Wetenschap - 5 februari 1998

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Coping with soil erosion in Ethiopia
In many parts of the world, farmland is overexposed to rainfall that flushes away the soil and its nutrients. Sadly, farmers are often reluctant to invest in soil conservation measures. Lack of knowledge about potential gains in production prevents them from taking action. Bayou Demeke provides such information in a mathematical model, for which he received his MSc degree on 22 January. The model is based on Central and Northern Ethiopia but, with site-specific data, it can also be used for other regions
Dry earth and incised hills, the Ethiopian highlands have become a barren, desolate region after nearly twenty years of soil erosion, Demeke says with a frown on his face. The local people have torn down most of the forests which provided the only protective cover against the irregular but violent rainfall. Then they began cultivating the land intensively. In time they saw the soil being eroded but did nothing because they were unaware of the economic consequences, Demeke adds
With this problem in mind, Demeke, a 24 year old Ethiopian, conducted research at Wageningen Agricultural University for an MSc degree in Agricultural and Environmental Economics and Policy. He tried to find a way of helping farmers to anticipate the economic effects of soil erosion and to decide what conservation measures they should take. He developed a mathematical model that embodies the economic analysis of soil erosion and soil conservation. The model uses extensive data on crops, soils, relief and rainfall
Demeke has succeeded in shedding new light upon the economics of soil conservation. In the first place, his analysis of the model's output confirms that soil erosion has a large impact on the production of crops. For example, barley yields drop by 15 percent as the result of a 10 percent decrease in the depth of topsoil in the Ethiopian highlands
He also shows that short term planning often leads to more soil erosion and less production. Farmers should adopt a longer term view of their business and take soil conservation measures if they want to prevent significant soil erosion and large production losses. The model indicates that when cultivation in the Ethiopian highlands continues for more than three years, investing in conservation measures becomes profitable
Tailor-made
A strong point of Demeke's model is that it can be tailored to fit the farmer's situation. This means that the budget, the available labour, land characteristics and planning horizon are all taken into account. According to the unique situation of the farmer, the model determines the best combination of crop types to grow and the type of conservation measures that should be taken in order to obtain the highest production yields possible
Although several models of soil erosion and soil conservation economics have already been developed, Demeke's model has several innovative features that bring it closer to reality. The reason for this is that the mathematical definitions are based on a very large data set. This includes data on land use, land characteristics and rainfall, collected at eight research stations in the Ethiopian highlands by the Soil Conservation Research Project (SCRP). The research has been led by the Swiss University of Berne since the early eighties
The large amount of data allowed Demeke to define with relatively high accuracy an important function in the model, that of crop yields. A non-linear function of soil depth, slope and rainfall was derived instead of a linear function, which has been used in other models
Risk
Another distinguishing feature of the model is that risk and uncertainty are included. The source of risk is rainfall variability. In previous models rainfall, which affects soil erosion and production, was assumed to be known. In Ethiopia, however, rainfall is irregular and unpredictable. This model is constructed in such a way that the amount of rainfall is selected at random from the ten years of SCRP-data available. This deals with rainfall fluctuation and the model becomes more realistic
According to Demeke, many farmers in Ethiopia take risks into account. Farmers often adapt their choice of crops to risks of price changes and extreme weather conditions. Where there is excessive rainfall there are great risks involved. When the soil gets saturated with water and drainage is hindered, some crops such as beans drown easily and their roots decay. To minimize this risk of waterlogging, farmers choose crops that are more resistant to water excess such as barley. However, these crops may increase the soil's sensitivity to erosion. For this reason, risk aversion often turns out to be a wrong decision in the long term
The model shows that growing barley instead of beans can increase soil erosion in the long term by up to 20 percent in the Ethiopian highlands. Demeke concludes that in this case risk aversive behaviour should be avoided and new technologies should be developed that reduce the effect of waterlogging on crops
Demeke's work has already acknowledged by many other scientists. Next June Demeke is to present his findings at the World Congress of Environmental Resource Economists in Venice, Italy. Afterwards, he will teach agricultural economics at the Alemaya University of Agriculture in Ethiopia
Demeke is confident about the potential benefits of his work. To make my model work properly we need a lot of data on crops and the environment. But when all the relevant data has been collected, the knowledge arising from the model will be a huge help for farmers around the world who are faced with problems of soil erosion.
Bird Life opens institute in Wageningen
The European department of Birdlife International will move from Cambridge, England, to Wageningen this year. Birdlife is a worldwide organisation for the protection of birds. Apart from its headquarters in Cambridge, Birdlife already has offices in Belgium, Indonesia and Ecuador
The department coming to Wageningen will be responsible for coordinating the joint projects of the national bird organisations in Europe. Birdlife will be housed in the new building of the DLO-institute for forest and nature conservation. The Wetlands Institute, an important partner of Birdlife International which came to Wageningen a few years ago, will also be housed in this building. Birdlife wants to spread its institutes geographically and was looking for a good place on the European continent from which to continue its European activities. When the Dutch government came with a generous offer to finance the bird protection programmes of the institute in the next five years, Birdlife chose Wageningen for its base. The presence of other institutes concerned with nature conservation is an advantage, according to a spokesperson for the institute
The Wageningen branch of the institute will consist of ten staff members. They will come and have a look at Wageningen and then decide if they want to make the move
Career Fair Discussion
The newly formed network of international students for exchange of ideas and information, Career Fair Discussion, is organising a discussion evening for Saturday 7 February at 17.00 in the ISOW building. The theme: Biotechnology - Hard and Soft Science Perspective, chaired by Professor Niels Roling

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