MSCAGR / Department of Soil Science / Soil hydraulic and hydraulic-related physical properties are key to soil productivity and these properties are widely studied. Nevertheless, their spatial variability is least understood. Two sites were selected for this study (University of Venda Experimental farm and Roodeplaat, Agricultural Research Council farm). The objectives of this study were to determine the spatial variability of soil water content, water infiltration and hydraulic conductivity on selected soils. Field measurements were done on a 20 m × 20 m. Soil hydraulic and hydraulic-related physical properties were studied at two depths, 0 – 0.2 m top soil and 0.2 – 0.4 m sub soil. The field was irrigated to saturation and let to drain freely for two days. The soil was quickly secured in water cans to avoid further loss of water by evaporation and taken to the laboratory for analysis. Data was analysed using ordinary kriging method in ArcMap® software version 10.4 to generate spatial variability maps and semi variograms. The University of Venda Experimental farm had lesser spatial variability with coefficient of variation ranging from 9.6 to 33.4%. The spatial variability of soil was very low confirmed by contour maps depicting slightly homogeneity. Whereas, the soil hydro-physical properties displayed greater spatial variability at Roodeplaat, Agricultural Research Council Experimental farm. The empirical variograms of spherical model fits were also assuming weak spatial dependence with a curve variogram. The coefficient of variation ranged from 10.5 to 51.9%. Therefore, the greater variability at Roodeplaat, Agricultural Research Council Experimental farm indicated that coarse soil texture under conventional tillage has a greater influence on the spatial variability of the soil hydro-physical properties. / NRF

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Soil is a fundamental, non-renewable resource in any ecosystem. To uphold food production for increasing global human populations, it is imperative to develop ways in which to sustain healthy biological productivity and sustainability of agricultural soils. Nematodes are one of the most abundant groups of Metazoa occurring in all soils, and form an integral part of the soil food web at several trophic levels. They respond rapidly to changes within their environments, and can easily be extracted from soil, identified and characterised into functional guilds. Nematodes thus have the potential to impart insight into the condition of the soil food web. This study aims to establish whether nematodes will be suitable bio-indicators of soil health for the deciduous fruit industry in the Western Cape. Three different objectives have been set to determine the practical use of nematode community structures as a tool for the measurement of soil health. The objectives include describing the nematode community structure, biodiversity and functionality within Fynbos soils; the characterization of organic and conventional orchards; and the differences in nematode soil communities in differently managed soils in an apple orchard. The number of nematodes in each soil sample was quantified and identified to family level. The nematode biodiversity and functionality for each site was determined by evaluating the nematode food webs for trophic group distribution, as enumerated by the Maturity Index (MI), the Enrichment Index (EI), the Structure Index (SI), the Basal Index (BI) and the Channel Index (CI), based on the weighted abundance of coloniser-persister guilds. The functional guild analysis of Fynbos samples indicated that the enrichment and the structure of any given sample were not bound to a certain area, but it was representative of each of the four quadrats within the faunal analysis. Different geographic areas were found to differ in nematode diversity and functionality, which was mainly associated with dominant plant families and species (such as strong associations between Fynbos families Fabaceae, Solanaceae and Celestraceae with the nematode family Pratylenchidae). The most abundant nematode families present in the Fynbos were Tylenchidae, which are plant-feeding nematodes, and Cephalobidae which are bacterial-feeding nematodes. Despite Tylenchidae and Cephalobidae both having coloniser-persister values (cp-values) of two, they are split up into different feeding types. Cp-2 nematodes are tolerant to disturbances, and occur in all environments. Only one omnivorous family, the Dorylaimida, was identified in Fynbos samples. The average MI value for Fynbos was found to be very low, with a mean value of 1.26. The value obtained indicated the presence of taxa with tolerance to disturbance, which, in turn, indicated the presence of a disturbed soil, in general. The number of plant-parasitic nematodes within the Fynbos soils was low, which was supported by the low plant-parasitic index (PPI) of 0.85. The diversity, richness and evenness values were low, indicating low nematode diversity, but a distribution of abundances amongst the families. The average Hill’s N0 index value was 8.0, indicating that, in general, eight nematode families would have been present in a Fynbos soil sample. A study was done to determine the biodiversity and the functionality of the nematodes associated with deciduous fruit orchards that were conventionally, or organically, managed. Herbivores were dominant in all the orchards. The organic apple orchard had the lowest numbers of herbivores and fungivores, with the highest number of carnivores. When comparing organic and conventional apricot orchards, higher numbers of plant-parasitic nematodes were found in the organic orchard. Criconematidae occurred in higher numbers in conventional apricot orchard soil. When comparing organic apricots and apples, higher numbers of Criconematidae occurred within the organic apple soil. Overall, higher levels of plant-parasitic nematodes occurred in the organic apricot orchard. The MI indicated that all orchard soils had values below 1.5, indicating disturbance. Conventionally managed apricot orchard soil had the highest MI value of 1.48. The PPI value was highest in organically managed apricot orchards. All orchard soils were located within Quadrat B of the faunal analysis, indicating enrichment and structure. Regarding the diversity, richness and evenness of the distribution, conventional apricot soil had the highest species richness, while organic apple soil had the most even family distribution. Different management practices did not show marked differences in community composition and structure. The species richness of Fynbos soils was comparable to those of deciduous fruit orchards. Soil samples from eight different soil surface treatments were collected from an apple orchard in the Grabouw area. Treatments were combined according to the soil surface treatments received (chemical control of cover crops and weeds, mulch and mulch + effective micro-organism spray). Bacterivores were dominant in all soil treatments, with the least number being present in the chemical control (of cover crops and weeds) treatment. Sites which received chemical control of cover crops and weeds had higher levels of fungivores, compared to the levels at the other sites. High numbers of Rhabditidae occurred within mulch and mulch + effective micro-organism (EM) treatment sites, while high numbers of Aphelenchidae occurred in chemical control sites. The carnivorous family Ironidae only occurred in mulch + EM sites. Strong associations were found between soil surface applications and nematode families present within the soil. Chemical control (of cover crops and weeds) applications had the highest MI value, while values were equal for the other soil applications. The faunal analysis indicated that the mulch and the chemical control fell within Quadrat A, indicating enriched, but unstructured, soil, while the mulch + EM treatment fell within Quadrat B, indicating enrichment and structure, as well as good overall soil conditions. All the systems were dominated by bacterial decomposition pathways. Controversially, sites that received chemical control of the cover crops and weeds had the highest species richness of all three applications, as well as the highest level of diversity, according to the Simpson Index. As only the cover crops and the weeds were chemically controlled, the soil can be regarded as undisturbed, which explains the results obtained in this study. Clear differences in nematode community structure and composition were observed between the different soil applications in the apple orchard. / AFRIKAANSE OPSOMMING: Grond is 'n fundamentele, nie-hernubare hulpbron binne enige ekosisteem. Ten einde voedselproduksie vir die toenemende globale menslike bevolking te handhaaf, is dit noodsaaklik om maniere te ontwikkel om gesonde biologiese produktiwiteit en volhoubaarheid van landbougrond in stand te hou. Nematodes is een van die volopste Metazoa in alle gronde en vorm 'n integrale deel van die grond voedsel-web op verskeie trofiese vlakke. Hulle reageer vinnig op veranderinge binne hul omgewings, kan maklik ekstraheer en identifiseer word; en ook maklik in funksionele gildes ingedeel word. Nematodes het ook die potensiaal om insig oor te dra ten opsigte van die toestand van die grond voedsel-web. Hierdie studie het ten doel om vas te stel of nematodes geskikte bio-indikatore van grond gesondheid kan wees spesifiek vir die sagtevrugte bedryf in die Wes-Kaap. Drie verskillende doelwitte is gestel om die praktiese gebruik van nematode populasie samestelling as 'n instrument vir die meting van grond gesondheid te gebruik. Die doelwitte sluit in die nematode populasie samestelling, biodiversiteit en funksionaliteit binne natuurlike Fynbos; organies verboude versus konvensionele boorde; en die verskil in nematode populasie samestelling tussen verskillend behandelde en bestuurde grondpersele binne ʼn appel boord. Die nematode biodiversiteit en funksionaliteit vir elke perseel was bepaal deur die evaluering van die nematode voedselweb vir trofiese groep verspreiding en enumerering deur die Maturity Index (MI) en die Enrichment Index (EI), Strukturele Indeks (SI), Basale Indeks (BI) en Channel Index (CI) wat gebaseer is op die geweegde oorvloed van koloniseerder-persister gildes. Die funksionele gilde vir Fynbos monsters het aangedui dat die verryking en struktuur van enige gegewe perseel nie gebonde is aan ʼn bepaalde gebied nie, aangesien dit verteenwoordig was in elk van die vier kwadrante van die Fauna Analiseerder. Daar is gevind dat verskillende areas verskil in nematode diversiteit en funksionaliteit, wat hoofsaaklik geassosieer was met die dominante plant families en spesies in die omgewing. Die volopste nematode familie wat teenwoordig was in die Fynbos was Tylenchidae, wat plant-voedende nematodes is, en Cephalobidae, wat bakterie-voedend is. Tylenchidae en Cephalobidae het beide ʼn cp-waarde van twee, maar is verdeel in verskillende VIII tipes voedingsgroepe. Die cp-2 nematodes is verdraagsaam vir versteurings en kom in alle omgewings voor. Slegs een omnivoor familie is geïdentifiseer in Fynbos monsters, nl. die Dorylaimidae. Die gemiddelde MI waarde vir Fynbos was laag, met 'n gemiddelde waarde van 1.26. Hierdie waarde is ʼn aanduiding van die teenwoordigheid van taxa met verdraagsaamheid tot versteuring, wat op sy beurt 'n versteurde grond in die algemeen aangedui het. Die aantal plant-parasitiese nematodes binne die Fynbos-gronde was laag, wat ondersteun word deur die lae PPI-waarde van 0.85. Die waardes vir die diversiteit, spesie-rykheid en egaligheid was laag, wat dui op 'n lae nematode diversiteit, maar 'n egalige verspreidings onder families. Die Hill’s N0 indeks waarde was gelyk aan 'n gemiddelde van 8.0 en dui daarop dat in die algemeen agt nematode families teenwoordig sal wees in 'n Fynbos grondmonster. 'n Studie is gedoen om die biodiversiteit en funksionaliteit van nematodes wat verband hou met vrugteboorde wat organies en konvensioneel bestuur is te bepaal. Herbivore was dominant in alle boorde. Organiese appels het die laagste aantal herbivore en fungivore gehad en die hoogste aantal karnivore. Wanneer organiese en konvensionele appelkoosboorde met mekaar vergelyk is, was hoër getalle van plant-parasitiese nematodes gevind in die organiese boord. Criconematidae was teen ʼn groter aantal in die grond van die konvensionele appelkoosboord gevind. Met die vergelyking van organiese appelkose en appels word, is ʼn hoër aantal Criconematidae binne die organiese appelgrond aangetref. In die algemeen was hoër vlakke van plant-parasitiese nematodes gevind in die organiese appelkoosboord. Die MI het getoon dat alle boord waardes laer as 1.5 gehad het, wat daarop dui dat die gronde versteurd is. Die konvensioneel bestuurde appelkoosboord het die hoogste MI waarde gehad met ʼn vlak van 1.48. Die waarde vir die PPI was die hoogste in organies bestuurde appelkoosboorde. Alle boord gronde is geleë binne kwadrant B van die Fauna Analiseerder, wat dui op verryking met struktuur. Met betrekking tot die diversiteit, spesie-rykheid en egaligheid van die verspreiding van families, het konvensionele appelkoos grond die hoogste spesierykheid, terwyl die gronde van die organiese appelboord die mees egalige familie verspreiding vertoon het. Verskillende bestuurspraktyke nie toon nie merkbare verskille in die gemeenskap samestelling en struktuur nie. Die spesie-rykheid van Fynbos gronde is vergelykbaar met dié van sagtevrugte-boorde. Monsters is geneem van agt verskillende grondeoppervlak-behandelings in ‘n appelboord in die Grabouw area. Die behandelings is gekombineer volgens die grond toediening wat dit ontvang het (chemiese beheer van dekgewasse en onkruid, deklaag en ‘n deklaag + effektiewe mikro- IX organismes). Bakterievoedende nematodes was dominant in elke grondoppervlak-behandeling, met die minste teenwoordig in die behandelings wat chemiese beheer van die dekgewasse en onkruid ontvang het. Behandelings wat chemiese beheer van die dekgewasse en onkruid ontvang het, het ook hoër vlakke van fungivore in vergelyking met die ander behandelings. ʼn Hoë aantal Rhabditidae het voorgekom in grondmonsters van die deklaag en die deklaag + EM (effektiewe mikro-organismes) behandeling persele, terwyl ʼn groot aantal Aphelenchidae voorgekom het in chemiese beheer persele. Die predatoriese familie, Ironidae, het slegs voorgekom in persele wat die deklaag + EM behandeling ontvang het. Sterk assosiasies bestaan tussen grond behandeling en nematode families wat in die grond teenwoordig was. Die chemiese beheer behandeling het die hoogste MI waarde getoon, terwyl waardes vir die ander behandelings laer en gelyk was. Die fauna analise het daarop gedui dat die deklaag en chemiese beheer binne kwadrant A is en dus verryk, maar ook ongestruktureerd is. Die deklaag + EM behandeling het binne kwadrant B geval wat aandui op toestande van verryking en struktuur wat 'n goeie algehele grondtoestand tot gevolg gehad het. Al die stelsels is oorbruggingsweë wat oorheers was deur bakteriële ontbinding. Kontroversieel, het persele wat chemiese beheer van die dekgewasse en onkruid ontvang het, die hoogste spesierykheid van al drie behandelings getoon asook die hoogste vlak van diversiteit volgens die Simpson-indeks. Slegs die dekgewasse en onkruid is chemies behandel, nie die grond nie, en dus kan die grond as onversteurd beskou word en die resultate wat verkry is in die studie verklaar. Duidelike verskille in die nematode gemeenskap struktuur en samestelling is waargeneem tussen die verskillende grond behandelings in appel boorde.

Thesis (MSc)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Mucoralean fungi are mostly saprotrophs that are frequently encountered in soil habitats. Using an isolation temperature of circa 25°C, other workers obtained these fungi from a wide diversity of geographical areas in southern Africa. However, it is known that psychrotolerant mucoralean fungi, able to grow at 25°C as well as at 5°C, occur in pristine Alti Mountain Grassland. Nothing is known about the diversity of these psychrotolerant soil fungi in other vegetation types of South Africa. Consequently, in this study, the psychrotolerant fungal taxa and numbers in soil from a vineyard and from pristine Mountain Fynbos were determined using an incubation temperature of 4°C and a complex isolation medium. The latter contained agar, malt extract, peptone, yeast extract, penicillin and streptomycin sulphate. Soil samples were analysed in late summer, autumn and mid-winter. It was found that, for the samples taken in late summer and autumn, the diversity of mucoralean species in the soil differed between fynbos and vineyard. In winter however, no significant difference was detected between the Shannon's diversity indices of mucoralean species in the soil samples taken from the two habitats. It was found that in both soil types, the percentage mucoralean fungi on the plates increased from summer to winter. In addition, the numbers of detectable Morlierella subgenus Morlierella on the plates were higher in winter than in late summer. The diversity of mucoralean species obtained during winter in fynbos and vineyard soil was significantly less than the diversity of these species in Alti Mountain Grassland soil. To determine if the Morlierella subgenus Morlierella isolates from the fynbos and vineyard soil, and those obtained from Alti Mountain Grassland, differ in the ability to grow at low temperatures, the radial growth rate on malt extract agar at 4°C and BOC was determined for each isolate. The results indicate that not only did seasonal changes occur in the taxa within Morlierella subgenus Morlierella, but that the isolates dominating the soil in different seasons also differed in the ability to grow at low temperatures. The percentage of isolates that had reached greater colony diameters after B days of incubation at 4°C, was higher for the isolates obtained in the cold wet month of July than for those obtained in the warmer dryer month of February. Similar results were obtained with the radial growth experiments conducted at BOC. The Morlierella subgenus Morlierella isolates obtained in winter from fynbos and vineyard soil showed less variation in low temperature growth rate than the isolates of this taxon obtained in winter from Alti Mountain Grassland soil during a previous study. This variation corresponds to the greater number (20) of Morlierella subgenus Morlierella species found in the grassland soil. Altogether only seven species of this subgenus was detected during the present study in the fynbos and vineyard soil samples. It was speculated that this difference in diversity between the fynbos and vineyard isolates, and the grassland isolates obtained in a previous study, might have been as a result of differences in the habitat or the enumeration methods used. The phylogenetic relationship between different psychrotolerant isolates of Morlierella subgenus Morlierella originating from the soil of the fynbos, vineyard and Alti Mountain Grassland, was subsequently determine through comparison of ITS regions, within ribosomal RNA repeats. Consequently, 45 psychrotolerant Morlierella subgenus Morlierella isolates originating from the three soil habitats was compared on the basis ITS 1 nucleotide sequence composition and radial growth rate at 4°C. Phylogenetic analyses showed that the isolates could be grouped into two clusters correlating with the ability to grow at low temperatures. Each cluster was further subdivided into two subgroups. It was found that except for one subgroup and the reference strain occurring in another subgroup, all the subgroups contain isolates originating from a single soil habitat. Therefore, the ITS 1 sequence of these fungi seems to indicate the original habitat and ability to grow at low temperatures. This correlation of the ITS sequence with the ecological habitat of a fungus has also been observed by other workers for other fungal groups. / AFRIKAANSE OPSOMMING: Mucoraliese fungi is meestal saprotrofe wat dikwels in grondhabitatte aangetref word. Deur gebruik te maak van 'n isolasietemperatuur van circa 25°C, het ander werkers dié fungi van 'n wye verskeidenheid geografiese gebiede in suidelike Afrika verkry. Dit is egter bekend dat die psigrotolerante mucoraliese fungi, wat in staat is om by 2SoC en ook by SaC te groei, in ongeskonde Alti Berg-Grasland voorkom. Niks is egter bekend oor die diversiteit van dié psigrotolerante grondfungi in ander veldtipes van suidelike Afrika nie. Die psigrotolerante fungustaksa en -getalle in grond van 'n wingerd en van ongeskonde Berg Fynbos is gevolglik in dié studie bepaal deur gebruik te maak van 'n inkubasietemperatuur van 4"C en 'n komplekse isolasiemedium. Laasgenoemde het agar, moutekstrak, peptoon, gisekstrak, penisillien en streptomisiensulfaat bevat. Grondmonsters is in die laatsomer, herfs en midwinter geanaliseer. Daar is 'n verskil gevind tussen die diversiteit van die mucoraliese spesies in die grond van fynbos en dié van wingerd in die monsters wat in die laatsomer en midwinter geneem is. In die winter is daar egter geen beduidende verskil gevind tussen die Shannon diversiteitsindekse van mucoraliese spesies in die grondmonsters wat uit die twee habitatte getrek is nie. In albei grondtipes is daar gevind dat die persentasie mucoraliese fungi op die plate toegeneem het van somer tot winter. Daarby was die aantal waarneembare Morlierella subgenus Morlierella op die plate meer in die winter as in die laatsomer. Die diversiteit van mucoraliese spesies wat in die winter uit fynbos- en wingerdgrond verkry is, was beduidend minder as die diversiteit van dié spesies in Alti Berg-Grasland grond. Om te bepaal of die Morlierella subgenus Morlierella isolate van die fynbos- en wingerdgrond en dié van Alti Berg-Grasland van mekaar verskil ten opsigte van hul vermoë om by lae temperature te groei, is die radiale groeitempo op moutekstrak by 4"C en aoc vir elke isolaat bepaal. Die resultate dui aan dat daar nie alleen seisoenale veranderinge in die taksa binne Morlierella subgenus Morlierella voorkom nie, maar dat die isolate wat tydens verskillende seisoene uit die grond verkry is, ook ten opsigte van hul groeivermoë by lae temperature van mekaar verskil. Die persentasie isolate wat groter kolonie diameters bereik het ná B dae inkubasie by 4°C, was hoër vir die isolate van die koue, nat Juliemaand as vir dié wat in die warmer en droër Februariemaand verkry is. Soortgelyke resultate is verkry met radiale groei-eksperimente wat by BOC gedoen is. Die MortierelIa subgenus MortierelIa isolate wat in die winter uit fynbos- en wingerdgrond verkry is, het In kleiner variasie in hul groeitempo by lae temperature getoon as die isolate in dié takson wat tydens 'n vorige studie in die winter uit Alti Berg-Grasland grond verkry is. Dié variasie stem ooreen met die groter aantal (20) MortierelIa subgenus MortierelIa spesies wat in die graslandgrond gevind is. Slegs sewe spesies van dié subgenus is gedurende die huidige studie in die fynbos- en wingerdgrondmonsters waargeneem. Daar is gespekuleer dat dié verskil in diversiteit tussen die fynbos- en wingerdisolate en die graslandisolate van die vorige studie die gevolg mag wees van verskille tussen die habitat of die enumerasiemetodes wat gebruik is. Die filogenetiese verwantskap tussen verskillende psigrotolerante isolate van MortierelIa subgenus MortierelIa uit die grond van die fynbos, wingerd en Alti Berg-Grasland, is vervolgens bepaal deur 'n vergelyking van interne getranskribeerde spasieerder (ITS) areas, binne ribosomale RNS herhalings. Daar is gevolglik 45 psigrotolerante MortierelIa subgenus MortierelIa isolate uit die drie grondhabitatte met mekaar vergelyk op grond van die basis ITS 1 nukleotied opeenvolgingsamestelling en radiale groeitempo by 4°C. Filogenetiese analises het die isolate in twee groepe verdeel op grond van hul vermoë om by lae temperature te groei. Elke groep is verder in twee subgroepe verdeel. Daar is gevind dat behalwe vir een subgroep en die verwysingstam wat in 'n ander subgroep voorgekom het, elkeen van die subgroepe bestaan het uit isolate wat van 'n enkele grond habitat verkry is. Dit wil dus voorkom of die ITS 1 opeenvolging van dié fungi 'n aanduiding gee van die oorspronklike habitat en die vermoë om by lae temperature te groei. Dié korrelasie tussen die ITS opeenvolging en die ekologiese habitat van 'n fungus is ook deur ander werkers vir ander fungusgroepe waargeneem.

Thesis (PhD (Soil Science))--University of Stellenbosch, 2007. / Trace elements occur naturally in soils, usually at low concentrations (<0.1% or <1000 mg kg-1 of the earth’s crust), as a result of weathering and pedogenic processes acting on the rock fragments from which soil develops (parent material). Since about 98% of human food is produced on land, soil is the primary source supplying these elements to the food chain. Although cases of trace element deficiency and toxicity have been documented in many parts of South Africa, no comprehensive description of trace element concentration has yet been attempted for South Africa as a whole. The Natural Resources Land Type mapping project, initiated in the mid-1970s, has provided a collection of samples (approximately 4500) from soil profiles selected to represent the main soil forms in each land type and therefore to provide representative coverage of most of the soils of South Africa. These archived samples have now been analysed for a spectrum of trace elements, in terms of both available and total concentrations as well as other soil properties. Although detailed information is available on a wide range of trace metals, the seven trace metals considered to be of most interest in a South African context due to natural geological occurrences were selected for this study, including Cd, Co, Cr, Cu, Pb, Ni and Zn. This data was used to: • determine baseline concentrations in SA soils; • determining threshold values for South African agricultural soils receiving sewage sludge at agronomic rates; • determining the influence of certain soil properties on the baseline concentrations of these trace elements in SA soils; and • development of a bioavailable trace element distribution map for SA. The range, the mean and standard deviation (both arithmetic and geometric), and the median were used to summarize the data statistically. The baseline concentration range was calculated using the quotient and product of the geometric mean and the square of the geometric standard deviation, including data below the instrument detection limit. The upper limit of the baseline concentration range was set at the 0.975 percentile value of the population in order to minimize the influence of contamination and the lower limit at the 0.025 percentile value to minimize problems that might be associated with analytical uncertainty near the lower limit of detection. The quantile regression statistical approach was followed to illustrate the relationship between soil properties and trace element concentrations in soils. The soil properties that showed the strongest relation were CEC, clay content, pH (H2O) and S value (base status). The soils were then divided into different classes according to these soil properties and baseline concentrations were derived for the different classes. Soils with low clay contents have lower trace element concentrations than soils with higher clay contents, soils with low or high pH levels have lower trace element contents than soils with intermediate pH values and mesotrophic soils have higher trace element concentrations than dystrophic soils. This information is useful for the compilation of trace element distribution maps for South Africa where different soil forms and series/families could be classified into different classes to determine areas of potential deficiencies as well as toxicities. South Africa, with its diverse geology, has areas of both trace element toxicities and deficiencies and for decision-making purposes it is necessary to identify these areas. Mapping of trace element levels based on soil samples would provide valuable information, which cannot be obtained from geological or geographical maps. Statistical analyses of the data (clay %, base status, pH (H2O) and NH4EDTA extractable trace element concentrations) indicated that soils could be divided into five trace element classes based on their clay content, pH and base status (dystrophic, mesotrophic and eutrophic). The soil series according to the binomial soil classification system for South Africa were then divided into these different classes. The geometric means for each clay class were determined and the baseline concentration range for each class was calculated. The land type maps were used as basis for the distribution maps. A general trace element distribution map for South Africa was derived from this data as well as Cu and Zn distribution maps. A random selection of 500 soil samples across the country was used to verify the accuracy of the distribution map. The general trace element distribution map indicate, with a confidence level between 89 and 96%, where the potentially available trace element content of South African soils are low (deficient) too moderately high, excluding rocky areas and areas with limited soil. The Cu and Zn maps indicate the distribution and expected baseline concentrations of these specific elements in South African soils. The same methodology could be applied to derive risk maps for all the individual trace elements to indicate the distribution and expected baseline concentrations of the elements in South Africa. This presentation of baseline concentrations, reflecting likely natural ranges in South African soils, is the first quantitative report on the spatial extent and intensity of Zn, Cu and Co deficiency in South African soils. The proposal of new threshold values for trace elements in agricultural soils will be valuable in setting more realistic norms for environmental contamination that accommodate the geochemical peculiarities of the region, one example being rather high Cr and Ni concentrations with low bio-availability. This information should be of value not only in environmental pollution studies but also in health, agriculture, forestry and wildlife management. The following recommendations are made: • The baseline concentrations could be used to determine site specific threshold values based on soil properties and soil type. Soils with lower pH, clay content and CEC would require more protection than soils with high pH, clay content and CEC and therefore the threshold levels for these soils should be lower. • Although the distribution maps can be used to indicate broad areas of trace element deficiencies and toxicities, more detailed investigations are recommended for areas where problems are experienced. The same methodology could be applied on smaller scale to increase the value of the map and to add more value on a regional scale. The maps could be used for regional soil quality assessment especially in areas where trace element deficiencies or toxicities could result in negative effects on plants and animals.

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.

Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Biochar is a carbon-rich solid material produced during pyrolysis, which is the thermal degradation of biomass under oxygen limited conditions. Biochar can be used as a soil amendment to increase the agronomic productivity of low potential soils. The aim of this study was to investigate the effect of applying locally-produced biochar on the fertility of low-nutrient holding, sandy soil from the Western Cape, and to determine the optimum biochar application level. Furthermore, this study investigates the effect of biochar on the leaching of an inorganic nitrogen fertilizer and a multi-element fertilizer from the sandy soil. The biochar used in this study was produced from pinewood sawmill waste using slow pyrolysis (450 °C). The soil used was a leached, acidic, sandy soil from Brackenfell, Western Cape. In the first study, the sandy soil mixed with five different levels of biochar (0, 0.05, 0.5, 0.5 and 10.0 % w/w) was chemically characterised. Total carbon and nitrogen, pH, CEC and plant-available nutrients and toxins were determined. The application of biochar resulted in a significant increase in soil pH, exchangeable basic cations, phosphorus and water holding capacity. A wheat pot trial using the biochar-amended soil was carried out for 12 weeks and to maturity (reached at 22 weeks). The trial was conducted with and without the addition of a water-soluble broad spectrum fertilizer. Results showed that biochar improved wheat biomass production when added at low levels. The optimum biochar application level in the wheat pot trial was 0.5 % (approximately 10 t ha-1 to a depth of 15 cm) for the fertilized treatments (21 % biomass increase), and 2.5 % (approximately 50 t ha-1 to a depth of 15 cm) for unfertilized treatments (29 % biomass increase). Since most biochars are alkaline and have a high C:N ratio, caution should be taken when applying it on poorly buffered sandy soil or without the addition of sufficient nitrogen to prevent nutrient deficiencies. In the second study, leaching columns packed with sandy soil and biochar (0, 0.5, 2.5 and 10.0 % w/w) were set up to determine the effect of biochar on inorganic nitrogen fertilizer leaching over a period of 6 weeks. It was found that biochar (0.5, 2.5, and 10.0 % w/w) significantly reduced the leaching of ammonium (12, 50 and 86 % respectively) and nitrate (26, 42 and 95 % respectively) fertilizer from the sandy soil. Moreover, biochar (0.5 %) significantly reduced the leaching of basic cations, phosphorus and certain micronutrients. This study demonstrated the potential of biochar as an amendment of acidic, sandy soils. Our findings suggest that an application rate of 10 t ha-1 should not be exceeded when applying biochar on these soils. Furthermore, biochar application can significantly reduce nutrient leaching in sandy agricultural soils. / AFRIKAANSE OPSOMMING: Biochar is ʼn koolstof-ryke, soliede materiaal geproduseer gedurende pirolise, wat die termiese degradasie van biomassa onder suurstof-beperkte omstandighede behels. Biochar kan gebruik word as ʼn grondverbeterings middel om die agronomiese produktiwiteit van grond te verhoog. Die doel van hierdie studie was om die effek van plaaslike vervaardigde biochar op die vrugbaarheid van die sanderige grond van die Wes-Kaap te ondersoek, en om die optimale biochar toedieningsvlak te bepaal. Verder, het hierdie studie die effek van biochar op die loging van anorganiese stikstof kunsmis en ‘n multi-elementkunsmis op sanderige grond ondersoek. Die biochar wat in hierdie studie gebruik is, is van dennehout saagmeul afval vervaardig d.m.v. stadige pirolise (450 °C). Die grond wat in hierdie studie gebruik is, is ‘n geloogde, suur, sanderige grond van Brackenfell, Wes-Kaap. In die eerste studie, is ‘n chemiesie ondersoek van die sanderige grond wat vermeng met is met vyf verskillende vlakke van biochar (0, 0.05, 0.5 en 10.0 % w/w) uitgevoer. Totale koolstof en stikstof, pH, KUK, en plant-beskikbare voedingstowwe en toksiene is in die grondmengsels bepaal. Die toediening van biochar het ‘n veroorsaak dat die grond pH, uitruilbare basiese katione, fosfor en waterhouvermoë beduidend toegeneem het. ‘n Koringpotproef was uitgevoer vir 12 weke en ook tot volwassenheid (wat op 22 weke bereik was) om die effek van die biochar op die sanderige grond teen die vyf verskillende toedieningsvlakke te bepaal. Daar was behandelings met en sonder die bykomstige toediening van ‘n wateroplosbare breë-spektrumkunsmis. Resultate toon dat die toediening van biochar teen lae vlakke koringbiomassa produksie verbeter. Die optimale biochar toedieningsvlak in die koringpotproef is 0.5 % (omtrent 10 t ha-1 tot ‘n diepte van 15 cm) vir die bemeste behandeling (21 % biomassa toename), en 2.5 % (omtrent 50 t ha-1 na ‘n diepte van 15 cm) vir onbemeste behandelings (29 % biomassa toename). Aangesien die meeste biochars alkalies is en ‘n hoë C:N verhouding besit, moet sorg gedra word wanneer dit op swak-gebufferde of lae N-houdende sanderige gronde toegedien word. Die resultate het aangedui dat die biochar versigtig aangewend moet word om grond oorbekalking te voorkom. In die tweede studie, was kolomme gepak met 2.0 kg van die sanderige grond gemeng met biochar (0, 0.05, 0.5, 2.5 en 10.0 % w/w) om die effek van biochar op die loging die anorganiese stikstof kunsmis oor ‘n tydperk van 6 weke om vas te stel. Daar is gevind dat biochar (0.5, 2.5 en 10.0 % w/w) die loging van ammonium (12, 50 en 86 % onderskeidelik) en nitraat (26, 42 en 95 % onderskeidelik) op sanderige grond aansienliek verminder. Verder, het biochar (0.5 %) die loging van basiese katione, fosfor en mikrovoedingstowwe aansienlik verminder. Hierdie studie het die potensiaal van biochar as verbeteringmiddel van suur, sanderige grond gedemonstreer. Ons bevindinge dui daarop aan dat ‘n toepassing vlak van 10 t ha-1 moet nie oorskry word nie wanneer biochar op hierdie gronde toegedien word. Die toediening van biochar op sanderige grond kan die loging van voedingstowwe aansienlik verlaag.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Northern Cape Province of South Africa has played host to numerous mining activities for over a century. To date, most of the mining activity has ceased, leaving the area laden with derelict mine sites and unlined tailings dumps. One such site is the Spektakel mine situated to the west of the town of Springbok. The unlined copper and sulphide rich tailings at the site have the potential to leach elevated concentrations of copper and acidic water into the Buffels River downslope of the site. This poses a threat to the surrounding communities that rely mainly on the river to supply water for drinking, livestock and irrigation. The soil surrounding the tailings dumps was characterised in terms of its mineralogical and chemical properties. The results indicate that the soil contains elevated concentrations of Cu2+, which is bound in the soil in the form of the secondary copper hydroxy mineral atacamite (Cu2(OH)3Cl). No other secondary copper minerals were identified at the site. Analysis of the solution present on the surface of the tailings dumps indicate that the tailings are the main source of the high Cu2+, Mg2+ and SO42- concentrations observed in the surrounding soils. As this solution migrates through the tailings dumps, into the soil, it accumulates Cl- through halite dissolution. The resulting acidic Cu2+, Mg2+, SO42- and Cl- solution reacts with the calcite in the soil, replacing it with atacamite. To determine why only a copper chloride mineral formed in the sulphate rich environment a synthetic solution with the composition of a solution in equilibrium with the soil was evaporated, both in the presence and absence of calcite. The results indicate that when the solution comes into contact with calcite, atacamite immediately precipitated, removing the Cu2+ from the solution. In the absence of calcite Cu2+ remains conservative, accumulating in the solution without precipitating a copper sulphate mineral. This establishes that the elevated Mg2+ concentration of the solution induces the formation MgSO4 aqueous complexes that reduce the activity of free sulphate, thus restricting copper sulphate mineral formation. The results from the soil characterization indicate that the atacamite stabilization mechanisms (circumneutral pH, high Cl- concentration and calcite) in the soil are diminishing. During sporadic rain events the acidic tailings solutions dissolve the calcite and temporarily reduce the Cl- concentration of the soil. To determine how these decreases will influence Cu2+ mobility in the soil, the stability of atacamite was tested by reducing the pH both in the presence and the absence of chloride. The results indicate that an elevated Cl- concentration and a pH > 6 stabilizes atacamite. A decrease in either of these parameters destabilizes atacamite and favours its dissolution. The study concludes that the current chemical conditions in the soil at Spektakel favour the stability of atacamite. However, continued sporadic rain events will reduce the Cl- concentration in the soil by increasing the SO42- concentration. This acidic solution will dissolve the calcite in the soil, thus reducing the buffering capacity of the soil, leading to the instability of atacamite, resulting in the leaching of large quantities of Cu2+ into the surrounding water bodies. / AFRIKAANSE OPSOMMING: Die mynbou bedryf was die ekonomiese dryfkrag van die Noord-Kaap Provinsie van Suid-Afrika vir meer as ‘n eeu. Die area was die gasheer vir ‘n verskeidenheid mynbou aktiwiteite tot die mynmaatskappye besluit het om mynproduksie te staak en die gebied te verlaat. Die mynmaatskappye het geen rehabilitasie aan die myne en mynhope verrig nie. Die verlate myne lê verspreid in die area met oop mynhope wat koper en ander swaar metale in die grond, sowel as in die water, na omliggende areas kan versprei. Een van dié verlate myne is die Spektakel myn 40 km wes van Springbok. Die mynhope by Spektakel kan moontlik koper en ander swaar metale in die Buffelsrivier, wat langs die myn verby loop, loog. Dit dien as ‘n bedreiging vir die omliggende gemeenskappe wat staatmaak op die water vir drinkwater en besproeiing. Die grond rondom die mynhope was ge-analiseer om te bepaal hoe erg ‘n bedreiging die mynhope vir die omgewing is. Die resultate dui daarop dat die grond hoë konsentrasies Cu2+ bevat wat vasgebind is in die sekondêre koper mineral atakamiet (Cu2(OH)3Cl). Geen ander sekondêre koper minerale is in die grond geïdentifiseer. Die analise van die oplossing wat bo-op die mynhoop aangetref is dui aan dat dié oplossing suur en gekonsentreerd is t.o.v. Cu2+, Mg2+ en SO42-. Terwyl die oplossing deur die mynhoop migreer los dit haliet in die grond op wat Cl- tot die oplossing byvoeg. Wanneer hierdie suur en Cu2+, Mg2+, SO42- en Cl- ryke oplossing met die kalsiet in die grond reageer word die kalsiet vervang met atakamiet (Garrels en Stine, 1948). Om vas te stel waarom slegs 'n koperchloried mineraal vorm in die sulfaat ryke grond was ‘n oplossing, met ‘n samestelling soortgelyk aan 'n oplossing in ewewig met die grond, verdamp in beide die teenwoordigheid en afwesigheid van kalsiet. Die resultate van die eksperiment dui daarop dat wanneer die oplossing in kontak kom met kalsiet atakamiet onmiddellik neerslaan en Cu2+ uit die oplossing verwyder. In die afwesigheid van kalsiet bly Cu2+ konserwatief in die oplossing; die Cu2+ hoop op in die oplossing en slaan nooit neer nie. Daar is vasgestel dat die verhoogde Mg2+ in die grondoplossing MgSO4 water komplekse vorm wat die aktiwiteit van SO42- verlaag en verhoed dat kopersulfaat minerale kan vorm. Verdere navorsing dui aan dat die chemiese meganismes wat atakamiet in die grond stabiliseer besig is om te kwyn. Gedurende sporadiese reën buie word die kalsiet in die grond opgelos deur die suur mynhoop oplossings wat die pH van die grond verlaag. Die mynhoop oplossing verryk ook die grond t.o.v SO42- wat die Cl- konsentrasie verlaag. Om te bepaal hoe hierdie afname in Cl- konsentrasie en pH die migrasie van Cu2+ beïnvloed was atakamiet oplossbaarheid bepaal. Atakamiet was onderskeidelik geplaas in ‘n suiwer water en chloried oplossing tewyl die pH verlaag was om te bepaal hoe atakamiet oplos in elk van die oplossings. Die resultate dui aan dat 'n verhoogde Cl- konsentrasie en pH > 6 atakamiet stabiliseer. Die afname van beide hierdie veranderlikes het veroorsaak dat atakamiet makliker ontbind en Cu2+ vrystel. Die gevolgtrekking van die studie is dat die huidige chemiese toestande in die grond by Spektakel gunstig is vir die stabiliteit van atakamiet. Met sporadiese reën buie neem die Cl- konsentrasie in die grond af en los kalsiet op. Hierdie afname in pH en Cl- konsentrasie maak atakamiet meer onstabiel wat gevolglik Cu2+ in die grond en water rondom Spektakel vrystel.

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Apple replant disease (ARD) is one of the major impediments to the establishment of an economically viable apple orchard on sites previously planted to apple. In spite of extensive research on ARD, the etiology remains to be fully elucidated. A possible biological origin of ARD etiology in South Africa was investigated by the dilution of replant field soil with sterilised soil. Commercial orchards with ARD were selected for use in pot trials and disease severity evaluated after three months, by measuring shoot length, dry mass of plants as well as root discolouration. Although diluting replant soil to 25 and 50% (v/v) significantly reduced the effects of ARD, symptoms were only absent in 0% replant soil. It was clear that seedlings planted in any mixture containing replant soil, even only 25% replant soil, consistently exhibited symptoms of stunted growth and root discolouration similar to those seedlings grown in 100% replant soil. This indicates that ARD in South Africa is primarily of a biological nature. As an initial step in formulating sustainable disease control alternatives to replace methyl bromide, pot trials were conducted to assess the impact of compost treatments as well as biological control products on ARD. Compost as well as sterilised and unsterilised compost teas (compost extract) significantly increased seedling growth even under optimum nutrient conditions when compared to the control, suggesting that they negate the effects of ARD. Results also indicated that applying high concentrations of compost does not necessarily provide additional growth benefits compared to lower concentrations. Results with biocontrol formulations were less favourable. Only one of the biocontrol formulations, a combination of Bacillus spp. (Biostart®) improved growth significantly compared to the control. There was, however, some inconsistency with results for the different trials conducted using this product. Fungal as well as nematode populations associated with ARD soils were characterised to the generic level to get a clearer understanding of the etiology of ARD in South Africa. Pythium and Cylindrocarpon spp. were consistently isolated from all six replant soils in all trials that formed part of this study, indicating that these fungi may have a role in ARD etiology in South Africa. Nematodes implicated in ARD development were inconsistently associated with ARD soils used in these studies. This suggests that nematodes do not have a primary causal role in ARD etiology in South Africa. Field trials were conducted in commercial orchards to assess the impact of organic amendments and promising biological control products, as indicated by the pot trials, on ARO severity under field conditions. These biological soil amendments were also compared with the standard chemical control methods for ARO, methyl bromide and chloropicrin. In all three trials established, compost and mulch as well as manure and mulch, consistently increased growth to the same extent as the standard chemical treatments and by combining these chemical treatments with organic amendments a significant, additional growth increase could be attained. Biocontrol formulations evaluated in field studies gave variable results. Biostart® improved growth when applied on its own, but not in combination with the chemical Herbifume (metham-sodium). Inoculating soil with effective microorganisms (EM), consisting primarily of photosynthetic bacteria, had no significant effect on growth. Results from this study indicate that application of organic amendments could possibly substitute for soil fumigation in replanted apple orchards. However, compost quality standards need to be implemented and because few types of compost are universally effective, different types of composts should be compared in specific soil environments before recommendations can be made. Oue to variable results with biocontrol products, ARO management with these biological soil amendments cannot be guaranteed at this stage and further studies are recommended. / AFRIKAANSE OPSOMMING: EVALUERING VAN DIE SPESIFIEKE APPELHERVESTIGING-PROBLEEM IN BOORDE IN DIE WES-KAAP Appelhervestiging-siekte (AHS) skep 'n groot probleem in die vestiging van jong appelbome op grond waar daar reeds voorheen appels verbou is. Ten spyte van omvangryke navorsing is die oorsaak van die probleem nog hoofsaaklik onbekend. 'n Moontlike biologiese oorsaakleer is in Suid-Afrika ondersoek deur die hervestigings-effek te probeer verminder deur die vermenging van hervestigingsgrond met gesteriliseerde grond. Kommersiële boorde met 'n appelhervestigingsprobleem is geselekteer en gebruik in potproewe. Die ernstigheidsgraad van die siekte is na drie maande se groei geevalueer deur lootlengte, droë massa en wortelverkleuring te meet. Alhoewel verdunning van die hervestigingsgrond tot 50 en 25% (vlv) die effek van AHS op groei betekenisvol verminder het, kon die skadelike effek van die veroorsakende faktor slegs uitgeskakel word deur saailinge in 100% gesteriliseerde grond te plant. Dit was duidelik dat saailinge wat in enige grondmengsel geplant is waarin hervestigingsgrond voorgekom het, selfs al was dit net 25%, konsekwent simptome van vertraagde groei en wortelverkleuring getoon het. Dit is 'n aanduiding dat AHS in Suid-Afrika hoofsaaklik biologies van aard is. Potproewe is uitgevoer as 'n eerste stap in die formulering van volhoubare siektebeheer-strategieë, om die impak van kompos-behandelings en biologiese beheer produkte op AHS te ondersoek. Kompos sowel as gesteriliseerde en ongesteriliseerde kompos-tee (kompos-water) het, selfs onder optimale voedingsomstandighede, die groei van saailinge betekenisvol verbeter. Dit dui aan dat hierdie behandelings die effek van AHS kan teenwerk. Resultate het ook daarop gedui dat hoër kompos konsentrasies nie noodwendig enige addisionele voordele vir groei inhou in vergelyking met laer konsentrasies nie. Resultate met biologiese beheer produkte was minder gunstig. Slegs een van die produkte wat geëvalueer is, 'n kombinasie van Bacillus spp. (Biostart®), het groei betekenisvol verbeter in vergelyking met die kontrole. Resultate was egter inkonsekwent vir die verskillende proewe waarin hierdie produk gebruik is. Swampopulasies sowel as aalwurmpopulasies wat met hervestigingsgrond geassosieer word, is geïdentifiseer tot op generiese vlak om vas te stel waardeur AHS in Suid-Afrika veroorsaak word. Pythium en Cylindrocarpon spp. is konsekwent van al ses hervestigingsgronde geïsoleer wat daarop dui dat hierdie twee swamgenera 'n beduidende rol in AHS ontwikkeling in Suid-Afrika mag hê. Aalwurms wat aangedui is in die literatuur om 'n moontlike rol in AHS te hê, was slegs in enkele gevalle geassosieer met hervestigingsgronde waarvan in hierdie studie gebruik gemaak is. Die gevolg-trekking is dus gemaak dat aalwurms nie 'n betekenisvolle rol speel as hoof-veroorsakende organisme onder Suid-Afrikaanse toestande nie. Veldproewe is uitgevoer in kommersiële appelboorde om vas te stel wat die effek van organiese materiaal, asook belowende biologiese beheermiddels, soos aangedui deur potproewe, op AHS onder veldtoestande is. Die biologiese grondtoedienings is ook vergelyk met die standaard chemiese beheermiddels (metielbromied en chloorpikrien). In al drie proewe wat gevestig is, het kompos met 'n deklaag, sowel as kraalmis met 'n deklaag, groei betekenisvol verbeter tot dieselfde mate as chemiese middels. Daar kon ook 'n beduidende, addisionele groeitoename gemeet word in gevalle waar chemiese middels met organiese materiaal gekombineer is. Resultate met biologiese beheer formulasies wat onder veldtoestande geëvalueer is, het gevarieer. Biostart® het groei verbeter wanneer dit alleen toegedien is, maar in kombinasie met die chemiese middel Herbifume (metham-sodium) het dit geen effek gehad nie. Die inokulering van grond met 'n oplossing van effektiewe mikroorganismes (EM) wat hoofsaaklik uit fotosinterende baterieë bestaan, het ook geen betekenisvolle effek op groei gehad nie. Die gevolgtrekking is gemaak dat toediening van organiese materiaal moonlik as plaasvervanger vir metielbromied-beroking kan dien in die beheer van AHS. Die nodige komposkwaliteit-standaarde moet egter eers geïmplimenteer word. Omdat feitlik geen kompos universeel effektief kan wees nie, is dit ook nodig dat verskillende tipes kompos met mekaar vergelyk moet word in spesifieke grondtoestande voordat verdere aanbevelings gemaak kan word. As gevolg van variërende resultate met biologiese beheer produkte kan AHS beheer met hierdie middels nie gewaarborg word op hierdie stadium nie en verdere studies word aanbeveel.

Although a considerable amount of work has been done on the fauna of the soil of temperate forests and pastures, very little is known about that of tropical and sub-tropical soils. Most of the work on tropical soils concerns the fauna of tropical forests ... . The present investigation represents an attempt to discover the effect of an imported perennial tropical and sub-tropical plant, the Pineapple, on the soil fauna of a semi-arid region (rainfall 15-25 inches). Intro., p. 1-2

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2005. / This thesis forms part of a research program that is investigated by ARC Infruitec- Nietvoorbij and the University of Stellenbosch. The aim of this program is to quantify the effect of soil and climate on wine quality and character as a basis for scientific demarcation of production regions. Natural factors are first quantified and characterised so that relative homogeneous natural terroir units (NTU) can be identified. Thereafter wines made from these different localities are assessed for similarities which permit grouping of localities into viticultural terroirs. The present study involved seven research plots in the Robertson district, making use of initial measurements by ARC Infruitec-Nietvoorbij in the 2000/01 and 2001/02 seasons together with more intensive measurements in the 2002/03 and 2003/04. The seven plots are located in two wards, Le Chasseur and Vinkrivier. Sauvignon blanc plots were marked at two localities, each with two sub-plots occurring in one block. Three Cabernet Sauvignon plots were marked out. Two plots occurred in one block in Le Chasseur and one plot in Vinkrivier. Plots within the same block were located on different soil types so that the effect of soil type on wine quality and character could be monitored. Morphological examination of soil profiles at each plot was carried out together with physical and chemical analysis of samples taken at 30cm depth intervals. Soil water content was measured at regular intervals to assess soil water tension. Vineyard performance was assessed in terms of phenology, root system studies, leafwaterpotential measurements, canopy quality assessment, leaf analysis, shoot growth, and data relating to ripening, harvest and pruning. Wines were made from each plot by ARC Infruitec- Nietvoorbij and evaluated by a tasting panel after six months and then again after eighteen months. Meteorological data were collected in each ward.