ENGLISH ABSTRACT: Agricultural production takes place in an uncertain and complex environment, with production the result of the culmination of a variety of factors within a greater system. Consequently, accounting for the influence of variables in the production system is very difficult, making it a daunting task for decision makers to make good decisions. In the wine grape production context, this problem is accentuated due to the capital intensive and perennial nature of investments, also giving rise to a path dependency. As a result it is essential to make strategically sound decisions in order to ensure the long-term profitability and financial feasibility of wine grape production. Decision making tools, like a model, can be of invaluable support for strategic decision making. A model is used to simplify reality, by imitating and simulating the actual system as closely as possible. A simulation model was therefore developed for this thesis to be able to evaluate the long-term financial impact of different wine grape production systems and to support strategic decision making. This model can be adapted to individual farm specific features, scenarios and preferences, in the evaluation and analysis of different investment and wine grape production system decisions. For this study, the nature of agricultural systems as well as qualities required by a simulation model, were investigated. The former is followed by an investigation of the effect of the grapevine and trellis specific qualities on the possibilities of the production system, as well as the implication of capital budgeting and financing considerations on the performance of the wine grape production system. In view of the above, the model was then applied to simulate and evaluate different wine grape production systems as well as a structural transition and expansion of wine grape production, for a simulated farm in the Breedekloof region, South Africa. The model can be used for decision making and scenario planning purposes by wine grape producers and stakeholders in the wine industry. / AFRIKAANSE OPSOMMING: Landbouproduksie vind plaas in ‘n komplekse omgewing met talle onsekerhede, waar produksie die resultaat is van ‘n aantal faktore binne ‘n groter geheel. Die uitdaging is dus om die spesifieke invloed van veranderlikes binne die produksiestelsel waar te neem sodat besluitnemers ingeligte besluite op grond daarvan kan maak. In die verbouing van langtermyn gewasse, spesifiek die van wyndruif verbouing, word hierdie probleem beklemtoon vanweë die kapitaal intensiewe en meerjarige aard van investerings, wat aanleiding gee tot die afhanklikheid van vorige besluite. Ten einde die langtermyn winsgewendheid en lewensvatbaarheid van wyndruif produksie te verseker, is strategiese en ingeligte besluite deurslaggewend. Hulpmiddels in die besluitnemingsproses, soos modelle, kan onskatbare ondersteuning bied in hierdie konteks. Die doel van ‘n model is om ‘n werklike stelsel te weerspieël, maar terselfdertyd word vereenvoudigende aannames gemaak. Vir die doeleindes van hierdie tesis is ‘n simulasie model ontwikkel om die langtermyn finansiële impak van verskillende wyndruif produksiestelsels te weerspieël en strategiese besluitneming te bevorder. Hierdie model kan aangepas word vir die individuele vereistes, voorkeure en kenmerke van individuele plase, ten einde verskillende investeringsbesluite en wyndruifproduksiestelsels te evalueer. Vir die doeleindes van hierdie studie is die aard van die stelsel waarin landbouproduksie plaasvind, asook eienskappe wat benodig word deur ‘n simulasiemodel, om ‘n goeie weerspieëling van die werklikheid te kan gee ondersoek. Daarna is die invloed van die prieëlstelsel oorweging op die wingerdstok, die uitvoerbaarheid van verskillende bewerkingspraktyke, asook die invloed van kapitaal- en finansiëringsoorwegings op die prestasie van die wyndruifproduksiestelsel ondersoek. In die lig van bogenoemde oorwegings is die model gebruik om verskillende wyndruifproduksiestelsels te simuleer en te evalueer, asook om ‘n strukturele oorgang en uitbreiding vir ‘n plaas in die Breedekloofstreek in Suid-Afrika te ondersoek. Wyndruif produsente en belanghebbendes in die wynbedryf kan hierdie model in scenario beplanning en besluitneming gebruik.

This dissertation develops a systems theory perspective of the concept of sustainable development, and explores a systematic approach to employ this concept to an economic analysis. An examination of interpretations, foundations and the framework of the concept of sustainable development is conducted; and an empirical application of this concept through a multiple criteria evaluation of agricultural management systems in Richmond County, Virginia is presented. Various interpretations of the concept of sustainable development are found to be based on Six "E" considerations: Economic, Energy, Environmental, Ecological, Equity, and Ethical. These interpretations with their different foci constitute a three dimensional view of economic development while neo-classical economics has a one dimensional view. The concept of sustainable development recognizes absolute resource scarcity, which is represented by the limited quantity of resources for inputs to economic systems; and is represented by the limits of the assimilative capacity of the environment for waste discharges. Advocates of the capacity of the environment for waste discharges. Advocates of the absolute quantity limit of resources generally employ the second law of thermodynamics, but a close examination indicates that this application of the second law is incorrect. The inapplicability of the second law thus widens the range of alternative choices that can be included in the design of a sustainable development path. For example, low-input sustainable agriculture loses its self-evidence meaning of sustainability. Its sustainablity should depend on its economic, environmental, and social values in different areas. To employ a multiple criteria approach to evaluating economic and environmental impacts of agricultural management systems in Richmond County, Virginia, a multi-objective dynamic programming model; coupled with the Chemical, Runoff, and Erosion from Agricultural Management Systems simulation model; is developed. The results of the model suggest an improvement in economic and environmental benefits can be achieved through use of a mixture of legume and non-legume cover crops rather than use of poultry litter as fertilizer source or simply lowering fertilizer application rates. The results also indicate there is no possibility of achieving a 40% reduction of nitrogen loading as required by Chesapeake Bay Agreement by employing the any of 14 agricultural management systems analyzed in this study. / Ph. D.

Theoretical studies have proposed that a critical threshold occurs below which a small change in the amount of habitat can cause an abrupt change in population persistence.  I tested the threshold concept using field voles (<i>Microtus agrestis</i>), their predator, the common weasel (<i>Mustela nivalis vulgaris</i>), and their ecto-parasites in a highly fragmented agro-ecosystem. I found strong support for a threshold in margin width, below which vole abundance was extremely low.  I also revealed that changes in the demography and behaviour of vole populations occurred in relation to the detected thresholds.  However, despite these responses, no effect was observed on their survival.  I found no evidence of a threshold response in either predator activity or parasite prevalence in relation to either prey/host abundance or habitat size.  Weasels may have been able to compensate for low vole abundances by consuming other rodents or by moving to areas with higher prey abundances.  The lack of any detectable effect of habitat loss on weasel activity may therefore be related to the scale of this study relative to their home range and their degree of diet specialisation.  The ecto-parasites observed infested all seven of the small mammal species trapped.  The high level of transiency and movement within this multi-host system may have facilitated the spread of parasites between margins.  The susceptibility of predators and parasites to habitat loss due to their trophic position may therefore have been offset by the high vagility of predators and the capability of both predators and parasites to predate/parasitise a range of host species.

Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references.

No description available.

No description available.

The following research developed an approach and methodology to simultaneously gather and integrate social and natural science farm system data of developing countries into one data base. The overall approach was based on Weber's theory of abstraction, which requires the identification of the broadest number of variables as possible. The first step to understanding the farm system was to overview a number of the key variables which represented a number of key farm components; the second step was to juxtapose and blend together the various forms of data in linear forms against a test variable of Striga infestation levels; the third step was to evaluate if the amount of knowledge gained in predicting Striga infestation levels was statistically significant by cross correlating soil nutrient levels, crop management approaches, farmers' perceptions of Striga infestation and spatial distances; the fourth step was to use parametric and non-parameterc analytical tools in conjunction with data compression to locate the best combination of parameters to better manage Striga. The final part of the process was to identify and integrate the crop, field and social data into a profile of farmer's who have the highest and lowest likelihood of being infested by Striga by using a soil nutrient concentration baseline as the indicator. The results were that natural and social science data could be successfully combined, integrated and have statistically significant cross correlations. These correlations indicate that specific spatial parameters combined with specific soil components, farmer's management and crop placement could be used as predictors of Striga infestation levels. As well the farmers' perception could be validated using natural science data.

Thesis (Ph. D. - Arid Land Studies)--University of Arizona, 1983. / Includes bibliographical references (leaves 147-152).

Thesis (M.App.Sc.) -- University of Adelaide, School of Earth and Environmental Science, Discipline of Soil and Land Systems, 2004. / "March, 2004" Bibliography: p. 112-136.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 111-116). Also available on the Internet.