Competitive Effects of Lolium perenne on Establishment and Forage Yield of Newly Seeded Alfalfa

Abstract

Lolium perenne L. (perennial ryegrass, Poaceae) represents a highly competitive grass weed capable of severely compromising the establishment success and early productivity of newly seeded alfalfa (Medicago sativa L.) stands, exploiting rapid seedling emergence, aggressive lateral spread, and superior resource acquisition capacity to suppress legume recruitment, reduce plant density, and diminish forage yield and quality during the critical establishment phase when alfalfa is most vulnerable to interspecific competition. Although L. perenne is widely cultivated as a companion grass in mixed forage systems, its competitive interference with establishing alfalfa monocultures under varying agronomic conditions remains insufficiently quantified, limiting the formulation of evidence-based seeding management strategies designed to optimize stand establishment and early-season productivity. This study evaluated the competitive effects of L. perenne on the establishment dynamics and forage yield of newly seeded alfalfa across a range of grass weed densities and spatial arrangements under field and controlled growth chamber conditions. Alfalfa seedling emergence rate, seedling survival, root collar diameter, shoot biomass accumulation, and canopy height were monitored at regular intervals throughout the establishment period in response to incrementally increasing L. perenne densities established prior to and concurrent with alfalfa seeding. Forage yield at first and second harvest cuts was quantified alongside botanical composition assessments to determine the relative contribution of alfalfa and competing ryegrass to total stand productivity. Replacement series and additive experimental designs were employed to partition intraspecific and interspecific competitive interactions and estimate competition coefficients. Nitrogen fixation capacity of establishing alfalfa plants was assessed through nodulation scoring and acetylene reduction assays to determine the influence of competitive stress on symbiotic performance. Results demonstrated that increasing L. perenne density imposed progressively severe suppression on alfalfa seedling survival and biomass accumulation, with threshold weed densities identified beyond which stand establishment failure became probable.