Érosion des sols cultivés et gestion conservatoire de l'eau dans les milieux de bouclier semi-aride : originalités de l'Inde du Sud au sein de la zone inter­tropicale / Water harvesting systems and soil erosion management in semi-arid South India and other shield regions of the Tropics

摘要

Abstract The estimation of soil loss in India has been based on rainfall erosivity proxies but has taken little account of soil vulnerability and the mitigating effects of traditional farming practices. An extensive survey of semi-arid peninsular India reveals that, by comparison with Madagascar, Brazil and West Africa where gullying of thick, relict lateritic weathering profiles is a chronic blight on agriculture, Indian soils belong predominantly to the Luvisol group and that the landscape is relatively unperturbed by accelerated erosion. Traditional fertility management of these eutrophic soils is centered around an ancient system of water harvesting from small catchments ('tank' irrigation) which collect surface runoff while arresting soil loss by retaining sediment within the village watershed. Desilting of the tanks, which traditionally ensured a redistribution of fertility back to the fields alongside manuring and, latterly, inorganic fertilisation has, however, become a thing of the past. Mining of groundwater has taken over under the impetus of the Green Revolution but a return to tank rehabilitation accompanied by total watershed management is most probably the key to the sustainable future of Indian dryland agriculture.