In the modern agriculture systems, there is a general tendency to reduce the amounts of mineral nitrogen inputs and maximize their use efficiency to minimize environmental pollution and its hazards on public human health. It is well known that cobalt is a necessary trace element to leguminous crops and bacterial communities responsible for biological nitrogen fixation (BNF). So, two field  trials were performed in a split-split-plot design with three replicates during two-successive winter seasons of 2019/2020 and 2020/2021 as the sake of studying the influence of Rhizobium inoculant, nitrogen application rates [100, 75 and 50% of nitrogen recommended dose (NRD) as starter, equivalent to 20, 15 and 10kg N fed^-1, respectively] and cobalt supplementation (seeds soaking and foliar application as combined method) at different concentrations of cobalt (0.0, 8.0 and 12.0 mg cobalt L^-1) on nodulation, nitrogenase activity and performance of faba bean  plants grown on saline clay soil. Findings of this study showed that plants inoculated prior to sowing with the strain of Rhizobium at rate of 10 g inoculant per 1.0 kg seeds under N fertilization at rate of 15 kg N fed^-1 with cobalt treatment at rates of 8.0 and 12.0 mg cobalt L^-1 realized better results than that fertilized with ammonium sulphate at rate of 20 kg N fed^-1 without both Rhizobium inoculation and cobalt treatment. Generally, cobalt treatments improved nodulation, nitrogenase activity and stimulated nodulation parameters, thus enhancing all studied growth criteria, green yield and its components of faba bean plants grown under salinity stress.