Les méthodes utilisées pour étudier les systèmes d'élevage ont bénéficié des avancées des approches systémiques dans d'autres domaines que l'élevage. Il faut aussi rappeler que les travaux des équipes anglophones et francophones, basés parfois sur des démarches différentes, se sont complétés et leur confrontation a été source de progrès (Roeleveld et Van den Broek, 1996). Ce document est organisé en 4 parties qui abordent successivement : 1. un rapide rappel sur les bases de la démarche d'étude des systèmes d'élevage, 2. les principaux outils de l'étude des systèmes d'élevage, 3. les paramètres zootechniques et leur utilisation, 4. la bibliographie. - Une annexe présente une démarche testée sur le terrain (exemple du Laos).

In the Hautes-Terres region of Madagascar, population pressure is accelerating the conversion of hilly areas with fragile and relatively infertile soils into cropland. As fertilizers are limited, crop yields remain low and erosion is destroying rice fields. Instead of clearing areas fallowed with Aristida sp. by burning, ibis biomass can be kept for use as mulch and for ",soil smouldering", (écobuage). The effects of this strategy were found to be spectacular, i.e. boosting rainfed rice yields to levels that could bc achieved with high chemical fertilizer inputs-to which farmers have no access for financial reasons. All fuels used (Aristida sp. or barley straw, rice husks, and Acacia mearnsii branches) significantly inereased crop yields relative to the control (without soil smouldering). A residual effect was noted in the second year, especially on volcanic soils with high organic matter levels. Hence, sustainable cropping systems that fulfil farmers' needs while protecting their rice fields can be developed through the use of soil smouldering-performed just once to boost soil fertility-associated with direct seeding techniques.

A produção algodoeira se instalou e se desenvolveu de maneira exponencial no decorrer dos 3 últimos anos nos Trópicos Úmidos do Oeste Brasileiro ( estado do Mato Grosso). A produtividade média do algodão nessas regiões é muito alta (superior a 200 @lha) graças ao uso maciço de insumos e de equipamentos mecanizados; todavia, os custos de produção são altos (quase sempre acima de 1.000, alcançando até 1.500 $lha), e em conseqüência, os agricultores correm um risco econômico importante. O CIRAD e seus parceiros da pesquisa e do desenvolvimento tem construído várias opções de cultivo algodoeiro com insumos mínimos, de baixo risco econômico ( algodão de safrinha). Os resultados mostram, nos 3 últimos anos (1997/2000), que se pode produzir entre 160 e 220 @lha de algodão em caroço com custos de produção oscilando entre 500 e 700 U.S.$/ha. 3 sucessões anuais estão propostas e respondem a estes objetivos. Todas elas são praticadas em Plantio Direto e integradas em sistemas de cultivo baseados em soja e arroz de alta tecnologia, que utilizam fortes biomassas de cobertura. Através desses modos de gestão em plantio direto, combinados com os melhores cultivares, a safrinha de algodão pode satisfazer plenamente suas necessidades em água e alcançar altas produtividades com adubação e herbicida minimos.

Since the 1990s, in the southern districts of Xayabury province in the Mekong corridor, traditional farming systems have changed through extensive agricultural development based on cash-crop production. This development, by way of intensification, depends on local market accessibility, transfer of technologies from Thailand and the financial capacities of local enterprises. Thai Inputs, heavy mechanisation and technical skills are imported and cropping is largely opportunistic, following Thai market demand. Land preparation, based on burning residues and ploughing on steep slopes, has allowed for cultivation of large upland areas. As a result of this development, combined with land allocation and increasing population density, fallow periods are disappearing. Furthermore, this resource-mining' generates land erosion, fertility loss, yield decline and chemical pollution as well as destruction of roads and paddy fields. In light of this, the Lao National Programme of Agroecology has implemented a holistic research approach in order to propose various systems for integrating crops and livestock production to farmers. From a large range of technologies that were tested, maize production using direct seeded grain on former crop residues under no-tillage systems has been implemented. Results achieved'under the various conditions are presented in this paper: the yields obtained are close to and sometimes even higher than those obtained in conventional systems. Labour, costs, soil erosion, net income and labour productivity are also all observed.

Les deux systèmes les plus fréquents et les plus étendus du Sud Ouest malgache sont particulièrement agressifs pour l'environnement et peu performants d'un point de vue durabilité et reproductibilité. La coopération française a demandé au Cirad de proposer des alternatives techniques et économiques à ces systèmes. l'hypothèse de l'intérêt des techniques associant semis direct et couverture permanente du sol fut posée et un travail pour la mise au point d'itinéraires techniques engagé. Les résultats obtenus en milieu semi contrôlé sont très intéressants du point de vue des rendements comme des marges. La diffusion de ces systèmes cohérents agronomiquement suppose néanmoins une amélioration de l'environnement de la production et la résolution de deux contraintes essentielles : la conservation des résidus pendant la saison sèche et la résistance à l'innovation. Cette diffusion nécessite aussi une bonne connaissance des objectifs, des stratégies et des pratiques des agriculteurs.