Résumé
MOMOS model (Modelling Organic changes by Micro-Organisms of Soil) is a nonlinear system of ordinary differential equations, which models the dynamics of carbon in soil. This "compartmental" model emphasizes the role of the microbial biomass which is responsible for the model nonlinearity. We show here that, for any initial condition, there exists a global unique solution. Moreover if we assume periodicity of model entries we prove existence and uniqueness of a periodic solution which is also a global attractor for any other solution of this periodic system.