Document Type : Original Article
Authors
1
Soils and Water Department, Faculty of Agric., Benha University , Egypt
2
Soil, Water and Environment Res. Inst, Agric, Res. Center (ARC), Giza, Egypt
Abstract
Faba bean is a protein-rich crop, yet its productivity is often limited by nitrogen deficiency. The current study evaluated the effects of cobalt, applied to soil as sulfate (CoSO4) or chloride (CoCl2) at different concentrations, on growth, yield, and biological nitrogen fixation (BNF) in faba bean. A two-season field experiment was conducted in a randomized complete block design with 7 treatments: three doses of Co (5.0, 10.0, and 15.0 mg L⁻¹) from each source were applied directly to the soil around plants, in addition to the reference control treatment (0 mg Co L⁻¹). Soil application of cobalt significantly, regardless of the salt type, enhanced BNF by increasing number and biomass of bacterial nodules, and also increased nitrogenase enzyme activity at doses up to 10 mg Co L⁻¹. These improvements subsequently elevated available N-content in soil and N-accumulation in plant shoots and seeds, resulting in concurrent increases in yield and yield components. However, higher Co doses (15 mg Co L⁻¹) negatively affected nodulation, despite increasing nitrogen and cobalt concentrations in shoots, and chlorophyll content. This dose did not improve straw or grain yield beyond those achieved with 10 mg L⁻¹, except for grain yield under CoCl₂. Overall, CoSO₄ outperformed CoCl₂ in most measured parameters, except straw yield. Strong positive correlations were found between cobalt concentrations in shoots and each of chlorophyll content, nodule weights and nitrogenase activity, supporting cobalt’s essential role in the legume–rhizobia symbiosis. Also, all growth and yield parameters, excluding number of branches per plant, showed significant correlations with nitrogen content in plant tissues and also with chlorophyll concentration. Future studies should focus on the long-term effects of different cobalt forms on soil microbes and biological nitrogen fixation, considering timing and dose of application and how cobalt interacts with other soil amendments. Such studies may effectively help in establishing sustainable fertilization programs to increase crop yields while preserving healthy soils.
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