Small-scale irrigation: opportunities for success
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CTA. 1991. Small-scale irrigation: opportunities for success. Spore 36. CTA, Wageningen, The Netherlands.
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Governments and international aid organizations have often seen the introduction of irrigation as a solution to the problems of low agricultural productivity, particularly in Africa. However, large-scale irrigation schemes have generally I proved...
Governments and international aid organizations have often seen the introduction of irrigation as a solution to the problems of low agricultural productivity, particularly in Africa. However, large-scale irrigation schemes have generally I proved expensive, and their performance has not matched expectations. One I reason for this has been a too simplistic approach based on the assumption that I the availability of land and water would result in successful irrigation management. Nowadays more people accept that socio-economic, political, and environmental issues must be adequately considered if success is to be achieved. Irrigated agriculture, the art and science of harvesting and making the best use of water to increase agricultural production, is older than recorded history. Whether it has been obtained from above or below ground, water for irrigation has permitted an increase in the production of food and cash crops. As a result famines have been avoided in those regions where irrigated agriculture has been practiced successfully, and populations have in creased and prospered. Neither has irrigation been confined to dry areas; the vast and complicated terraced irrigation structures of humid southern and south-eastern Asia have not only influenced technological progress there but also, through their land distribution and tenure, the whole socioeconomic organization of enormous areas and vast populations. However, there have been many cases where the introduction or intensification of irrigation has reduced the productivity of the land, increased the consumption of nonrenewable resources and disrupted wider patterns of water use. This has been the case all too often in sub-Saharan Africa, particularly where irrigation schemes have been on a large scale and designed and implemented by 'outsiders'. Large-scale schemes with modern technology appear to offer faster, more easily managed and more effective ways of introducing the benefits of irrigation. However, while there is obviously a role for large-scale schemes, the problems that have been encountered have led to extensive reappraisals of the assumptions and methods usually employed in their implementation. In Africa (with the exception of the Nile valley) there is little tradition of irrigation. This is perhaps because population densities have always been relatively low and also because much of the land area is flat, rivers are highly seasonal in their flow, and other surface waters and even groundwater at shallow depth are not widespread. In addition, the rate of evapotranspiration is very high and leads to enormous losses of potentially useful water. Large-scale small-scale Large schemes have attempted to overcome some of these problems by vast investments in dam construction, feeder canals and energy-hungry pumping equipment. The scale and complexity of managing such schemes has been outside the experience and capability of the farmers and on many schemes they have been little more than labourers. Because of their minimal involvement and commitment, farmers have failed to adapt to new crops or new varieties of crops. They have not observed the strict disciplines required where water availability is by rota and where water use must be optimized by careful integration with cropping cycles. Social and economic problems have also arisen, from a number of different causes: from uncertainties over land tenure of newly settled lands and conflicts between settlers, to differences in cropping priorities between farmers and project managers. And farmers have not always reacted favourably to water charges which have been levied in order to recover part, at least, of the project cost. The opportunities for expanding small-scale irrigation in Africa are considerable. While large-scale schemes are 'top-down' in concept and execution, small-scale irrigation is 'bottom-up' and if implemented mobilizes indigenous knowledge and skills at low investment cost, while increasing farm productivity. The potential for increasing agricultural output through small-scale irrigation also exists in many Caribbean and Pacific countries. Small-scale irrigation may be defined a! irrigation, usually on small plots, in which private farmers have the major controlling interests, and which uses a level of technology which farmers can effective!, operate and maintain themselves. Aspects of small-scale irrigation It is essential that farmers are involved in, or even initiate the planning and design construction, and most aspects of the operation and maintenance of the scheme. Farmers should also have control over cropping, cultivation techniques, irrigation harvesting and marketing. And, so the farmers are able to exercise control over their irrigated lands, it is important that the types and levels of technology are appropriate; all systems and equipment must be comprehensible to small farmers, who must be able to maintain and repair them. Problems often arise on irrigation schemes because insufficient account has been taken of the needs and preferences of the farmers. Some schemes that have failed were plane and designed without farmer participation; farmers have been told what crops to grow and when to plant them; they have then faced charges for mechanized cultivation, harvesting, and for water supply. It is not easy for small, traditionally independent farmers to accept the high degree of discipline and cooperation that is necessary if large formal irrigation schemes are to function efficiently. Small-scale irrigation projects, where individuals retain their independence and develop cooperation, rather than have it imposed, are more likely to succeed. It is important that irrigation water costs are kept to a minimum to avoid burdening small-scale farmers with unrealistic charges. Water catchment from buildings and water harvesting on the ground are both economical options and can be implemented using family labour. Small dams can also be constructed and water may be diverted from rivers where the river banks are not too high and weirs can be built across the stream. Springs and shallow wells are further options and which is most appropriate will depend on topography, rainfall, depth of water table and the technology available for extracting and pumping water. Water sources The area to be irrigated will depend on crop demand and the availability of water during the cropping cycle. One hectare of maize may require on a single hot day 100 cubic metres of water, which is sufficient for the domestic needs of more than 3000 people. Irrigated crops are also very labour intensive, needing perhaps 500 man days per hectare. Therefore crops selected for irrigated production must repay the investment in all aspects of water harvesting, extraction and application. Irrigation may also be combined with rainfed agriculture. In a traditional irrigation scheme on the alluvial terraces of the Wadi Azum in western Sudan the terraces are planted to crops that are rainfed during the wet season and then parts are irrigated during the dry period. The water extraction method limits total production: 42% of the area is watered by hand gourds, 47% by 'shaduf' end 11% by mechanical pumps. Because of the high labour requirement almost 50% of the farmers have less than half a hectare of irrigated crops and about 30% have less than one-twentieth of a hectare. Onions and condiments are grown on the irrigated land providing income to complement the major food crops of millet, sorghum and maize that are grown on the rainfed land. Maize is also a main staple of the Chagga people who live on the slopes of Kilimanjaro in northern Tanzania. They have a long history of tapping the snowmelt from the famous white cap of the mountain. The intricacies of engineering the furrows are skills which are handed down over generations. The Chagga have expanded their traditional skills to meet modern opportunities and multi-storey cropping is practiced with bananas and coffee, cereal crops, vegetables and legumes for livestock feed. Manure and mulch are returned to the soil to complete the cycle. In the Yatenga area of Burkina Faso a very simple system of water harvesting has been developed which involves lines of stones placed along the contour. They impede runoff, increase infiltration, reduce erosion and can Fibre-reinforced, pre-cast irrigation channels increase yields by up to 50%. In central Mali the Dogon people terrace the steep rocky hillsides with stones, again placed along the contours. To the soil which accumulates naturally behind the stone barriers they add soil taken from the river bed at the bottom of the escarpment. The Dogon also excavate cisterns to store water for dry season irrigation. The individual terraces or beds are only a few square metres in area and are used for growing onions for sale to Mopti and Bamako. Power to the people Although irrigated agriculture has not been so widespread in sub-Saharan Africa as in Asia, it is clear that there are traditional skills and known techniques available over a wide area and a range of ecological zones. Had these skills been recognized earlier, the present food crisis in many countries might have been mitigated. However, the trend in Africa is now towards small-scale schemes which use these skills, not least because governments and parastatal organizations are increasingly devolving management and responsibility to individuals or small groups. In Senegal the National Society for the Development and Use of the Delta (SAED-Societe rationale d'amenagement et d'exploitation des terres du delta et des vallees des fleuves Senegal et de la Faleme) is passing responsibility to farmers' associations known as Economic Interest Groups (GIE - Groupements d'interet economique) because, as legally constituted bodies, EIGs will be better able to negotiate with banks for finance. Since 1987, in the semi-arid Yaguoua area of Cameroon, the Society for the Expansion and Modernization of Rice Production (SEMRY - Societe d'expansion et de modernisation de la riziculture a Yaguoua) has been passing responsibility for financial and technical management of its lands and infrastructure to its former tenants. The hope is that they will now become entrepreneurial farmers. And in Zimbabwe attempts are being made to pass the real costs of operations (Zim $780/ha) from the State to the farmer. The Zimbabwean smallholder considers the infrastructure as belonging to the State and not to himself; even though he has been paying from Zim $30-145 for use of water and other charges. In the past he has made little or no attempt to improve the area allotted to him. At the CTA seminar on Irrigated Agriculture in Africa, held in Harare 25-29 April 1988, M. Rukuni, Dean of the Faculty of Agriculture, University of Zimbabwe concluded that in existing schemes a process should be developed for allowing farmers to take on the burden of costs where schemes are financially viable, as well as the management of the scheme itself. In the case of new schemes, farmers should be responsible for the full operating and maintenance costs from the outset, wherever the scheme is financially viable. This policy could be achieved by restricting development to low-cost, gravity schemes where financial viability is low, but, where a scheme is nevertheless essential for food security. Pumping and costly storage works should also be restricted to cases where schemes are financially viable. While irrigation offers many opportunities for improving incomes and living standards it can also cause problems. Waterborne diseases are perhaps the most obvious: malaria, schistosomiasis and filariasis are three hazards to public health which have been associated with large-scale irrigation. These diseases can pose an equivalent, or even greater, risk in small-scale schemes where monitoring of disease vectors and preventative measures are not implemented. Crop diseases may also become more prevalent where irrigation makes the micro-climate more humid. This occurred in 1984 in parts of northern Nigeria, where widespread dry-season irrigation appears to have led to an estimated 80% loss of the pepper crop due to disease. Problems that can arise To exploit the full potential of irrigation, farmers may need fertilizers, pesticides and even seed of new crops or new varieties of traditional crops. A system for providing credit to purchase the necessary inputs may have to be instituted. Irrigation can obviously lead to rapid increases in production of crops which may then cause a glut on the market. Highly perishable crops, such as tomatoes, are particularly susceptible to inadequate marketing, and prior planning of transport and marketing is essential. Finally, the introduction of small-scale irrigation can have a deleterious effect on the interests of women in the community. The introduction of irrigation is intended to benefit the whole family through increased income and improved nutrition. However, women may actually face an increase in their labour due to increased or more intensive cropping, and irrigation may favour crops that are seen as belonging to men rather than women. Also, if only a restricted range of crops is grown, nutrition may be adversely affected. On balance, however, small-scale irrigation is seen as having an important role in the rural development of Africa and other ACP countries and in contributing towards food self-sufficiency. In development it can be an initiating process, one that encourages flexibility and step-by-step learning, and so encourages self-reliance. The mobilization of human resources utilizes and promotes respect for local skills and can slow the exodus from rural areas. And, despite its low investment requirement, small-scale irrigation can achieve sustainability by harnessing local human and natural resources. It has been said that small-scale irrigation has many pitfalls for the unwary but, where there is awareness of the likely problems, small-scale irrigation is full of opportunities. For further reading: Small-scale irrigation in Africa by Harry Underhill, 1990, Cranfield Press, Building 33, Cranfield Institute of Technology, Bedford MK43 OAL, UK NGO casebook on small-scale irrigation in Africa, FAO Irrigated agriculture in Africa Proceedings of a CTA Seminar' Zimbabwe , 1988 The nature of small-scale irrigation, Richard Carter 1989, John Wiley & Sons Ltd I Oldlands Way, Bognor Regis PO22 9SA, UK Sustainable small-scale irrigation development, Linden Vincent, ODI from Water resources development Volume 6 Number 4 December 1990 Petite hydraulique agricole a Madagascar J.Hecq & F.Dugauquier 1990, CTA
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