Thesis (M.Sc.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Full text also available online. Scroll down for electronic link.

Thesis (Ph. D.)--Oregon State University, 1994. / Typescript (photocopy). Includes bibliographical references (leaves 109-125). Also available on the World Wide Web.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2000. / Includes bibliographical references (p. 517-565).

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Full text also available online. Scroll down for electronic link.

Thesis (MScAgric)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Plant roots are central to C- and N-cycling in soil. However, (i) plants differ strongly in tissue recalcitrance (e.g. lignin content) affecting their mineralization in soil, and (ii) rhizodeposits also vary strongly in terms of the metabolites that they contain. Therefore, (i) we used 13C labelled ryegrass root and shoot residues as substrates to investigate the impact of tissue recalcitrance on soil processes through controlled incubation of soil, (ii) we assessed variations in root C-deposition between barley genotypes and their respective impacts on soil processes using 13CO2 labelled plants, (iii) using 13C/15N enriched ryegrass root residues as tracer material, we investigated the impacts of barley genotypes on mineralization of recently incorporated plant residues in soil and plant uptake of the residue-derived N, and (iv) we applied a quantitative trait loci analysis approach to identify barley chromosome regions affecting soil microbial biomass and other soil and root related traits. In the first study, addition of root residues resulted in reduced C-mineralization rates, soil microbial activity and soil organic matter (SOM) priming relative to shoot residues. Planted experiments revealed (i) genotype effects on plant-, SOM- and residuederived surface soil CO2-C efflux and showed that incorporation of plant derived-C to the silt-and-clay soil fraction varied between genotypes, indicating relative stabilization of root derived-C as a result of barley genotype, (ii) that plant uptake of residue released N between genotypes was linked to genotype impacts on residue mineralization, and (iii) barley chromosome regions that influence plant-derived microbial biomass C. These results (i) suggest that greater plant tissue recalcitrance can lower soil C-emissions and increase C-storage in soil, and (ii) demonstrate the barley genetic influence on soil microbial communities and C- and N-cycling, which could be useful in crop breeding to improve soil microbial interactions, and thus promote sustainable crop production systems.

The Matsqui area of the Lower Fraser Valley exhibits extreme soil heterogeneity, as the alluvial soils in the area have been deposited by the Fraser River as a series of coarse-textured ridges and finer-textured depressional areas. This variability poses some obvious problems with respect to agricultural management. The main aim of this study was to evaluate soil spatial variability in four fields, and to relate this soil variability to corn production and quality. Site conditions, topography, and soil chemical and physical variables were related to corn biomass and nutrient concentrations using conventional correlation/regression analyses, and more spatially representative techniques such as those provided by remote sensing and geographic information systems. Variations in such biophysical variables as soil moisture, elevation, and bulk density had consistent impacts on corn productivity, although these effects varied from field to field, being influenced by inherent soil properties and individual field management. Good relationships were found between pixel brightness values extracted from digitized colour infra-red photos and corn quality variables. In three out of four fields, near infra-red pixel values gave good estimates of total corn crude protein content. Significant relationships were also found between pixel brightness values and corn phosphorus and calcium contents in certain fields. The spatial variability of corn quality and biomass could be quantified using image analysis classification techniques. The resulting classified images indicate to the farm operator where high vs low quality corn is being produced, and thereby provide a tool for selectively managing and harvesting the fields. The relationships and quantification of corn productivity and quality in the fields can further be improved through incorporation of the image data with the biophysical data base using GIS techniques. A multiple regression equation showing a significant relationship between elevation and pixel brightness values, and total corn phosphorus concentration was incorporated within the GIS to produce a quantitative corn quality map for the field exhibiting this relationship. The GIS overlay capability facilitates the classification of several corn variables, and allows the results to be displayed in a spatial manner. For example, corn biomass and quality maps were overlain using GIS techniques, to produce a combination map which then reflected both the quality and quantity of corn found in the field. Through integration of remote sensing and GIS techniques, soil and crop variability can be displayed in a spatial manner. The output from such procedures can aid farm operators in making selective field management and harvesting decisions. / Land and Food Systems, Faculty of / Graduate

The sustained-yield policy presently practiced in British Columbia necessitates intensive management of forest land especially in the coastal region of the province. Soils, their nature and distribution, provide an ideal framework for a successful implementation of such management. A mapping system encompassing geology and soil and providing units interpretable for forestry practices was developed for the coastal forested lands of British Columbia. The system contains several steps of mappings corresponding to different intensities or levels of abstraction. These levels are: 1. Bedrock geology, 2. Surficial geology, 3. Geologic units, 4. Geologic unit - drainage classes, 5. Soil associations, and 6. Soil catenas. Mapping employs air-photo interpretation extensively and can be directly undertaken at any desired level for inventory of interpretation purposes. Grouping of units can also be made from any level of mapping. Maps showing the distribution of bedrock types, surficial materials and soils were prepared. Vancouver volcanics, Coastal intrusives and Cretaceous sandstones are the main bedrock formations. The surficial materials encompass the inter-glacial, glacial, post glacial and recent deposits, and consist of glacial tills, glaciofluvial, alluvial and marine sediments. The soils encountered represent the Podzolic, Brunisolic, Regosolic, Gleysolic and Organic Orders. The area is comprised of primarily Douglas-fir plantation, 20 to 30 years of age. Studies involving the soil-stand growth relationship were undertaken on the well drained soils developed on the major surficial materials. Morphological, physical, chemical and minera1ogica1 characteristics of soils and the growth statistics of stands were determined. The growth performance of Douglas-fir varied with the kind of soil. Growth was best on soils developed from marine clay. Soils developed from stony outwash exhibited the slowest growth and lowest productivity. Till soils had productivity between these two extremes. The textural components of soil (coarse sand, medium sand, total sand, total silt, coarse clay, fine clay and total clay), were correlated to growth. With respect to chemical nutrients, organic matter, calcium and magnesium, phosphorus and zinc appeared to be important factors. The soil moisture retention characteristics such as field capacity and available water showed correlation with growth. The relationship between the growth and soil characteristics became more apparent as stand age advanced. Interpretation of soil series and mapping units at different levels was carried out for: productivity for Douglas-fir, species suitability, logging hazard, slash burning hazard, natural regeneration probabi1ity, brush hazard, browsing hazard, thinning prescription, fertilizer recommendation, road construction suitability, and erosion. Two groupings, potential productivity and thinning recommendation for Douglas-fir, were undertaken. The study indicated that knowledge of soils and their distribution are prerequisite to the operational and economical management of forest and soil resources. Consequently, a classification scheme such as the one presented is the first and essential step towards the intensive management of the coastal forested lands in British Columbia. / Land and Food Systems, Faculty of / Folded map and table in back pocket. / Graduate

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M. S.