Influence of Tall Fescue Ecotype on Biomass Production, Radiation Interception and Use Efficiency in Alfalfa-Based Pasture Mixtures

Ecotypic variation in tall fescue (Lolium arundinaceum (Schreb.) Darbysh.), with differences in phenology, may affect the performance of mixtures with alfalfa (Medicago sativa L.). However, the effects of ecotypic variation within mixtures remain largely unexplored. The aim of this study was to evaluate the aerial dry matter (ADM) production and radiation model components of alfalfa–tall fescue mixtures, with particular emphasis on their implications for radiation interception and radiation use efficiency (RUE) at the canopy level. We evaluated from March 2017 to May 2018 in the Pampas (Argentina) monocultures of alfalfa and tall fescue Mediterranean and Continental ecotypes, and their mixtures with a sowing ratio 1:1 under frequent defoliation without fertilization. ADM was higher in alfalfa monoculture and mixture with the Mediterranean ecotype than the mixture with the Continental ecotype (+20%; 3225 kg ha−1). Alfalfa monoculture exhibited the highest radiation interception, whereas the mixture with the Mediterranean ecotype compensated for reduced interception through increased RUE (≈10%). The Continental mixture exhibited lower interception indicating stronger interspecific competition. Tall fescue monocultures were the least productive due to low interception and RUE. These findings highlight the potential of Mediterranean tall fescue ecotype and the importance of species/ecotype selection for grassland productivity.