1. Grime’s CSR and Tilman’s resource-ratio theories are two major contributions to our understanding of plant community dynamics. They have both been corroborated empirically, whilst providing several contradictory predictions. Notably, contrary to Tilman, Grime predicts that competition for soil resources is unimportant on poor soils. 2. We show that Grime’s CSR theory can be modelled with the same type of differential equations for resource and plant biomass dynamics used by Tilman in his resource-ratio theory. 3. Using this unified modelling framework, we demonstrate that both models predict intense competition for soil resources on poor soils, as long as biomass loss per unit mass is modelled as a size-independent process. When considering biomass loss per unit mass as a size-dependent process mimicking farming activities, both models predict a unimodal relationship between soil fertility and the intensity of soil resource competition, and a decreasing relationship between disturbance rate and resource competition. 4. Synthesis. Our modelling analysis reveals that the resource-ratio and CSR theories make different predictions regarding competition on poor soils, not because of their differing schemes of plant strategies, but because of the different disturbance types that they are considering. Tilman’s predictions apply to little disturbed natural habitats, whilst Grime’s predictions apply to disturbed ones.