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Environmental benefits can be achieved by organic farming systems; however, weed pressure and timely crop nutrition remain important drawbacks for many field crops. Agroecological practices, such as double cropping (e.g., intercropping and relay cropping), using forage legume species can provide nitrogen (N) to the companion crop through biological N fixation and tackle weed issues by competing for light, water and land. The present study investigated the effect of intercropping (IC) and relay-cropping (RC) systems of durum wheat (Triticum turgidum subsp. durum (Desf.) Husn) and forage legumes (Trifolium subterraneum L., Medicago polymorpha L., and Lotus corniculatus L.) by varying organic N fertilization with the aim to reduce N-requirement and weed pressure and increase wheat grain yield and grain protein content in Mediterranean organic farming systems. N fertilizer significantly improved wheat grain yield and grain protein, while a null effect on legume and weed biomass yields was found. Double cropping (T. durum-M. polymorpha, and T. durum-L. corniculatus) enhanced wheat grain yield as compared to the control and the T. durum-T. subterraneum. IC significantly improved legume yield, grain protein and the land equivalent ratio (LER) and reduced weed dry biomass as compared with the RC and the control. Among legume species, T. subterraneum outperformed the others and was less affected by the wheat’s competitive performance. Nonetheless, M. polymorpha was as effective as T. subterraneum in controlling weeds. Weed dry biomass was linearly reduced by increasing legume yield; the relationship improved by cumulating wheat grain yield to legume yield. Overall, this study indicated that double cropping, especially IC, can be a suitable agroecological practice to tackle weed issues and reduce N-requirement in Mediterranean organic cereal-based systems.

For guar, a well-known drought and heat-tolerant industrial legume with a spring–summer cycle, limited research has been conducted into measuring the effects of drought on yield potential. A two-year field experiment was conducted to explore the effects of different irrigation regimes on yield, yield components and water use efficiency (WUE) on five cultivars of guar (Kinman, Lewis, Matador, Monument, and Santa Cruz) in a semi-arid Mediterranean environment. Three different water replenishment levels were used: fully irrigated (IH, 100% of the ET), and 50% (IM) and 25% (IL) irrigated. Seed yields ranged from 1.24 (IL) to 3.28 t ha−1 (IH) in 2011, and from 0.98 (IL) to 2.88 t ha−1 (IH) in 2012. Compared to IH, the two-year average seed yield reductions for IL and IM were 49% and 26%, respectively. Lewis and Santa Cruz showed significantly greater grain yields under fully-watered and water-limited conditions. The number of pods per plant achieved the highest positive direct effects on seed yield (r = 0.924***). The highest values of water use efficiency were observed in the IL water regime (1.44 kg m−3 with increments in improved water use efficiency of +34 and +95% when compared with IM and IH, respectively).