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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Seeds of Threat| Insecure Tenure and Governance in the Community Gardens of D.C.

Osborne, Amanda Paige 10 July 2013 (has links)
<p> Community gardens have begun to increase in numbers in many highly urbanized areas across the United States. Community gardens are a form of urban green space that have many functions and can provide a plethora of benefits to its participants. While community gardens have proven to be very successful in urban areas, their success may be undermined by insecure land tenure. With the shift to governance and the adoption of neoliberal urban policies, community gardens may face foreclosure to free the land for economic development projects. Community gardens are public spaces, but legal access does not necessarily guarantee equal access for surrounding urban populations. Certain subsets of urban populations can experience unequal access to community gardens, both socially and spatially. This research employed a mixed methods approach to examining community gardens within the District of Columbia, including semi-structured interviews, participant observation, and spatial analysis. Issues of land tenure, management, community, and access were examined in three community gardens within the District of Columbia. This research has shown that the governance of community gardens can be messy, contributing to management issues. Additionally, the governance of these spaces affect who has access to these spaces. Access was found to be a multifaceted and complex issue, showing how community gardens can become spaces of exclusion. Finally, the gardeners interviewed did not agree upon the definition or existence of "community" within their community garden.</p>
72

The cook, the farmer, his wife, and her grocer: Plotting a new urban/rural interface

LaRocca, Jonathan Vail January 2007 (has links)
Plotting a new urban/rural interface provides a design proposal for a new kind of sustainable landscape within built-up areas: urban agriculture. The reintroduction of productive landscapes into the contemporary city changes the appearance of modernday urban conditions towards an unprecedented economic, social, and environmental productiveness. Such landscapes adopt a strategy of systemic intensification which searches out reclaimable (unproductive) space with the existing urban fabric. By growing food within an urban rather than exclusively rural environment, productive landscapes within city boundaries reduce the need for industrialized production, packaging and transportation of foodstuffs from rural areas to the city dwelling consumers. This project offers an examination of food as a fundamental aspect of a city, the study of how food relates to the economic, political, social and cultural environments of a city, and the study of how food imprints on the built environment. Urban agriculture is a theory that positions food is a primary transforming force capable of organizing the city and enhancing the urban experience. The possibilities of urban agriculture in the United States are presented through a proposal for active farming and food retail projects in Houston as strategies for achieving sustainable growth.
73

Resource capture and productivity of agroforestry systems in Kenya

Howard, Stephen B. January 1997 (has links)
Resource capture and utilisation were studied in two agroforestry systems at the International Centre for Research in Agroforestry (ICRAF) Research Station at Machakos, Kenya. The agroforestry systems examined contained two contrasting tree species, leucaena (Leucaena leucocephala (Lam.) de wit) and grevillea (Grevillea robusta), and the C3 and C4 crops, cowpea (Vigna unguiculata) and maize (Zea mays, Katumani composite). The leucaena-based trial was established in November 1989 and the trees were grown with ten maize crop rows on either side of a pruned hedgerow (HM) or unpruned tree row (LM). A sole maize control (SM) was also grown. Paired sets of treatments were irrigated to eliminate below-ground competition for water (HMI, LMI and SMI respectively). Interception of photosynthetically active radiation (PAR) by leucaena and maize was measured on a row-wise basis in all treatments at 7-10 day intervals using a sunfleck ceptometer. Sap flux was measured for the maize and both pruned and unpruned leucaena using heat balance gauges. Results are presented for the 1992 April-July rainy season. Total PAR interception was 30 % greater in LM and LMI than in the SM and SMI sole maize treatments. However, little more than 30 % of the light intercepted by the LM and LMI systems was captured by the crop component, and competition for light alone reduced maize yields by over 30 %. Total water uptake by the LM leucaena and maize comprised 60 % of the seasonal rainfall (237 mm) as compared to 30 % for sole maize. However, as for light interception, only 30 % of the water transpired in LM was used by the intercropped maize, and competition from the trees for soil water reduced maize yields at distances of over 6 m from the leucaena. The leucaena was more effective at resource capture, yet less efficient in resource utilisation since it exhibited a lower dry matter:radiation quotient and a lower transpired water:dry matter ratio than maize. Thus the leucaena in the agroforestry systems captured more of the resources that could have been used more effectively by the maize, causing the performance of the mixture to be sub-optimal; these results suggest that the two components would be best grown separately. Intensive monitoring of resource capture and use by trees and crops was subsequently transferred to the Complementarity In Resource Use on Sloping land trial (CIRUS). Although it had been intended to study both trials during the long rains of 1993, the leucaena trees were almost completely defoliated by psyllid (Heteropsylla cubana) infestation shortly before the onset of the rains: in subsequent seasons, CIRUS was studied in preference to the leucaena trial as the trees had only partially recovered. CIRUS was designed to investigate the effects of competition and the extent of complementarity between grevillea and associated crops using the following treatments; sole crops (Cg) of cowpea during the short rains and maize during the long rains, dispersed-planted trees with (CTd) and without crops (Td), and across (CTa) or on-contour-planted (CTc) tree rows with crops. Light interception and water use were monitored using a similar measurement regime to that employed in the leucaena trial. Results are presented for the 199213 and 1993/4 short rainy seasons; the failure of the 1993 long rains forced the abandonment of experimental measurements during this season. Light interception by the Td and CTd grevillea increased greatly between the two short rainy seasons. Thus, total seasonal interception of PAR was three times greater in sole cowpea than in sole grevillea during the 1992/3 short rains, but by the following short rainy season was over 50 % greater in the grevillea than in the cowpea. Cumulative interception of PAR by the CTd grevillea and cowpea combined was more than twice that of the sole cowpea and over 40 % greater than that for sole grevillea during the 1993/4 short rains. Experiments involving artificially imposed shade showed that there was no reduction in total above-ground dry matter production in cowpea until 75 % shading was imposed. To quantify the degree of below-ground complementarity in water use between grevillea and cowpea, sap flux was measured using heat balance gauges attached to the stems of young grevillea (10-18 months old), both before and after excavating the crop rooting zone (upper 60 cm of soil) around the stem base. The crop rooting zone was removed to establish the capability of the grevillea to extract water from deeper horizons. After excavation, the trees maintained sap fluxes of up to 85 % of the unexcavated values. During both short rains, soil evaporation was by far the largest component of the water balance in all treatments. However, continued extraction of water by the trees during the dry season greatly increased resource capture~ thus total water uptake was three times greater for the sole trees than for the sole crop when dry season water use was included. During the 1993/4 short rains, water use was greatest in the CTd treatment, in which 25 % of the total seasonal rainfall was transpired by the trees and crops. Although transpiration by the CTd trees exceeded interception losses, the latter may have had a greater effect on crop growth by reducing the total quantity of water available within the system. The existence of below-ground complementarity and the shade tolerance of the cowpea suggest that deep-rooted tree species and certain C3 crops may be combined successfully in the semi-arid tropics, but the sensitivity of crop yield to any reduction in water availability within the system demonstrates the need for caution when implementing such systems. The results obtained are discussed in relation to previous research on intercropping and agroforestry and their implications for the successful adoption of agroforestry systems in the semi-arid tropics.
74

A study of the adoption of innovations by Syrian farmers

Razzouk, Talal Ahmad January 1990 (has links)
The objective of this research was to "investigate, study, analyse, and report conditions under which Syrian "rainfed" wheat farmers live interact and adopt innovations and improved cropping practices. The purpose of this was to help in understanding forces that can influence farmers' decisions to adopt innovations and which influence their adoption behaviour. The research, also, has attempted to develop concepts and methods which have rarely been used before in Syrian conditions. The recommendations for the policy makers and the Extension organisations in Syria were based on the major findings as well as other findings which were revealed throughout the research. The study was carried out in the two largest rainfed cropping areas in the country; Aleppo province to the north and Hassakeh province to the east, the sample of farmers was distributed in First Stability Zone (Zone 1) and Second Stability Zone (Zone 2). A total sample of 60 farmers were randomly selected from both areas. Nine agricultural innovations and improved cropping practices were selected and farmers' adoption behaviour with regard to these innovations and improved practices were investigated. The nine innovations and practices were; "the use of nitrogen", the use of "phosphorus", "following the recommended time of nitrogen application", "the use of improved wheat varieties", "the degree of following the seed renewal for wheat", "the use of herbicides", "the use of pesticides", "the use of sowing machines", and "following the recommended seed bed preparation". The "Sten Score" method was adopted in order to score the adoption behaviour of farmers for the nine selected innovations and improved cropping practice. The method was modified in order to achieve the best classification of farmers on the basis of their adoption behaviour. Four major aspects and characteristics were selected, investigated and later were analysed in relation to the adoption behaviour of farmers with regard to the nine selected innovations and improved practices. These aspects and characteristics were Personal and Socio-Economic, Economic and Institutional, Communicational, and Psychological Factors. The study has concentrated on characteristics which usually have been ignored or avoided in past adoption and diffusion research. Special methods have been devised in order to help in measuring these aspects and characteristics. Special attention was paid to the role of personality and the Self-image of farmers as important aspects affecting their adoption behaviour. Until recently research into farmers' decision making to adopt or reject innovations did not pay attention to the role played by these factors at the time of taking the decision to adopt innovations. The major findings in Zone 1 revealed that the adoption of innovations and improved practice by farmers were related highly and significantly with farmers' "Self-image", the "availability of credit and cash money" and "having an Extension plot or field demonstration on the farm". The three variables together explain over 70% of the variation in the adoption behaviour of farmers. In Zone 2, the farmers' "Self-image", and the "availability of machinery and equipment on the farm" were found to be the best related variables with the adoption behaviour of farmers. The two variables together explain over 60% of the variation in the adoption behaviour of farmers. The recommendations for the policy makers and the Extension organisations in Syria were based on the major findings as well as other findings which were revealed throughout the research.
75

Phytoextraction of cadmium from soils treated with sewage sludge

Maxted, Andrew P. January 2003 (has links)
The efficacy of phytoextraction strategies were tested by pot and field trials on soil contaminated with heavy metals, including Cd, derived from long-term disposal of sewage sludge. The strategies investigated were: i) the use of hyperaccumulators; ii) chemically-enhanced uptake using arable species and iii) the use of short rotation coppice (SRC). Chemical interventions including EDTA, chloride salts, HCl and herbicide were used to enhance uptake by arable and SRC species. Tissue Cd concentrations in the Ganges population of Thlaspi caerulescens were lower than reported in other studies; the mean Cd concentration was 265 mg kg". It was deduced that Cd uptake was limited by a low Cd2+ concentration in soil and the rate at which solution Cd was replenished. High rates of plant mortality were observed, raising questions over the successful husbandry of T. caerulescens for phytoextraction. Chemical interventions produced significant increases in metal uptake by arable and SRC species. For example, Cd uptake by Z. mays following application of 10 mmol EDTA kg'' and by Salix caprea x cineria x viminalis following combined application of EDTA and HCI. However, concentrations were still well below those required for successful remediation. Furthermore downward migration of metal was observed through the soil profile following EDTA application. For example, the soil Cd concentration in the 0- 10 cm profile was reduced from 32.0 to 25.5 mg kg' seven months after application of 10 mmol EDTA kg'', yet only 1% of this reduction could be accounted for by Z. mays Cd off-take. Realistic estimates for phytoextraction timescales and costs were made in line with legislative thresholds. Overall the time required to reduce total soil Cd concentrations below 3 mg kg-1 was large and the costs were prohibitive. For example, although Cd off-take by Ganges was greater than for any of the other species tested, it was estimated that well over one century would be required to reach target metal concentrations.
76

The environmental control of development in winter wheat

Baker, C. K. January 1979 (has links)
1. The relevance of studies of development in crop-weather investigations is reviewed and the aims of the present work are outlined. 2. The procedures used in studying development in field crops of winter wheat are described. The developmental progress of the plants was ascertained by frequent dissections. 3. Primordium initiation at the stem apex is strongly dependent upon apex temperature, which could be accurately estimated from standard meteorological screen temperatures. Like numerous other complex biological processes, initiation has a markedly linear response to temperature: the number of primordia initiated is therefore in direct proportion to accumulated temperature (thermal time). To calculate this requires estimation of the base temperature (Tb). 4. The linear dependence upon temperature of the initiation rates of leaves, spikelets and florets (R1, Rs and Rf ) was evident. Spikelets were initiated faster than leaves ; rate changed at a distinct inflexion point, usually at about the end of leaf initiation but sometimes later. Tb = 0 grad. C for leaves but was higher for spikelets and florets. The shift in Tb apparent17 occurred because Rs and Rf were strongly influenced by the day length at inflexion point. When temperature was corrected for day length influence, Tb = 0°0 for each developmental phase. Inflexion point timing apparently depended upon interaction between vernalisation before crop emergence and photo thermal time afterwards. 5. Leaf appearance rate in thermal time was linear but apparently influenced by the direction and magnitude of day length change at emergence, with a possible secondary effect of current day length. Leaf extension was strongly related to temperature. The gradient of lamina size up the stem appeared to be ontogenetically determined. 6. Compared with early-sown or fully-fertilised crops, floret survival and grain yield was lower in those sown late or inadequately fertilised, probably on account of their smaller amount of growth per unit of developmental time.
77

The development of a single strategy for the integration of quantitative and qualitative data types for the production of decision support systems

Burgess, Robin January 2008 (has links)
The research described in this thesis expresses the importance of quantitative and qualitative data types and how these can be incorporated and combined to produce an agricultural management decision support system (DSS). Researchers cannot solely depend on numerical data and relationships when designing, modelling and producing decision management tools. The relevance of the social sciences and peoples interpretations of these tools is equally important. The DSS described here focuses on the management of rainwater harvesting (RWH) in Tanzania. Numerical data related to natural resources (water and nutrients) and yields of rice and maize have been collected for the production of the DSS. With regard to the social science factors, the DSS tackles the concept of common pool resources (CPR) of water and nutrients. The importance of CPR is well understood, however their inclusion in the production of models is a relatively new concept. Criteria related to social status is linked with the by laws that govern the allocation of natural resources in Tanzania to help derive a numerical method for including CPR within the DSS. The production of the DSS is a novel way of combining this research into a tool that aims to benefit all socio-economic community groups. During the production of the DSS, a single generic approach for the inclusion of quantitative and qualitative information has developed. Particular focus was on the development of a model base (programming and mathematical relationship building), database (storage of the data used for the relationships) and a dialog system (the user-interface and communication strategy). This method is termed the ‘dialog, data, and models (DDM)’ paradigm (Sprague and Carlson, 1982). From this research, a DSS has been produced that aims to optimise RWH management in Tanzania with the aim of alleviating poverty and enhancing sustainable agriculture for all community members. Also an overall strategy for the production of DSSs has been produced. It illustrates how both quantitative (numerical and physical data) and qualitative (socio-economic considerations) can be utilised individually and in combination for the production of DSSs and can be extrapolated for further research and to new areas.
78

Ecophysiology of indigenous trees in agroforestry systems in the semi-arid tropics

Broadhead, Jeremy January 2000 (has links)
Increasing demand for timber, fuelwood and other forest products has outstripped production in many areas of the semi-arid tropics, leading to deforestation and land degradation resulting from erosion and nutrient depletion. Agroforestry offers the potential to provide forest products, improve productivity and reduce soil erosion and environmental degradation. However, as previous reports have shown that competition between trees and crops for water in semi-arid areas adversely affects crop yields, attention has turned towards studies of the existing practice of boundary planting, where low tree planting densities and the associated benefits of land demarcation and soil stabilisation increase the viability of incorporating trees into crop land. The aim is to select and manage tree species in ways that limit their negative effect on crop yields and improve the overall value of the system. The present study was carried out at Machakos (1° 33' S, 37° 14' E, altitude 1660 m) in the Kenyan highlands, where the bi-modal annual rainfall of c. 740 mm is divided approximately equally between two rainy seasons (short rains, October-February, long rains, March July). The experiment was set up in April 1993 to examine the influence of tree/crop interactions on system productivity. Each 18 x 18 m plot, except for the sole crop plots, contained a central row of trees planted at 1 m spacing. Four overstorey agroforestry treatments were examined between March 1996 and March 1998; these included two indigenous species, Croton megalocarpus and Melia volkensii, and two exotic species from Central America, Senna spectabilis and Gliricidia sepium. Beans (Phaseolusulgaris) and maize (Zea mays) were grown during the short and long rains respectively. M. volkensii and S. Spectabilis exhibited similar leafing phenology patterns, losing almost all leaf cover during the long dry season (July-October) and flushing before the ensuing rains. During the short dry season, S. spectabilis lost few leaves, whilst M. volkensii lost some leaves before flushing prior to the onset of the long rains. M. volkensii lost a large proportion of its leaf cover during the 1997/98 short rains due to the unusually high soil moisture content. C. megalocarpus although predominantly evergreen, lost a large proportion of its leaves during dry periods, whereas leaf area increased rapidly under wetter conditions. G. sepium had one annual period of low leaf cover during the long dry season and did not regain full leaf cover until mid-way through the short rains. The three-dimensional model of canopy photosynthesis and transpiration, MAESTRA, was parameterised for C. megalocarpus and M. volkensii using existing models to describe the response of photosynthesis to light and temperature and stomatal responses to light and vapour pressure deficit. The photosynthesis model fitted the experimental data well, but stomatal conductance in C. megalocarpus, although showing responses to light and vapour pressure deficit, was not closely correlated with ambient environmental conditions. M. volkensii had higher leaf area than C. megalocarpus for most of the 18 month simulation period, comprising three rainy and three dry seasons; modelled assimilation for this period was 49 % greater in M. volkensii, while canopy water use efficiency and transpiration were respectively 35 and 11 % higher. These differences accounted for the more rapid growth rate and greater competition with adjacent crops associated with M. w1kenrii relative to C. megalocarpus. Above-ground woody biomass production was greatest in M. volkensii, followed by S. spectabilis, C. megalocarpus and G. sepium; production during the fourth and fifth years after planting ranged between 2.8 and 4.9 t ha-¹ yr¹. Crop production in the agroforestry treatments was always lower than in sole crops due to below-ground competition for water and, in seasons with higher water availability, shading by the trees. Of the agroforestry systems examined, seed production for beans was highest under M. volkensii and G. sepium, followed by C. megalocarpus and S. spectabilis. Grain production in maize was greatest under C. megalocarpus, followed by G. sepium, S. spectabils and M. volkensii. Mean annual aboveground biomass production including maize grain and stover, bean seed, woody biomass and tree leaves in the M. volkensii treatment exceeded that for the sole crop plots, even though rainfall during 1996 and 1997 was only 61 and 95 % of the long term average. Although the biomass production of leaves was not estimated for S. spectabilis and G. sepium, the results obtained suggested that biomass production was greater than that obtained under sole crop cropping. The inverse correlation between tree and crop yield suggests that the value of the tree products must exceed the associated crop losses if benefits are to be obtained from agroforestry. M. volkensii is valued in areas of Kenya where markets for its products exist and therefore shows great promise for extension in semi-arid areas; where necessary, pruning may be used to reduce competition with crops and increase the length of clear bole. C. megalocarpus is widely used as a shade tree in East Africa and seems well suited for this purpose as its impact on adjacent crops was least of all the tree species examined. S. spectabilis, although having straight unbranched stems, exhibited a level of competition with adjacent crops that would necessitate a high value for its timber products to warrant its adoption. The least suitable tree species of those examined was G. sepium, whose poor form and susceptibility to attack by fungal pathogens and insects severely undermined its potential value for use in agroforestry systems.
79

The development of azadirachtin as a soil-applied, granular insecticide

Daly, Gordon Wilson Scarlett January 2004 (has links)
The aim of this project was to develop azadirachtin as an insecticide that is applied to the soil, using a granular formulation, for root uptake and subsequent systemic plant protection. A method was developed whereby azadirachtin could be rapidly isolated to approximately 95% purity using flash chromatography. This material was used in all subsequent chemical and biochemical studies. To increase the speed of crude extract analysis, a colorimetric technique was assessed to rapidly quantify azadirachtin. However, this method was generally unsuitable for the requirements of this project because it was non-specific and not stable. Granular formulations based on sodium alginate, starch-kaolin and poly(e-caprolactone), and containing different neem seed extracts were successfully prepared. These granules exhibited differnces in the rate of azadirachtin release into water. Additives such as kaolin clay and rapeseed oil could be used to modify the speed of release. Following application to soil, the position of granules did not affect release rates. However, granule application method was shown to affect the rate at which the limonoid was accumulated within the nasturtium plants. Azadirachtin was shown to be moderately water-soluble (1.29 g/l). During mixing studies between distilled water and n-octanol, the limonoid partitioned more favourably into the non-aqueous phase at a ratio of 7:1. Based on calculated Koc values (<40), azadirachtin was classified as very highly soil mobile. Adsorption occurred principally to the organic matter of soils. Clay minerals were comparably non-sorbent. Desorption from both of these sites occurred readily. Azadirachtin was not persistent within soil where the limonoid’s DT50 was as short as 1.06 days. Initial breakdown resulted in the acetyl moiety being cleaved from the molecule. In addition, azadirachtin was shown to exhibit a pH sensitive hydrolytic degradation. The limonoid’s half-life in solution ranged from 57 days at pH 5 to 7.15 hours at pH 9. In conclusion a suitable granule for a controlled-release of azadirachtin was developed.
80

The determination of ammonia emissions from mechanically ventilated poultry houses: An examination of the issues involved

Casey, Kenneth David. Unknown Date (has links)
Thesis (Ph.D.)--University of Kentucky, 2005. / (UnM)AAI3198303. Source: Dissertation Abstracts International, Volume: 66-12, Section: B, page: 6754. Director: Richard S. Gates.

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