Soil rehabilitation and erosion control through agro-ecological practices on Reunion Island (French Overseas Territory, Indian Ocean)

Abstract

On the western slopes of Reunion Island, the trends in cropping systems for perfume pelargonium are causing serious erosion problems. This paper reviews the causes of these trends, presents the consequences of this deterioration, and assesses the agro-ecological solutions by means of cover plants and hedging with agroforest species. Firstly, the short term effects of cover plants ( Lotus uliginosus, Pennisetum clandestinum) associated with the pelargonium crop are considered. Using rainfall simulation, it is shown that such associations have immediate effects in controlling erosion, although runoff is not significantly reduced. The more long-term effects of this type of cover are then compared with pelargonium monoculture on bare soils, and with pelargonium in rotation with stable crops. The effect of hedging along plot boundaries is also observed. Descriptions of soil profiles highlight the advantages of plant cover, in improving soil structure and biological activity. Near hedges, the same tendencies are even more marked. Soil hydraulic conductivity, measured in the various situations, confirms the complementarity of cover plants and hedges in association. The plant cover reduces erosion, with only a slight increase in water infiltration. At the same time, soil under hedges gives rise to very high water conductivity which should enable a large proportion of runoff water to be absorbed.