Mbengue M. auteur aut IRD Fall S. auteur aut IRD Diedhiou I. auteur aut IRD Cournac Laurent auteur aut IRD Clermont Dauphin Cathy auteur aut IRD text journalArticle eng text/pdf reformatted digital access Legumes such as cowpea (Vigna unguiculata), significantly contribute to sustainable agriculture by offering economic, ecological, and nutritional advantages. A key mechanism behind these advantages is their capacity to fix atmospheric nitrogen through symbiosis with soil bacteria. This study quantified the nitrogen fixation of a local and a research-derived cowpea variety intercropped with millet across six farmers' fields. These fields presented contrasting histories of farmyard manure application. N fixation was assessed using the natural abundance of 15N method. Interestingly, while the local cowpea variety obtained a smaller proportion of its nitrogen from the atmosphere (61%), it fixed a considerably larger amount of nitrogen (40 kg ha-1) and assimilated more total nitrogen (72 kg ha-1) particularly in amended fields. The substantial increase in nitrogen uptake per unit area, driven by significantly higher biomass production of the local variety in amended fields, was associated with a trade-off: the cowpea competed strongly with the intercropped millet, likely for the limited soil water resources. We concluded that organic input and cowpea variety influenced cowpea nitrogen fixation in these agroecosystems. Farmers typically sow the local cowpea variety at lower density than tested here, probably to minimize its competition with millet. The selection of cowpea varieties should therefore balance the goal of limiting cowpea-millet competition against maximizing cowpea grain and fodder yields. specialized SENEGAL 076AGRO10 098AGRIC 99 79-89 2025 1958-5853 https://www.documentation.ird.fr/hor/fdi:010097716 10.17180/ciag-2025-vol99-art08-GB 1958-5853 [F B010097716] https://www.documentation.ird.fr/hor/fdi:010097716 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2026-08/010097716.pdf IRD - Base Horizon / Pleins textes 2026-07-21 2026-08-06 fdi:010097716 fre