Early vigour is essential for rapid crop establishment and resource acquisition (light, water and nutrients), and by consequence for competition with weeds (Caton et al. 2003). Rice is known to be a poor competitor, particularly in poorly controlled systems prone to weeds and abiotic stresses. Crop modellers consider early vigour a source-acquisition driven process, consisting of intercepting light and converting it into biomass, some of which is partitioned to leaf area growth (Brisson et al. 1998). Recent works suggested that sink dynamics may be a driving force of resource acquisition and thus, early vigour. Luquet et al. (2006) presented a rice growth model (EcoMeristem) that simulates two-way interactions between growth and development processes. Organogenesis and morphogenesis thereby drive structural growth and light capture, mobilization of transitory reserves and, to some extent, affect leaf photosynthetic rates by feedback. According to this concept, early vigour of the rice plant depends on development rate (DR, inverse of phyllochron, in °C.d-1), tillering capacity and potential leaf size which together constitute incremental demand for assimilates. The present study aims to test this hypothesis for rice, model plant for branching cereals. Experimental and modelling approaches are combined.