The exogenous organic materials (EOM) resulting from agricultural activities within the city are numerous. We present here descriptions of these EOMs, and have modeled management problems and competition in disposing and using them (e.g. agricultural recycling vs. production of renewable energies). In the Indian Ocean region (Madagascar and La Réunion Island), both the volume and variety of EOM are increasing. We have developed innovative methods (e.g. near infra-red spectroscopy [NIRS]) to characterize a large variety of tropical EOM and to evaluate the risks involved in either their agricultural or energy utilization. In order to represent the EOM from various origins and of different types, the development of models is carried out on several levels. On the one hand, NIRS models are presented to make use of the technique. Indeed, on a "simple" spectrum basis, one can make predictions of interesting parameters which are difficult to measure according to conventional methods. Many useful data to assess the scenarios of agricultural or energy valorization can thus be quickly produced at lower costs. On the other hand, we have developed models of EOM transformations in soils that are adapted to the tropics. These models can provide scenarios for the agricultural valorization of typical EOM, and can run with entry parameters which have been measured by conventional analyses, or resulting from NIRS models (double modeling). The various scenarios set out for either agricultural or energy utilization must be balanced against possible hazards due to trace elements and the release of N2O, a powerful greenhouse gas. (Texte intégral)