Call edition 2012

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Study of the spatial patterns of stoniness in a tropical river catchment, Tigray, Ethiopia

Els LAVRYSEN student laureate

°1978 Belgium
Licence in geography (physical geography), Katholieke Universiteit Leuven, Belgium, 2000

Studie van de ruimtelijke spreiding van stenigheid in een tropisch bergrivierbekken, Tigray, Ethiopië

Desertification is a serious problem in Ethiopia. Due to the combination of high population pressure and low technical development, the balance between man and nature is very unstable. An ill-considered exploitation of the environment in order to survive inevitably leads to a spiralling land degaradation and a loss of soil productivity which is very often irreversible.

The fields in the catchment of the Hetchi-Harena river, in the Ethiopian highland province of Tigray, are covered by huge amounts of stones. Those stones are brought up to the surface by ploughing, by repeated swelling and shrinking of the clayey soil and by lateral downward movement from the surrounding slopes. The high stoniness hampers the tilling and further cultivation of the fields, therfore, farmers take out the stones. However, those stones also play a positive role: they keep the moisture in the soil, protect the soil surface against the devastating direct impact of the rain drops and slow down the erosion by overland water flow.

Here again, an equilibrium has to be reached. Where can stones be removed, how much and which kind, in order to allow for easy cultivation and yet preserving the advantages of stoniness? This research offers answers to those very practical questions.

The stone cover has to be kept high on steep slopes; on gentle slopes the removal of stones can be recommended. This is especially the case on basalt slopes where even weak slopes show a high stoniness. It is also important to know which kind of stones can be removed. Small stones reduce the erosion and improve the crop production. Big stones, with a diameter larger than 5 cm, cover too much soil and hence reduce the yield; they should be picked out selectively.

report by Prof. Dr. Morgan De Dapper, Department of geography, Research unit 'Physical geography, geomorphology & geo-archeology of Mediterranean and tropical areas', Universiteit Gent, Belgium