Evaluation of alfalfa-tall fescue mixtures across multiple environments

Binary grass-legume mixtures can benefit forage production systems in different ways helping growers cope both with increasing input costs (e.g., N fertilizer, herbicides) and potentially more variable weather. The main objective of this study was to evaluate alfalfa (Medicago sativa L.) and tall fescue [Schedonorus phoenix (Scop.) Holub] mixtures across a wide range of environments to assess herbage accumulation, weed suppression and fertilizer nitrogen replacement values (FNRV). A common field experiment was established in 2009 and 2010 at six study sites in the United States: Maryland, Pennsylvania, Utah, Virginia, Wisconsin, and Wyoming. Experimental treatments included an alfalfa monoculture, three alfalfa-fescue mixtures with seed ratios of 75:25, 50:50, and 25:75 of alfalfa/tall fescue, and tall fescue monocultures that received nitrogen applications of 0, 50, 100, 150, 200, and 300 kg N ha^-1, respectively. Data were collected over a 2-yr period. The responses of tall fescue monocultures to N fertilization differed among sites, and this contrasted with mixture yields, which did not exhibit site × treatment interactions (P > 0.05). Herbage accumulation and weed suppression were consistently higher in mixtures compared with alfalfa monocultures and tall fescue monocultures receiving less than 100 kg N ha^-1. The FNRVs for alfalfa were within the range reported for other studies and averaged 143 kg N ha^-1. The consistent herbage accumulations across these multiple environments suggest binary mixtures of alfalfa-tall fescue may be a good option for many forage-livestock producers although yields could be improved with location specific cultivar selection.