Mixed Swards of Annual Legumes and Ryegrass Improve Biomass, N Yield and Resource Use in Mediterranean Conditions

ABSTRACT Legumes, through atmospheric N fixation, enhance soil health and fertility by increasing organic matter and nitrogen (N) availability. This study evaluated the productivity, N fixation and N transfer from annual legume mixtures (LM) to a companion ryegrass ( Lolium multiflorum ) in mixed swards, under Mediterranean conditions. The LM swards with different phenologies (designated M400, M500 and M600), comprised cultivars of Trifolium subterraneum , T. michelianum and Medicago polymorpha , grown either alone or in combination with ryegrass (LM + R ). Plots were established in May 2014 and were evaluated from 2014 to 2017. Dry matter production varied significantly among LM, LM + R and ryegrass monocultures across the different years. The LM + R swards produced 35%–47% more dry matter than LM swards and 33%–68% more than ryegrass alone. The mixture M400 + ryegrass achieved the highest production (6.64 t ha −1 average; 14.85 t ha −1 in 2015). N derived from the atmosphere ranged from 84% to 94% in LM swards. The mixture M500 fixed the highest amount of N across years. The nitrogen yield (kg N ha −1 ) was higher in LM + R swards compared to LM alone. M600 showed the highest N transfer to ryegrass. All LM + R swards had land equivalent ratio (LER) > 1, indicating better resource use than monocultures. The demonstrated benefits of mixed cropping systems—higher productivity, enhanced N fixation, effective N transfer and improved resource use efficiency—align with the goals of reducing synthetic fertiliser dependency and mitigating environmental impacts.