Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2005. / The seven evergreen Disa species are indigenous to South Africa. These orchids grow on mountain ranges subject to winter rainfall and are found on stream banks, around waterfalls and in other damp areas. Although the Disa genus accommodates more than 130 species, by far the most commonly grown is Disa uniflora and hybrids stemming from this species. Disas have great potential as cut flowers and pot plants, but production techniques need to be further investigated since cultivation methods vary greatly between hobbyists. This study evaluated the effect of N-source, shading, root medium temperature, electrical conductivity (EC), irrigation method, foliar feeding at different plant growth stages and substrate on the growth of evergreen Disa hybrids in a controlled environment. Results showed that Disa plants can be classified as being ammonium tolerant. Disa unidiorosa performed best with 40% of the applied N in the NH4 form, while D.kewensis was more tolerant towards a higher level of NH4 and grew best at 60% NH4. Shading levels (56% and 69%) were compared and did not differ regarding the growth of plants. A cooled root medium was found to have a negative effect on root growth and a positive effect on leaf length. High EC levels produced heavier mother plants with a bigger root:shoot ratio and a bigger stem diameter. Biomass accumulation was the best in plants receiving ‘Drip’ irrigation, compared to ‘Ebb-and-Flood’ irrigation treatments. Plants in the vegetative reproducing stage were more susceptible to leaf abscission and new leaves formed at a low rate compared to small- and potential flowering plants. Where foliar feeding is concerned plants seemed to benefit more by the presence of NH4NO3 than urea. There were no significant differences in root development between substrates in the ‘hardening-off’ phase. ‘Hydroton’ (clay pebbles) was not suitable as substrate for the cultivation of Disa plants. The growth and flowering properties of plants were optimal with sphagnum moss and peat but were negatively affected when the pH of acid peat:sand mixtures were increased. More research is needed before Disas can be cultivated on a commercial scale, while the effect of the treatments on flowering properties has to be investigated.

Thesis (MScAgric (Agronomy))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: See full text for the abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MScAgric)--University of Stellenbosch, 2000 / ENGLISH ABSTRACT: Approximately 7000 ha of potatoes are cultivated under irrigation. The greatest part of the planting is entered under the South African Certification Scheme as seed potatoes, representing between 35 and 40 % of seed production in South Africa. The production of high-quality tubers is, therefore, in the interest of the entire country. Some production factors in the area, however, have a very negative influence on quality with a resultant increase in input costs. These factors include mainly low clay content of the soil «5 %), low organic matter content (% C = 0,2 to 0,4 %), a low pH value as well as a high level of chlorides (400 mg.kg") in the irrigation water. Nitrogen conversion as well as uptake can be influenced by these factors. There may also be negative influences on the environment if leaching of nitrates to subterranean water sources is involved, which can pose a threat to sensitive protected areas. Leaching of various nutritional elements occurs as a result of the low clay content of the soils. Over-irrigation or intense thundershowers could lead to the leaching of nearly all of the fertilisers from these soils. Various management aids are therefore needed to facilitate the decision-making process for corrective steps. Soil, leaf or total-plant analyses are possible, but it is a time-consuming process and the results could become available too late to be of any use. Consequently, the development of methods to determine the nutritional element status of plants on the land and the establishment of norms are both essential. A method which has been tried on a wide scale with varying results is the use of the nitrate content of the petiole, which is determined by means of a reflectoquant and nitrate strips. To evaluate the sensitivity of the method two sites in the Sandveld have been selected. A trial planting has been established at Wadrift and information was also obtained from a leaching trial at Sandberg. The cultivars Up-to-Date and Hertha were established in four nitrogen treatments (100, 200, 300 and 400 kg N.ha-1 ), and repeated over two seasons. At Sandberg irrigation was applied at three application levels and three fertigation divisions for one season. Drip irrigation was applied in both cases to enable the accurate distribution of water and fertilisers during the planting season. Petiole samples were taken weekly or every second week in all the trials. The first mature leaf was sampled (about 20 to 30 leaves per plot). During the initial planting at Wadrift nitrate N in petiole sap (measured by means of nitrate strips and a reflectoquant) was compared to nitrate N of dried petioles measured with an auto-analyser. In all test cases a good correlation was found. The readings from the auto-analyser were about 14.5 times higher than the readings from the petiole sap as a result of moisture loss during the drying process. A better correlation was obtained during the second season when the petiole sap was used for strips as well as the auto-analyser. The petiole nitrate content was increased by high N application rates and the 400 kg N.ha-1 treatment showed significant differences from the other N treatments. A substantially higher yield was obtained during the last season. Varying results were obtained regarding specific gravity for cultivars and nitrogen treatments. At Sandberg (1998) over-irrigation lowered the nitrate content of the petiole sap significantly. It was found that the optimum irrigation level and frequency, is two fertigations a week and kept at field water capacity. From the trial it was clear that the use of nitrogen strips in combination with the reflectoquant gave a good indication of the nitrate-N content of the petiole sap. It is, however, difficult to lay down a norm or critical range, as conditions during the growth period on sandy soil as well as the growth stage have a significant influence on the nitrate-No If yield is the only objective the 400 kg N.ha-1 curve can probably be used as an optimum nitrate-N norm for the particular cultivars. It is also not clear whether the nitrate N content of the petiole sap gives a good reflection of growth and yield potential. / AFRIKAANSE OPSOMMING: In die Sandveld word bykans 7000ha aartappels onder besproeiing verbou. Die grootste deel van die aanplanting word as saadaartappels onder die Suid-Afrikaanse sertifiseringskema ingeskryf en verteenwoordig tussen 35 en 40% van Suid Afrika se saadproduksie. Die produksie van hoë kwaliteit knolle is dus van landsbelang. Somminge produksiefaktore van die area het egter 'n uiters negatiewe invloed op kwaliteit en het 'n meegaande verhoging van insetkostes tot gevolg. Faktore wat veral hieronder tel is die grond se lae klei inhoud «5%), lae organiese materiaal inhoud (%C = 0.2 tot 0.4%), lae pH asook hoë chloriede (400mg.kg-1 ) in die besproeiingswater. Hierdie faktore kan 'n invloed op die omsetting van stikstof en die opname daarvan hê. Daarmee saam kan dit 'n negatiewe effek op die omgewing hê indien loging van nitrate na ondergrondse waterbronne plaasvind wat sensitiewe bewaarareas kan bedreig. Weens die lae klei-inhoud van die gronde vind loging van verskeie voedingselemente plaas. Oorbesproeiing of hewige reënbuie kan tot gevolg hê dat bykans alle bemestingstowwe uit hierdie grond geloog word. Bestuurshulpmiddels is dus nodig om die besluitnemingsproses vir korrektiewe stappe te vergemaklik. Grond-, blaar- of hele plantontledings is moontlik maar is tydrowend en resultate daarvan kan soms te laat beskikbaar wees. Die ontwikkeling van metodes om die voedingselement inhoud van plante op die land te bepaal en die daarstelling van normes is dus noodsaaklik. 'n Metode wat reeds wyd deur ander navorsers met wisselende resultate beproef is, is die gebruik van nitraat inhoud van die petiool wat met 'n reflektoquant en nitraat strokies bepaal is. Om die sensitiwiteit van die metode te evalueer is twee proefpersele in die Sandveld gebruik. 'n Proef is by Wadrift geplant terwyl data ook van 'n logingsproef te Sandberg verkry is. By Wadrift is die kultivars Up-to-Date en Hertha by 4 N-behandelings (100, 200,300 en 400 kg N.ha-1) en vier herhalings vir twee seisoene aangeplant. By Sandberg is besproeiings teen drie toedingspeile met 3 sproeibemestingsverdelings vir een seisoen gedoen. In alle gevalle is van drupbesproeiing gebruik gemaak om akkurate plasing van water en bemestingstowwe oor die plantseisoen moontlik te maak. Petiool monsters is weekliks of tweeweekliks van alle behandelings geneem. Die eerste volwasse blaar is gemonster en daar is tussen 20 en 30 blare per perseel geneem. Tydens die eerste planting te Wadrift is nitraat-N in petioolsap, gemeet met nitraatstrokies en reflektoquant, vergelyk met nitraat-N van gedroogde petiole, gemeet met In outo-analiseerder. Hierdie waardes was goed gekorreleerd vir alle gevalle wat getoets is. Die outo-analiseerder se lesing was ±14.5 keer hoër as die petioolsap lesings weens die vog wat tydens droging verwyder is. Tydens die tweede seisoen is In beter korrelasie verkry waar petioolsap vir strokies asook vir die outo-analiseerder gebruik is. Petiool nitraat is deur hoë Ntoedieningspeile verhoog en die 400 kg N.ha-I behandeling het betekenisvol van die ander N-behandelings verskil en die laaste seisoen ook In betekenisvol hoër opbrengs gelewer. Wisselende resultate is t.o.v. soortlike gewig vir kultivars en stikstofbehandelings verkry. By Sandberg (1998) is gevind dat oorbesproeiing In betekenisvolle verlagende effek op die nitraat-N inhoud in die petioolsap het. Daar is getoon dat die optimum besproeiingspeil en frekwensie, veldwaterkapasiteit met twee sproeibemestings per week is. Uit die ondersoek is dit duidelik dat die nitraatstrokies in kombinasie met die reflektoquant In uiters bruikbare aanduiding van die nitraat-N in die petioolsap gee. Dit is egter moeilik om In norm of kritiese nitraat-N grens aan te dui, aangesien toestande tydens die groeiperiode op sandgrond en die groeistadium In beduidende effek op die nitraat-N het. Indien opbrengs as enigste doelwit gestel word, mag die 400 kg N.ha-I kurwe moontlik as aanduiding van 'n optimum nitraat-N norm vir die betrokke kultivars dien. Daar bestaan ook onduidelikheid of nitraat-N in die petioolsap wel In goeie refleksie van groei en opbrengspotensiaal is.

Thesis (MScAgric.)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Experi!11entsin KwaZulu-Natal showed that seed treatment with molybdenum (Mo) could double the yield and increase the protein content by 1.9% of soybeans grown on acidic soils. However, it was also found that soybean yield at five of the localities was reduced on average by 8% after Mo seed treatment. It was surmised that the yield reductions observed after Mo seed treatment were connected to the quality of the seed used for planting. The aim of this project was to assess the relationship between seed quality and Mo seed treatment and find a fast, easy quality assessment test that could be used to adapt Mo treatments according to seed quality. The first investigation entailed assessing the quality of the seed obtained, from various seed lots, for planting. A number of different seed quality testing techniques were performed and they included the accelerated ageing test, tetrazolium test, conductivity test, standard germination test and an emergence . test planted at different depths with incubation at different temperatures. All the test results were compared with the accelerated ageing test results, to find the test most closely correlated to the accelerated ageing test, which is regarded as the most accurate indicator of soybean seed vigour. It was found that the emergence test where the seeds where planted at 10 cm presented a close correlation with the accelerated ageing test. An assessment of seed quality revealed that the four different seed lots provided seed of three significantly different levels of quality, which could be used for further investigations. The second investigation was concerned with the reaction of the seed of different quality levels to Mo seed treatment. Firstly, seeds from four different seed lots were treated with five different concentrations of Mo and planted under acidic conditions. The establishment was monitored up until six weeks, at which point the experiment was terminated. In the second planting, seeds from the four different seed lots were treated with six different concentrations of Mo and planted under optimum pH conditions. Emergence was monitored and after thinning out the remaining plants were left to mature and produce seed. The emergence percentage results from both of these two plantings did not reveal the alleged positive effect Mo seed treatment has produced in the field and no definite relationship between seed quality and Mo seed treatment was observed. The third investigation was concerned with the effect that osmoconditioning had on the reaction of seed to Mo seed treatment. Seeds from two seed lots, one of very poor quality and the other of good quality, were pre-treated with four different levels of poly-ethylene glycol (PEG 6000) and then treated with four concentrations of Mo. They were planted under optimum pH conditions and establishment was monitored. After being thinned out the remaining plants were allowed to mature and produce seed. The emergence percentage results revealed that the PEG pre-treatments greatly improved emergence percentages, especially in the poor quality seed. There were some positive effects of Mo seed treatment observed where the lower concentrations of Mo were used, but again, no definite relationship between seed quality and Mo seed treatment was found. PEG pre-treatment appeared to help make the seeds more "resistant" to the harmful effects of Mo. / AFRIKAANSE OPSOMMING: Navorsing in KwaZulu-Natal het aangetoon dat saadbehandeling met molibdeen (Mo) die opbrengs van sojabone op suurgrond kan verdubbel en die proteieninhoud met tot 1.9% kan verhoog. Daar is egter ook gevind dat sojaboonopbrengs op vyf lokaliteite met gemiddeld 8% gedaal het na saadbehandeling met Mo. "nVermoede bestaan dat die opbrengsverlagings wat voorgekom het na saadbehandeling met Mo verband hou met die kwaliteit van saad wat vir die aanplantings gebruik is. Die doel van die projek was om vas te stel wat die verband tussen saadkwaliteit en Mo saadbehandeling is en om "n vinnige en maklike toets te vind om saadkwaliteit te bepaal om sodoende Mo behandelings aan te pas volgens saadkwaliteit. In die eerste eksperiment is die kwaliteit van verskillende saadlotte wat verkry is, getoets. "n Aantal verskillende tegnieke om saadkwaliteit te bepaal is uitgevoer. Die tegnieke was die versnelde verouderingstoets, tetrazoliumtoets, konduktiwiteitstoets, standaard ontkiemingstoets en "n vestigingstoets waar saad op verskillende dieptes geplant en by verskillende temperature geïnkubeer is. Die resultate van die verskillende toetse is gekorreleer met die resultate van die versnelde verouderingstoets, wat beskou word as die toets wat die beste aanduiding gee van saadgroeikragtigheid. Daar is gevind dat sade wat 10 cm diep in sand geplant is, se opkoms die beste korrelasie met die versnelde verouderingstoets toon en dus as "n goeie aanduiding van die kwaliteit van saad beskou kan word. Daar is gevind dat daar drie saadlotte is met duidelike kwaliteitsverskille wat gebruik kon word in verdere eksperimente. Die tweede eksperiment het die reaksie van saad van verskillende kwaliteitsvlakke teenoor molibdeen saadbehandeling ondersoek. Eerstens is saad van vier verskillende saadlotte behandel met vyf verskillende konsentrasies Mo en onder baie suur toestande geplant. Die vestiging is gemonitor vir ses weke waarna die eksperiment gestaak is. Daarna is saad van dieselfde vier saadlotte behandel met ses verskillende Mo konsentrasies en onder optimum pH toestande geplant. Vestiging is gemonitor en na ses weke is die plante uitgedun en twee plante per pot is gelaat om saad te produseer. Die ~ vestigingspersentasie van beide die eerste en tweede plantings het nie die verwagte positiewe effek teenoor Mo saadbehandeling getoon nie en geen betekenisvolle verwantskap tussen saadkwaliteit en Mo saadbehandeling kon waargeneem word nie. Die derde eksperiment het die invloed van osmokondisionering op die reaksie van saad op Mo saadbehandeling ondersoek. Saad van twee saadlotte, een van goeie kwaliteit en een van swak kwaliteit, is voorafbehandel met poli-etileen glikol (PEG 6000) en daarna met vier konsentrasies van Mo behandel. Die sade is onder optimum pH toestande geplant en die vestiging is gemonitor. Nadat dit uitgedun is, is die oorblywende twee plante gelaat om saad te produseer. Die vestigingspersentasies het getoon dat PEG voorafbehandelings vestiging betekenisvol verbeter, veral in die geval van lae kwaliteit saad. Daar was 'n . positiewe effek van Mo saadbehandeling waar relatief lae konsentrasies molibdeen toegedien is, maar daar kon weereens nie 'n duidelike verwantskap tussen saadkwaliteit en Mo saadbehandeling waargeneem word nie. Dit blyk dat PEG voorafbehandeling die sade meer bestand teen die skadelike invloed van Mo gemaak het.

Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Guayule (Parthenium argentatum Gray) is a semi-desert plant with the potential to become an established crop on arid land in South Africa. The plant produces latex, which can be processed into rubber that is useful in application where disease transmission needs to be limited, such as for surgical gloves and condoms. The poor germination and natural dormancy characteristics of the embryo and the seed coats of guayule seed, motivated germination experiments. Germination of seed treated with solutions of gibberellic acid, smoke water and smoke watergibberellic acid was determined. Furthermore, combinations of gibberellic acid, smoke water and sodium hypochlorite treatment solutions were applied to seed to determine the germination responses. Vegetative propagation of guayule by means of cuttings was also investigated to determine the rooting responses of cuttings with treatment solutions of indole butyric acid, naphthalene acetamide and naphthalene acetic acid. Rooting percentage, root length and root weight was determined for each treatment. Dryland field trial plantings were established at different areas in South Africa to determine the growth potential and biomass production of guayule cultivars under different environmental conditions. Stand count, height, canopy diameter and stem diameter was determined for the different cultivars and areas. Lastly, latex production of guayule cultivars established in trial plots at Elsenburg, Oudtshoorn and Graaff- Reinet was determined after one year of growth. Treatment solutions of an aqueous smoke extract (commonly referred to as smoke water) and gibberellic acid were evaluated to determine their effectiveness in stimulating germination of four guayule seed lines (AZlOl, AZ-3, N565 and 11591). The split-plot analyses of variance showed no significant interaction between cultivar and treatment factors (P = 0.71), but when the day factor was included interaction was highly significant (P < 0.0001). The applied treatment thus had an effect on the time required for the germination response. Investigations into optimum germination responses indicated that smoke water-gibberellic acid required the shortest number of days (6.3 days) for optimum germination to occur with cultivar AZ-3. Furthermore, gibberellic acid treatment resulted in the greatest germination with the four cultivars 11591, AZ- 3, AZI0l and N565, at 93.78%, 93.35%, 94.41% and 99.42% respectively. These results show that guayule seed can be stimulated to germinate by treatment with gibberellic acid and smoke water solutions. Specific concentrations of treatment solutions of gibberellic acid, smoke water and sodium hypochlorite, and combinations thereof were used to evaluate the germination response of guayule seed cultivar AZ-2. Combinations of treatment solutions did not result in significantly increased seed germination responses. Single treatment solutions of gibberellic acid and smoke water did not significantly enhance germination, but sodium hypochlorite however, significantly (p <0.0001) suppressed germination at the 1% Cl and 2% Cl concentrations with about 5% and 10% respectively when compared to the control. Therefore, the applied seed treatments did not effectively increase the germination of guayule cultivar AZ-2 seed. Specific concentrations of indole butyric acid, naphthalene acetamide and naphthalene acetic acid treatment solutions were applied to guayule cuttings of cultivar AZ-3 and rooting response was determined for rooting percentage, root length and root weight. Naphthalene acetic acid treatment rooted the highest percentage of cuttings (52.38%) at a concentration of 60 mgll. Indole butyric acid treatment produced the longest roots (147.83 mm) at a concentration of 120 mg/l. Naphthalene acetamide obtained the heaviest roots (1.8 g) at a concentration of 120 mgll. Treatment solutions of indole butyric acid, naphthalene acetamide and naphthalene acetic acid indicated specific concentrations for optimum effect to improve root formation (by 30%), root length (by 50 mm) and root weight (by 1.5 g) when compared to the controls. Guayule trial plots of IOx10 m, rows 1 m apart and 30 cm between plants, and each cultivar (10 plants per unit) placed at random and replicated 6 times, were established in different areas under different environmental conditions in South Africa. Plantings were evaluated as a dryland practice, though irrigation was supplied only for establishment. Growth (stand count, height, canopy diameter, stem diameter) and biomass (wet and dry weight) were recorded for (1) oneyear old plantings established in April 2001 at Elsenburg, Graaff-Reinet and Oudtshoorn, and (2) six-month old plantings established in October 2001 at Bethulie, Glen and Upington. Analysis of variance was done to determine mean growth and biomass for the different areas and cultivars. (1) There were significant interactions between the factors area and cultivar for stand count and height, while canopy diameter and stem diameter differences were significant only within factors. The greatest growth potential was produced by cultivars AZ-2 and AZ-3, and Oudtshoorn was the best area for growth potential and biomass production. (2) Interaction between area and cultivar was significant for plant height, but were not significant for stand count, canopy diameter and stem diameter. Cultivars produced similar results for biomass production, but were significantly different in the different areas of Bethulie, Glen and Upington. Growth potential and biomass production of guayule was influenced by the availability of water during the growth of the plant. Latex production of guayule cultivars (AZ-2, AZ-3, N565, 11591) established in trial plots at different areas (Elsenburg, Oudtshoorn, Graaff-Reinet) in South Africa was investigated. Branch samples of one-year old plantings were harvested in April 2002, dipped in 1% ascorbate, sealed in plastic bags and chilled during airfreight to the United States Department of Agriculture (USDA) - Agricultural Research Service (ARS) in Albany CA. Latex extraction and quantification was done and mean latex production and comparisons of latex production for the cultivars in each area were determined. The evaluation of latex production show generally similar results in the different areas. Cultivars generally do not differ significantly from each other in the amount of latex produced in each area. Environmental stress factors on latex production occur in especially Oudtshoorn and Graaff-Reinet where the temperatures are above 25°C and below 1DoC. Since guayule is a slow growing shrub, latex accumulation is also slow and takes 4-6 years to reach economic harvesting potential. Production results are therefore preliminary and require further evaluation after each year of growth to present a complete view of guayule latex production over time. Propagation investigations were successful in identifying techniques to germinate guayule seed and promote rooting of cuttings with specialized treatment solutions. Field establishment of guayule under South African environmental conditions has identified suitable areas and indicated cultivar performances in these areas. Evaluation of the latex production of field plantings has demonstrated the potential of guayule in these areas. Currently the path to guayule development is paved with a network of research activities that is strengthened through cooperation between research institutions and private sector companies that bridge the gap between academic research and market exhibition. / AFRIKAANSE OPSOMMING: geen opsomming

Thesis (PhD (Agronomy))--University of Stellenbosch, 2006. / Vegetation dynamics and restoration strategies of degraded rangeland were investigated near a watering point in the Allaidege communal grazing area in Administrative Zone 3 of the Afar Region in the northeastern lowlands of Ethiopia. The degradation gradient formed by grazing pressure in the study area was stratified into four different areas based on the vegetation cover; severely degraded (SD), moderately to severely degraded (MSD), moderately degraded (MD) and lightly degraded (LD) areas. The study was initiated at the start of the rainy season in June 2003 and lasted untill December 2004. The objectives were to study the effects of the grazing pressure on plant species composition; on plant biomass production and basal cover; on rangeland forage quality; on the rangeland soil status and to determine and quantify viable restoration strategies for forage species in severely degraded rangelands. The botanical composition of the different degradation areas was determined by making a 250 point wheel point method survey in each of four 30 m x 30 m quadrats in each degradation area using the nearest plant approach. The botanical composition of each degradation area was determined by measuring the frequency of occurrence of the different life forms (perennial grasses, annual grasses and forbs) of the species recorded in the field. Accordingly, a significant interaction was observed in both seasons between the different degradation areas and life forms considered. A high abundance of annual grasses was evident in SD and MSD areas in both seasons. In the MD and LD areas, a three-fold increase in frequency was recorded for perennial grasses compared to the MSD area in 2003. In 2004, the frequency of annual grasses, forbs and perennial grasses in the MD area was almost similar to that of the LD area. The abundance of perennial grasses in the MD and LD areas was two- and five-fold higher compared to perennial grasses in the MSD and SD areas respectively. Biomass production was recorded by cutting the vegetation in 1 m x 1 m quadrats in each grazing area at ground level. The dry matter content of subsamples was determined in order to calculate the dry matter production of the quadrat. The differences in dry matter yield recorded in the different degraded areas was not significant for the 2003 season, although an increasing trend in yield was observed from the SD to MD areas. Significant yield differences were however recorded when one outlier in the data was excluded from the analysis. The significant differences occurred between the MD and SD areas where the MD area produced 2.4 t ha-1 more dry matter than the SD area. Similarly, in 2004 no significant yield difference was observed between the degradation areas. However, the contribution of different species to dry matter yield varied in the different degradation areas. Setaria verticillata, Sporobolus ioclados and Paspalidium desertorum were found to be the major species contributing to the dry matter producion in the SD area, S. verticillata and P. desertorum in the MSD area, Chrysopogon plumulosus and P. desertorum in the MD area and C. plumulosus and Panicum coloratum in the LD area. The percentage basal cover was calculated from the number of basal strikes recorded at 1 000 points in each plot of each degradation area using the wheel point method. The total basal cover percentage did not significantly change along the degradation gradient in any of the seasons. However, data for both seasons showed an increasing trend of total basal cover percentage closer to the watering point compared to areas further away from the watering point, except for the SD area, which had the lowest basal cover percentage. The contribution to percentage basal cover by some species decreased while it increased for some other species in grazing areas near the watering point. Forage quality was investigated by analysing sub-samples of the forage samples taken to determine biomass production. The forage samples were analysed for neutral detergent fibre (NDF), acid detergent fibre (ADF), crude protein (CP), lignin, in vitro dry matter digestibility (IVDMD), phosphorus (P), and calcium (Ca) content. The forage showed a decrease in NDF and ADF content in areas close to the watering point in both seasons. This decrease in fibre content was accompanied by an increase in CP content close to the watering point. The increase in CP was significant for the SD area in both seasons. Although a similar trend was observed in both seasons, the CP content was found to be significantly higher in 2004 than in 2003. The results of the lignin analysis were inconclusive if the data of both seasons are considered. It does appear however as if the lignin content of the forage was generally higher in 2003. The 2 years pooled average of P content of the forages showed insignificant variation along the degradation gradient. However, an increase in P concentration of the forages was evident in areas far from the watering point. Contrary to this, Ca concentration was significantly higher in the SD area compared to areas further away from the watering point. Hand clipped forage samples and esophageal collected forage samples were analysed to compare the quality of the samples. Due to the fact that only two animals were available for esophageal collection, differences were in most cases not significant at the 5% level, but trends indicate that animals select higher quality forage than what is assumed based on hand clipping. Organic carbon (OC) content, total nitrogen (N) content, available phosphorus (P) content, available potassium (K) content, exchangeable calcium (Ca) and magnesium (Mg) contents, cation exchange capacity (CEC), total exchangeable bases (TEB), exchangeable sodium percentage (ESP), soil acidity (pH) and base saturation of soils in the different degradation areas were determined by means of acknowledged laboratory methods. No significant differences in OC, N, P, K, Ca, Mg and K content of soil in the different degradation areas could be observed. There was however an increasing trend for OC and N content with distance from the watering point. Sodium concentration and pH increased significantly in areas close to the watering point. Cation exchange capacity content of the soil was variable and no clear trend could be established. Significantly higher TEB and ESP contents were observed in the SD area. In general, the differences in plant biomass production and basal cover, botanical composition, forage quality and soil status over the degradation gradient clearly implicates the negative impact of unrestricted grazing pressure on the rangeland around the watering points. In the rangeland restoration trial, establishment of three local and three exotic grass species in the SD area was investigated. Treatments applied included application of inorganic fertilizer, dry dung organic manure and grass mulch. The mulch treatments caused a significant yield increase for all the sown species. Among all the species, Ischaemum afrum and Tragus berteronianus performed better and produced significantly higher dry matter yields than Enteropogon rupestris, Chloris gayana and Panicum coloratum. In general the study indicated the importance of mulching when planning to restore degraded rangeland under arid environmental conditions.

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

Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2007. / The Cape Floristic Region is a highly distinctive phytogeographical unit which is recognized as a floral Kingdom on its own. Buchu (Agathosma betulina) plants fall under this important Kingdom. Buchu is one of the traditional medicinal plants originating in the Western Cape province of South Africa and the essential oil derived from the leaves is exported in large volumes. Due to high demand, under supply, restrictions of wild harvesting and high prices for Buchu essential oil, growers have started to introduce and commercialize this species as a crop. This commercialization of Buchu necessitated agronomic research to optimize production techniques. The objective of this study was to determine the optimum pH range for the cultivation of high yielding Buchu with acceptable essential oil quality under controlled conditions and compare this with the conditions in the natural habitat. Plant, soil and climatic data were gathered from eleven sites in the natural habitat of Buchu (A. betulina) in the Cederberg Mountains. At all sites most rainfall occurred from May to September, while high temperatures were recorded in summer. Soil analyses indicated low levels of nutrients and low soil pH, ranging from 3.7 to 5.3 at all the sites studied. Low levels of nutrients were also obtained from foliar analysis collected from plants at each of the different sites. Chemical analyses of the essential oil indicated that the plants were from a high quality diosphenol chemotype. In the greenhouse experiment, five different pH levels (pH 33.99, 4-4.99, 5-5.99, 6-6.99 and 7-7.99) were evaluated to determine the effect on growth, yield and quality of A. betulina. Complete nutrient solutions were used to irrigate the plants grown in pots filled with a sand and coco peat mixture. Although the plants subjected to the pH treatment of 4-4.99 tended to have the highest growth rate and yield, this did not differ significantly (P=0.05) from plants subjected to pH values between 3 and 6.99. In contrast, the pH 7-7.99 treatment lead to reduced growth and lower vegetative yields. Levels of nutrients obtained from the leaf mineral analysis differed significantly with different pH treatments. High pH levels resulted in high nitrogen, phosphorus, sodium, manganese and boron contents, but lower contents of copper. Nitrogen, phosphorus, calcium and zinc were higher than those recorded for plants from their natural habitat, but still within the norm reported for most plants. Levels of manganese, sodium, magnesium and copper were found to be more or less similar to the values obtained in plants from the natural habitat. No significant differences were found in essential oil quality in response to the pH treatments. However, high pulegone levels (10.8 to 13.2 %) were obtained from all the treatments in the greenhouse experiment. The high levels of this essential oil constituent could have a negative effect on the marketability of the oil and this aspect may need some attention in future studies.

Thesis (MScAgric (Agronomy)--University of Stellenbosch, 2007. / Soil salinity is a serious constrain to crop production in many countries. In the Western Cape canola production area, large variability in soil properties within the same field is a very common feature. Some of this variability may be ascribed to differences in salinity. These saline patches affected the germination and survival of cereal crops like wheat and may therefore also be a reason for the high variability and generally low canola yields obtained in this area. It will therefore be important to quantify the effect of such saline conditions on the germination and seedling establishment of canola in an effort to improve yields. In this study several experiments were conducted under controlled conditions in either Petri dishes in an incubator or pots in a temperature controlled glasshouse to determine the salinity response of canola. Results of the experiments done in Petri dishes, showed that the germination response of canola (Brassica napus L., cv. Tornado) to increasing levels of salinity is very similar to that of wheat (Triticum aestivum L., cv SST 88). Although canola germinated more rapidly than wheat at a temperature of 20 ºC, the final percentage germination for both crops decreased severely when NaCl induced salinity exceeded levels of an EC of 8 dS m-1, but less severe responses were obtained with NaCl/CaCl2 induced salinity. Under soil conditions an interaction between soil type and salinity level showed that the responses in sandy soil to an increase in salinity from 0 to 8 iv dS m-1 were less severe than in loamy soil and especially when salinity stress was induced by NaCl. Although cultivar Spektrum showed more tolerance to saline conditions during the germination and seedling stages in pot experiments when compared to other cultivars tested, these results will have to be confirmed in field trails where grain yield and quality can be measured.

Thesis (MScAgric (Agronomy))--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: Little is known about the nutrient requirements of broccoli grown for seed production. During 2006 and 2007 broccoli were grown for seed production in sand bags in a net structure, using a drain to waste hydroponic system. The experimental design was a randomized complete block with seven treatments replicated in four blocks. In 2006 seven nutrient solution treatments were tested. The Standard solution based on Steiner’s universal solution was compared with different levels of N, S, K and Ca with regard to the effect on total biomass, nutrient concentration, nutrient assimilation, seed yield and quality. No significant differences in total biomass produced were found. Total dry mass increased by 225% from the mature head stage until harvest of seed. Nutrient concentration in plant samples were not influenced by treatments except where low levels of K and S in nutrient solutions led to significantly lower levels of K and S concentrations. The total assimilation of elements were calculated to determine the effect of the much longer growth period needed for seed production in comparison to normal head production on nutrient requirements. Major elements assimilated ha-1 was: N 173.0 kg, P 35.5 kg, K 348.4 kg, Ca 114.7 kg, Mg 30.5 kg, S 42.2 kg. The seven treatments used during 2007 included three of the treatments which were used in 2006 as well as treatments with foliar sprays containing Ammonium Nitrate and Calcium Metalosate. The standard solution treatment was also used in 2007 to compare results with 2006. Plant analysis done on plants from the standard solution (2006 & 2007) showed similar trends. As the plants developed towards maturity there was a relative increase in concentration in the top plant parts (pods, flowers and stems) for Ca, Mg and S. Contrary, N and P concentration declined. The minor elements, Fe, Mn and B also increased in concentration in the top plant parts at harvest indicating a strong relative flow of these elements to the top plant parts towards maturation. Concentration values of major elements in plant samples were generally different when the two years were compared. Element concentrations in the seed pods were in general higher than in the rest of the plant indicating the pods as a strong sink on the plants. During both years the two best nutrient solutions for yield were the same, namely the Standard solution and Standard - K which contain low levels of K. During 2006 no significant differences in seed quality were found. During 2007 no significant differences were found for seed quality measurements, except for size (of the cotyledons). The results indicate that no special adjustments need to be made to the Standard solution in order to produce good broccoli seed yield of good quality. As substantial differences in nutrient solution composition did not significantly affect the quality of broccoli seed produced. Seed yield was however significantly affected by nutrient solution composition. Key words: Brassica seed, broccoli seed, seed production, broccoli nutrition, hydroponic production, broccoli production, nutrient assimilation. / AFRIKAANSE OPSOMMING: Min inligting is bekend rakende die voedingsbehoeftes van brokkoli wat gekweek word vir saadproduksie. Gedurende 2006 en 2007 is brokkoli gekweek vir saadproduksie in sakke sand in ‘n net struktuur met ‘n oop hidroponiese besproeiingstelsel. Die proefontwerp was ‘n ewekanisige geheel blok met sewe behandelings wat ewekansig binne bloke toegeken is en herhaal is in vier blokke. Sewe voedingsmengsel behandelings is gedurende 2006 toegepas. Die Standaard mengsel is geskoei op Steiner se universele mengsel en dit is vergelyk met verskillende vlakke van N, S, K en Ca t.o.v. die invloed daarvan op biomassa produksie, voedingselement konsentrasie, voedingselement assimilasie, saad opbrengs en saad kwaliteit. Biomassa geproduseer het nie wesenlik verskil nie. Totale droë massa het met 225% toegeneem vanaf die volwasse kop tot die oes stadium. Die konsentrasie van voedings elemente in plant monsters is nie beïnvloed deur behandelings nie behalwe in gevalle waar lae konsentrasies van K en S in die voedingsmengsels gelei het tot lae konsentrasies van K en S in plantontledings. Die totale opname van voedingselemente is bereken om die effek van die veel langer groeiperiode wat benodig word vir saadproduksie in vergelyking met normale kop produksie te bepaal t.o.v. voedingselement behoefte. Makro element opname per hektaar was as volg: N 173.0 kg, P 35.5 kg, K 348.4 kg, Ca 114.7 kg, Mg 30.5 kg, S 42.2 kg. Die sewe behandelings van 2007 het drie behandelings van 2006 ingesluit asook behandelings van blaarbespuitings met Ammonium Nitraat en Kalsium Metalosaat. Die Standaard voedingsmengsel is weer gebruik ten einde die resultate van 2006 en 2007 te vergelyk. Voedingselement ontledings op plante van die Standaard mengsel (2006 & 2007) is vergelyk en het soortgelyke tendense aangedui. Soos wat plante ontwikkel het na volwassenheid was daar ‘n relatiewe toename in konsentrasie in die boonste plant dele (peule, blomme en stele) van Ca, Mg en S. In teenstelling hiermee het die konsentrasies van N en P afgeneem. Die mikro elemente Fe, Mn en B het ook in konsentrasie toegeneem in die boonste plant dele teen oes wat daarop dui dat daar ‘n sterk relatiewe vloei van hiedie elemente na die boonste plant dele plaasvind met volwasse wording. Die konsentrasie vlakke van makro elemente in plantontledings het in die algemeen wesenlik verskil tussen die twee jare. Die voedingselement konsentrasies was in die algemeen hoër in die saad peule as in die res van die plant wat daarop dui dat die peule as ‘n sterk sink op die plant funksioneer. In beide jare was die hoogste opbrengs afkomstig van die Standaard voedingsmengsel en die Standaard – K mengsel wat lae vlakke van K bevat het. Gedurende 2006 is geen wesenlike verskille in saadkwaliteitsnorme gevind nie. Soortgelyke resultate is gevind in 2007 behalwe vir grootte van die kiemblare. Die resultate dui daarop dat dit nie nodig is om die Standaard voedingsmengsel samestelling te verander ten einde goeie opbrengs saad van goeie gehalte te produseer nie. Wesenlike verskille in voedingsmengsels het geen invloed op die kwaliteit van brokkoli saad gehad nie. Saad opbrengs is egter wesenlik beïnvloed deur die samestelling van die voedingsmengsels. Sleutel woorde: brassica saad, brokkoli saad, saad produksie, brokkoli voeding, hidroponiese produksie, brokkoli produksie, voedingstof assimilasie.