Name the team used for scientific water and soil conservation. Mention its advantages
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Answer:
The lower rainfall in semi-arid areas compared with that in humid climates does not mean a corresponding low level of soil erosion by water. Indeed rainfall erosion can be higher in semi-arid areas than in any other climatic zone. This is partly because the rainfall of semi-arid areas has a high proportion of convective thunderstorm rain of high intensity and high erosive power. It is also because there is poor protective vegetative cover, especially at the beginning of the rainy season.
Some of the soils common in semi-arid areas are particularly vulnerable, either because they have poor resistance to erosion (high erodibility), or because of their chemical and physical properties. An example from Mexico is illustrated in Plate 4.1 For example, alfisols suffer a particularly high loss of productivity per unit loss of soil (Stocking and Peake 1985). Gully erosion can be severe in semi-arid climates and the benefit/cost of gully control needs to be considered. Successful but expensive gully conservation like the Australian example shown in Plate 4.2 might not be suitable for third world countries.
4.1.2 Soil Conservation and Water Conservation
There are always strong links between measures for soil conservation and measures for water conservation, and this applies equally in semi-arid areas. Many measures are directed primarily to one or the other, but most contain an element of both. Reduction of surface run-off by structures or by changes in land management will also help to reduce erosion. Similarly, reducing erosion will usually involve preventing splash erosion, or formation of crusts, or breakdown of structure, all of which will increase infiltration, and so help the water conservation.
4.1.3 Integrated Programmes
The approach by soil conservationists in the 1980s is moving away from using mechanical works and structures in soil conservation programmes paid for by a government or a donor-funded project. An example is the increasing awareness of the ineffectiveness of terracing programmes alone. Also, we are moving towards the view that the only effective programmes are those which have the full support of the people. The subsistence farmer cannot afford to respond to philosophical or emotional appeals to care for the soil, and this means that conservation measures must have visible short-term benefits to the farmer. For the subsistence farmer the benefit he would most appreciate might be increased yields per unit of land, or perhaps better production per unit of labour, or perhaps improved reliabi- lity of yield.
The idea of working together in groups on tasks which require a big labour force is well-established in many countries, particularly for planting or harvesting. The practice can be successfully extended to conservation works. The advantages are:
· a village ao group can tackle jobs too big for an individual or family;
· it generates a sense of community care for the land
· work groups are a good forum for extension workers to encourage improve farming methods (Plate 4.3)
4.1.4 Design Requirements
If we accept the argument that soil conservation must be cost- effective to be acceptable to the farmer, then the low value of production from semi-arid soils means that only cheap and simple solutions are appro- priate. On a fertile soil with good rainfall it may be sensible to invest a lot of labour or money in sophisticated schemes for controlling the run- off, but not in semi-arid areas with low and unreliable yields. It follows that attempts to eliminate soil erosion completely may be unrealistic, and that some level of erosion may have to be accepted, and also some risk' of soil conservation measures failing. An example of a realistic approach to the risk of failure are the flood diversion dams built in the People's Democratic Republic of Yemen for spate irrigation schemes. Each end of the diversion is built of stone, or nowadays concrete, with a simple earth centre section. It is accepted that the earth section will be destroyed by big floods but it is cheap to repair or replace (Thomas 1982). To upgrade the design and construction so that they could withstand the 25-year flood would increase the construction effort beyond what the farmers can provide. This same approach should be applied to all mechanical conservation programmes in semi-arid areas.
4.1.5 Relevant Technology
Many conservation programmes have failed because the technology was inappropraite, or misapplied, or because they did not take account of the social situation and did not involve the people. The record of soil conservation in north Africa is striking. Heusch (1985) concludes that the large conservation programmes in Algeria, Morocco and Tunisia, from 1950 to 1975, were based on inappropriate technology imported from the totally different conditions of the United States, and the whole effort was a mistake which should not be repeated. Similar criticisms have been levelled at the GERES project in Burkina Faso.
