[en] Four leguminous cover crops, Calopogonium mucunoides (calopo), Mucuna prupriens (mucuna), Crotalaria juncea (sunn hemp) and Crotalaria retusa (devil bean) were evaluated on the field in Northern Ghana for N₂ fixation capacity and N release. The proportion on N derived from the atmosphere (% Ndfa) by the cover crops ranged from 64.7 to 81% with mucuna giving the highest % Ndfa and calopo the least. The total N₂ fixed ranged from 59 to 109.5 kg ha⁴ with devil bean giving the largest and the least from calopo. The dry matter yield of cover crops was positively correlated with the amount of N₂, fixed but not with the percent of N derived from the atmosphere (%Ndfa). Sunn hemp, which had the best residue quality (least per cent cellulose, lignin, C N ratio and Lignin N ratio), released 50% of its N within the first two weeks while the other cover crops with relatively poor residue quality released 25% of their N within the same period. By the end of the rainy season sunn hemp had released 90% of the residue N while the other cover crops had released 80%. (author)