[en] Ecuadoris a mountainous, volcanic country typical of the tropical part of the Andes range. The situation in the mountains—the Sierra—is special. Following an agrarian reform process with questionable results, many small farmers were shifted to slopes and highland areas, where many small cropped fields form a checkerboard pattern with low productivity, the "minifundio". This highland agrosystem enhances the acceleration of soil erosion in a mountain environment where this type of risk is naturally high. The minifundio small farmers are confronted with catastrophic erosion affecting their food production potential. The absence of effective erosion control measures adapted to the socioeconomic context of the small farmers concerned strongly penalizes agrosystem sustainability. In order to combat the erosion of this land, a research programme with an important role awarded to farmer participation, combining cognitive research and practical application and with three complementary phases was launched with co-operation between the Ecuadorian Ministry of Agriculture and IRD. The initial qualitative and spatial phase set out the main elements of an appraisal of the erosion situation in the Ecuadorian Sierra. This showed the dominant effect of concentrated runoff, especially in the northern and central parts of the Sierra where the soils, or andosols, have formed from volcanic materials. The outcropping of 'cangahua', a formation consisting of indurated horizons, revealed the large area affected by erosion. The next phase concerned the study of the main causal factors of erosion and their interrelations by measurements performed at seven experimental stations in large drainage basins representative of the Sierra agrosystems. The results revealed the great erodibility of the tilled andosols (from 50 to over 100 t ha-1 per year-1). The main recommendations that emerged from analysis at this stage of the programmes concerned the slowing of the beginning of runoff, working on slope gradients and making farmers aware of erosion control and encouraging them to perform sustainable actions. The third and last phase has made it possible to test erosion control works inspired by local practices. They are aimed at dissipating runoff energy and were tested first in large 1 000-m2 runoff fields and then under on-farm conditions. Erosion decreased considerably over the five years of observation (to less than 10 t ha-1 per year-1) and crop yields improved, leading to the surpluses that farmers hope for. Although they are encouraging, these results will not be sufficient unless they are incorporated in a general process of improvement of agricultural production and of agrosystem sustainability. In addition to soil conservation, this should include fertilization, irrigation, varietal improvement of seed, etc. From the technical point of view, this evolution is possible in most parts of the world, including the Andes. Our research in the Ecuadorian Sierra shows that man has the means to achieve better protection of soil fertility and the dynamic equilibrium of landscapes in order to move towards agrosystem sustainability. Small farmers cannot take up this challenge unaided. There is a need for true concertation between the population of the minifundio, researchers/technicians and political leaders. The basis for sustainable mountain farming in the tropics can only be achieved with strong joint participation by the state and small farmers. This type of agriculture concerns not only farmers in the Andes but also small farmers in the mountain areas in East Africa, Asia and the Mediterranean.

[fr] En milieu montagnard tropical, où les risques d'érosion sont naturellement élevés, la mise en culture des terres entraîne l'aggravation des processus. Ainsi, les versants des Andes équatoriennes, intensément cultivés, connaissent une érosion qui affecte la fertilité des sols et donc la production agricole dont dépend le petit paysannat (minifundio) pour son alimentation. Il est urgent d'apporter des mesures de lutte antiérosives efficaces et adaptées aux conditions socio-économiques de la population. Mais les connaissances sur l'érosion et la lutte antiérosive dans le monde tropical, en particulier dans les milieux montagnards, sont encore fragmentaires, les scientifiques ayant longtemps privilégié l'étude théorique des processus. L'objectif de la recherche présentée dans cet ouvrage est de proposer une approche qui associe recherche fondamentale et appliquée permettant la mise en œuvre pratique de méthodes de lutte érosive. Cette étude s'est déroulée en trois étapes : diagnostic de l'érosion, mesures des processus, proposition et validation de méthodes antiérosives. Menée à l'échelle du terroir et de la parcelle paysanne, suivant une démarche formative et participative associant paysans, chercheurs et décideurs, elle montre que la lutte contre l'érosion est possible sur les hautes terres andines. Cette approche peut servir d'exemple pour poser les bases d'une agriculture de montagne durable en milieu tropical. Cet ouvrage s'adresse aux universitaires et chercheurs en géographie, pédologie, hydrologie et agronomie et par sa présentation didactique aux étudiants ainsi qu'aux décideurs.