Context-Dependent Allelopathic Interactions Between Winter Cereal Rye and Grain Legumes in Relay-Row Intercropping Systems

Plant–plant interactions in agroecosystems are shaped by both biochemical interference and resource-mediated competition, yet the relative contribution of these mechanisms under field conditions remains unclear. This study evaluated whether allelopathic activity expressed by winter cereal rye (Secale cereale L.) and grain legumes under controlled conditions is associated with competitive outcomes in relay-row intercropping under organic farming. Greenhouse bioassays and laboratory screening assays were combined with a field experiment conducted under certified organic farming conditions. Aqueous leachates and biomass extracts influenced early root development of a sensitive recipient species in a time- and concentration-dependent manner, indicating measurable biological activity. Secondary metabolite profiles differed significantly among species, particularly in belowground biomass. However, under field conditions, no persistent suppression of grain legumes was observed. Aboveground biomass accumulation and land equivalent ratio (LER) values exceeded 1.0 in all intercrops, with the highest LER recorded for the cereal rye–lentil combination. The results suggest that under the conditions of this study, resource partitioning, species compatibility, and other ecological interactions may have had a greater influence on intercrop performance than the allelopathic effects detected under controlled conditions.