The work in this project is concerned with the headspace analysis of potato volatiles. In the context of the thesis, the term potato volatiles deals with the headspace volatiles that are naturally evolved by raw potato tubers, and the anthropogenic volatile sprout suppressant chemicals that are applied to stored potato tubers. Both aspects of potato volatiles were investigated and consequently this thesis is divided into two sections: Section 1 deals with the headspace analysis of the volatiles that are produced by raw potato tubers; Section 2 deals with the headspace analysis of two widely used commercial potato sprout suppressants. After harvesting, potato tubers undergo a period of dormancy which is defined as the time when the tuber buds are not growing: when dormancy is broken, the buds grow and elongate into sprouts. The mechanism of tuber dormancy is extremely complex, and the transition from the dormant to non-dormant state is associated with several physiological changes in the composition of the tuber. The first section, Section 1, of the project is an account of the investigations of the volatile compounds that are naturally evolved by raw potato tubers, in relation to the question of tuber dormancy. It has been shown that the volatiles produced by dormant potato tubers have sprout suppressant properties, thereby delaying the breaking of tuber dormancy (Burton, W. G., 1952), (Burton, W. G., Meigh, D. F., 1971). Further to this, it has been shown that the dimethylnaphthalene class of compounds is present in raw potato tubers and has been shown to possess potent sprout suppressant properties Neigh, D. F., et al, 1973), (Beveridge, J. 1980). However, it was thought that dormant potato tubers evolved volatiles, apart from the dimethylnaphthalenes, that had sprout suppressant properties. The aim of the project was the isolation and identification of the headspace volatiles that are naturally evolved by raw potato tubers and to relate these volatiles to tuber dormancy. The bulk of the work was taken up with the development of the analytical techniques for the isolation and separation of raw tuber headspace volatiles. Various systems were tested for the containment and separation of the headspace volatiles, from the outset the porous polymer adsorbent Tenax G. C. was used to trap the headspace volatiles, and high resolution gas chromatography using capillary columns was used for their separation. Three systems were developed for sampling: the first using an aluminium tank proved to be unsuitable due to background volatiles arising from the tank, the second and third which were constructed from glass and PTFE were found to be successful from the point of view of isolating a sample of potato tuber volatiles free from background volatiles. These two systems were used to study the headspace volatiles produced by sprouted and dormant potato tubers and to relate the breaking of dormancy to any changes in the volatiles produced. In addition, a gas chromatographic system was developed for the transfer of volatiles adsorbed on a Tenax G. C. precolumn into a capillary column, the final system adopted involved the thermal desorption of the volatiles from the Tenax G. C. into a small volume cold trap to concentrate the volatiles into a small volume and then a rapid reheat of the cold trap for the introduction of the volatiles into the capillary column.

The sensitivity of spring barley (Hordeum vulgare, cv. Carnival), field beans (Vicia faba, ev. Maris Bead) and sugar beet (Beta vulgaris,cv. Monoire) to topsoil compaction induced by tractor wheelings, post sowing, on a coarse gravelly loam of the Arrow series was investigated in 1983 and 1984. The study revealed that in both years topsoil compaction increased the dry bulk density, vane shear strength and cone resistance of the soil. Although compaction reduced only the plant population of sugar beet in 1983 (by 35%) in 1984 it both delayed emergence and decreased the field bean, spring barley and sugar beet populations by 41%, 50% and 64% respectively. In 1983 the order of sensitivity of crop yield to soil compaction was spring barley < field beans <sugar beet and the following year a similar trend was apparent with spring barley ≈ field beans < sugar beet. Compaction reduced the total dry matter production of field beans and sugar beet in 1983 and of all the three crops examined a year later. No clear trend could be established on the influence of soil compaction on plant nutrient uptake. The total length and distribution of roots in the soil profile was reduced in field beans (28%), spring barley (27%) and sugar beet (49%) by topsoil compaction in 1983. However, the reduced root length of spring barley was an order of magnitude greater than that of the other crops. In 1984 there was a trend for compaction to restrict the total root length of all crops throughout most of the growing season. Compaction did not restrict the maximum depth of rooting but it reduced the amount of deep roots in all crops. In 1983 and 1984, compaction restricted lateral proliferation of roots and the order of sensitivity of root distribution to soil compaction was similar to that for the sensitivity of yield: spring barley <field beans <sugar beet. The maximum effective rooting depth, as measured by neutron probe, was consistently less for field bean and sugar beet compact treatments, while the evaporation was only reduced in compact sugar beet crops. Thermocouple psychrometer data indicated that compaction had generally delayed soil drying and reduced the extent of water use in all crops in 1984. The principal effect of soil compaction on crop growth and dry matter production was to reduce the leaf area index, by an initial restriction to individual leaf size and by a reduction in plant numbers such that the fraction of light intercepted by the leaf canopy was reduced. The efficiency of conversion of photosynthetically active radiation absorbed to dry matter was not affected by soil compaction. Diurnal and seasonal plant water status was not detrimentally changed by soil compaction. It is suggested that plants adapt to adverse soil physical conditions by a reduction of leaf area expansion rather than by lowered leaf water potential. The severity of the response of crops to topsoil compaction was strongly influenced by the environment, in particular the distribution of rainfall which appeared to determine the effect of compaction on crop emergence and the ability of that crop to compensate for a low plant population. The results of this study are discussed in relation to the use of plant breeding, irrigation and management techniques in overcoming the detrimental effects of soil compaction on crop growth and development.

Foliar urea was applied as a source of late-N between flag leaf emergence and anthesis to winter wheat crops that had received varying rates of basal-N fertilizer in the spring in order to produce crops with differently sized GAI). The crops grown were: no N fertilizer applied (NO), conventionally fertilized (Net), a Canopy Managed crop grown to a GAI 5 (GAI 5), at IACR-Rothamsted in 1995, with the addition of a GAI 3 crop (GAI 3) at IACR-Rothamsted in 1994 and at Sutton Bonington in 1995. Each of the applications of late-N as foliar urea resulted in the prolongation of GAI of Canopy Managed crops, irrespective of the timing, amount of N applied, or whether adjuvants were used. The date of complete death of canopy green area was similar for all foliar urea treatments due to the sunny, warm, dry weather at the end of July in both 1994 and 1995, at both sites. The duration of canopy green area was associated with its N content at anthesis, as well as with water availability and the prevailing weather conditions, such that Ncf crops, containing significantly more N than GAI 5 crops at anthesis, retained green area for a longer period than the GAI 5 crops. The application of foliar urea did not always result in an increase in grain yield or quality and the partitioning of biomass and N to the grain was also seemingly unaffected by the application of foliar urea. However, yields from GAI 5 crops receiving late-N as foliar urea, irrespective of the method of application, were not significantly different to those obtained from Ncf crops. The amount of N deposited and the pattern of deposition were affected by canopy size. Applications made prior to ear emergence penetrated more deeply into the canopy. The top half of the canopy, flag leaf to flag-1 and the ear when present, was the most important site for both N interception and uptake. A maximum of 60 % of the applied N was intercepted by the GAI 5 crops and 10 % remained on the surface of the crop 96 hours later. 35 % of the N 'lost' from the crop surface was taken up over 96 hours. Of the remaining 40 % of the applied N, an estimated 10 % was lost by volatilization, 5 % by drift and 25 % penetrated to the soil surface. N uptake from the leaf surface probably followed an exponential pattern through time. The time for half of the N present initially to be lost (t0.5), was unaffected by the side of the leaf to which N was applied, the age of the leaf growth stage of the plant or the amount of N applied. t0.5 was improved only by the addition of a spreader or a penetrant. By harvest up to 64 % of the fertilizer N applied was recovered by the GAI 5 crop of which 87 % was present in the grain. Studies using N15 labelled urea suggested that N was transported away from the flag leaf immediately after application, but it was not clear whether N was transported directly to the ear or used in leaf metabolism elsewhere.

This thesis attempts to provide a general history of the tithe system during the last century and a half of its existence in its old form. It attempts this partly through a detailed study of one county, thus enabling a wider variety of legal, administrative, ecclesiastical and parochial documents to be used than has been attempted in previous studies of the tithe system. Staffordshire was selected partly because of its excellent source materials in the Stafford County Record Office, the William Salt Library and the Lichfield Joint Record Office, and partly because the county provides a most useful admixture of different agricultural and industrial settlements. As Caird wrote in 1850: 'The state of agriculture in Staffordshire is influenced by such a variety of circumstances that examples of every system pursued in England may be found in this county.'(1) It was therefore possible to assess whether the tithe system had a differential impact on different types of farming, and how much it penetrated industrial areas. The thesis attempts to show how tithe was collected in the eighteenth and early nineteenth centuries, and how far tithing in kind remained. The importance of lay as well as clerical tithe owners is studied and the thesis attempts to indicate the amount of social tension occasioned by the system. As litigation over tithe was frequent in much of the period, the complexities of the legal situation are studied and an analysis made of the Staffordshire cases, indicating the major reasons for litigation, what evidence was considered valuable, how cases were settled, and the importance of legal costs in the progress and determination of disputes. One particularly lengthy tithe battle - from Cheadle - is treated as a separate case study. A case study of the Quaker attitude to tithe, as the leading dissenting sect objecting ID its payment, is also made, indicating the degree of non-payment by Quakers, their legal tussles, persecution and campaigns to change tithe law. The national campaign against tithe is studied with consideration and evaluation of the arguments of both sides in the light of the actual situation. The reasons for the increasing momentum and bitterness of the campaign from the late eighteenth century onwards are assessed. As the eighteenth century enclosure movement provided the first major opportunity since the Reformation for a change and redistribution of tithe property, attention is paid to the impact of the movement, indicating how far tithe was exchanged for land at enclosure. The relative benefits to land and tithe owner are assessed. The thesis concentrates finally on the parliamentary attempts to reform the system, and the difficulties encountered there. The origins of the 1836 Commutation Act are studied together with an analysis of the Act and its intentions. The last chapter is devoted to a study of the Act in operation, showing how easily commutation was effected, how tithe values were altered, and how the parties concerned reacted to the changes which commutation would bring. The thesis ends at 1850 with most commutations, and their attendant redistribution, complete. Above all, however, this study attempts to explain how men attempted to make an anachronistic system work in an increasingly complex society, how far compromises were necessary and acceptable, and how far tithe was responsible for tension in the village community. It attempts to provide a general history of tithe, but it does so in the belief that, because tithe was a local and parochial burden, its proper impact and effects cannot be properly understood without detailed reference to local situations.

Two selective media which specifically allow the cultivation of Bacillus thuringiensis while it is in the vegetative as opposed to the spore form were developed. Using these media it was conclusively proved for the first time that B. thuringiensis can reside on the phylloplane in a metabolically active form. This was corroborated by evidence, also for the first time, that conjugation can take place on the phylloplane between such endemic strains. A new bacteriophage, infecting one of the endemic stains, which was activated by the process of genetic recombination, was isolated and characterized. The appearance of naturally occurring strains of B. thuringiensis in vegetative and spore form was followed over a growing season on clover (Trifolium hybridum) in the field. Simultaneous and sudden rises and declines of both spore and vegetative cell densities were observed. These could not be correlated with weather conditions. A genetically stable population of strains seemed to be maintained throughout the growing season. The most common other spore-former on these leaves was Bacillus cereus but the fluctuations in appearance of these two very closely related species were not co-incident. Using specific PCR primers, a considerably diversity of toxin types was found with the majority of isolates possessing multiple d-endotoxin genes. Bioassays against a lepidopteran insect (Pieris brassicae) of purified d-endotoxins showed that they were not more potent than those from a laboratory-adapted strain. A high percentage, however, of the endemic isolates (82%) possessed the ‘Vegetative insecticidal protein’ (Vip) gene, vip3. This might indicate an involvement of Vips in the establishment of these strains on the phylloplane. A mechanism for colonization of annual plants by B. thuringiensis was demonstrated for the first time. It was shown that spores added to seeds, even in non-sterile soil, can germinate and replicate on the resulting seedlings. The level of colonization achieved did not have a consistent influence on the feeding behaviour of third instar larvae of P. brassicae which were present on the plants for three days. Nevertheless, the fact that the number of CFU of B. thuringiensis recovered per gram of insect increased with time is evidence of proliferation of the bacterium inside the insects. Four isolates of B. thuringiensis that had been recovered in the vegetative phase from the phylloplane of T. hybridum were grown for 500 generations in a rich medium. Changes were observed in all of the strains but one isolate changed remarkably in all of the characteristics assessed which included: structure; plasmid profile; fatty acid composition; and d-endotoxin production. Moreover, the sequence of the Vip3 protein harboured by the evolved strain showed changes when compared with that of the parental strain.

The present study evaluated the effect of three host plants: chickpea, Cicer arietinum, tomato, Lycopersicon esculentum and cotton, Gossypium hirsutum, on the efficacy of Helicoverpa armigera nucleopolyhedrovirus (HearNPV). The results showed that HearNPV was inactivated within one hour when sprayed on to the leaf surface of chickpea indicating that leaf surface factors on this plant were responsible for the effect. In contrast, virus that has been sprayed onto the leaf surface of cotton and tomato was not significantly affected compared to untreated HearNPV. This study also showed that HearNPV was inactivated on the chickpea leaf surface in field experiments. One compound was shown to be induced on the chickpea leaf surface in response to spraying with 0.02% Triton X-100 which was used as a surfactant. The induced compound was isolated and identified as sissotrin, and isoflavonoid. Sissotrin was shown to reduce the efficacy of HearNPV, although not by as much as when the virus was exposed to the chickpea leaf surface. The results indicated that sissotrin was partially responsible for the inactivation of HearNPV and that other compounds which accumulated on the leaf surface after spraying with HearNPV must also have an additional effect in combination with sissotrin. This is the first study to show that isoflavonoids reduce the efficacy of baculovirus against Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae). Field trials were also conducted with different low cost additives mixed with HearNPV on chickpea crop and these increased the efficacy and persistence of HearNPV under field conditions. This study may therefore help to improve biopesticide based pest management on chickpea.

The thesis examined the effects of climatic change on livestock production within Scotland. In order to achieve this, a systems model of the dairy, beef and sheep enterprises was developed. Climatic change primarily affects livestock production through its effects on forage production. Under climatic change, the model predicted that the length of the growing and grazing season will increase with the extensions occurring at both ends of the season. Relative to current climatic conditions elevated CO2 concentrations coupled with the associated changes in climate resulted in an enhancement in harvestable dry-matter yield that ranged from 20% to nearly 60% and increases in the percentage of white clover in the harvestable material by up to 126% In general, global warming is predicted to increase forage and livestock production within Scotland. However, the location of the site is also important in determining the effect of climate change as the magnitude and, in some cases, the directions of the changes varied between sites. The effects of climate change were also dependent on the actual level of changes in temperature. In addition, there were interactions between CO2 concentration and both temperature and rainfall, as well as interactions between temperature and rainfall. Although the three enterprises showed similar trends in their response to climate change, there were differences in the magnitude of the response as well as differences in the factors that resulted in significant changes. There were also differences in the response of the grazed and the ungrazed swards. This underlines the complexity of the interactions and the difficulty of extrapolating the results to other locations and to other levels of climatic conditions. The advantage of developing a model is that all these complex interactions can be captured and potentially the site - specific consequences of climate change on forage and livestock production predicted.

This study relates to the reforms by the Education Ministry in Botswana of decentralising the coordination of teachers’ In-service Professional Development (IPD) to the Regional Offices with the overall aim of improving students’ academic performance (Republic of Botswana, 2006). In the absence of other research data, the study aims to understand how secondary school teachers of agriculture in Botswana perceive their IPD. The study endeavours to identify gaps in current IPD provision and make recommendations to guide IPD policy reforms at regional level. Based on a review of the literature and the overarching research purpose, a set of research questions was devised. Considering the research questions, a Realist perspective to the research that endorses a flexible pragmatic stance was adopted. The research employed a mixed methods design. A questionnaire was developed and administered to all the Agriculture teachers in the Central Region (n=247). A purposive sample of teachers (n=36) and every Agriculture Education Officer (n=8) were interviewed. The quantitative data was analysed using SPSS software, with descriptive and inferential statistics reported. A coding guide was developed to analyse the interview transcripts which was done with the assistance of NVivo software (Bazeley, 2007). The findings show that the main source of motivation for teachers to attend IPD is to update their knowledge and skills in the subject. The study revealed workshops and meetings to be the most popular IPD opportunities of all IPD opportunities found to be relevant by teachers. The study also identified satisfactory and unsatisfactory characteristics of IPD; the contextual factors that adversely influence IPD in the region; and a wide range of IPD needs. The findings have implications for future IPD policy reforms; most important of these include the need to:  adequately resource IPD and create time for it as an integral part of the education programme;  remove restrictions associated with funding teachers’ enrolment in part time courses;  revise teachers’ workload policy to help them find time for IPD; and  have IPD emphasise acquisition of agriculture skills by teachers. Beyond policy, the findings also suggest improvement of the design and organisation of IPD, which include strategies for making IPD interesting, meaningful, sustainable and accessible to all teachers in the region.

Food sovereignty is an alternative agricultural and rural development paradigm advocated by the international peasant movement La Vía Campesina. This investigation analyses food sovereignty through a historical cross-scale analysis focusing on the livelihoods of peasants in the sertão in North-Eastern Brazil. The overall aim is to assess the implementation and local effects of a policy, which is based on three food sovereignty principles, and determine in what ways and to what extent it promotes food sovereignty in practice. The three food sovereignty principles considered were support of peasants and small-scale family farmers, prioritisation and support of local food systems and commerce and promotion of agroecology. The policy analysed is the Brazilian government’s Food Acquisition Programme (FAP), as implemented in Mirandiba, Pernambuco by the NGO Conviver from 2005-2008. The analysis involved an assessment of the production and earnings by 359 participating families from 18 poor rural communities, as well as detailed case studies of the livelihood strategies of 14 families from two communities. A number of policy debates are explored, including rural poverty, food security and sustainable agricultural and rural development, to which this research provides three main contributions. Firstly, a new framework to explain the process of marginalisation of peasants through the influence of five mediating factors. Secondly, this framework helps deconstruct misconceptions about peasants and thereby provides support to La Via Campesina’s defence of ‘peasants’ and their livelihoods. Finally, as the first known indepth study of the implementation of the FAP on a local level, this investigation contributes to fill a gap in the research and literature on the operation and local impacts of both the FAP and governmental food procurement programmes more generally. This thesis argues food sovereignty can be achieved locally even within a context of general globalisation, through policies such as governmental food procurement programmes. The investigation concludes that food sovereignty is being pursued in areas of Brazil through the FAP and other progressive policies and movements, which are enabling peasants to improve their well-being, food security, self-esteem and to forge an adequate livelihood. The FAP is also contributing to the development of local food commerce systems and the promotion of agroecology both in Mirandiba and Brazil

Future food security is under threat from both climate change and human population growth. Water scarcity is a major limitation to crop production worldwide and the effects of climate change are likely to exacerbate this. Furthermore, an ever increasing human population is driving our demand for food, fuel and fibre. In combination, climate change and population growth, and their interaction, creates a complex problem with regards to improving plant productivity with which to maintain food security. If crop production can be made more efficient, agricultural intensification can be achieved without the need to expand the world’s cropped area, which is unfeasible. Leafy salad crops are of significant nutritional value and are eaten globally, thus making them an exciting target for improving resource use efficiency in agriculture. This research focuses on water as a resource and takes two complementary approaches. Firstly, to improve the crop genetically so it produces more ‘crop per drop’ without a detrimental impact on yield. Secondly, the aim was to improve irrigation management in a commercial setting in order to use water more efficiently while attaining optimal crop yield and quality. Candidate SNPs within the lettuce genome have been elucidated which control both fresh weight and water use efficiency and these can now be used to inform a marker assisted selection breeding program. This breeding will produce a more water use efficient lettuce crop, which is not compromised in its ability to produce biomass, while also retaining the favoured traits of currently used commercial crops. Furthermore, it has been demonstrated using thermal imagery that water savings of almost 20% can be made in a commercial setting without any impact on crop yield or quality. The water savings which we have provided, if extended commercially, will confer significant savings in terms of water, waste and money.