Enhancing the Potential Use of Durum Wheat Straw as a Ruminant Feed Resource Through Forage Legume Living Mulch—Part I: Chemical Composition and Nutritional Quality

Durum wheat straw is an abundant by-product in Mediterranean cereal systems, but its low protein and high fiber content limit its use as ruminant feed. Integrating forage legumes as living mulches in durum wheat may enhance its feeding value through the addition of nutrient-rich legume biomass. A two-year field trial evaluated three forage legumes (Vicia sativa L., Trifolium michelianum Savi, Trifolium subterraneum L.) grown as living mulch with organic durum wheat (Triticum turgidum subsp. durum (Desf.) Husn.) under two NPK fertilization rates (target 60 and 120 kg N ha−1), with or without rhizobial inoculation. Chemical composition and forage quality indices were determined for sole-wheat straw (SB) and legume biomass (LB) and subsequently used to estimate the nutritional characteristics of wheat straw–legume biomass mixtures (TSB). Biomass production was significantly affected by legume species in the first growing season and by legume species and rhizobial inoculation in the second, with Vicia sativa consistently showing the best performances. Correlation analysis showed that increasing LB contribution was significantly associated with all forage quality indices of the resulting TSB. These results indicate that rhizobially inoculated forage legume living mulch may improve the potential use of wheat straw as an on-farm feed resource in Mediterranean organic farming.