Fine-Tuning N Fertilization for Forage and Grain Production of Barley–Field Bean Intercropping in Mediterranean Environments

Optimizing the productivity and efficiency of cereal–legume intercropping through ex-ploiting differences in nitrogen (N) acquisition of the two crops is crucial in Mediterranean areas. A two-year field study was conducted in Central Italy to determine how N fertilization rate affected forage and grain production as well as intercropping efficiency in a barley (Hordeum vulgare L.) and field bean (Vicia faba L. var minor) intercrop. Crops were grown as monocrops or intercropped in alternate rows in an additive design and fertilized with five N rates from 0 to 200 kg ha−1. Forage production was determined both at heading and early dough, while grain yield was assessed at full ripening. Besides, land equivalent ratio, competitive ratio, and aggressivity index were calculated. Consistently between years, results highlighted that intercropping of barley with field bean can be a sustainable cropping system because both forage production and efficiency indices improved. Anyway, with 150 and 200 kg N ha−1, the grain yield was lower in intercropping than in sole crops, due to higher interspecific competition. We concluded that the optimal N fertilization depends on the farmer’s objective in terms of forage or grain production and the targeted proportion between the cereal and the legume at harvest.