Assessing Competitive Interactions in Weed Communities Under Crop Rotation and Tillage

Understanding how weed species interact over long timescales is essential for predicting community dynamics and developing sustainable weed management strategies. This study analyzes the structure and stability of competitive interactions within a weed community composed of Descurainia sophia, Fumaria spp., Papaver rhoeas and Veronica hederifolia using a 20-year dataset from a long-term cereal–legume rotation experiment conducted under conventional and no-tillage systems in central Spain. Intra- and interspecific interactions were quantified using discrete-time, density-dependent population models based on Lotka–Volterra competition theory, and the extent to which crop phase and tillage system altered competitive relationships was evaluated. Results indicated that competitive structures remained stable as neither tillage nor crop phase modified the estimated coefficients. This suggests that management primarily affected population densities rather than the strength of the interactions. Competitive hierarchies were characterized by asymmetric effects among species, with Fumaria spp. exerting strong suppressive effects on weaker competitors. Overall, the findings support the prominent role of density-dependent regulation, particularly intraspecific competition, in shaping long-term weed community dynamics. These results provide a basis for more targeted weed management by helping to identify species that may require active control versus those that could be tolerated under specific conditions, potentially supporting reduced herbicide inputs and more sustainable agroecosystem management.