Thesis (MScAgric)--Stellenbosch University, 1954. / No Abstract Available

Thesis(DScAgric.)--Stellenbosch University, 1932. / No Abstract Available

Thesis (MScAgric )--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The main object of this study was to estimate heritabilities and possible genetic correlations for and between reproductive traits in a composite multi breed beef cattle herd. Reproduction is a complex process with many components. Due to the nature of the data, obtained from the two farms of the Johannesburg Metropolitan Council from 1974 to 1993, only calving date (CD), calving date with a penalty score (CDP), calving success (CS), calving interval (CI), age at first calving (AFC), longevity and stayability at 36, 48, 60, 72 and 84 months were investigated. A GFCAT set of programmes was used and fitted on a sire model to analyse all the categorical traits. Heritabilities and product moment correlations between predicted breeding values for stayability at 36, 48, 60, 72, 84 months, calving success (CS) and longevity, were estimated. The estimated heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08, respectively. Product moment correlations between breeding values for stayability traits were very low. The highest correlation of 0.22 was obtained between 36 and 48 months. Heritability estimates and correlations between traits appear to be of such a low magnitude that selection for these characteristics would result in limited improvement and indicate that the sire had little influence on his daughter's stayability, longevity and CS. For the analyses oflinear traits (CI, CD, CDP and AFC), a REML procedure fitting a multitrait animal model (using REML VCE 4.2.5 package of Groeneveld, 1998) was used. Heritabilities and geneticcorrelations for and between calving interval (CI), calving date (CD), calving date with a penalty score (CDP) and age at first calving (AFC) were estimated as traits of the dam. The estimated heritabilities for CI, CD, CDP and AFC obtained in this study were 0.01, 0.04, 0.06 and 0.40, respectively with a repeatability of 0.07, 0.12 and 0.13 for CI, CD and CDP, respectively. Genetic correlations between traits obtained varied from low to moderate, except for the high correlations between CD and CDP (0.98), CI and CD (0.75) and CI and CDP (0.79). Heritabilities, genetic correlations and repeatabilities of CD and CDP obtained in this study suggest that CD and CDP are the same traits and that selection for CDP rather than for CD does not have any additional advantage. Due to the additional advantages of CD over CI and the fact that CD is a less biased measurement of the female reproductive complex, CD appears to be of genetic value and should.be considered-as a possible selection criterion to ensure genetic improvement for reproduction in a beef cattle herd. / AFRIKAANSE OPSOMMING: Die doeI met hierdie studie was om oorerflikhede vir en moontlike genetiese korrelasies tussen verskillende reproduksiekenmerke in 'n meerras vleisbeeskudde te bepaal. Reproduksie is 'n komplekse proses en bestaan uit veelvuldige komponente. Weens die aard van die data, verkry vanaf die Johannesburg Metropolitaanse Raad se twee plase (vanaf 1974 tot 1993), is slegs kalfdatum (CD), kalf datum met 'n verswaringswaarde (CDP), kalwingsukses (CS), kalfinterval (CI), ouderdom met eerste kalwing (AFC), langlewendheid en volhoubaarheid van die moeders om reproduktief in die kudde tot op onderskeidelik 36, 48, 60, 72 en 84 maande te bly, bestudeer. Kategoriese kenmerke is deur middel van 'n GFCAT stel programme, wat op 'n vadermodel gepas is, geanaliseer. Oorerflikhede vir en die produkmoment korrelasies tussen die voorspelde teelwaardes vir CS, langlewendheid en volhoubaarheid op onderskeidelik 36, 48, 60, 72 en 84 maande, is bereken. Die oorerflikhede vir bogenoemde kenmerke was onderskeidelik 0.03, 0.08, 0.06, 0.10, 0.06, 0.03 en 0.11. Die korrelasie tussen die voorspelde teelwaardes vir die verskillende volhoubaarheidskenmerke was laag. Die hoogste korrelasie, n1. 0.22, is tussen 36 en 84 maande verkry. Die oorerflikhede en korrelasies tussen die kenmerke blyk van so 'n lae omvang te wees dat direkte seleksie vir die kenmerke slegs tot 'n beperkte genetiese verbetering sal lei en dui daarop dat die vader slegs 'n beperkte invloed op CS, volhoubaarheid en die langlewendheid van sy dogters het. Vir die analise van die lineere kenmerke (CI, CD, CDP en AFC), is 'n REML-prosedure gebruik wat op 'n multikenmerk dieremodel gepas is (deur die gebruik van die REML VCE 4.2.5 pakket van Groeneveld, 1998). Oorerflikhede vir en genetiese korrelasies tussen CI, CD, CDP en AFC is bereken as kenmerke van die moeder. In hierdie studie is die beraamde oorerflikhede vir CI, CD, CDP en AFC as onderskeidelik 0.01, 0.04, 0.06 en 0.40 bepaal, met herhaalbaarhede van onderskeidelik 0.07, 0.l2 en 0.13 vir CI, CD en CDP. Genetiese korrelasies tussen die kenmerke het van laag tot matig gevarieer, behalwe vir die hoe korrelasies tussen CD en CDP (0.98), CI en CD (0.75) en CI en CDP (0.79). Die oorerflikhede en herhaalbaarhede vir en genetiese korrelasie tussen CI en CDP verkry in hierdie studie, veronderstel dat CD en CDP in wese dieselfde kenmerk is en dat seleksie vir CDP in plaas van CD geen addisionele voordele inhou nie. Weens die addisionele voordele wat CD inhou, bo die van CI, en die feit dat CD 'n minder sydige bepaling van die vroulike reproduksiekompleks is, blyk CD van genetiese waarde te wees en moet dit as 'n moontlike seleksie kriterium, om genetiese verbetering in 'n vleisbeeskudde te verseker, oorweeg word.

Thesis (MScAgric) -- Stellenbosch University, 1987. / INLEIDING: Van al die plaasdiere, is die vark die enigste spesie wat slegs vir vleisprodukte aangehou word. Alhoewel daar verskeie varkrasse in Suid-Afrika bemark word, word hierdie varke, ongeag die ras, hoofsaaklik in die vleisbedryf vir twee doeleindes aangewend. Die ligter varkkarkasse (karkasmassa onder 50kg word as vleisvarke, en die swaarder varkkarkasse (karkasmassa bo 50kg) word as spekvarke verwerk. In hierdie projek is die doeltreffendheid van verskeie karkaspararneters ondersoek en as onafhanklike veranderlikes, afsonderlik of in kombinasie, in lineêre regressievergelykings gebruik, om sodoende regressievergelykings te verkry wat 'n hoë voorspellingswaarde van die varkkarkassamestelling i.t.v. vleis, vet en been sowel as van die groothandelsnitopbrengs en -samestelling van die karkasse besit.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Although transport and lairage of ostriches are accepted causes of production losses, these losses have not yet been quantified. Transport and lairage regulations focus on the wellbeing of the birds and, by default reduce some losses. This thesis investigated weight losses and meat quality of ostriches as a result of transport density, lairage duration and lairage feed availability (ad libitum). All birds were reared on the same farm and loaded and transported together. They were randomly divided into their respective groups on loading for the transport trial, and on offloading for the lairage trial. Bird grouping was according to density for the transport trial (4 groups, H1, H2: 0.56m2/bird and L1, L2: 0.96m2/bird) and according to time spent in lairage and feed availability for the lairage trial (n=30 birds/group; L0hr and L24hr; n=15 birds/group L48hr and L48hr ad libitum feed). Behavioural observations of the ostriches showed a tendency of the ostriches to lean against objects and to orientate towards forces exerted on it to help keep its balance. Reactions to sound fluctuations were noted, with birds reacting towards changes in sound volume during transport and lairage. Timepoint numbers were allocated for each time the birds were weighed during the trial. Time points 1, 2, 3, 4 and 5 were allocated to loading, arrival, 19 hr in lairage, 31 hr in lairage and 39 hr in lairage respectively for Trial 2. Results showed no differences (P > 0.05) in live weights or meat quality parameters between Groups H1, H2, L1 and L2 during transport. Differences (P < 0.05) were found in cumulative weight losses between L0hr and the rest of the groups for time point 1. Differences between L48hr and L48hr ad libitum were found for time point 4 for cumulative weight loss. L48hr also differed significantly between the other lairage duration groups for dressing percentages as a function of loading weight. Ad libitum feed availability had a significant effect on live body weight changes but not the meat quality parameters for the groups held for 48hr in lairage. The number of birds having bruises (≈50% per group) was similar between groups and lairage had no influence on bruising. Results seem to indicate that the evaluated transport densities had no effect on the weight loss or meat quality of ostriches. However, the results indicate that the lairage period should be studied further with specific reference to weight losses during lairage. Meat quality was unaffected by the lairage parameters reported in this thesis. / AFRIKAASE OPSOMMING: Hoewel vervoer en voorslag hou (“lairage”) aanvaar word as die oorsake van produksieverliese, is hierdie aspekte nog nie gekwantifiseer nie. Regulasies in terme van vervoer en voorslag hou fokus op die welstand van die voëls en gevolglik verminder sommige verliese met hierdie faktore. Konflik tussen boere en sekondêre produsente (abattoirs en verwerkers) oor die kostes verbonde aan hierdie gewigsverliese, is in wese ‘n oorsaak van oorbruggingsfases (vervoer). Daarom is die voorslag hou-parameters van tyd, voerbeskikbaarheid en laai digtheid ondersoek. Twee proewe is geloods; een vir vervoer en een vir voorslag aanhou. Voëls is voor hulle op vragmotors gelaai is, geweeg en op spesifieke tye daarna geweeg. Diere van die laaidigtheidsproef is ingedeel in vier groepe (H1, H2: 0.56m2/voel en L1, L2: 0.96m2/voel). Met aflaai is die eerste toets groep geslag terwyl die tweede toets groep ingedeel is volgens die tyd gespandeer en voer beskikbaarheid in voorslag aanhou (n=30 voëls/groep - Groepe L0u, L24u; n=15 voëls/groep - L48u en L48u ad libitum gevoer). Gedrag van voëls is aangeteken tydens vervoer. Finale gewig was slagpale gewig en elke tyd periode waar die voëls geweeg is, is aangeteken as ‘n tydpunt. Vleiskwaliteit analises is gedoen op die linker boud se fan filet. ‘n Standaard rak leeftyd toets is ook gedoen om kwaliteit parameters te toets oor tyd. pH is gekatorigiseer volgens groepe om moontlike verskille te beklemtoon. Gedrag is opgeteken volgens die oriëntasie en steunings gewoontes van die volstruise gedurende vervoer. Voëls probeer hulle balans te hou deur op voorwerpe en op mekaar te leun, asook om hul liggaam oriëntasie te gebruik. Reaksies tot klank veranderinge is ook opgemerk tydens vervoer en voorslag aanhou. Resultate toon geen betekenisvolle verkille tussen digtheid groepe H1, H2, L1 en L2 nie. Geen gewigsverskille is gevind tussen vervoerdigtheid groepe nie. Vleiskwaliteit-parameters is ook ondersoek en geen verskille is gevind tussen groepe nie. Resultate toon wel betekenisvolle verskille in gewigsverlies-persentasie tussen groepe vir tyd in voorslag aanhou. Groepe L48u en L48u ad libitum, het onder andere betekenisvol verskille getoon vir tydpunt 4. Betekenisvolle verskille in uitslagpersentasie as funksie van begin-gewig tussen 48 uur en die res van die groepe is ook gevind. Verdere vleiskwaliteit-parameters (drupverlies, pH, ens.) tussen groepe het geen betekenisvolle verskille getoon nie. Resultate dui aan dat voer beskikbaarheid het ‘n invloed op gewigsverskille in voorslag aanhou. Regulasies vir voorslag hou, vervoer en welstand van volstruise sal moontlik verder ondersoek moet word met spesiale klem op die nut van voorslag aanhou en die se invloed op gewigsverlies. Vleiskwaliteits-parameters is nie beïnvloed deur die aspekte ondersoek nie.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Haliotis midae (HM) is one of five indigenous abalone species occurring along the coast of South Africa, and is the only species commercially cultivated in open flow-through systems. Commercial production of HM contributes the most to income generated from aquaculture species in South Africa. Exports in 2011 totalled 1036 ton, which amounts to an income of ZAR 369 million (40 million USD). Commercial production of HM is characterized by a long interval (i.e. up to five years) to harvest. Genetic modification of HM to improve growth rate in HM can potentially decrease the interval from hatch to harvest, which will contribute to optimising the cost-efficient production of HM. However, a major concern in the production of genetically modified (GM) abalone is their escape from production systems, and the potential impact of the GM animals on the natural stocks in the surrounding environment. The implementation of containment methods to prevent the escape from GM abalone from production systems will assist in the management of the potential ecological risks escaped GM abalone may pose. Currently no containment strategies exist for the South African abalone industry, which limits the use of transgenic biotechnologies to optimise the cost-efficient production of HM. The study therefore investigated the potential of biological methods (triploid induction), mechanical methods (polypropylene filter bags and obstructive materials), and chemical methods (sodium hypochlorite and chlorine dioxide) to contain transgenic HM in open flow-through systems. Histological evaluation of gonad tissue samples of 16 triploid male and 15 triploid female HM indicated that triploid induction was unsuccessful in arresting gonad differentiation, development, and function. A combination of immature and mature gametes was observed on both triploid male and female gonads. The fertilizing potential of biopsied sperm obtained from triploid and induced diploid male HM was assessed in fertilization trials using ova obtained from diploid HM. No larvae were observed from the fertilization treatments of triploid male biopsied sperm, however, abnormal larvae (0.01% fertilization) were observed when induced diploid sperm were used to fertilize diploid ova. Polypropylene filter bags (100 μm) were not effective in containing male and female gametes in the broodstock section of the abalone culture system used in this study, and future studies should address specialized methods of containment of HM gametes. Polypropylene filters (100 μm), resulted in effective containment of larvae and settlement larvae, and in this study was not a more effective method of containment than the current on-farm larvae containment protocol. The three obstructive materials were effective in containing HM spat, and did not differ in their ability as containment methods. Sodium hypochlorite and Biox™, chlorine-based chemicals, were effective in containing the five life stages of HM, i.e. sperm, ova, larvae, settlement larvae and spat. The respective life stages were exposed to varying concentrations of the respective chemicals (i.e. 10 ppm, 50 ppm and 100 ppm) over five exposure times (i.e. 4, 6, 8, 10 and 12 minutes). Sodium hypochlorite and Biox™, at the different concentrations and exposure times, resulted in mortalities in all five HM life stages, with higher incidences recorded at the higher concentrations evaluated. Future research on the effect of triploid induction on the endocrine system, and how effective gonad maturation and function is suppressed, needs to be conducted. The aspects of mosaics occurring in induced diploid animals warrant further investigation with a larger sample size to verify the findings of this study. The production of true sterile individuals would improve the results to use of GM animals as a method of biological containment. Incorporation of mechanical containment methods need to be kept in mind when abalone production systems are designed. The use of chemical containment methods warrants additional studies on the practical administration and the economic feasibility of the chemical into the water supply of open flow-through abalone culture systems. / AFRIKAANSE OPSOMMING: Haliotis midae (HM) is een van vyf inheemse perlemoen spesies wat langs die kus van Suid-Afrika voorkom en is die enigste spesie wat kommersieel in oop deurvloeistelsels geproduseer word. Kommersiële produksie van HM dra die meeste tot kommersiële akwakultuur produksie by, met uitvoere van 1036 ton in 2011, wat gelykstaande aan ‘n inkomste van ZAR 369 miljoen (40 miljoen VSA dollar). Kommersiële produksie van HM word gekenmerk deur 'n lang interval (d.i. tot 5 jaar) vanaf uitbroei tot oes. Genetiese modifisering van HM om die groeitempo te verbeter kan potensieel die interval tot slagmassa verkort, wat potensieel tot die optimalisering van die kostedoeltreffende produksie van HM kan bydra. 'n Groot bron van kommer met die produksie van geneties gemodifiseerde (GM) perlemoen is hul ontsnapping uit produksiestelsels en die potensiële impak van die GM diere op die natuurlike perlemoenpopulasies in die omliggende omgewing. Die implementering van beheermetodes om die ontsnapping van GM perlemoen uit produksiestelsels te voorkom sal die bestuur van die potensiële ekologiese risiko's wat GM perlemoen mag inhou, vergemaklik. Tans bestaan daar geen inperking strategieë vir GM diere vir die Suid-Afrikaanse perlemoenbedryf nie, wat die gebruik van transgeniese biotegnologieë vir die kostedoeltreffende produksie van HM beperk. Die studie het dus die potensiaal van biologiese metodes (triploïed induksie), meganiese metodes (polipropileen filters en obstruktiewe materiaal) en chemiese metodes (natriumhipochloriet en Biox™) om as inperk strategieë vir die bestuur van transgeniese HM in oop deurvloei produksiesisteme gebruik te word, ondersoek. Histologiese evaluering van gonadeweefsel monsters van 16 manlike en 15 vroulike triploïed HM het aangedui dat triploïed induksie onsuksesvol was om gonade differensiasie, ontwikkeling, en funksie te onderdruk. 'n Kombinasie van onvolwasse en volwasse gamete is in gonades van beide manlike en vroulike triploïed HM waargeneem. Die bevrugtingsvermoë van sperme wat versamel is met behulp van ʼn biopsie metode van triploïed en geïnduseerde diploïed HM is geëvalueer in bevrugtingsproewe met ova wat van diploïed HM versamel is. Geen larwes is waargeneem met die gebruik van die triploïed sperme nie, maar abnormale larwes (0.01% bevrugting) het wel voorgekom met die evaluering van sperme versamel van geïnduseerde diploïed HM. Die voorkoms van mosaïek diere (d.i. ʼn kombinasie van beide diploïed en triploïed selle in een individu) wat ontstaan a.g.v. onvolledige triploïed induksie noodsaak verdere navorsing met ʼn groter monster diere om die vermoë van triploïed induksie om HM steriel te maak, te verifieer. Polipropileen filters (100 μm) was nie effektief om beide manlike en vroulike gamete wat in die teelafdeling in die perlemoenkultuursisteem in hierdie studie geproduseer is, vas te vang nie. Toekomstige studies moet gespesialiseerde metodes wat insluiting van HM gamete moontlik sal maak, ondersoek. Polipropileenfilters (100 μm) was effektief met die inkamping van larwes en vestigingslarwes, met die filters wat nie meer doeltreffend as die bestaande inkampingsmetodes in die produksiesisteem was nie. Die drie obstruktiewe materiale was doeltreffend ten opsigte van die inkamping van onvolwasse perlemoen individue, met die 3 materiale wat ewe doeltreffend in hulle vermoë was om die onvolwasse HM se ontsnapping uit die sisteem te voorkom. Natriumhipochloriet en Biox™, chloor-gebaseerde chemikalieë, was effektief om die onderskeie 5 lewenstadiums, d.i. HM sperme en ova, larwes, vestigingslarwes en onvolwasse HM se voorkoms tot hulle onderskeie afdelings binne die produksiesisteem te beperk. Die onderskeie lewensstadiums is blootgestel aan verskillende konsentrasies van die onderskeie chemikalieë (d.i. 10 dpm, 50 dpm en 100 dpm) oor vyf tydsintervalle (d.i. 4, 6, 8, 10 en 12 minute). Natriumhipochloriet en Biox™ het ʼn letale effek op al vier lewensstadia gehad, met hoër sterftes wat met hoër konsentrasies aangeteken is. Toekomstige navorsing oor die uitwerking van triploïed induksie op die endokriene stelsel en hoe doeltreffend die rypwording en funksie van die gonades onderdruk word, moet aandag geniet. Die voorkoms van mosaïek diere regverdig ook spesifieke aandag in toekomstige navorsing. Die produksie van ware steriele individue sou die gebruik van GM perlemoen as 'n metode van biologiese inkamping moontlik maak. Inlywing van meganiese inkampingmetodes moet in gedagte gehou word wanneer perlemoen produksiestelsels ontwerp word. Die gebruik van chemiese inkampingmetodes benodig verdere studies om te verseker dat die chemiese middels so bekostigbaar en prakties as moontlik in water van 'n oop deurvloei perlemoen produksiestelsel toegedien kan word.

Thesis (MScAgric)--Stellenbosch University, 2014. / ABSTRACT ENGLISH: Canola is increasingly becoming an important economic field crop in South Africa, because it can be used to produce high quality cooking oil and margarine, animal feed, biofuel and in crop rotation systems to break the disease cycle and improve weed management. Effect of temperature on phenological responses with respect to required number of days, growing degree days, photothermal units to specific growth stages, growth rate, as well as vegetative and reproductive growth of canola were studied under controlled conditions. Seven canola cultivars selected from early and mid-maturing groups of canola cultivars, presently planted in the Western Cape canola production area, were grown in 3 litre plastic bags filled with a mixture of sand and compost at ratio of 1:1 and irrigated with fully balanced nutrient solution at EC=2.0 in two glasshouses at night/day temperature regimes of 10/15oC and 15/20oC. Number of days, growing degree days (GDD) and photothermal units (PTU) from planting to seedling emergence, first true leaf appearance, visible flower buds, first flower opening, seed ripening and seed physiological maturity were recorded. Plant heights were measured at 14 day intervals from 28 to 84 days after planting (DAP). Plants were sampled for leaf area (LA) and above ground dry mass (DM) at budding, flowering and seed physiological maturity. Plant growth rates (PGR) from planting to budding, from budding to flowering and from flowering to physiological maturity were calculated. Relative growth rates (RGR) and net assimilation rates (NAR) from budding to flowering and from flowering to physiological maturity were also calculated. Days after planting, GDD and PTU at budding, flowering and physiological maturity were correlated with leaf area, dry mass, number of pods plant-1 and pod dry mass plant-1 at budding, flowering and physiological maturity to determine whether there were relationships between the variables. The study showed that by increasing night/day temperature from 10/15⁰C to 15/20⁰C plant height, number of leaves plant-1 at budding stage, leaf area at budding , plant growth rate (PGR) from planting to budding stage and relative growth rate (RGR) from budding to flowering stage were increased. However, PGR from budding to physiological maturity, RGR from flowering to physiological maturity, net assimilation rate (NAR) from budding to flowering stage, leaf area at flowering and physiological maturity stages , as well as number of flower stems, number of pods plant-1, above ground total dry mass at flowering and physiological maturity stages were decreased. Pod dry mass at physiological maturity decreased by 22.24% to 40.35% for different cultivars which clearly demonstrated the sensitivity of canola cultivars to increasing night/day temperatures. By increasing the mean daily mean temperature from 12.5⁰C (10/15⁰C night/day) to 17.5⁰C (15/20 ⁰C night/day) the duration of the period from planting to seedling emergence as well as the vegetative and reproductive growth stages were decreased. With the exception of the vegetative growth stage, GDD and PTU requirements to reach specific growth stages increased with an increase in temperature. Plant growth parameters such as dry mass, leaf area, number of pods plant-1 and pod dry mass plant-1 at specific growth stages showed a positive correlation with the number of days needed to reach that growth stage, but not with GDD or PTU requirements. Although the responses of cultivars to increasing temperatures did differ for most parameters measured, responses did not always correlate with the maturity grouping of cultivars, suggesting that responses to temperature may to a large extent be determined by the genetic make-up (breeding company) of cultivars. These results indicate that number of days, GDD and PTU requirements to reach physiological maturity may be used to describe the cultivar maturity groupings, but because of the effect of temperature and day length, GDD and PTU should be more accurate. / AFRIKAANSE OPSOMMING: Canola se waarde as ekonomies belangrike akkerbou-gewas in Suid-Afrika het die afgelope aantal jare skerp toegeneem, omdat dit gebruik kan word om hoë kwaliteit kook-olie en margariene asook bio-brandstowwe en dierevoere, te vervaardig. In wisselboustelsels kan dit gebruik word om die siekte-ketting te breek en onkruidbeheer te vergemaklik. In hierdie studie is die invloed van temperatuur op die fenologiese reaksies van canola in terme van die aantal dae, gewasgroeidae en fototermiese eenhede, benodig om spesifieke groeistadiums te bereik, asook die invloed op groeitempo, vegetatiewe- en reproduktiewe groei onder gekontroleerde toestande nagevors. Sewe canola cultivars vanuit die kort en mid-groeiseisoen volwassenheidsgroepe wat tans in die Weskaap verbou word is geplant in 3-liter plastiek houers gevul met „n 1:1 sand: kompos mengsel as groeimedium en besproei met „n volledig gebalanseerde voedingsoplossing met EC=2.0. Twee glashuise met nag/dag temperature van onderskeidelik 10/15oC en 15/20oC is vir hierdie doel gebruik. Die aantal dae, gewasgroeidae (GGD) en fototermiese eenhede (FTE) wat vanaf plant tot saailingverskyning; eerste volwasse blaarverskyning; eerste blomknop verskyning; eerste blom; saad verkleuring en fisiologies volwasse stadiums vereis word, is bepaal. Plant lengte is gemeet met 14-daagse tussenposes vanaf 28 tot 84 dae na plant. Plante is gemonster is tydens die eerste blomknopverskyning asook blom- en fisiologies volwasse stadiums om blaaroppervlakte (BO) en droëmassa (DM) te bepaal. Plant groeitempos (PGT) vanaf plant tot blomknopverskyning; blomknopverskyning tot blom en vanaf blom tot fisiologiese volwasse stadium is bereken. Relatiewe groeitempos (RGT) en netto-assimilasietempos (NAT), is bereken vanaf blomknopverskyning tot blom en vanaf blom tot fisiologiese volwasse stadium. Die aantal dae vanaf plant, asook GGD en FTE benodig om blomknopstadium, blomverskyning en fisiologies volwasse stadiums te bereik, is gekorreleer met BO en DM plant-1 asook die aantal peule en peulmassa plant-1 tydens genoemde groeistadia om moontlike verwantskappe te bepaal. Die studie het getoon dat deur die nag/dag temperatuur te verhoog vanaf 10/15⁰C tot 15/20⁰C, plant lengte, aantal blare en BO plant-1 tydens blomknopverskyning, asook PGT vanaf plant tot blomknopverskyning en RGT van blomknopverskyning tot blomstadium, toeneem. Daarteenoor het PGT van blomknopverskyning tot fisiologies volwassenheid, RGT van blom tot fisiologies volwassenheid, asook NAT van blomknopverskyning tot blomstadium en BO tydens blom en fisiologies volwasse stadium, afgeneem. Reproduktiewe ontwikkeling soos gemeet aan die aantal bloeistele, peule plant-1 en peulmassa plant-1 is ook benadeel deur genoemde verhoging in temperatuur. Die afname in peulmassa het gewissel tussen 22.24% en 40.35% vir verskilende cultivars en is „n duidelike aanduiding van die verskillende canola cultivars se gevoeligheid teenoor toenemende nag/dag temperature. Die toename in gemiddelde nag/dag temperatuur vanaf 12.5⁰C (10/15⁰C) tot 17.5⁰C (15/20 ⁰C) het die aantal dae vanaf plant tot saailing verskyning asook die vegetatiewe en reproduktiewe groei fases verkort. Met die uitsondering van die vegetatiewe groei fase, het die GGD and FTE vereistes om spesifieke groeistadiums te bereik toegeneem met „n toename in temperatuur. Plant komponente soos DM, BO, aantal peule plant-1 en peulmassa plant-1 tydens spesifieke groeistadia het „n positiewe verwantskap getoon met die aantal dae wat benodig is om spesifieke groeistadiums te bereik, maar sodanige verwantskap is nie bevestig met GGD en FTE vereistes. Hoewel die reaksie van verskillende cultivars teenoor „n toename in temperatuur vir die meeste gemete plantkomponente verskil het, het die reaksie nie altyd verband gehou met die volwassenheidsgroepering van die cultivars. Dit wil dus voorkom asof die reaksie teenoor temperatuur tot „n groot mate ook verband hou met die genetiese samestelling van die cultivar soos bepaal deur die telingsmaatskappy. Hierdie resultate toon dat die aantal dae, GGD en FTE wat vereis word om fisiologiese volwassenheid te bereik gebruik kan word om die cultivar se volwassenheidsgroepering te beskryf maar dat GDD en FTE waarskynlik meer akuraat sal wees weens effek van temperatuur en daglengte op die ontwikkkeling van cultivars.

Thesis (MScAgric)--Stellenbosch University, 1973. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The effect of long-term tillage on basic soil properties with respect to sustainability was investigated in this dissertation. Over the last three decades soil conservation has become an important prerequisite for sustainable agriculture. The primary aim of this study was to evaluate the effect of different tillage practices on the physical and some of the chemical properties of soil after 37 years of continuous application. This study was conducted on the Langgewens experimental farm, 18 km north of Malmesbury in the Western Cape. The experiment was initiated in 1975 on a Glenrosa (Haploxeralf) soil form with a gravelly sandy-loam texture. It was treated with four main tillage methods, namely conventional, tine, minimum and no-tillage. Important basic soil properties studied were the electrical conductivity (EC) and total carbon percentage, water stable aggregate percentage, bulk density and hydraulic conductivity. Most of the properties were analysed for the 0-100 mm and 100-200 mm depths. Seasonal bulk density variation for the 0-100 mm soil depth was determined by a Troxler surface gamma-neutron meter for in situ measurement. ANOVA’s and Tukey’s LSD posthoc tests were computed to assess whether significant statistical differences existed between tillage treatments. No-tillage proved to be beneficial in terms of salinity and had the lowest electrical conductivity, indicating that salts leeched out of the profile. Total carbon content was in general very low and in the 0-100 mm soil depth it decreased in the order of: no (0.92%), minimum (0.86%), tine (0.83%) and conventional tillage (0.51%). Aggregate stability was significantly the lowest under conventional (47.82%) and tine tillage (45.02%) compared to minimum (61.43%) and no-tillage (78.40%) at 0-100 mm depth. This can be explained by the relatively low amount of total carbon in the soil combined with the tillage intensity. The same trend was observed for the 100-200 mm depth. Significant correlation between total carbon content and aggregate stability for the 0-100 mm confirmed that an increase in total carbon in the soil would lead to an increase in aggregate stability. Significant, increased aggregate stability under the no-tillage treatment would therefore indicate that there may be some stable structure present in the soil. Seasonal bulk density variation was the lowest in no-tillage, which supports the manifestations of stable soil structure. More intensive tillage treatments such as conventional and tine tillage initially showed lower bulk densities, but only for the first month. Thereafter it increased to significantly higher values as the season progressed. This was mainly as a result of hardsetting of the soil which is driven by natural processes and rainfall. It is also due to the sandy loam texture that is particularly prone to compaction. Hydraulic conductivity studied for conventional and no-tillage showed significant differences. No-tillage (41 mm.h-1) showed a noticeably higher conductivity, which remained constant compared to conventional tillage (20 mm.h-1) that decreased over time. The main reasons for this increased hydraulic conductivity under no-tillage was higher water stable aggregates and lower bulk density. In the long term no-tillage thus stimulated structure formation of a Glenrosa soil form that significantly improved soil properties studied. These properties may influence processes such as water infiltration, water storage, run-off and drainage positively, due to soil property interaction. No-tillage, in terms of sustainability, quantified by the soil properties studied, thus proved to be superior compared to conventional and tine tillage but to a lesser extent if compared to minimum tillage. / AFRIKAANSE OPSOMMING: In hierdie tesis word die effek van langtermynbewerking op basiese grondeienskappe met betrekking tot volhoubaarheid ondersoek. Oor die afgelope drie dekades het grondbewaring ‘n belangrike aspek in landbou geword, ten einde volhoubaarheid te verseker. Die primêre doel van hierdie studie was om die effek van verskillende bewerkingspraktyke op die fisiese en chemiese eienskappe van grond na 37 jaar van deurlopende bewerking te ondersoek. Die studie is uitgevoer op die Langgewens eksperimentele plaas, 18 km noord van Malmesbury in die Wes-Kaap. Die eksperiment is in 1975 geïnisieer op 'n Glenrosa (Haploxeralf) grondvorm met ʼn klipperige sandleem-tekstuur. Dit bestaan uit vier hoof-bewerkingsbehandelings, naamlik konvensionele, tand-, minimum en geenbewerking. Belangrike basiese grondeienskappe wat bestudeer is, is die elektriese geleidingsvermoë (EG) en die totale persentasie koolstof, persentasie waterstabiele aggregate, bulkdigtheid en hidrouliese geleiding. Die meeste van die eienskappe is ontleed op die 0-100 mm en 100-200 mm diepte. Seisoenale bulkdigtheidsvariasie vir die 0-100 mm gronddiepte is bepaal deur 'n Troxler oppervlak gamma-neutron meter deur middel van in situ meting. ANOVA en Tukey se LSD posthoc-toetse is bereken om te bepaal of daar statisties-beduidende verskille tussen die bewerkingsmetodes is. Geenbewerking het geblyk voordelig te wees in terme van die soutgehalte en het die laagste elektriese geleidingsvermoë gehad, wat daarop dui dat die soute uit die profiel loog. Die totale koolstofinhoud was oor die algemeen baie laag en in die 0-100 mm gronddiepte het dit afgeneem in die volgorde geen- (0.92%), minimum- (0.86%), tand- (0.83%) en konvensionele bewerking (0.51%). Aggregaatstabiliteit was betekenisvol die laagste onder konvensionele (47.82%) en tandbewerking (45.02%) in vergelyking met die minimum (61.43%) en geenbewerking (78.40%) by die 0-100 mm diepte en kan verduidelik word deur die relatief lae totale koolstofinhoud in die grond gekombineer met die bewerkings-intensiteit. Dieselfde tendens is waargeneem vir die 100-200 mm diepte. ‘n Beduidende korrelasie tussen totale koolstofinhoud en aggregaatstabiliteit is vir die 0-100 mm diepte gevind en dit bevestig dat 'n toename in totale koolstof in die grond sal lei tot 'n toename in aggregaatstabiliteit. Betekenisvolle verhoogde aggregaatstabiliteit onder die geenbewerking-behandeling sal dus aandui dat die grond 'n meer stabiele struktuur vertoon. Seisoenale bulkdigtsheidsvariasie was die laagste in geenbewerking en ondersteun die manifestasies van 'n stabiele grondstruktuur. Meer intensiewe bewerkingsbehandelings, konvensionele en tandbewerking het vir die eerste maand ‘n laer bulkdigtheid getoon, waarna dit tot aansienlik hoër waardes gestyg het soos die seisoen verloop het. Dit was hoofsaaklik as gevolg van grondkonsolidering wat gedryf word deur natuurlike prosesse soos reënval en ook as gevolg van die sandleemtekstuur wat veral geneig is tot verdigting. Hidrouliese geleiding is bestudeer vir konvensionele en geenbewerking en het beduidende verskille getoon. Geenbewerking (41 mm.h-1) het 'n merkbare hoër geleidingsvermoë gehad wat konstant gebly het, in vergelyking met konvensionele bewerking (20 mm.h-1) wat met die verloop van tyd afgeneem het. Die vernaamste redes vir hierdie verhoogde hidrouliese geleiding onder geenbewerking is hoër waterstabiele aggregate en ‘n laer bulkdigtheid. Op die langtermyn het geenbewerking dus struktuurvorming van 'n Glenrosa-grondvorm gestimuleer, wat die grondeienskappe wat bestudeer is, aansienlik verbeter het. Hierdie eienskappe kan prosesse soos waterinfiltrasie, waterretensie, -afloop en -dreinering positief beïnvloed as gevolg van grondeienskapinteraksie. Geenbewerking, in terme van volhoubaarheid, gekwantifiseer deur die grondeienskappe wat bestudeer is, is dus bewys as superieur in vergelyking met konvensionele en tandbewerking, maar tot 'n mindere mate in vergelyking met minimumbewerking. / Water Research Commission

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The herbicide atrazine (ATZ, 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) has been identified as an environmental endocrine disruptor and possible human carcinogen. The presence of atrazine, along with its degradation products, in soils and water supplies therefore raises concern. Atrazine biodegradation in soils is well-covered to date, however, atrazine degradation by abiotic mineral surfaces, and the chemical mechanism by which it occurs, is not fully understood. Furthermore, with a changing global climate, the effects of wetting and drying cycles on soil processes (e.g. atrazine degradation) is largely unknown, but increasing in importance. This study therefore investigated atrazine degradation on six common soil mineral surfaces, namely birnessite, goethite, ferrihydrite, gibbsite, Al3+-saturated smectite and quartz, as well as the effects that drying these surfaces has on atrazine degradation. In the first part, a comparison was conducted between the reactivity of fully hydrated and drying mineral surfaces toward atrazine, by reacting atrazine-mineral mixtures under both moist and ambient drying conditions, in parallel, for 14 days. Under moist conditions, none of the mineral surfaces degraded atrazine, but under drying, birnessite and goethite degraded atrazine to non-phytotoxic hydroxyatrazine (ATZ-OH, 2-hydroxy-4-ethylamino-6-isopropylamino-1,3,5-triazine) as major product and phytotoxic deethylatrazine (DEA, 2-chloro-4-amino-6-isopropylamino-1,3,5-triazine) as minor product. The mineral surface reactivity was birnessite (66% degradation) > goethite (18% degradation) >> other mineral surfaces (negligible degradation), indicating possible atrazine oxidation. In the second part, the effects of drying rate were investigated on birnessite only (the most reactive surface), by conducting the drying (1) gradually at ambient rates, (2) rapidly under an air stream, and (3) gradually in the absence of water using only organic solvent. After 30 days of ambient drying, 90% of the atrazine was degraded to ATZ-OH and DEA, but the same extent of degradation was achieved after only 4 days of rapid drying with an air stream. Thirty days of gradual drying using only organic solvent did not increase atrazine degradation compared to the water-moist drying surface. In each case, degradation initiated at a critical moisture content of 10% of the original moisture content. In the third part, the degradation mechanism was further investigated. To test for the possible oxidation of atrazine by the birnessite surface, moist atrazine-birnessite mixtures were dried under a nitrogen (N2) stream to eliminate possible oxidation by atmospheric oxygen (O2). Dissolved Mn2+ was extracted at the end of the experiment to observe any reduction of birnessite. Under N2, the same products were formed as before, with no appreciable Mn2+ production, indicating non-oxidative atrazine degradation by birnessite. The final part investigated the effects ultraviolet (UV) radiation has on the degradation of atrazine by drying mineral surfaces. The UV-radiation enhanced the degradation of atrazine, but no other degradation products were formed. It was therefore concluded that atrazine degradation on redox-active soil mineral surfaces is enhanced by drying, via a net non-oxidative mechanism. Furthermore, this drying-induced degradation is an atrazine detoxification mechanism which could be easily applied through agricultural practices such as windrowing, ploughing and any other practice that (rapidly) dries a Mn- or Fe-oxide rich agricultural soil. / AFRIKAANSE OPSOMMING: Die onkruiddoder atrasien (ATS, 2-chloro-4-etielamino-6-isopropielamino-1,3,5-triasien) is as 'n omgewings endokriene versteurder en moontlike menslike karsinogeen geidentifiseer. Die teenwoordigheid van atrasien, tesame met sy afbreekprodukte, in grond en water toevoere wek dus kommer. Die bio-afbreking van atrasien in gronde is tot dusver goed gedek, maar die afbreking van atrasien deur abiotiese mineraaloppervlaktes, en die chemiese meganisme waarmee dit plaasvind, word nie heeltemal verstaan nie. Verder, met 'n veranderende globale klimaat, is die effekte van benatting- en drooging-siklusse op grondprosesse (bv. atrasien afbreking) grootliks onbekend, maar toenemend belangrik. Daarom het hierdie studie atrasien afbreek op ses algemene mineraaloppervlaktes, naamlik birnessiet, goethiet, ferrihidriet, gibbsiet, Al3+-versadigde smektiet en kwarts, ondersoek, asook die effekte wat drooging van hierdie oppervlaktes op atrasien afbreking het. In die eerste deel, was 'n vergelyking gedoen tussen die reaktiwiteit van volgehidreerde en droëende mineraaloppervlaktes teenoor atrasien, deur atrasien-mineraal mengsels, in parallel, onder albei nat en omliggende droogings toestande te reageer vir 14 dae. Onder nat toestande, het geeneen van die mineraaloppervlaktes atrasien afgebreek nie, maar onder drooging het birnessiet en goethiet atrasien afgebreek na nie-fitotoksiese hidroksieatrasien (ATS-OH, 2-hidroksie-4-etielamino-6-isopropielamino-1,3,5-triasien) as hoofproduk en fitotoksiese deetielatrasien (DEA, 2-chloro-4-amino-6-isopropielamino-1,3,5-triasien) as minder-produk. Die mineraaloppervlakte-reaktiwiteit was birnessiet (66% afbreking) > goethiet (18% afbreking) >> ander mineraaloppervlaktes (geringe afbreking), wat moontlike atrasien oksidasie aandui. In die tweede deel, is die effekte van droogingstempo ondersoek, op birnessiet alleenlik (die mees reaktiewe oppervlak) deur drooging by (1) 'n omliggende geleidelike tempo, (2) 'n versnelde tempo onder 'n lugstroom, en (3) 'n geleidelike tempo in die afwesigheid van water, deur slegs gebruik te maak van 'n organiese oplosmiddel. Na 30 dae se geleidelike drooging, is 90% van die atrasien afgebreek na ATS-OH en DEA, maar dieselfe hoeveelheid afbreking is bereik na slegs 4 dae onder versnelde drooging met die lugstroom. Dertig dae van geleidelike drooging met slegs organiese oplosmiddel het nie atrasien afbreking vermeerder in vergelyking met die water-nat droëende oppervlak nie. In elke geval, is afbreking geïnisieer by 'n kritiese water inhoud van 10% van die oorspronklike water inhoud. In die derde deel is die afbrekingsmeganisme verder ondersoek. Om te toets vir die moontlike oksidasie van atrasien deur die birnessiet oppervlak, is nat atrasien-birnessiet mengsels onder stikstof (N2) gedroog, om die moontlike oksidasie deur atmosferiese suurstof (O2) te verhoed. Opgeloste Mn2+ was teen die einde van die eksperiment geekstraëer om enige reduksie van birnessiet waar te neem. Onder N2 is dieselfde produkte as voorheen gevorm, met geen aansienlike Mn2+ produksie nie, aanduidend van 'n nie-oksideerende afbreek van atrasien deur birnessiet. Die laaste deel het die effekte van ultraviolet (UV) straling op die afbreek van atrasien op droëende mineraaloppervlaktes ondersoek. Die UV-straling het atrasien afbreek vermeerder, maar geen ander afbreek-produkte is gevorm nie. Die gevolgtrekking is dus dat atrasien afbreking op redoks-aktiewe mineraal-oppervlaktes verhoog word met drooging, deur 'n netto nie-oksidasie meganisme. Verder is hierdie drooging-geinduseerde afbreking 'n atrasien ontgiftingsmeganisme wat eenvoudig toegepas kan word deur landboupraktyke soos windrying, ploeg en ander praktyke wat (vinnig) 'n Mn- of Fe-oksied ryke landbou grond verdroog. / National Research Foundation (NRF)