Studies on nitrogen fixation characters in some varieties of cowpea

Under a polythene bag culture experiment, three high-yielding varieties of cowpea (Vigna unguiculata L.) of Karnataka, namely KBC-2, V-322 and GC-2 were evaluated for various nitrogen fixation-related characters at 35, 50 and 65 DAS (days after sowing) during kharif. The acetylene reduction activity (ARA) of root nodule nitrogenase and leghemoglobin (Lb) contents were higher at 35 DAS, but they decreased linearly with an increase in growth stages in all the varieties. The highest mean ARA was noticed in KBC-2 (11.6 μ moles C₂H₄ formed/h/g fw of nodules) and the lowest was in V-322 (7.1 μ moles C₂H₄). The mean Lb content was found highest in GC-2 (1.26 mg/g fw of nodules) and lowest in V-322 (1.18 mg). The shoot and root ureide content and the relative abundance of ureides (RAU) were also higher at 35 DAS in all the varieties. The nitrate-N content increased while the total-N content in the shoots decreased with the increased growth stages. The highest nitrate-N content was noticed in KBC-1 (306 μg/g dry w) while the lowest was in V-322 (204 μg/g dry w). The highest mean total-N content was observed in KBC-2 (3.12%) whereas the lowest was in GC-2 (2.50%). The overall results suggested that KBC-2 was superior in nitrogen fixation among the cowpea varieties studied.