Autotoxicity is the chemical influence of one plant on the development of individuals of the same species. Autotoxicity in perennial plants can be a useful mechanism to avoid future conspecific competitors, however, the ecological role of autotoxicity in annuals, if any, remains uncertain. In this paper, we analyse the autotoxic phenomenon in Lolium rigidum, an annual, self-incompatible grass from semi-arid environments suspected to be autotoxic, and we dissert on the mechanisms of intraspecific interference, carrying out density-dependent experiments with additions of conspecific competitors and plant residues. Our experiments show that chemical interference and resource competition are density-dependent processes that act in opposite directions. Inhibitory chemical interference increases at low population densities whereas competition for resources intensifies at high densities. Based on these results, the manuscript theorizes on the ecological role of the autotoxic phenomenon in short-lived plants. We hypothesize that autotoxicity enhances population viability by restraining the development of populations with few individuals, which should decrease the chances of outcross and experience inbreeding depression. If this hypothesis proves true, it could contribute to explain the unusually high within-population diversity encountered in this species, which contrasts with reported values from other similar wind-pollinated, self-incompatible grasses.