous species composition and biomass production. The point-to-tuft distance was also determined as a proxy for basal cover. Woody density, species composition and tree equivalents were determined in 200m2 belt transects in each HVU replicates. The germination method for soil seed bank evaluation was also employed to find plant species composition and density. The soil nutrients (OC, N, P, K, Na, Ca, Mg, Zn, Cu and Mn) and pH were analysed through solution preparation and observation under photospectrometer to determine functional capacity of the soil of Peddie rangeland. The farmer‟s perceptions comprised of 63% females and 37% males (n = 120) with a mean household of 8 people, 5 adults and 3 children. It was perceived by 93.3% respondents that the rangeland of Peddie have undergone changes over two decades. These changes were perceived by 83% respondents to be accompanied by decline in livestock numbers. Woody encroachment and overgrazing were perceived to be the major attributes of these vegetation changes. The scientific rangeland condition assessment confirmed that these changes were more pronounced as bush density increases. Dense bushland had a significantly high (p<0.05) encroached condition with 6650 trees ha-1 and 4909.5 TE ha-1 beyond the recommended thresholds of 2400 trees ha-1 and 2500 TE ha-1 respectively. Scattered bushland had a fair condition of 1950 trees ha-1 and 1198.1TE ha-1. Themeda triandra as a key species was significantly higher (p<0.05) in grassland (31.1%) than scattered (15.6%) and dense bushland (6.1%). There was a declining trend in biomass production from grassland to dense bushland. The summer biomass production was significantly higher (p<0.05) in grassland than scattered and dense bushland but winter biomass was not significantly different (p>0.05) from all homogenous vegetation units of Peddie rangeland. However, the soil fertility increased with an increase in bush density except organic carbon (OC) which was 1.61% in grassland, 1.46% in scattered and 1.53% in dense bushland respectively. Soil N, K, P, Mg2+ Na+, Ca2+, Cu, Zn, Mn and pH were significantly higher (p<0.05) in dense bushland than grassland and scattered bushland. High soil fertility in dense bushland may be attributed to by abscission of woody plants and litter decomposition. In the soil seed bank, the abundances of forbs were significantly higher than sedges (χ2 = 12, df = 1, p = 0.001) and grasses (χ2 = 8.333, df = 1, p = 0.004) in all homogenous vegetation units while sedges were not significantly different (χ2 = 3, df = 1, p = 0.083) from grasses. The Sorensen‟s index indicated that soil seed bank and extant vegetation were significantly different (p<0.05). Annual and biennial forbs and sedges had high abundances while perennial grasses formed a bulk in above ground vegetation. This provided an insight that a reliance on soil seed bank for restoration of Peddie rangeland would not be advisable because it can result in retrogression. The communal rangeland assessment provided clear qualitative and quantitative data when the combination of indigenous knowledge and scientific assessments was done. The rationale is that conclusions and recommendations of range assessment are relient on the farmer‟s perceptions pertinent to their livestock production systems and their rangeland management objectives. This study has shown that inclusion of communal farmers in policy making can provide better insight because those are the people experiencing the consequences of range degradation.

The current interest in conservation agriculture (CA) technologies is a result of the need to reduce excessive land degradation in most crop producing areas as well as to enhance sustainable food production. Cover crops that are usually grown under CA to provide soil cover, may offer secondary benefits, depending on the farming system. The concept of growing cover crops is a relatively new phenomenon to smallholder farmers. Production of large biomass yields and weed suppression from cover crops were major challenges affecting success and uptake of CA technologies by smallholder irrigation farmers. Coupled with this, low soil fertility limit maize productivity and reduce water use efficiency on smallholder irrigation schemes in what is largely a water strained agro-ecology in South Africa. While cover cropping can increase maize productivity, benefits of different types of mulch are not well understood, leading to challenges in selecting the most appropriate cover crop species to grow in the Eastern Cape Province (EC) of South Africa (SA) which has a warm temperate climate. With respect to any new technology, smallholder farmers are more interested in the economic benefits. Cover crops have been defined as leguminous or non-leguminous plants used for ground cover in various temporal and special configurations used in crop or animal production systems. The purpose of these cover crops is to improve on or more of the following: soil erosion, availability and cycling of N, P, K, Ca and other nutrients, soil moisture and water infiltration, and weed or pest control (Eilitta et al., 2004).. Improvement of animal or human diet may be additional goals. This definition accommodates diverse systems which may include intercrop and sole-cropping systems. In the Eastern Cape Province of South Africa, a government initiative has promoted the growing of winter cover crops in smallholder irrigation schemes (Allwood, 2006). In other parts of Africa, legume food crops have been simultaneously grown with cereal staples to improve both soil cover and human diet (Eilitta et al., 2004). Winter experiments were undertaken in 2007 and 2008 to evaluate biomass accumulation, C and N uptake, weed suppression and response to fertilization. Winter cover crops planted included; oats (Avena sativa), grazing vetch (Vicia dasycarpa), faba bean (Vicia faba), forage peas (Pisum sativum) and lupin (Lupinus angustifolius). After cover crops were terminated, the effects of residues on weeds, fertility, moisture conservation and maize productivity were undertaken in the 2007/08 and 2008/09 summer seasons. Field studies were also done in the 2007/08 and 2008/09 summer seasons to investigate effects of strip intercropping patterns (3:2; 4:2; and 6:2 patterns) of maize (cv. PAN 6479) with mucuna (Mucuna pruriens) or sunnhemp (Crotalaria juncea) on maize productivity and summer cover crop biomass production. In a separate experiment effects of relay intercropping sunnhemp, mucuna and sorghum (Sorghum bicolor) on biomass accumulation and maize productivity were investigated. Decomposition, N and P release from both winter cover crops and summer cover crops were also assessed in laboratory incubation experiments. Oats, grazing vetch and forage peas cover crops produced mean dry mass of 13873 kg/ha, 8945.5 kg/ha and 11073 kg/ha, respectively, while lupin had the lowest dry mass of 1226 kg/ha over the two seasons. Oats responded to fertilization while, there was little or no response from the other winter cover crops. Oats and grazing vetch also reduced weed density by 90 % and 80 % respectively while lupin only reduced weed density by 23 % in relation to the control plots. Nitrogen uptake was 254 kg N/ha for oats while it was 346 kg N /ha for grazing vetch. In the subsequent summer season, grazing vetch and forage pea residues significantly (P < 0.01) improved soil inorganic N. Oat and grazing vetch residues significantly (P < 0.05) reduced weed dry masss and weed species diversity compared to plots with lupin residues and the control. Lack of maize fertilization tended to reduce maize yields but not for maize grown on grazing vetch residues. From an economic perspective, grazing vetch resulted in the highest returns. Decomposition of winter cover crops was much faster for grazing vetch followed by forage peas and lastly oats. Oats had 40 % ash free dry mass remaining after 124 days while grazing vetch and forage peas had 7 % and 16 % respectively. Maximum net mineralized N and P were greater for grazing vetch (84.8 mg N/kg; 3.6 mg P/kg) compared to forage peas (66.3 mg N/kg; 2.7 mg P/ha) and oats (13.7 mg N/kg; 2.8 mg P/kg). In the strip intercropping trials, sunnhemp achieved the highest biomass yield of 4576 kg/ha in the 3:2 pattern while mucuna achieved 1897 kg/ha for the same strip pattern. The 3:2 strip intercropping pattern slightly depressed yields, however, yield reduction was more pronounced in the first season where water stress was experienced. Growing maize on previous cover crop strips failed to increase maize productivity probably due to weed growth during the fallow reducing mineral N in these strips. Decomposition was faster in sunnhemp leaves and mucuna compared to sunnhemp stems. Sunnhemp stems had about 65 % of ash free dry mass remaining after the end of the experiment at 132 days while just over 10 % of mucuna and sunnhemp leaves still remained. Mucuna mineralized 60 mg N/kg and 3.2 mg P/kg and sunnhemp mineralized 45 mg N/kg and 3.5 mg P/kg. Relay intercropping did not significantly (P > 0.05) affect maize biomass and grain yield. Sorghum experienced the largest drop in biomass when relay-intercropped with maize. Mucuna resulted in the highest N uptake (271 kg N/ha) in sole cropping while sorghum had the lowest (88 kg N/ha). Grazing vetch results in high biomass yields with minimal fertilizer application in a warm-temperate climate. Grazing vetch mulch is also the most cost effective mulch for better early weed control, improving soil mineral N status, water conservation and ultimately enhanced maize productivity in smallholder irrigation maize-based systems. The 3:2 pattern maximizes summer cover crop biomass yields compared to the 6:2 and 4:2 patterns. However, the 3:2 pattern may slightly depress yields in a water stressed environment. Relay intercropping mucuna, sunnhemp and sorghum into a maize crop at 42 days after maize sowing has no effect on maize productivity while cover crop biomass yields are low. Having a long winter fallow period after maize harvesting, a common practice in the study area, reduces the positive impact of legume cover crops on soil mineral N. Results suggest that winter cover crops may result in weed control, soil fertility and maize yield improvement benefits while a long fallow period may cancel-out these benefits for summer cover crops. Grazing vetch is a cost effective cover crop that produces high maize yields with minimal fertilizer input. Maize growing on oat mulch requires more fertilizer application than crops growing on grazing vetch mulch. Conservation agriculture systems in which summer cover crops are grown alongside the maize crop with a long winter fallow period do not produce the intended CA benefits.

The objective of the study was to assess the farmers’ knowledge and perceptions of P. incana invasion and impacts on rangeland, livestock production and livelihood in four communal grazing areas. Twenty households per village that own livestock were randomly selected to conduct an interview using an open and closed ended questionnaire. In each household, an old and knowledgeable respondent about P. incana invasion was used as a selection criterion. For scientific assessment of range condition, the experiment was conducted in a 270 m x 100 m trial plots that were established in 2014. The area was divided into 3 open and 3 fenced subplots each having an area of 45 m x 100 m established laid down a slope gradient. Each plot was divided into four equal subplots to apply the control treatments. Therefore, the trial layout was a stratified block experiment of four treatments replicated three times. The four control treatments applied to P. incana invasion were chopping and resting (CR), resting without chopping (RWOC), grazing and chopping (GC), grazing without chopping (GWOC). A step point method was applied in each transect to monitor species composition and P. incana cover. On the fenced plots two exclosures of 1mx1m size were randomly distributed to make sure that resting is maintained. Within exclosures 0.25 m2quadrates in each were put randomly to measure biomass. Density of P. incana was determined from 5 m x 5 m quadrates that were placed randomly within each sub-plot. The density and height of individual shrub plant was measured. All rooted live woody plants were recorded and counted in each quadrate. The results revealed that species composition was not affected (P>0.05) by the treatments applied. The herbage height and basal cover had greater values (P<0.05) under rested plus chopping (CR) treatment followed by grazed plus chopping (GC). Grass biomass production and essential nutrients showed a greater concentration (P<0.05) under CR treatment than any treatments applied. The results on perceptions revealed that goats had the highest mean household holding number than any other livestock species across the selected villages in all the villages. Respondents indicated that both goats and cattle had equal or more importance than sheep. Three out of four villages raised cattle primarily for income generation and secondarily for cultural purposes like slaughtering during weddings ceremonies, amazila and also during woman circumcisions (Ntonjane). Similarly, goats and sheep were primarily raised for cash income generation. The results revealed that livestock population decreased over ten to twenty years (one-two decades) and poor rangeland condition is assumed to be the cause of the situation as feed is the key factor for production. The area was dominated by the grasses rather than by browse woody species so the above results are possible as the P. incana is more competitive than grasses. It was concluded that P. incana is detrimental to both rangeland and animal production. Forage and animal performance as well as farmers’ economic status (livelihoods) were negatively affected by P. incana invasion and the scientific assessment reported it to be detrimental to agriculture. Thus chopping and resting (CR) treatment resulted in a greater improvement of the basal cover, biomass production, soil nutrients as well as grass height than the other treatments applied. Therefore it can be concluded that chopping and resting the veld invaded with P. incana can improve the range and consequently animal production.

Thesis (MScAgric)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Soils of semi-arid regions generally have low organic matter contents, primarily attributed to prevailing climatic conditions. Yet, the spekboom thicket, located in the semi-arid region of the Eastern Cape (South Africa) has been distinguished to accumulate large amounts of soil carbon. To further understand this remarkable accumulation, a detailed investigation was carried out to evaluate the distribution, speciation and stability of the soil carbon from directly beneath spekboom (Portulacaria afra) and other “nonspekboom” vegetation within the intact thicket, and from adjacent, degraded (overgrazed), open thicket sites. In the first experimental chapter, the distribution of organic and inorganic C, as well as general soil properties (pH, EC, exchangeable and water soluble cations, hydrophobicity, water stable aggregates) were investigated in the intact (spekboom and nonspekboom) and degraded (open) thicket soils. There were no significant differences in the C content (organic or inorganic) between the spekboom and nonspekboom sites in the intact thicket. Soil organic carbon (SOC) content however was greatly influenced by thicket degradation, whereas, inorganic C remained unaffected. Mean organic C (0-50 cm) ranged from 19-34, 22-62, and 19-58 g C kg-1 for open, spekboom, and nonspekboom sites, respectively. Whereas, mean inorganic C ranged from 2-9 g C kg-1 irrespective of sites, representing 4-22 % of total soil C. However, no significant differences were detected between degraded and intact sites for all (total, organic and inorganic) C stocks, attributed to variation in bulk density. Spekboom soils contained significantly higher concentrations of exchangeable and water soluble Mg, Na, and K, and consequently had higher pH and EC compared to the other sites. Soils tended to be hydrophobic especially at shallower depths in the intact thicket irrespective of vegetation type, whereas soils from the adjacent open sites were not significantly hydrophobic. Macro-aggregates were considerably more stable under intact sites compared to open sites. The second experimental chapter investigated the effects of degradation and vegetation type on the stability and structural chemistry of SOC. This involved partitioning the soil organic matter into particulate and mineral-bound (stable) fractions, and then examining the relationships between the stable organic C fraction and various soil properties as an attempt to elucidate the stabilization mechanism(s). Particulate organic C ranged from 7.0, 9.3, and 14.4 g C kg-1 for open, spekboom, and nonspekboom respectively; representing 22-34 % of total SOC. Stable (mineral-bound) organic C accounted for the largest fraction ca. 60-66 % of total SOC; 28.0 and 26.2 g C kg-1 for spekboom and non-spekboom respectively, versus 17.2 g C kg-1 for open sites. It was concluded that SOC stability was influenced by the inherent residue quality (recalcitrance) rather than soil properties, attributed to the aliphatic (lipids and waxes) and highly aromatic nature of the spekboom litter substrate and particulate OM. These research findings are of fundamental significance in understanding soil organic matter stabilization in semi-arid environments.
AFRIKAANSE OPSOMMING: Gronde van semi–ariede streke het oor die algemeen 'n lae organiese materiaalinhoud, wat hoofsaaklik aan die heersende klimaatstoestande toegeskryf kan word. Tog, het die spekboomruigtes, geleë in die semi-ariede streek van die Oos-Kaap (Suid Afrika), onderskeidelik groot hoeveelhede grondkoolstof geakkumuleer. Om hierdie merkwaardige akkumulasie verder te verstaan, was 'n gedetailleerde ondersoek uitgevoer om die verspreiding, spesiasie en stabiliteit van die grondkoolstof direk onder spekboom (Portulacaria afra) en ander “nie-spekboom” plantegroei binne die intakte ruigte en van die aangrensende gedegradeer (oorbeweide), oop gras areas te evalueer. In die eerste eksperimentele hoofstuk, is die verspreiding van organiese en anorganiese C, sowel as algemene grondeienskappe (pH, uitruilbare en wateroplosbare katione, hidrofobisiteit, water-stabiele aggregate) was in die intakte (spekboom en nie-spekboom) en degradeerde (oop) ruigtes ondersoek. Daar was geen betekenisvolle verskille in die C-inhoud (organies of anorganies) tussen die spekboom en nie-spekboom gronde in die intakte ruigtes gevind nie. Grond organiese koolstof (GOK) inhoud is grootliks deur die ruigte se agteruitgang beïnvloed, maar anorganiese C-voorrade was egter nie beïnvloed nie. Die gemiddelde organiese C-inhoud (0-50 cm) het van 19-34, 22-62 en 19-58 g C kg-1 onderskeidelik vir 'n oop, spekboom, en nie-spekboom areas gewissel. Die anorganiese C-inhoude het vanaf 2-9 g C kg-1 gewissel, ongeag van ligging, wat 4-22 % van die totale grond C uit maak. Daar is egter geen beduidende verskille tussen vervalle en heel terreine vir almal (totaal, organiese en anorganiese) C aandele opgespoor, toegeskryf word aan die variasie in die massadigtheid. Spekboom gronde het beduidende hoër konsentrasies van uitruilbare en wateroplosbare Mg, Na, en K waardes bevat. Dit het ook hoër pH en EC, in vergelyking met die ander areas gehad. Gronde was geneig om hidrofobies te wees, veral op vlakker dieptes in die intakte ruigte, ongeag van die plantegroei, terwyl die gronde van die aangrensende oop areas nie beduidend hidrofobies was nie. Makro grond aggregate was aansienlik meer stabiel onder intakte ruigtes as in die oop areas. Die tweede eksperimentele hoofstuk het die gevolge van die weiding-geïnduseerde degradasie en tipe plantegroei op die stabiliteit en strukturele chemie van GOK ondersoek. Dit het die skeiding van die grond organiese materiaal in die vrye en mineraalgebonde (stabiele) fraksies behels. Daarna is die verhoudings tussen die stabiele organiese C fraksie en verskeie grondeienskappe ondersoek om die stabiliseringmeganisme(s) uit te lig. Die chemiese aard van die blare, plante oorblyfsels, fyn en minerale gebinde organiese C is met behulp van spektroskopie ondersoek. Vrye organiese C voorraad het van 7.0, 9.3, en 14.4 g C kg-1 vir oop, spekboom, en nie-spekboom onderskeidelik gewissel, wat ongeveer 23-34% van die totale GOK verteenwoordig. Stabiele (minerale gebind) organiese C-voorrade is vir die grootste fraksie ca. 60-66% van die totale GOK verantwoordelik. Dit was 28.0 en 26.2 g C kg-1 onderskeidelik vir spekboom en nie-spekboom, teenoor 17.2 g C kg-1 vir 'n oop area. Die mineraalgebonde GOK het geen noemenswaardige korrelasies met die ondersoekte grondeienskappe getoon nie. Dus is tot die gevolgtrekking gekom dat GOK stabilisering eerder deur die plante oorblyfsel se chemiese kwaliteit beïnvloed word. Strukturele chemiese karakterisering (13C CP-MAS KMR) van die spekboom afval en vrye C fraksie het gewys dat weerspannigheid die mees prominente meganisme van koolstof stabilisering van organiese koolstof in die gronde is. Dit word aan die alifatiese (lipiede en wasse) en sterk aromatiese aard van die spekboom substrate toegeskryf. Hierdie ondersoek het tot die fundamentele kennis van grond organiese materiaalstabilisering in 'n semi-ariede omgewings bygedra.

Arable crop production in Nkonkobe Municipality is low due to abandonment of potentially productive land and low productivity of the cultivated land. Little attention has been given to farmers perspectives with regards to crop production and land abandonment. Understanding the relationships of indigenous knowledge systems, where local approaches to soil classification, appraisal, use and management and land evaluation, and scientific approaches could be important for the effective use of available soil resources while avoiding those resources that are vulnerable to degradation. In addition, the interactions between soil factors and climate could be useful in understanding the erodibility of soils. The intergration of scientific research and indigenous knowledge systems could help in the identification and delineation of high potential land and on crop suitability evaluation. The objectives of the study were: (i) to determine farmers‟ perspectives with regards to land utilisation and abandonment, constraints on crop production and crop preferences, (ii) to integrate and compare indigenous knowledge systems with scientific approaches of soil classification and potential, (iii) to determine the effect of climate and soil factors on erodibilities of soils in the Municipality (iv) to delineate arable land and evaluate its suitability for maize, potato, sorghum and cowpea under rainfed agriculture. Using semi-structured and open-ended interviews, information on limitations to crop production, cropping preferences, indigenous soil classifications, cropping potential ratings and erosion was captured. Descriptive and correlation statistics were used to analyse farmers‟ responses. The information was later used for a pilot participatory mapping and the determination of the agricultural potential of the soils in three selected villages of the Municipality. Field boundaries of soil texture, colour, depth, and slope position were captured using global positioning systems (GPS). The relationship between the degree of erosion and soil and slope factors was analysed by step-wise regression. Crop suitability for rainfed agriculture was done using the FAO guidelines for Land evaluation for rainfed agriculture. The spatially referenced crop suitability classes were produced by applying the Law of Limiting Combinationusing GIS Boolean Logic. The major biophysical factors, affecting crop production and land utilisation were soil degradation and low and erratic rainfall, while other factors included lack of farming equipment and security concerns. Maize, spinach and cabbage were the main crops grown, with maize sorghum and wheat the most abandoned crops. While it was difficult to accurately correlate indigenous classification with international scientific classification, the importance of colour, texture and soil depth for both classification and soil potential, suggests that some form of correlation is possible which enabled communication and other extension information to be conveyed. The shallow and stony soil (urhete) correlated well with the Leptosols in World Reference Base (WRB) or Mispah and shallow Glenrosa soils in the South African system. The red structured clays (umhlaba obomvu) matched the Nitisols in WRB or Shortlands in the South African system. The non-swelling black clayey soils (umhlaba omnyama) matched soils with melanic A horizons in both the WRB and South African soil classification systems. The dongwe and santi soils developed in alluvial sediments belonged to the Dundee, Oakleaf or Augrabies soils in the South African classification system and fluvisols or Cambisols in the WRB system. There was good agreement between farmers assessment of the cropping potential and scientific approaches but scientifically high potential red soils were rated lowly by the farmers due to difficulties in management caused by shortages of farm machinery, especially under dryland farming. Overall, the soil factors affecting erosion were influenced largely by climate, while parent material was also important. Climate had a dominant influence on soil factors most notably fine sand and very fine sand fractions and exchangeable sodium percentage being more important on soil forms occurring in arid and semi-arid climate and less in the sub-humid and humid areas, where clay mineralogy, particularly kaolinite and sesquioxide dominated. Dolerite derived soils were the most stable and should be given the highest priority for cropping development while mudstone and shale derived soils had a lower cropping potential. While slope gradient and length had some effect on soil erosion in arid and semi arid environments its influence was generally overshadowed by soil factors especially in humid zones. Cow pea and sorghum were the most adapted crops in the region while potato and maize were marginally suitable under rainfed agriculture. The study revealed that most adapted crops were not necessarily the most preferred crops by the farmers. A small percentage of the land was delineated as arable and therefore optimisation of this available land should be prioritized.

This study was conducted to determine livestock production, rangeland management and the mineral levels of soils, grass and cattle blood serum in two communal areas (Kwezana and Dikidikana). A total of 77 farmers from both Kwezana and Dikidikana were interviewed to determine farmers’ perceptions. Soil and grass sampling was done at three sites in each communal area. Soil and grass samples were analysed for N, Ca, Mg, K, P, Fe, Cu, Zn, Mn and Bo. Three, two and half year old Nguni heifers were randomly selected from each communal area and blood samples were collected for the analysis of Ca, Mg, K, Cu and Fe. Soil, grass and blood samples were all collected in two seasons (winter and summer). The results of the study revealed that feed availability was the major constraint in livestock production as indicated by 83 percent of thefarmers at Kwezana and 88 percent at Dikidikana. At both villages less than 20 percent practiced supplementation and grazing management. From both villages, 83 percent of the farmers did not know the forage species preferred by their cattle. The second study revealed significant seasonal variations in soil N in both study areas while forage N exhibited seasonal variations (P<0.05) only at Dikidikana. Spatial variation (P<0.05) in soil Mn was apparent in both seasons at Dikidikana and in summer at Kwezana. At Dikidikana forage P varied (P<0.05) both seasonally and spatially. In both study areas, there was a positive correlation (P<0.05) between soil and forage levels of Cu and Zn. The blood serum of animals from both study areas had higher (P<0.05) K and Na in winter than in summer. Farmers do not understand the composition of their rangelands but are concerned about cattle nutrition during winter. Indeed the mineral status of soils, forages and Nguni cattle blood serum tend to vary not only seasonally but also spatially. There is need therefore to assist the farmers to understand these changes in order to find ways of managing the rangelands in a way that will manipulate both seasonal and spatial variations in soil nutrients for the benefit of the grazing livestock. Further research is required to determine the digestibility of the forages and the amount of energy available from these forages for the grazing livestock.

The Palmiet wetlands located along the Kromrivier in the Eastern Cape province of South Africa have experienced severe degradation through gully erosion during the past decennia which has been threatening the water quality and water security of large towns in the Nelson Mandela Metropolitan hub. Water scarcity is a growing problem in this region as a result of land degradation and growing erratic rainfall patterns. The main causes of wetland degradation are argued to be land use and land cover change. With the aim of protecting the wetlands along the Kromrivier a total of eleven large gabion and concrete erosion-control structures were constructed between the 2002 and 2013 by the government initiate Working for Wetlands. This study aims to map the groundwater table in order to derive how erosion-control structures and gully erosion affect groundwater dynamics along the Kromrivier. This was achieved by several steps. Firstly, water table elevations were measured along several transects by installing a series of piezometers which allowed do investigate how the structures affected the water table. This also allowed for a comparison in groundwater dynamics between eroded and non-eroded reaches so that effects of gully erosion could be identified and potential causes discussed. Secondly, the analysis of aerial images allowed for the development of the aerial extent of the Palmiet wetland and gullies to be seen over a ten year period and longitudinal profiles provided specific characteristics of the wetland and gullies. Lastly, particle size distribution and organic matter content were analyzed as groundwater flow and gully erosion can vary greatly depending on soil characteristics. The hydraulic gradient was highest in proximity to the structures as a result of the created potential induced by the drop in surface water elevation. The radius of influence to where the structures were affected the water table was estimated to be approximately 40 m from the channel. Further away from the channel, the gradual slope of the water table indicated that the porous gabion side walls of the structures did not affect the water table. The groundwater flow is determined by Darcy's Law and the relatively flat water table along the non-eroded reaches of site A displayed local drainage points, thereby indicating variations in the local flow direction. In May the water table along the non-eroded reaches was sloping away from the channel resulting in an area of groundwater discharge with respect to the channel. Not only was the water table generally higher during August, the regime had also changed, indicating a potentially large seasonal variability. Along the eroded reaches downstream from the structures the water table was above the gully bottom during both months resulting in an area of groundwater recharge with respect to the channel. Also here the regime had changed from an approximately constant hydraulic gradient sloping towards the channel during May to a water table with a divide in flow direction. Since their implementation in 2003, the structures have been effective with respect to preventing the headcut in the main channel from migrating further upstream. However, the gullies downstream of the structures had significantly increased in width between 2003 and 2013 and the Palmiet wetland had also slightly decreased in size during the same period. However, it was unclear whether this decrease was part of the longer term ongoing trend or part of a shorter term cycle and/or seasonal fluctuation. For a gully bank to collapse, the shear strength of the slip surface needs to be exceeded and this often occurs because of an increase in pore water pressurewhich causes a reduction in shear strength. A large gully height of up to 4 m with nearly vertical slopes, a water table above the gully bottom and an increase in moisture content between May and August indicated that it is not unlikely that a high pore water pressure. played a significant role in the slumping of the gully walls. The two structures together were responsible for an surface water elevation difference of 7.76 m. Through damming this resulted in an elevated water table in the upstream Palmiet wetland, thereby increasing the saturation and promoting diffuse flow across the wetland. However, the structures also trap most of the sediment in upstream direction which appears to have resulted in the de-stabilization of the downstream streambed at site A as these eroded reaches now receive a significantly lower sediment load. By increasing the retention volume in the wetland, the structures also facilitated in ensuring flood retention as the wetland could now hold more water during high flows, thereby cutting off the peak flow. As gully erosion is known to occur during periods of high flow it is not unreasonable to argue that slumping of the gully walls would have been more severe without the structures in place. In this sense the structures increase the water quality and decrease the flux of sediment where the latter leads to a decrease in the sedimentation rate of the downstream Churchill Dam. Consequently, this contributes to securing the fresh water supply to towns in the Nelson Mandela Metropolitan hub. The discovery of Palmiet rests up to 2.6 m below the surface indicated that cycles of gully erosion followed by the re-establishment of Palmiet have been occurring in this valley for thousands of years. However, it seemed that land use and land cover changes had accelerated gully erosion during the past decades resulting in a loss of Palmiet wetland at a rate which was beyond 'natural'. Even though the structures could be seen as disruptions of long term natural cycles, they are in favor of the well-being of mankind as they protect the wetlands to a certain extent. The main results of this study provided a basic understanding of how the water table behaves in response to the structures and along eroded and non-eroded reaches of the Kromrivier. Furthermore, this study discussed the larger scale affects of the structures and showed how the gullies and the aerial extent of the Palmiet wetland have evolved since the implementation of the structures in 2003. In order to manage these Palmiet wetlands more effectively in the future, it is highly important that groundwater dynamics, gully erosion and the size and health of the wetland are annually monitored in order to get a more accurate idea of how effective these structures are. This new obtained knowledge could also assist in managing other peat lands in South Africa more effectively.

Communal rangelands occupy 13 percent of the agricultural land in South Africa, and these rangelands serve as a source of feed to livestock. These areas are threatened by bush encroachment due to poor rangeland management. This study was conducted in Alice (Sheshegu communal area) and the objective was to assess farmers' perceptions and the impact of bush encroachment on herbaceous vegetation and soil nutrients. Structured questionnaires were used to assess indigenous knowledge of communal farmers on the impact of bush encroachment on rangelands. Fourty (40) respondents from households who owned livestock were randomly selected and interviewed at Sheshegu village. About 89 percent of communal farmers perceived that change of their grasslands to encroached savannas was caused by unreliable rainfall, prolonged drought, and poor rangeland management. Rangeland assessment was performed at four sites (Scattered, Moderate, Mixed and Dense bushland. 100mx50m were demarcated per site, and four 100m transects were laid parallel to each other, 30m apart. The step point method was used to determine both species composition and basal cover. Biomass production was determined by harvesting forage within randomly-paced a 0.25m2 quadrats. Aristada congesta and Eragrostis obtuse were the most dominating grass species in dense, mixed and moderate bushland. Scattered bushland was dominated by Themeda triandra. Biomass production increases with increase in bush density and basal cover improved from winter to summer season. Increaser grass species increase with the increase in bush density, this indicated that the rangeland was poorly managed and palatable species were being replaced by less palatable ones. Species composition of woody plants was determined within a 200m2 belt transect in all sites. Maytenus polycantha, Aloe ferox, Erehia rigida and lucas capensis were the most dominant woody species in Mixed bushland while Acacia karroo was most dominated in Scattered, Moderate and Dense bushland. Woody density showed no significant differences (P> 0.05) between Dense, Mixed and Moderate bushland. Woody plant density in all these sites exceed 2500 plants/ha, which showed that the rangeland was encroached with woody plants. Soil nutrient content was determined for each site. Five samples of soil were collected per site to test the effect of bush encroachment on soil nutrient composition. The concentration of nitrogen and soil pH increased with increase in bush density, while that of potassium, phosphorous, magnesium, sodium and sulphur showed no significant differences (P>0.05) across all homogenous vegetation units. The study revealed that Sheshegu communal farmers are aware of both negative and positive effects of encroachment on their community, and also argue that the government is not willing to support communal farmers in the process of reducing the spread of bush encroachment. It was concluded that the concentration of nitrogen and soil pH increased with increasing bush density and that bush encroachment had negative effects on herbaceous species. It was recommended that communal farmers should be formulating rangeland rules and regulations to manage rangeland resources. Rangeland rules and regulations should be based on the management of livestock management during grazing and harvesting of rangeland resources. The harvesting of woody and good timing of application of fire can also reduce the spread of bush encroachment. Veld resting and rotational grazing can also improve fuel load which is required for burning of woody plants. Furthermore, Department of agriculture should also provide workshops or training to communal farmers use different approaches or cheap ways of reducing bush encroachment and conserving rangeland resources.

Extensive areas of the Eastern Cape Province have been invaded by Pteronia incana (Blue bush), a non-palatable patchy invader shrub that is associated with soil degradation. This study sought to establish the relationship between the invasion and a range of eco-physical and land use gradients. The impact of the invader on soil moisture flux was investigated by comparing soil moisture variations under grass, bare and P. incana invaded surfaces. Field based and laboratory spectroscopy was used to validate P. incana spectral characteristics identified from multi-temporal High Resolution Imagery (HRI). A belt transect was surveyed to gain an understanding of the occurrence of the invasion across land use, isohyetic, geologic, vegetation, pedologic and altitudinal gradients. Soil moisture sensors were calibrated and installed under the respective surfaces in order to determine soil moisture trends over a period of six months. To classify the surfaces using HRI, the pixel and sub-pixel based Perpendicular Vegetation Index (PVI) and Spectral Mixture Analysis (SMA) respectively were used. There was no clear trend established between the underlying geology and P. incana invasion. Land disturbance in general was strongly associated with the invasion, as the endemic zone for the invasion mainly comprised abandoned cultivated and overgrazed land. Isohyetic gradients emerged as the major limiting factor of the invasion; a distinct zone below 619mm of mean annual rainfall was identified as the apparent boundary for the invasion. Low organic matter content identified under invaded areas was attributed to the patchy nature of the invader, leading to loss of the top soil in the bare inter-patch areas. The area covered by grass had consistently higher moisture values than P. incana and bare surfaces. The difference in post-rainfall moisture retention between grass and P. incana surfaces was significant up to about six days, after which a near parallel trend was noticed towards the ensuing rainfall episode. Whereas a higher amount of moisture was recorded on grass, the surface experienced moisture loss faster than the invaded and bare surfaces after each rainfall episode. ii There was consistency in multi-temporal Digital Number (DN) values for the surfaces investigated. The typically low P. incana reflectance in the Near Infrared band, identified from the multi-temporal HRI was validated by field and laboratory spectroscopy. The PVI showed clear spectral separability between all the land surfaces in the respective multi-temporal HRI. The consistence of the PVI with the unmixed surface image fractions from the SMA illustrates that using HRI, the effectiveness of the PVI is not impeded by the mixed pixel problem. Results of the laboratory spectroscopy that validated HRI analyses showed that P. incana’s typically low reflectance is a function of its leaf canopy, as higher proportions of leaves gave a higher reflectance. Future research directions could focus on comparisons between P. incana and typical green vegetation internal leaf structures as potential causes of spectral differences. Collection of spectra for P incana and other invader vegetation types, some of which have similar characteristics, with a view to assembling a spectral library for delineating invaded environments using imagery, is another research direction.

It is imperative to understand the strong coupling between the carbon capture process and water use to sustainably manage rangelands. Woody encroachment is undermining rangelands grass production. Evapotranspiration (ET) highlights the links between ecosystem carbon capture process and water use. It forms the biggest flux of the hydrological cycle after precipitation yet it is not well understood. The Grassland and the Albany Thicket (AT) biomes in the Eastern Cape, South Africa, provide an interesting space to study the dynamics in rangelands biomass production and the associated water use. Therefore, the main purpose of this study was to contribute towards management of rangelands by understanding the dynamics in rangeland grass production and water use. To achieve this aim, the impact of Acacia mearnsii, an invasive alien plant, on soil chemical properties and rangelands grass production was investigated. This was achieved by analysing the biophysical attributes of A. mearnsii as they related to grass production. Secondly, selected soil variables that could be used as a prognosis for landscape recovery or deterioration were evaluated. In addition, aboveground grass biomass was measured in areas cleared of A. mearnsii and regression equations were prepared to help model aboveground grass biomass in areas cleared of A. mearnsi. The thesis also explored dynamics in water vapour and energy fluxes in these two biomes using an eddy covariance system. Consequently, water vapour and energy fluxes were evaluated in order to understand landscape water use and energy partitioning in the landscape. The study also tested the application of Penman-Monteith equation based algorithms for estimating ET with micrometeorological techniques used for validation. Pursuant to this, the Penman- Monteith-Leuning (PML) and Penman-Monteith-Palmer (PMP) equations were applied. In addition, some effort was devoted to improving the estimates of ET from the PMP by incorporating a direct soil evaporation component. Finally, the influence of local changes in catchment characteristics on ET was explored through the application of a variant of the Budyko framework and investigating dynamics in the evaporative index as well as applying tests for trends and shifts on ET and rainfall data to detect changes in mean quaternary catchment rainfall and ET. Results revealed that A. mearnsii affected soil chemical properties and impaired grass production in rangelands. Hence, thinning of canopies provided an optimal solution for enhanced landscape water use to sequestrate carbon, provide shade, grazing, and also wood fuel. It was also shown that across sites, ET was water limited since differences between reference ET and actual ET were large. ET was largely sensitive to vapour pressure deficit and surface conductance than to net radiation, indicating that the canopies were strongly coupled with the boundary layer. Rangeland ET was successfully simulated and evaporation from the soil was the dominant flux, hence there is scope for reducing the so-called ‘unproductive’ water use. Further, it was shown that the PML was better able to simulate ET compared to the PMP model as revealed by different model evaluation metrics such as the root mean square error, absolute mean square error and the root mean square observations standard deviation ratio. The incorporation of a soil evaporation component in the PMP model improved estimates of ET as revealed by the root mean square error. The results also indicated that both the catchment parameter (w) and the evaporative index were important in highlighting the impacts of land cover change on ET. It was also shown that, despite changes in the local environment such as catchment characteristics, global forces also affected ET at a local scale. Overall, the study demonstrated that combining remote sensing and ground based observations was important to better understand rangeland grass production and water use dynamics.

Two ant species, Pheidole megacephala (Fabricius) and Anoplolepis custodiens (Smith) reach pest status in citrus orchards through precipitating outbreaks of homopterous pests. However, predacious ants, including these two ant species, play an important role in pest suppression in agroecosystems and are therefore beneficial to these systems. If A. custodiens and P. megacephala are important natural control agents in citrus, using ant bands to break the mutualism between the ants and the Homoptera as a method of ant control is preferable to poisoning. Ant communities were sampled by pitfall trapping in three experimental subunits of 2-, 4-, 15- and 30-year-old citrus orchards, in the Grahamstown area of the Eastern Cape. In one subunit in each orchard, populations of P. megacephala and A. custodiens were suppressed by poison applications. In a second subunit, trees were banded with trunk barriers so that ants were prevented from foraging in the trees and a third subunit served as the untreated control. Bait pupae of bollworm, false codling moth and fruit fly were planted in bait trays in all of the subunits to investigate predation on these citrus pests in the relative absence of predacious ants and where they were excluded from the trees. Pheidole megacephala dominated exclusively in all of the plots. Community composition did not change dramatically with increasing age of the trees, but species diversity and species abundance did. Rank-abundance curves showed that community diversity was highest in the 2-year-old plots and lowest in the 30-year-old plots. The Simpson and Shannon-Wiener diversity indices and their evenness measures indicated that diversity and equitability were highest in the poisoned subunits and lowest in the banded subunits. Principle component analysis revealed that the poisoned subunits were similar and distinct in species composition, that there was significant monthly variation in species composition and that community stability increases with an increase in orchard age. The presence of P. megacephala was significantly negatively correlated (rs = -0.293; p < 0.001) with pest pupal survival. Pupal survival was significantly higher for bollworm (p < 0.001), FCM (p < 0.001) and fruit fly (p < 0.001) in the poisoned subunits, than in the banded and control subunits. There was a general trend for survivorship to increase with an increase in the age of the trees. A significant difference (p < 0.001) was found between the months in which the trials were carried out. Pupal survival was significantly lower (p < 0.001) for FCM than for bollworm and fruit fly. In citrus orchards, ant communities are organised by ecological processes and interactions and are influenced by methods of ant control. Ant bands are preferable to poisoning as a method of ant control, so that beneficial species are left on the ground to prey on pests that pupate in the soil. Maintaining high ant species diversity in citrus orchards would be beneficial as predation on the pupae was more effective where ant species diversity was higher.

Species which play particularly important roles in ecosystem patterns and processes are recognised as keystone species or ecosystem engineers. The conservation of these species is critical for the maintenance of the ecological role they play in ecosystem function. The aardvark, Orycteropus afer, is known to play a role in biopedturbation through digging for refuges and for prey, and as a consequence of these digging activities is expected to serve the role of an ecosystem engineer and keystone species. This study aimed to describe and quantify the ecological patterns and processes driven by the aardvark through their digging activities, within the eastern Karoo, and thereby evaluate the significance of aardvarks as ecosystem engineers and keystone species in a semi-arid environment. The landscape pattern (dig abundance and distribution) and soil displacement of aardvark forage and refuge digs in a semi-arid Karoo landscape, as well as the ecological processes (generating fertile, seed retention hotspots) driven by aardvark forage digs was measured. Refuge digs occurred in the highest densities in areas characterised by a specific suite of soil, vegetation and elevation features, while forage digs occurred in high abundance in most habitats measured, and were likely driven by prey availability. Forage digs served as litter and seed retention hotspots, with accelerated decomposition rates of litter as a function of increased soil moisture in digs. The functional processes (i.e. resource capture, shelter for plants and animals, germination sites, soil aeration, organic turnover, mineralization rates, fertile soil displacement and transport) driven by aardvark digs are not restricted to refuge digs. Forage digs occurred in most habitats measured and their functional role is unique and perhaps greater across the landscape in comparison to refuge digs. The aardvark has a disproportionate effect in ecosystems, in terms of its refuge and forage digs relative to its abundance and therefore its role as a keystone species and ecosystem engineer is confirmed. Conservation and protection of this species is therefore essential to maintain its important role in ecosystem function.

This study investigated the vegetation and soil characteristics in relation to distance from water points under different land management systems in semi-arid rangelands of South Africa. Six study sites, two each from communal grazing, commercial farming and game reserves were selected. Two watering points were selected in each study site. Two 500 m transects were laid from the selected watering points. Each transect was divided into sub-transects at 25 m, 50m, 100m, 200m, 300m and 500m from water points. A 100 m2 plot was marked in each sub-transect to record grass biomas, species composition, structure and distribution of woody vegetation and physical and chemical soil properties. Data were collected for two seasons 2012/13 (winter and summer). Thirty and 41 grass and woody species respectively were identified in all study areas. The most common and dominating grass species include Cynodon dactylon, Digitaria eriantha, Eragrostis obtusa, Setaria sphacelata and Sporobolus fimbriatus. Cynodon dactylon and S. sphacelata occurred more abundantly (p < 0.05) in the game reserves than in the other land management catergories. All the grass species had similar (p > 0.05) abundance along distance gradient from water points. Grass dry matter (GDM) showed significant differences (p < 0.05) between and within land management systems. However, GDM was not significantly affected by season, location of water point within each farm or reserve and distance along water points. Acacia karoo, Coddia rudis and Ehretia rigida were the most dominant woody species. Tree equivalent (TE) density of all encroaching woody plants combined was significantly (p < 0.05) higher on the communal area (1732 TE ha-1) than the commercial ranches (1136 TE ha-1) and game reserves (857 TE ha-1), but with no marked variations along distance from water points under all the land management systems. The electric conductivity (EC) was significantly (P < 0.01) higher in game reserves than in communal grazing areas and ranches. Soil organic matter percentage showed greatest and lowest values in the game reserves and commercial respectively. Soil pH and bulk density did not vary but soil organic matter (SOM), EC, bulk density and soil compaction were significant different with no increasing or decreasing trends. Soil properties were affected by herbivore pressure and trampling around water points with inconsistence magnitude and direction. In conclusion, grass species composition and GDM did not respond to distance from water points because either grazing gradient was absent or the length of transects was not enough to explain the absence or presence of gradients. High proportion of A. karoo and high densities of seedlings and saplings would seem as very good indicators of the woody vegetation changes in the different land management systems and distance from water points. The soil quality indicators around the water-points showed that livestock and game affected soil parameters.

Studies of the dunefield systems crossing the Cape St. Francis headland in the Eastern Cape have focused on the role that wind plays in sediment transfer in coastal dunefield systems, with limited consideration of the role of water. The aim of this study was to improve understanding of the morphology, processes and patterns within the Oyster Bay HBD system, focussing particularly on surface water and groundwater interactions and the role of surface water in sediment transfer across the dunefield system. An extensive field survey was conducted, to collect related data, complimented by spatial and temporal analysis of the study area using GIS. The key findings from this research were the apparent differences between the western and eastern regions of the dunefield with regard to specific drivers and the respective processes and responses. Wind is the major driver of change up to and across the crest of the dunefield. In the eastern region water (ground water, surface water and the Sand River System) is the primary agent of sediment flux through processes of aggregation and slumping as well as episodic events including debris flows. This study has highlighted a need for further quantitative studies that investigate the movement of sediment through dunefield systems such as this (where water is at or near the land surface). The paradigm that sediment flux is entirely due to wind is almost certainly simplistic, and deeper understanding of these systems is needed
Maiden name: Elkington, Lauren

Bibliography: leaves 140-151.
The Swartland and Sandveld are situated in the Western Cape province (political limits) in what is also known as the southwestern Cape region . This area falls within the winter rainfall (or Mediterranean) region of South Africa and has a sharply defined seasonal climate. Vegetation in the region is unique. The soils in the Swartland and Sandveld vary greatly over short distances, making this area vulnerable to varying erosion rates. Land use in the Swartland and Sandveld is mainly agricultural. Soil erosion is driven by the force of wind and or water. Sheet flow is what is considered as unconstrained water erosion together with rainsplash, while piping, rill and gully erosion are all forms of constrained water erosion. Erosivity and erodibility are both important factors in determining the vulnerability of an area to soil erosion. By their understanding of the factors involved in the course of degradation, researchers can determine the most effective conservation policies for a region. Of course, the influence of humans on the land should never be under-estimated and should be seen as a potent determinant of the erosion potential. The use of remote sensing and G.I.S. are essential in the development of erosion maps, and to assess possible changes that over time in the erosional situation in a region. As an analytical and data storage tool, these techniques are very useful, even essential. The total decrease in gully erosion from 1938 to 1989 in the Swartland amounts to 85% compared to the gully erosion in 1938. In the Sandveld wind erosion decreased with 17% from 1928 to 1986. Soil conservation in South Africa has come a long since the 1930's and much of the experience and the lessons gained in the last six of seven decades have been incorporated in the countries new conservation Act. It has been concluded that the slowing down of the denudation process in the region, coinciding with effective new conservation strategies, are the principal reasons for the results obtained in this research project. It must be noted however that without the intervention of the conservation efforts in the Swartland and Sandveld, the remarkable improvement in the water erosion situation (85%) would not have been obtained. The overall improvement (17%) in the Sandveld lags that in the Swartland and even shows a slight deterioration of the wind erosion situation found in 1974. There are therefore grounds for caution, since wind erosion is still very much relevant and not fully contained in the Sandveld. Further research into this situation would indeed be beneficial.

The goal of this study was to determine the nature and factors influencing smallholder farmers in their adoption decision-making regarding the use of soil conservation practices introduced by extension practitioners in South Africa, using the case of farming at Qamata Irrigation Scheme, Eastern Cape. Using a central argument (thesis statement), the study argued that an adequate understanding and definition of smallholder farmers’ adoption decision-making process is very crucial to solving the problem of soil erosion/ degradation problem amongst smallholder farmers. Adopting the case study research design, information from 70 crop farmers (in a farmer focus group interviews) form the basis of the study. Basic models of analysis were the multiple, probit and logit, as well as the binary logistic regression analyses. According to the empirical results, perception was found very relevant in adoption decision-making, interacting positively and significantly with eight of the seventeen adoption variables chosen for the study. The indication therefore is that age (p<0.050), education (p<0.0030), and marriage (p<0.036), have more potentials to improve farmers’ perception. Similarly, higher farmer incomes (from crops [p<0.017], off-farm [p<0.038] and overall [p<0.011] income) also have a likelihood to improve farmers’ perception regarding soil conservation, for improved adoption. Further indication is that farmers who are aware (p<0.015) of the soil practices introduced by extension are also those who participate in their use (p<0.041). Employing the binary logistic, probit and logit regression models, results suggest that the nature of adoption decision-making processes of smallholder farmers is complex (not straight), being influenced by multiple factors. While age (p<0.099), gender (p<0.031), total income (p<0.081) impacted positively significant on smallholder farmers’ adoption decision-making, marital status (p<0.025), sources of land (p<0.063), length of continuously farming on same piece of land (p<0.013), and level of crop production (p<0.002) impacted negatively. The indication therefore was that older farmers preferred their own practices to the recommended practices by extension, which is in line with literature. Also as expected, more females preferred their own practices to extension recommended, while more males preferred the recommended practices. Similarly, marriage, land ownership, farming continuously on a spot for a long period, as well as increase in the level of crop production, all had a propensity to influence farmers toward the adoption of extension recommended practices as against farmers’ practices. Further results indicate, that farmers’ education (p<0.032), household size (p<0.37), and income (off-farm [p<0.036] and total [p<0.004]), measures used to measure farmers’ livelihood standards in the study, were positively significant in association with adoption. The indication was that, adoption decision-making is potentially capable of improving education level of farmers; increase the size of household, thus providing easy family labour; and as well improve level of income for the farmer. Based on the foregoing, the suggestion therefore is that any technology intervention programme that will succeed must begin with a clear understanding and analysis of farmers’ adoption process. This is better achieved when the adoption process is seen as a four-stage process, where the farmer first forms a view about the innovation (perception stage), and then decides whether or not to use it (adoption stage), as well as how much of the innovation to adopt (level of adoption stage), and finally how much is this innovation going to affect my livelihood (impact of adoption stage). Also, due to the particular relevance of perception in the adoption decision-making process, technology disseminators (extension), researchers and policy makers alike must never conclude on the rejection of any technology, not until factors determining perception of individuals have been well studied. The notion here is that, even at the confirmation stage of the adoption process of an individual adopter, when a rejection is confirmed, for an example, analysing factors of the adopter’s perception at play at the particular time of the innovation in question, could go a long way to redirecting the course of the adoption process of the said individual.

This study was conducted in the old arable land located in Lushington communal area in the Eastern Cape province of South Africa. The objectives of the study were to assess the effect of legume introduction on biomass yield, forage and soil mineral levels of the arable lands planted to four leguminous pastures in four seasons. Planting was done in March and October 2008 in Lushington. All legumes were subjected to grow under rain fed conditions. Trifolium vesiculosum (arrowleaf clover), Lespedeza cuneata (sericea lespedeza), Trifolium repens (white clover) and Lotus corniculatus (birdsfoot trefoil) are the four forage legume species that were sampled for the purposes of this study. The four legume species persisted out of the fourteen species that were initially tested for adaptability and persistence in the environmental conditions of Lushington communal area. The legumes, grasses and soils from these legume plots were sampled to determine the effect of legume introduction on the forage yield, mineral contents of the companion grasses and soils over four seasons. Plant and soil samples were collected once in spring (November) 2013, summer (February), autumn (March) and winter (May) 2014 for biomass production, macro and micronutrients determination. Results indicated that legume inclusion and season affected (P < 0.05) the total dry matter (TDM) yield production. Plots with Lespedeza cuneata had the highest TDM (1843 kg/ha) and control plots had the least dry matter production (1091 kg/ha). Summer season provided the highest (P < 0.05) TDM compared to the other seasons. Both legume and grass quality was also affected (P < 0.05) by legume inclusion in different seasons. Accordingly, grasses harvested from Trifolium repens plot showed higher CP level (10.90 percent) than those harvested from other plots whereas the lowest grass CP content (6.90 percent) was measured in the control treatment. L. cuneate had the highest (P < 0.05) CP level (11.00 percent) and T. repens had the least CP (6.63 percent) level. Grasses harvested in autumn had the highest (P < 0.05) CP level (12.50 percent) and those harvested in winter had the least CP level (4.60 percent). Similarly, all legume pastures harvested in spring had superior (P < 0.05) CP (10.80 percent) levels and those harvested in winter had the least CP (3.50 percent) level. Legume inclusion had an effect (P < 0.05) on both grass and legume macro nutrient contents. Trifolium repens plot had the highest grass K (1.07 percent), Ca (1.50 percent) and Mg (1.83 percent), whereas there were lower K (0.12 percent), Ca (1.25 percent) and Mg (1.08 percent) contents in grasses harvested from the control and T. vesiculosum plots, respectively. In legumes, macro nutrient concentrations: K (0.68 percent), Ca (1.75 percent) were superior in the T. vesiculosum plot in comparison to other plots. Season also affected (P < 0.05) both grass and legume macro nutrient content. There was higher K (0.90 percent), Ca (1.30 percent) and Mg (0.94 percent) content in grasses harvested in autumn whereas there were lower levels in winter harvests. In legumes, superior K (0.74 percent) and Mg (1.87 percent) content were attained during spring while the least were measured in winter (0.07 percent) and autumn (0.75 percent), respectively. Likewise, both legume inclusion and season had an significant effect (P < 0.05) on the forages micronutrient levels. During spring, there was superior soil P content (36.28 mg/kg) while during autumn; there was less P (22.58 mg/kg) content. The highest SOC level (1.49 percent) was measured in the T. repens plot whereas the lowest SOC (1.15 percent) was attained in the control plot. The results of this study showed that grass legume mixtures produced forages with high nutrient content and herbage yield. Legume planting in the old arable lands has a potential to improve soil quality parameters such as soil P and SOC content.

Albany thicket is prevalent in the Eastern Cape Province of South Africa. Its spread has diminished through overgrazing and heavy browsing by animals, land clearance and urban expansion. The result is highly degraded land characterized by invasion of alien species. There is a wealth of documented evidence on the high carbon sequestration ability of thicket biome, but not much has been done to assess its effect on carbon dioxide emissions from the soil. Given that the concentration of atmospheric greenhouse gases has been constantly rising since the industrial era, it is imperative to assess the influence of thicket biome as a source or sink of these gases. There is evidence of shifts in the climate in southern Africa as reflected by changes in rainfall patterns, increased temperatures, recurrent droughts and fires. As such, the historical rainfall variability in an Albany thicket region and its interaction with the temporal land use / cover changes was studied. This served to give some background information about the study area for more detailed study on C and carbon dioxide effluxes in thicket vegetation under different levels of degradation. This study thus aimed to determine the influence of thicket vegetation at various levels of degradation on soil carbon and carbon dioxide fluxes. The impact of plant photosynthetic pathway on soil C residence time and gas effluxes were analysed to elucidate on the land-use and cover patterns occurring in the area. All this was done to shed some light on the role of soil and thicket vegetation on carbon dioxide emissions and C storage in the spectrum of a shifting climate. The main area of research was Amakhala reserve in an Albany thicket in Eastern Cape Province; and it concentrated on three land cover types namely intact thicket, degraded thicket and grassland. The objectives mentioned above were achieved by assessing historical rainfall variability from 1970 to 2010 through trend and time series analysis at nine rainfall stations located at Amakhala reserve, Grahamstown, Bathurst, Port Alfred, Uitenhage and Port Elizabeth. The land use changes that have occurred in the Albany thicket region covering Amakhala reserve, Grahamstown, Bathurst and Port Alfred were also assessed for 1989, 1999 and 2009 through satellite image analysis with Idrisi Andes GIS software; then their interaction with rainfall variability were determined. To elucidate on the vegetation species composition and land use / cover changes that have occurred in the study area, plant biomass as well carbon (C) and nitrogen (N) isotope measurements were done. Plant biomass was assessed for the dominant species through use of pre-existing allometric equations that required data on plant basal diameter, canopy area, stem numbers and height. The plant carbon was then estimated through use of a conversion factor of 0.48 on above-ground biomass, while soil organic C was determined through the modified Walkely - Black method. Carbon and N isotope ratios were determined from the foliar material of three replicate samples of dominant plant species then analyzed through mass spectrometry. Soil carbon dioxide effluxes were then monitored in each of the intact thicket (IT), degraded thicket (DT) and grassland (G) over a 10 month period; by measuring the net carbon dioxide exchange rate (NCER) through the dynamic chamber method. An automated carbon dioxide exchange analyzer, coupled to a soil temperature probe and photosynthetic active radiation (PAR) sensor was used; with NCER measurements taken every 20-30 days. Soil temperature, moisture, penetration resistance and PAR readings were taken during each assay and later used to interpret the NCER. Results showed that long term variability in annual rainfall had a declining trend at Grahamstown (r = -0.59), Uitenhage and Bathurst stations (r = -0.32 at both stations), but was not significant at Amakhala, Port Alfred and Port Elizabeth stations. Most reductions in rainfall occurred in the 1980s and 1990s with the autumn, winter and summer rainfalls, the daily rainfall index and the daily rainfall subclasses of 10 mm and above showing a similar trend. The land use change detection gave a significant increase in proportion of degraded and transformed (moderately degraded) land between 1989 and 2009 with most of the increases occurring from 1989 to 1999, while farmland area decreased by 1.8 percent over the years. Thus the Albany region had over 30 percent of its land occupied by transformed vegetation, with heavy browsing and uncontrolled grazing being attributed to the destruction of pristine vegetation. Land-use change to game ranching and goat pastoralism was attributed to the reduction in farmland. Rainfall variability – land use change linkages were most significant in 1999 that recorded the least rainfall and had the lowest mean, maximum and sum of the NDVI. Grahamstown had the most significant rainfall-NDVI trends as it had the lowest NDVIs in 1999 when rainfall was lowest, the highest NDVI in 1989 when rainfall was highest and moderate NDVIs in 2009 when rainfall was moderate. Vegetation at the IT was characterized by a dense thicket with diverse growth forms of canopy trees, woody shrubs, succulent shrubs and ephemerals which mostly had the C3 type of pathway. This was in contrast with the IT soil isotopy that showed more positive C isotope ratios, indicating a switch between C3 and CAM photosynthesis in original vegetation. Most of the canopy trees had disappeared in the DT to be replaced by herbs, shrubs and grasses. As such, there was a huge difference in isotope ratios between DT plants and soils with the plants having mostly C3 metabolism while the soil showed a predominance of CAM plants in previous vegetation, indicating significant changes in land cover. The G site mostly comprised the grasses Themeda triandra and Panicum maximum and a few herbs. It maintained a dominance of C4 metabolism in both plants and soils showing very little change in species composition over the years. Because of the higher species diversity at IT, its soil organic C was quite high reaching levels of 3.4 percent (i.e. 3.4 t C / ha) in the top 10 cm then decreasing with depth (p < 0.001); but was moderate at DT (1.1-1.3 percent) and very low at G ( 0.5 percent C) (p < 0.001). In the same manner above-ground biomass was highest at IT i.e. 330 000 kg/ha; but was only 22 000 kg/ha in DT and as low as 6 700 kg/ha in G vegetation. High biomass at IT was mostly attributed to the succulent shrub Portulacaria afra and the canopy trees Euclea undulate, Rhus longispina and Schotia afra. This above-ground biomass translated to biomass C amounts of 158 000 kg/ha at IT, 10 600 kg/ha at DT and 3 200 kg/ha at G. Thus the IT had the highest while G the least and DT moderate plant and soil C sequestration ability. In all, the conversion of IT to DT led to a net loss of 147 000 Kg of biomass C / ha and 12 000kg less organic C / ha of land. Soil carbon dioxide effluxes were however variable between seasons as they were affected by differences in soil properties and seasonal weather patterns. High soil moisture levels (up to 16 percent gravimetric moisture) resulted in reduced soil penetration resistance (1 to 4 Kg/cm2) which raised effluxes at G and DT sites (up to 1.2 μmols m-2 sec-1) in winter, while low moisture (2 percent) resulted in hard dry soil (14 Kgm-2 penetration resistance) with suppressed CO2 effluxes in spring (0.2 μmols m-2 sec-1) especially in DT and G soils. Rising temperature generally caused accelerated gas emissions but only when moisture was not limiting (as was the case in IT). Thus the high summer temperatures (up to 40oC) gave lower effluxes especially in DT and G (< 1 μm-2sec-1) due to limited moisture supply (< 10 percent); while the Autumn period that had very high temperature (up to 48 oC) and good moisture (up to 16 percent) saw accelerated soil CO2 emissions (averaging 2 μmols m-2 sec-1) from all cover types. The high biomass and litter fall at IT served as ready substrate for soil respiration as long as moisture was not limiting and temperatures were favourable, while reduced cover at DT resulted in poor moisture conservation and creation of hard dry soils in spring and summer with reduced respiration. It was concluded that the DT had high CO2 effluxes in winter and reduced emissions in summer; while the opposite was true for the IT. All the cover types had minimal CO2 effluxes in spring and accelerated emissions in autumn. The grassland on the other hand was a fairly moderate source or sink of CO2 in most seasons compared with the other two covers. It was observed that an environment of good moisture and low-moderate temperatures (such as that in the winter) minimises effluxes while maintaining good plant productivity. It was concluded that thicket vegetation is a good sink of carbon that should be preserved in its natural condition to optimize its carbon sequestration potential. All three land covers served as sources or sinks of CO2 depending on soil and seasonal conditions. Thus high moisture and low penetration resistance generally increased effluxes of thicket ecosystems. The effect of increasing temperature on effluxes was only significant when moisture was not limiting. Conditions of good moisture and low-moderate temperatures gave reasonable amounts of effluxes while maintaining good plant productivity. Though the dry soil conditions significantly reduced effluxes in all land covers; they were not desirable since they decreased plant productivity and ultimately its C sequestration potential. Moreover, prolonged dry conditions only serve to exacerbate recovery of thicket plants as they increase mortality of canopy species in degraded and transformed areas in comparison with intact thicket.

The Kompanjiesdrif basin is an unchannelled valley bottom palmiet wetland located near the headwaters of the Kromrivier in the Eastern Cape of South Africa. The wetland itself is underlain by Bokkeveld shales with the bordering mountain ranges comprising more resistant Table Mountain Group quarzitic sandstones. The valley is relatively planar and broad in form over a width of approximately 200 m. None of the existing controls that are considered to lead to valley widening and longitudinal slope reduction are immediately apparent. The basin lies on the Post Africa II erosion surface; with no evidence of a resistant lithology which might act as a local base level, limiting rates of vertical erosion and inducing lateral planing in upstream reaches via a meandering channel. The possible role of sagging of the basin due to long term deep chemical weathering of bedrock is discounted as the lithologies in the basin are sedimentary in origin and thus not susceptible to chemical weathering. The degree to which climate and sea level changes affected rates of incision and subsequent slope reduction is unclear, although their potential influence should be acknowledged. This study examined the geomorphic dynamics as discerned from the sedimentary record and morphology of the wetland basin, which provide a snapshot into the long-term processes which lowered the longitudinal slope and widened this valley. Coring within the wetland to depths of 1 - 3.3 m revealed that the sedimentary fill generally comprised an upward fining sequence, with sand or fine sand at the base, grading into silt and clay and organic material in the upper sections of cores. Occasional instances of multiple fine sand layers were observed in a few of the cores. An increase in the organic content of material from the north to the south side of the wetland and the occurrence of multiple thin layers of sand in the stratigraphy, highlighted the role of the northern tributary alluvial fans in influencing valley form. Sediment from north bank alluvial fans seem to periodically, partially impound the wetland basin. Surveyed transects across the wetland basin along with subsurface coring to the depth to refusal, illustrated a localised increase in longitudinal slope downstream of the nodes of tributary alluvial fan deposits, which impinge on the trunk stream basin. Coupled with the presence of deep, drowned, trench-like features (up to 8 m deep) beneath floating mats of palmiet, which were predominantly free of sedimentary fill and found opposite tributary alluvial fans; confirmed that the northern tributaries play a major role in the structure and geomorphic dynamics of the basin. The trench-like features appeared to be remnants of deep, narrow, discontinuous gullies. Dating of sediment from the base of these features (460-7040 BP) confirmed that they were formed prior to European settlement in the area. Therefore, it is suggested that the localised increase in longitudinal slope, caused by sediment deposition on the alluvial fans, transgresses a geomorphic threshold slope and that gully erosion is thus initiated. The process of repeated gully erosion leads to planing of bedrock and longitudinal slope reduction. Gully erosion forms an integral component of a cycle of deposition and incision referred to as “cut-and-fill”. During each iteration of the cycle of cutting and filling, gullies form in novel locations leading to gradual valley widening. Over geological time scales, the planing of bedrock and resultant valley widening creates a broad planar valley with a very low longitudinal slope; producing conditions suitable for unchannelled valley bottom wetland formation.

Some cyanobacteria strains have biofertilization and bioconditioning effects in soils. The objective of this study was to identify cyanobacteria with potential to improve the N fertility and structural stability of degraded soils and evaluate their effectiveness in soils of the Eastern Cape, South Africa. Isolation and characterization of the indigenous cyanobacteria strains with desirable properties was first to be undertaken because their effects are known to differ from strain to strain. Cyanobacteria strains 3g, 3v, and 7e were identified from 97 strains isolated from selected soils. Nostoc strains 3g and 3v had greater ability to produce exocellular polysaccharides (EPS) but low potential to fix atmospheric N2 (4.7 and 1.3 nmol C2H4 μg chl-1 h-1, respectively). On the other hand, strain 7e had the highest capability to fix atmospheric N2 (16.1 nmol C2H4 μg chl-1 h-1) but had the least ability to produce EPS. Evaluation of the strains was done in glasshouse studies starting with Nostoc strain 9v isolated from a Tanzanian soil, followed by the indigenous strains isolated from soils in Hertzog and Qunu, South Africa. Inoculation was done by uniformly applying cyanobacteria on the surface of potted soils at a rate of 6 g m-2. First harvest and soil sampling took place after six weeks, and the top 25 mm of the soil was mixed, replanted, and sampled again after a further six weeks (second harvest). Inoculation with Nostoc strain 9v increased soil N by 40 percent and 17 percent in Guquka and Hertzog soils, respectively, and consequently increased maize dry matter yields by 40 and 49 percent. Soil C increased by 27 percent and 8 percent in Guquka and Hertzog soils, respectively, and this increase was significantly associated with that of soil N (R2 = 0.838). Higher contents of soil C, soil N and mineral N, however, were found in non-cropped soils. Scanning Electron Microscopy (SEM) revealed coatings of EPS on soil particles and fragments of non-cropped inoculated soils, with iii other particles enmeshed in networks of filaments, in contrast to cropped and/or non-inoculated soils. The proportion of very stable aggregates was increased by inoculation but cropping with maize reduced the aggregate stability. Inoculating Hertzog soil with indigenous strains 3g and 7e increased the nitrate N in the first cropping by 49 percent and 69 percent respectively, in cropped soils. In the second cropping increases in mineral N were 41 percent and 43 percent in 3g and 7e inoculated soils, respectively. Maize dry matter yields were higher on inoculated soils both in the first and second harvest in response to the improved N status of the soil. Increases in aggregate MWD in cropped soil as determined by fast wetting, mechanical breakdown and slow wetting were 85 percent, 33 percent, 33 percent, respectively, for 3g inoculation, 64 percent, 41 percent, and 41 percent, respectively, for 7e inoculation and 60 percent, 24 percent, 50 percent for inoculation with 9v. In non-cropped soil, increases in MWD as determined by fast wetting, mechanical breakdown and slow wetting were 11 percent, 0 percent, 7 percent, respectively for 3g inoculation, 21 percent, 11 percent, and 7 percent, respectively for 7e inoculation, and 25 percent, 36 percent, and 19 percent for strain 9v inoculation. Scanning electron microscopy observations, which were confirmed by chemical results, revealed that inoculated soils had high EPS and filaments that encouraged soil aggregation and improved aggregate stability. Results of this study show that cyanobacteria strains isolated and selected for their ability to fix atmospheric N2 and produce EPS improved the fertility status and aggregate stability of degraded soils from South Africa.

Fire is generally used as a management tool for different vegetation types such as savannas and grasslands in southern Africa. In the False Thornveld of the Eastern Cape, fire is commonly used to control bush encroachment and to increase grass production, as grasses are important source of forage for domestic livestock. At the University of Fort Hare farm in the Eastern Cape, a trial was set up in 1980 to investigate the effect of burning frequency on vegetation. There are six treatments replicated twice in a completely randomized design on a 100 m x 50 m plots. The treatments comprise no burn, annual, biennial, triennial, quadrennial and sexennial burns. From this trial a study was conducted to investigate long term effect of burning frequency on species and soil seed bank diversity. Two 100 m line transects located 25 m apart were laid within each plot, and the herbaceous and woody species were identified and recorded along the line transects. Relative abundances (%) for each species were calculated for each treatment. Soil samples were collected at an interval of 13.3 m along the line transects. The samples were placed in paper bags and kept for use in a germination experiment. The seedling emergence germination method was used in the glasshouse to determine emerging seedlings, pots were filled with Hygromix growth medium and the soils from the fire trials 12 X 6 = 72 were spread on top. Soil from the control plots were also pre-treated with heat, smoke and the combination of heat and smoke. The experiment started in January 2010 and was terminated in April 2010. The Shannon-Weaver Diversity Index was used to determine species diversity for standing vegetation and germinated seedlings. Data were tested for normality and species abundances were transformed. Analysis of Variance (ANOVA) was applied to test treatment effects on geminated seedlings, species abundance and diversity at α = 0.05 significance level. Significant differences between treatment means were determined by post v hoc tests using Fischer‟s Least Significant Difference test at α = 0.05. The Pearson Moment Correlation test was used to test the relationship between vegetation and soil seed banks. Treatments had significant effects on herbaceous, woody species abundance and diversity (P < 0.05), but there was no significant treatment effect on soil seed bank diversity and on pre-germination treatments (P > 0.05). The annual, biennial and triennial burns were dominated by Themeda triandra while the quadrennial, sexennial and the control treatments were dominated by Sporobolus fimbriatus and Melica decumbens. A. karroo dominated the woody component across all treatments, but it did not change in abundance. S. fimbriatus was the most abundant in the soil seed bank across all the treatments and also in all pre-germination treatments. Species diversity was high in standing vegetation in the quadrennial, sexennial and the control treatments. There was no significant correlation between the standing vegetation and soil seed bank diversities (P > 0.05). Based on these findings it is apparent that fire can change vegetation in an area to be dominated by fire tolerant or fire intolerant species. Fire frequency, heat and smoke affects soil seed banks to a lesser extent in the False Thornveld. For the management of the False Thornveld of the Eastern Cape, less frequent burning is recommended as it increases aboveground species diversity.

This study is based on assessing the potential use of GIS and Remote Sensing in trying to fill the various soil maps of selected regions at different scales with spatial soil data. A variety of processes are available for use. These include band ratios, principal component analysis as well as use of a digital elevation model (DEM). With the advent of GIS and Remote Sensing, these principles in the new niche of study are investigated to check if they can be used to augment the current processes available in soil mapping techniques. Such processes as band ratioing, principal component analysis and use of Digital Elevation Models (DEMs) are investigated to check if they can be used in soil mapping techniques. From the results produced it is evident that these processes have the potential to be used in the Digital Soil Mapping process. Despite the limitation of remote sensing to a few centimetres of the topsoil these processes can be used together with the soil mapping techniques currently being used to come up with soil maps.

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.

False codling moth (FCM), Thaumatotibia leucotreta is an extremely important pest of citrus in South Africa and with the shift away from the use of chemicals, alternate control options are needed. One avenue of control which has only recently been investigated against the soil-borne life stages of FCM is the use of entomopathogenic fungi (EPF). In 2009, 12 entomopathogenic fungal isolates collected from South African citrus orchards showed good control potential during laboratory conducted bioassays. The aim of this study was to further analyse the potential of these isolates through concentration-dose and exposure-time response bioassays. After initial re-screening, concentration-dose response and exposure-time response sandconidial bioassays, three isolates were identified as exhibiting the greatest control potential against FCM in soil, Metarhizium anisopliae var. anisopliae (G 11 3 L6 and FCM Ar 23 B3) and Beauveria bassiana (G Ar 17 B3). Percentage mycosis was found to be directly related to fungal concentration as well as the amount of time FCM 5th instar larvae were exposed to the fungal conidia. LC50 values for the three isolates were not greater than 1.92 x 10⁶ conidia.ml⁻ₑ and at the LC₅₀, FCM 5th instar larvae would need to be exposed to the fungus for a maximum of 13 days to ensure a high mortality level. These isolates along with two commercially available EPF products were subjected to field persistence trials whereby net bags filled with a mixture of autoclaved sand and formulated fungal product were buried in an Eastern Cape citrus orchard. The viability of each isolate was measured on a monthly basis for a period of six months. All isolates were capable of persisting in the soil for six months with the collected isolates persisting far better than the commercially used isolates. Two of the isolates, G 11 3 L6 and G Ar 17 B3, were subjected to small scale laboratory application trials. Two formulations were investigated at two concentrations. For each isolate, each formulation and each concentration, FCM 5th instar larvae were applied and allowed to burrow into the soil to pupate before fungal application or after fungal application. Contact between fungi and FCM host is essential as, in contrast to pre-larval treatments, percentage mortality in post-larval treatments was low for both formulations and both isolates. For isolate G Ar 17 B3, a conidial suspension applied as a spray at a concentration of 1 x 10⁷ conidia.ml⁻ₑ obtained the highest percentage mortality (80 %). For isolate G 11 3 L6 however, both formulations performed equally well at a high, 1 x10⁷ conidia.ml⁻ₑ concentration (conidial suspension: 60 %; granular: 65 %) The results obtained thus far are promising for the control of FCM in citrus, but if these EPFs are to successfully integrate into current FCM control practices more research, some of which is discussed, is essential

The degradation of soil quality due to undesirable farming practices has reached alarming scales in the Eastern Cape and this has had negative repercussions on soil productivity and the environment in general. There is growing evidence that conservation agriculture (CA) practices involving minimal mechanical disturbance, maintaining permanent surface cover and embracing diverse crop rotations increase soil organic carbon (SOC) and therefore has potential to mitigate soil quality deterioration. A study was carried out at two sites located in two ecotopes to investigate the effects of crop residue retention and crop rotations in a no till system on overall soil quality using the Soil Management Assessment Framework (SMAF) as the soil quality assessment tool. The CA study trials were laid out in 2012 at two different locations, one at the Phandulwazi Agricultural High school within the Phandulwazi Jozini ecotope and the other one at University of Fort Hare Research Farm within the Alice Jozini ecotope. The experiment was laid out as a split-split plot arrangement in a randomized complete block design with three replicates. Tillage treatments were applied on the main plots while crop rotation treatments were applied as subplots. Crop residue retention treatments were applied as sub-sub plots. The rotational treatments were maize-fallow-maize (MFM), maize-fallow-soybean (MFS), maize-wheat-maize (MWM) and maize-wheat-soybean (MWS). The initial assessment of the overall soil quality of the two ecotopes using the SMAF soil quality index (SQI) revealed that the soils at the Alice site were functioning at 80% while the soils at the Phandulwazi site were functioning at 79 percent of their optimum capacity. The slight difference in the soil quality of the two ecotopes could be attributed to their different soil organic C contents where the Alice Jozini ecotope had significantly higher soil organic C contents than the Phandulwazi Jozini ecotope. After 3 years of continuous treatment application, crop residue retention significantly improved most of the measured soil quality parameters. Generally across the sites, more soil organic C, microbial biomass C (MBC), ß-glucosidase (BG) activity, mineral N, extractable P and K, Cu, Zn, Mn, Fe, and macro-aggregates were recorded in treatments where crop residues were retained. Crop rotations alone did not have a significant impact on most of the measured soil quality indicators. The crop rotations influenced significantly the availability of mineral N across the two sites, highlighting the importance of using a legume in rotations on available N for the subsequent crops. Most of the measured soil attributes were not significantly influenced after 3 years of continuously applying combined treatment of CA components. Mineral N (NO3 + NH4), K, Zn and Fe were significantly impacted on by the interactions of CA components at the Phandulwazi site, while N, Cu, Zn and Mn were significantly increased at the Alice site. Low response of SOC to combined CA treatments in the short-term prompted the need to examine treatment effects on individual soil carbon fractions. The interaction of crop rotation and residue management techniques were significant on the fine particulate organic matter – C fractions and microbially respired C. These soil C fractions were more sensitive to short-term treatments of combined CA components than SOC and MBC, therefore they can be used as short-term indicators of CA effects on SOM. Soil organic carbon, MBC, extractable P and K, soil pH, EC, b, AGS (aggregate stability) and BG activity were measured and the Soil Management Assessment Framework (SMAF) used to calculate soil quality index (SQI) values for each treatment. The combination of the crop rotations with crop residue retention showed the potential to significantly improve SQI values in the long term. The highest soil quality improvement at both sites was achieved by the maize-wheat-soybean (MWS) rotation with crop residue retention.

Wetland degradation in the form of channel incisioning can significantly alter the hydrological functioning of a wetland. In this study in a small headwater wetland in the Hogsback area, Eastern Cape Province, the impact of channel incisioning on soil water levels and soil morphology was examined. A good correlation (R2 = 0.89) exists between the depth of channel incisioning and average water table depths in most of the 21 installed piezometers. In localised cases the upslope supply of water was in equilibrium with drainage from the piezometers. Although all the studied soils show hydromorphic characteristics, those continuously saturated close to the surface exhibit redox accumulations in oxygen supplying macropores, whereas gleyic colour patterns occur deeper in soils where the water table has been lowered by channel incision. The nature and occurrence of different hydromorphic soil indicators observed confirm the contribution of soil morphology as a valuable indicator of long-term average soil water conditions. The study evaluates the effects of hydrological processes on plant species composition and distribution in a Hogsback wetland. Twenty-four circular plots with a radius of 2 m were established between March and August 2013. Within each sample plot, the habitat information and species present were recorded including Braun-Blanquet cover-abundance value for each and every species present in the plot. Plant species were identified in the field and the unknown plant species were collected, pressed, oven-dried and identified at the National Herbarium, South African Biodiversity Institute (SANBI), Pretoria and Schonland Herbarium, Rhodes University, Grahamstown. A total of 39 taxa belonging to 19 families and 34 genera were recorded from the Hogsback wetland. Of the documented taxa, three were exotic and three endemic to South Africa, indicating diversity and dynamic nature of Hogsback wetland flora. Plant families with the highest number of species were: Poaceae (11 species), Asteraceae (5 species), Onagraceae and Cyperaceae with 3 taxa each. The low number of exotic plant species in Hogsback wetland (three taxa in total) indicates limited anthropogenic influence. Unique species recorded in Hogsback wetlands are three species that are endemic to South Africa, namely, Alchemilla capensis, Helichrysum rosum and Lysimachia nutans. Five main floristic associations were identified from the Hierarchical Cluster Analysis whilst Detrenched .Correspondence Analysis (DCA) identified four groups. The Canonical Correspondence Analysis (CCA) indicates that edaphic factors, particularly in an area covered with water, erosion category, organic matter content and water table depth were the most important environmental variables measured accounting for the vegetation pattern present in the Hogsback wetland.

Mycobacterium bovis and other species of Mycobacterium tuberculosis complex (MTBC) can result to a zoonotic infection known as Bovine tuberculosis (bTB). MTBC has members that may contaminate an extensive range of hosts, including wildlife. Diverse wild species are known to cause disease in domestic livestock and are acknowledged as TB reservoirs. It has been a main study worldwide to deliberate on bTB risk factors as a result some studies focused on particular parts of risk factors such as wildlife and herd management. The objectives of this study were to design questionnaires from commercial farms and smallholding farms; isolate and identify MTBC from collected samples using culture and PCR assays recovered from Fort Hare, Middledrift and Seven star dairy farms; and assessing genotypic drug resistance through detection of mutations conferring resistance to INH and RMP associated with first line treatment for MTBC infection. Questionnaires were administered to thirty (30) smallholding farm owners in the two villages (kwaMasele and Qungqwala) and three (3) three commercial farms ( Fort Hare dairy farm, Middledrift dairy farm and Seven star dairy farm). Detection of M. tuberculosis complex was achieved by Polymerase Chain Reaction using primers for IS6110; whereas a genotypic drug resistance mutation was detected using Genotype MTBDRplus assays. Nine percent (9%) of respondents had more than 40 cows in their herd, while 60% reported between 10 and 20 cows in their herd. Relationship between farm size and vaccination for TB differed from forty one percent (41%) being the highest to the least five percent (5%). The highest number of respondents who knew about relationship between TB cases and cattle location was ninety one percent (91%). Approximately fifty one percent (51%) of respondents had knowledge about wild life access to the farms. Relationship between import of cattle and farm size ranged from nine percent (9%) to thirty five percent (35%). Cattle sickness in relation to farm size differed from forty three (43%) being the highest to the least three percent (3%); while thirty three percent (33%) of respondents had knowledge about health management. Respondents with knowledge about the occurrence of TB infections in farms were forty eight percent (48%). The frequency of DNA isolation from samples ranged from the highest forty five percent (45%) from water to the least twenty two percent (22%) from soil. Fort Hare dairy farm had the highest number of positive samples forty four percent (44%) from water samples; whereas Middledrift dairy farm had the lowest positive from water, seventeen percent (17%). Twelve (22%) out of 55 isolates showed resistance to INH and RMP that is, multi-drug resistance (MDR) and nine percent (9%) were sensitive to either INH or RMP. The mutations at rpoB gene differed from 58% being the highest to the least (23%). Fifty seven percent (57%) of samples showed a S315T1 mutation while only 14% possessed a S531L in the katG gene. The highest inhA mutations were detected in T8A (80%) eighty percent and the least was observed in A16G (17%). The results of this study reveals that risk factors for bTB in cattle and dairy farm workers is a serious issue abound in the Eastern Cape of South Africa; with the possibility of widespread dissemination of multidrug resistant determinants in MTBC from the environment.

There are apprehensions that genetic modification of maize with Bacillus thuringiensis (Bt) may have negative effects on soil biodiversity, ecosystem processes and functions. This study aimed at determining the effect of Bt maize crop, Bt maize residues and its genetic modification on microbial biomass carbon (MBC), selected enzyme activities, vesicular arbuscular mycorrhizal (VAM) fungi and N and P release patterns. The study was conducted under field, glasshouse and laboratory conditions. In 2010/2011 season, four maize cultivars; DKC 61-25B (Bt), DKC 61-24 (non-Bt), PAN 6Q-321B (Bt) and PAN6777 (non-Bt) were planted. Determination of MBC, enzyme activities and fungal spore count was done at 42, 70, and 105 days after planting (DAP). A loam soil amended with Bt or non-Bt maize leaf residues from a study of 2009/2010 season was incubated to investigate effects of Bt maize residues on MBC and soil enzyme activities. Leaf residues of Bt and non-Bt maize cultivars (DKC 61-25B, DKC 61-24, PAN 6Q-321B and PAN6777) were used and soil without residues was used as a control. Samples were collected at 7, 28 and 56 days of incubation (DOI). An incubation study was also carried out in the laboratory to determine the effect of Bt maize residues (i.e. leaf, stem and root) and its genetic modification on N and P release patterns. Residues of DKC 61-25B, DKC 61-24, PAN 6Q-321B and PAN6777and soil without residues as a control were incubated in the laboratory. After destructive sampling at 0, 7, 14, 28, and 56 DOI, N in the form of NH4-N and NO3-N and P mineralisation were determined. Amendment of soil with residues enhanced MBC (p < 0.05) at all the sampling dates. For example MBC increased from 95 in the control to 146.3 mg/kg in the DKC 61-25B treatment at the end of the glasshouse trial. In the field DKC 61-25B had 9.1 mg/kg greater MBC than DKC 61-24, while PAN 6Q-321B had 23.9 mg/kg more MBC than PAN6777 at the end of the trial. However, no differences (p < 0.05) were observed in enzyme activities under field and glasshouse conditions except for dehydrogenase that had greater activity where DKC 61-25B and PAN 6777 were grown. There were no differences between the type of residues (Bt and non-Bt) on enzyme activities tested. However, differences were observed among the sampling dates. No effects of Bt maize crop on fungal spore count were observed. Similarly no differences were observed in leaf, stem and root tissues composition between Bt and non-Bt maize cultivars. Net N and P mineralisation from Bt maize cultivars did not differ from that of non-Bt maize cultivars. However, differences were observed among the cultivars. The results of this study suggested that Bt maize with Bt MON810 event can be grown in the central region of the Eastern Cape (EC), South Africa without affecting MBC, soil enzyme activities, VAM, and release of N and P nutrients from its residues.

This study is concerned with the physical and human causes of soil. erosion. Some quantitative information on the magnitude of soil erosion for different ecoregions in South Africa is available. However, such quantitative data is available only from a few sites. One objective of this thesis is to add to the existing data. Site specific data is provided for the two study areas in the Eastern Cape Province, namely, Chani area in Mt Frere and Brooks Nek area in Mt Ayliff. A comparison is made between the physical and chemical characteristics of the soils found in both study areas. The spatial and temporal extent of the erosion problem is also given. Another major objective is to evaluate the soil rehabilitation measures used at these two areas. An evaluation of the relevance and efficiency of the erosion control measures is made. (For gully erosion especially, the present study provides an evaluation of the suitability and effectiveness of the gully control mechanisms adopted.) Most importantly, a third objective of this study is to investigate the awareness and attitudes of the members of the communities affected by the erosion problem. Among the many different factors found to be important in the causal nexus that results >f in soil erosion, it has been found that many of the problems originate from social causes, like that of too large a population for the limited available resources. Added to this, factors like poor development programmes, bad agricultural practices, bad road management, have exacerbated the erosion problem. In other words, from research and interviews conducted in the study areas, erosion problems linked to recent political policies; to farming and to other practices were found to be associated, inter alia, with the shortage of land, unemployment, the lack of the necessary farming equipment, overgrazing and so on. To stress the point, the five important factors contributing to erosion were identified as an over exploitation of the land resource for basic needs, bad road management, floods, drought, and concentrated flow on furrows made by both on and off-road vehicles. We noted that another important feature of this thesis is to give an account of the psychological attitudes of individuals living near the areas affected by erosion, Respondents to interviews and to questionnaires generally agree that there has been a lot of change in their natural and man-made environments, especially in terms of gully development and vegetation reduction. However, there is a disturbing level of ignorance concerning the causes and consequences of erosion. When asked to estimate the date of gully initiation in Brooks Nek, for instance, none of the respondents could give even rough estimates or a specific incident leading to the current dominant erosion problem. The general attitude towards the problem in their midst was one of indifference. The general belief is that erosion is caused not by themselves but by natural phenomena. Further, most respondents thought it is someone else's (e.g. government's) responsibility to ameliorate the harmful consequences associated with land deterioration and soil loss. The data for this thesis have been obtained through surveying the landscape directly over a three-year period (1994-6), and by using aerial photographs for 1982 (Mt Frere site) and 1993 (Mt Ayliff site). Detailed analysis was undertaken of chemical and physical characteristics of soil at both sites. In addition, quantitative and qualitative surveys of people in the area were attempted; to ascertain their understanding and contribution to the problem. The implications, as shown from the results of this investigation, are that the soil erosion problem at both study areas are largely independent of soil characteristics. On the contrary, this study will show that human practices are the major initial causes for soil erosion in all the cases investigated. It was found that over the years, the land use practices in both sites have changed significantly. Factors accelerating the development of erosion forms at Brooks Nek, for instance, include the footpaths and stock trails. In contrast, artificial contouring and poor gabion layout are the major causes in Chani. However, it must be mentioned that it is not always easy to separate the effects of human from natural causes. Once the effects of human activities exceed the optimum limits of soil resistance and resilience, erosion starts. Then erosion acceleration will not necessarily be confined to the original cause(s). Natural storms and floods, or even drought will contribute in accelerating the erosion rates.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg as a requirement for the Degree of Master of Science. Johannesburg, 1992.
The effect of sodium on clays dominates the formation and ecology of granitic eatenas in the Eastern Transvaal Lowveld. This study reviews the process involved and explains the soil, vegetation and erosion patterns in this landscape. Weathering parent rock gives rise to sodium in sufficient amounts to promote clay dispersion. Dispersed, mobile, clays respond to seasonal pulses of laterally moving soil water resulting in alternating zones of clay illuviation and clay deposition down hillslopes [Abbreviated Abstract. Open document to view full version]
AC2017

Advances in hillslope hydrology have been numerous in the past two decades. However many of these advances have been highly site specific in nature, without identifying any means of linking processes across different spatial scales. Meaningful Prediction in Ungauged Basins (PUB) requires the understanding and observation of processes across a range of scales in order to draw out typical hydrological controls. Contempory tracer based methods of quantifying a combination of hillslope processes have identified hillslope geology as the main determinant in different catchment response types. A range of hillslope scale models have been developed in the last 20 years, using different levels of detail to simulate hillslope hydrological responses. Often the data heavy requirements of hillslope scale models make them impractical to apply at larger scales. While catchment scale models lack the ability to represent hillslope scale processes. In order to overcome this, a scale applicable model with the ability to represent hillslope and catchment dynamics is required to accurately quantify hillslope and catchment hydrological processes. This study aims to characterize typical hillslope soil type responses through inferring qualitative hillslope descriptions into a numerical catchment scale model allowing for lateral subsurface routing between adjacent soil horizons. Hydrometric and tracer observation are used to describe and quantify dominant hillslope hydrological processes. Simplifications of hillslope process descriptions are used to calibrate the model to represent the subsurface hillslope connectivity. Results show that hillslope scale hydrological process characteristics can be faithfully simulated with quaternary scale climate, land use and soils data, discriminating only between different hillslope soil types. The simplification of hillslope soils into three distinct groups allows for the further derivation of dimensionless descriptors of hillslope hydrological response using the Advection Dispersion Function. Slopes with shallower stratified soils showed rapid responses to rainfall in the soil water, while those with deeper soils and less horizontal stratification showed appreciably slower responses to rainfall, with older hillslope water dominating soil water for longer periods. This identifies soils as a dominant determinant in hillslope runoff characteristics. This allows for the characterization and ultimately a simplified classification of different hillslope soils and their response types, which is applicable at a range of scales.
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.