Weed suppression and reduced fertilizer requirements in organic durum and bread wheat using forage legume living mulches in Mediterranean systems

Living mulch is a promising strategy for addressing agricultural challenges in organic wheat-based systems. However, success depends on selecting and managing living mulch species able to reduce interspecific competition with the main crop. This study aimed to assess whether forage legume living mulches can improve weed suppression, reduce nitrogen (N) fertilizer requirements, and enhance wheat performance across two growing seasons (2022/23 and 2023/24) in a Mediterranean organic farming system. Two wheat species, Triticum turgidum subsp. durum (var. Core) and Triticum aestivum (Evolutivo population - Evo) were grown individually with forage legume (Trifolium subterraneum or Medicago polymorpha or Lotus corniculatus) and compared with wheat-sole crops under no, medium, and high N fertilization (F-rates). Compared with wheat sole crops, wheat-living mulches slightly decreased or increased grain yield in Core (-3% to +40%) and Evo (-9% to +20%), and maintained or increased the grain protein content (+1 to +10%). The relationship between kernel dry weight and growing degree days showed that wheat sole crops achieved the greatest kernel weight at the highest F-rate. In contrast, the wheat-living mulch systems maintained stable kernel weights under reduced F-rates. Depending on environmental conditions, Trifolium living mulch provided the highest biological N-fixation (21 to 73 kg N ha-1 yr-1), while Medicago living mulch was the most effective in suppressing weed dry biomass (-58 to -94%) as compared with both Core and Evo sole crops. These findings indicate that forage legumes can be safely integrated as living mulches in organic wheat without compromising yield, while improving weed control and reducing dependence on external N, particularly under low nutrient and low-yielding conditions.