No description available.

In recent years, freshwater fish farmers have come under increasing pressure from the Water Authorities to control the quality of their farm effluents. This project aimed to investigate methods of treating aquacultural effluent in an efficient and cost-effective manner, and to incorporate the knowledge gained into an Expert System which could then be used in an advice service to farmers. From the results of this research it was established that sedimentation and the use of low pollution diets are the only cost effective methods of controlling the quality of fish farm effluents. Settlement has been extensively investigated and it was found that the removal of suspended solids in a settlement pond is only likely to be effective if the inlet solids concentration is in excess of 8 mg/litre. The probability of good settlement can be enhanced by keeping the ratio of length/retention time (a form of mean fluid velocity) below 4.0 metres/minute. The removal of BOD requires inlet solids concentrations in excess of 20 mg/litre to be effective, and this is seldom attained on commercial fish farms. Settlement, generally, does not remove appreciable quantities of ammonia from effluents, but algae can absorb ammonia by nutrient uptake under certain conditions. The use of low pollution, high performance diets gives pollutant yields which are low when compared with published figures obtained by many previous workers. Two Expert Systems were constructed, both of which diagnose possible causes of poor effluent quality on fish farms and suggest solutions. The first system uses knowledge gained from a literature review and the second employs the knowledge obtained from this project's experimental work. Consent details for over 100 fish farms were obtained from the public registers kept by the Water Authorities. Large variations in policy from one Authority to the next were found. These data have been compiled in a computer file for ease of comparison.

This thesis provides a detailed study of methods for dissolving oxygen in water to reduce water requirements for fish farming. The principal sources of oxygen are air or pure oxygen gas. Aeration methods have the distinct advantage of the universal availability of air. However, the effectiveness of such methods is diminished by the presence of nitrogen in the air and, in general, the maintenance of dissolved oxygen levels above 70% saturation is likely to result in excessive power requirements. Pure oxygen has five times the solubility of oxygen in air and it is possible, therefore to achieve much higher transfer rates. However, oxygen is expensive and its economic use is essential: it is important, therefore, to dissolve a high proportion of the oxygen. Four distinct oxygenation systems were evaluated by the author. A detailed analysis of a column oxygenator is given first. The column was designed so that the oxygen bubbles generated are trapped within the column until dissolved. In seawater, much smaller bubbles are formed and this led to the development of a jet oxygenator which disperses gas rubbles within the rearing tank. Both the above systems were designed primarily for oxygenating recycled tank water. For oxygenating a primary water source, a U -tube device was evaluated. Lastly, the possibility of supporting fish stocks without any external power source, other than a pressured supply of oxygen from a liquid oxygen store, was considered. Experience of running commercial-scale oxygenation systems in high-intensity fish farms has made it possible to estimate operating costs of both aeration and oxygenation systems. The significance of these costs is discussed.

This thesis explores the physical and the socio-economic conditions for aquaculture in Tabasco, Mexico, seeking to find how aquaculture can best be supported to reduce poverty. On-farm physical, technical and social surveys were carried out in four municipalities, covering different physiographic regions. The surveys establish that the environmental conditions are frequently good for aquaculture. Despite efforts to bring farmers into more intensive commercial systems, aquaculture has developed mainly to improve subsistence, as one component of semi-subsistence farms. In order to evaluate these semi- subsistence systems, the thesis explores current debates on 'sustainability' and on 'subsistence'. As no single approach to sustainability per se seems appropriate to apply to these systems, new indicators and methods need to be developed which are appropriate to evaluate systems poor in cash generation but rich in social assets. Subsistence aquaculture is arguably more sustainable than commercial, monocultural aquaculture in environmental and social terms. It has become part of the economic diversity of the communities, increases food security, reduces the use of fossil fuels, promotes the careful management and recycling of wastes and the careful stewardship of natural resources, can help in the protection and enhancement of biological diversity and yields a feeling of self- empowerment. From the surveys, socio-economic and cultural realities are more important than physical conditions in determining the present state of aquaculture in Tabasco. The existence of some successful farmers' micro-businesses shows that once farmers receive continuous technical assistance, subsidies and access to markets, bringing them into commercial aquaculture is possible. Such help however, is rarely provided at present by the local extension institutions, which face internal problems resulting from inadequate budgets. This thesis argues that, in these circumstances, semi-subsistence aquaculture is a good option for the poor as many semi-subsistence systems are highly valued and have the potential to become more efficient and productive if locally based research is conducted with an understanding of farmers' cultures and motivations.

No description available.

In recent years, Taiwan¡¦s agriculture has faced difficult situations. But as the trend of travel is raising, leisure farming is also gaining ground and gives a great opportunity for traditional farming industry. However, due to the lack of knowledge and experiences of managing leisure farms, many owners who were originally farmers have found difficulty when it comes to create distinguish features. Moreover, imitating each other also leads to collectively poor performance. Therefore, this study has two goals. On one hand, it sums up the past researches and literatures to find out the key factors resulting in success in managing leisure farms; on the other hand, it offers best practice from the case study of well-run existing leisure farms. The conclusions of this study can be presented as followings: 1. The operating activities of a leisure farm should be in accord with its own resources and tourists¡¦ demand. It has to create a unique theme to distinguish itself from others. 2. Once a leisure farm has positioned itself, its products and services should fit its position to avoid giving tourists conflicting messages. 3. Internet may be helpful to the marketing of leisure farms, but tourists can easily gain information as well. Therefore, without non-stop innovation, a leisure farm cannot sustain its distinctive position.

No description available.

Thèse--Paris. / At head of title: Faculté de Droit de l'Université de Paris.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2003. / Appendix reprints five papers and manuscripts co-authored with others. Includes bibliographical references. Also issued electronically via World Wide Web in PDF format; online version lacks appendix.

A year-long case study of nutrient cycling within an agro-pastoral community of southern Mali revealed substantial differences in nutrient balances between households and between settlement sub regions of the study area. Inter-household differences should, in great part, bb attributed to differential access to livestock products such as manure and animal traction (both ox-ploughs and donkey carts). Exchanges of manure, carts, and ploughs between owners and non-owners of livestock account for the different levels of access. Exchanges within the settlement sub-regions were more numerous than those between them, had exchanges between e pastoral Fulani and the other communities were limited. The farming systems of the sub-regions presented three patterns of agricultural intensification: 1) cotton-centred rotations sing ploughs and carts to increase yields on perm - anently cultivated sites at the core of the village and in the adjacent hamlets,2 ) cotton-centred rotations on sandiers oils of the village periphery supported largely by intensive hand cultivation with the borrowing of carts to transport nutrients,and3 ) cereal-centred cultivation of small fields heavy manure by large cattle herds owned and managed by Fulani, with plough-ownerships seeming to ensure that household labour could remain available for herding. None of these models of intensification correspond fully with the owner/manager operation of a "mixed farm" and suggest that the potential for better crop-livestock integration in the sub-humidz one may be under-estimated and mis-represented by the "mixed farming" model. Although the overall nitrogen balance of the region after the 1996 cropping year was -8.2 kg N/ha, the different systems described above are associated with significantly different balances:the villa.g1 >. e core and hamlet cores were- 3.2 and- 4.7 kg N/ha, the village periphery- 21.4 kg N/ha, and the Fulani system+ 23.3k g N/ha. Phosphorus and potassium were in positive balance throughout the study area. 0 The different degrees of crop-livestock integration associated with each sub-region suggest that the importance of soil fertility problems must be understood with reference to local algro-pastoral practice. The growing livestock population and the presence of transhumant Fulani pastoralists in the sub-humid zone are key components of these practices and must not be excluded. The access of different actors to key resources such as manure, animal traction, pasture and crop-land deten-nine the ability to increase agricultural production and the degree to which agricultural intensification will mine the soil of nutrients. b ateg eneralisations about the extent of Regional or national studies that make aggregate nutrient loss misrepresent the soil fertility of the region, and risk feeding into an unrealistic" crisis narrative".