La diversité de gestion des systèmes herbagers en Amazonie. Cas des élevages bovins brésiliens

In the Amazon region of Brazil, there are socioeconomic challenges of extreme importance for the development of a sustainable agriculture, particularly for livestock farming. In agronomical terms, they concern the perenniality of the pastures created after the clearing of forest lands, because of the rapid and strong encroachment by weeds. On the farms producing milk and meat, the forage systems are characterized by the exclusive grazing of pastures. The adequation of the stocking rate to the available forage resources is described as an essential factor for the technical and economic sustainability of these systems. This advice however, technically uniform and essentially stable, goes against the present context of animal farming, with diverse and very rapidly changing production systems. In order to apprehend the diversity of the forage systems and their determining factors, the practices of 7 dairy farmers were monitored for one year. Three criteria of diversity accounting for the variability of the farmers' practices, their objectives and their determining factors were defined. Linkages among these factors were observed, showing the existence of 2 contrasting policies, producing or maintaining the herd. Over one year, the management policies corresponded to other expectations than the adjustment between herbage supply and herd demand, according to the role of stock rearing, collective work organization and production structures. The information supplied would help to characterize and analyse the forage structures, but they would have to be validated on other situations of livestock farming in the Amazon region. L'envahissement des prairies cultivées est une contrainte forte à la viabilité socio-économique des élevages bovins lait-viande sur les fronts pionniers amazoniens, mais la gestion du système fourrager répond souvent à des logiques autres que la pérennité des prairies. Les pratiques de gestion du système fourrager de sept éleveurs ont été décrites pour formaliser des critères plus synthétiques. Trois critères (conduite des vaches au pâturage, gestion des effectifs bovins et entretien de la ressource herbagère) sont caractérisés pour rendre compte de la gestion des systèmes fourragers et soulignent les oppositions entre les logiques d'éleveurs. Les pratiques de gestion des systèmes fourragers et leurs déterminants sont très variables et répondent à des objectifs autres que le message technique véhiculé en Amazonie.